Sureal goings on at the rear!

[Mr Gazza]

In 42 years of motorcycling I have never had an MOT failure. At one time I even used to take my AJS & Matchless club mate's bikes to the testing station after giving them a personal once over (Just the bikes..:mad:).

Last Saturday was MOT time for the Monster and I presented it sparkling as usual and was suitably flattered by the testers gasps...He owns a 748.

Then he started looking worried as he turned the rear wheel, and bashfully said to me " it won't turn backwards"..."Ah that's Ducatis hill start device" I told him.
But seriously the wheel would not turn backwards...WTF? This was so perplexing that soon there were three of us turning the wheel and jiggling the caliper.
It seemed that the caliper..The fully floating set up,,,was racking over a little and jamming the disc somehow. If we pulled it outwards at the rear end with the hose it would clear and revolve freely.
We couldn't fathom what was going on, but needless to say he gave me a failure as something was clearly not right.

Back home I stripped and cleaned the pivot bushes for the floating caliper bracket and cleaned the pads and caliper....Everything looked perfectly normal and complete.

There is some play in the bush assembly allowing the caliper bracket to twist visibly when asembled and tight on the axle. Also the outer pad has worn slightly wedge shaped and the inner has too, in the opposite sense but much less so.
The thin end of the outer pad is the forward edge, facing the normal direction of rotation.
When the wheel was pulled round backwards the caliper tipped in at the rear and the pad must have been acting something like a pawl in a sprag clutch?

Anyway I'm changing all three pivot bushes in the assembly just to be sure and also the pads.

Now the brake works very well indeed in the normal sense and doesn't drag. The pistons expand and retract when the lever is operated..All good.
Except that I found it next to impossible to push the pistons back to make it easier to get the pads over the disc, even with the resevoir cap off. In the end I let some oil out of the bleed nipple whilst pushing hard on the pistons and this improved things dramatically.
Strangely the pistons keep returning to the more retracted position after every lever application, where as I thought it would pump back to where it was?
I'm now wondering if the master cyl filling port is blocked or masked by the piston?
I don't really want to fork out for a new Master aswell, in fact the greater retraction is working in my favour at the moment...Any Ideas?

[RossObey01]

I'll just be talking a load of crap I imagine, but piston returning to original position could point to the piston seals could it not? A kinked/nipped seal would explain the piston being hard to push back. Did you have them apart when they were off?

[utopia]

Its a weird one alright.
I haven't studied the master cylinder design closely or stripped one down to have a look but the over-retraction of the pistons does sound like the reservoir is isolated somehow and the pistons are therefore being sucked back.
I'm not familiar with the fine detail of the floating rear brake set-up either, but I would be inclined to check that everything lines up laterally like it should (once the play in the bushes has been eliminated).
When I was fitting the ally swingarm I assembled everything but left the pads out of the caliper. Its easy then to see if the disc is sitting central in the caliper body.
I guess I'd be checking wheel alignment too, but I can't really see that being far enough out to cause sufficient misalignment at the disc ... not that I would expect such error on your bike anyway, but when you're clutching at straws they all look worth grabbing.
Not a huge amount of help there I suppose ... but I'll be pondering.

I can't help thinking that its less likely that both the "won't turn backwards" and "sucked pistons" are two independent faults occurring coincidentally .. more likely that the two faults are somehow related.
BUT I can't see the link at all .. yet.

[Mr Gazza]

Thanks for taking the time to give it some thought chaps. :thumbsup:

Ross, I have had each piston all the way up and down their travel, but with my apparently, closed circuit system, one comes out as the other goes in....No I haven't had it apart, I would never do so unless I had planned a complete re-build with new seals at the ready.

Utopia, I will try and look at alignment when the new bushes and pads arrive, but rather difficult to actually check in reality. There is nothing to adjust in any way. It goes together as is and that's that.
Wheel alignment cannot effect calliper/disc alignment either, as they are common to the wheel spindle, in the case of both floating and non floating set ups.
It is possible that my calliper bracket is twisted? this was brand new from Ducati only about 4/5000 miles ago ( the powder coaters lost my original). The middle bush, pads and torque rod ends were all changed at the same time....And yes I cleaned all the powder coat from all critical areas.

I think the master may have been sealed or restricted from the res for some time. Maybe I only just managed to get the pistons back enough when fitting the new pads? The pads have sometimes shown signs of dragging a bit, sometimes clicking in the calliper when turning the wheel so perhaps they have been tight enough to wear in the wedge shape and also load the bush enough to cause problems there too.
The irony is that it seems to be working really well assembled back dry, with the pads nice and clear of the disc. But I don't have the balls to take it back to the tester without really addressing the problem...Knowing my luck the pistons would move out properly on the journey there and bring back the hill start wheel syndrome again.
Looks like the master will have to come apart...I hate messing with hydraulics!!

[Mr Gazza]

Shortly after my previous post, and reflecting on the matter. I ordered a new master from Moto Rapido.
I couldn't bear the thought of dismantling my master to find it un-repairable. So the new one will remain in it's wrapper until mine is condemned or otherwise...More news on that story later...:biggrin:

[utopia]

Yep, agreed about the wheel alignment.

In the unlikely event that you do detect any misalignment, I could always make you the odd shim/bush/etc to correct it ... probably.

Another semi random thought ...
My original rear pads had stainless backing plates which cover about 60 to 70% of the piston contact area .. on the "downstream" side if I remember correctly.
This presumably causes the trailing edge of the pad to be "favoured" over the leading edge, and I assumed its purpose was to eliminate any sharpness in action which might be caused by the leading edge of the pads digging in .... if you catch my drift.
My replacement EBC pads came without these backing plates, but I swapped them over.
Do you have those plates ?
I'm guessing that you do, but worth checking in the absence of owt else.

Also, don't totally rule out the possibility of a "rogue" badly machined component.
I recently had a chain adjuster block which had the wheel spindle hole machined way out of square to the side faces .. I had to bore and bush it square before the wheel spindle would go through.

Is the pedal returning nicely ?
If not, that might cause the path to the reservoir to remain closed .....?
The std operating rod (via clevis to master cyl) is zinc plated and mine corroded and caused an issue .. though my master is in a totally different orientation on my rearsets, and that didn't help.
I fitted a titanium rod and clevis.

....posted before reading your last.

[Mr Gazza]

Thank you for the offer of some machining Jeff...We have some bits of sheet shim at work for tweaking ageing woodwork machines, so I have that option if needed.

I have no plates of any kind between pad and calliper..Perhaps you have put your finger on the problem, or part of it. I just have piston to pad direct (with a bit of coppaslip.)

It certainly does look like the pads, or definately one pad has been "leading in". But curiously the locking effect that I suffered happens when the thick end of the wedge is leading (When rotated backwards).

I did clean up the actuating rod soon after I got the bike, as it had considerably corroded. I haven't re-checked it yet, but the lever action apears to be satisfactory and has the all important free play which I often check.

Still hoping that this is all down to something shag-witted that I've missed...Dammit I can't wait for the bits to arrive. I'm going to hoik it apart tonight...:biggrin:

[utopia]

On the backing plates though ..
I'm by no means certain that all monster rear calipers are fitted with them.
In fact they may be a rarity, I dunno, my info is limited.

Ok, so how about this ...
Firstly, your pistons are retracting too far, thus allowing too much clearance and allowing the pads room to rattle further than they normally would.
Secondly, the leading edge of the pads tends to dig in (perhaps more so without the backing plates ?) and thus the pads wear to wedge shaped, thicker at the trailing edge.
Since the trailing edge is thicker, and becomes the leading edge when the wheel is rotated backwards, this picks up first on the disc and pulls the pads so that they tip to an exaggerated position due to the excessive clearance, the result being a wedging action which locks the wheel.

Does that make any sense ?

[Mr Gazza]

It's quite easy to remove the entire hydrualic system complete with calliper, master and resevoir, without breaking any hose connections or losing any fluid.

So i have bench tested it with master and calliper in vices. It's much easier to push the pistons back when I can get to it properly and apply decent leverage...Unlike trying to do it with the calliper in my hand under the bike on 6" of free hose.
Fluid flows into the resevior when the pistons are pushed in and returns as the pistons pump out when I push an allen key into the master. Everything in that department seems to be working properly. So no need to even open the envelope from Moto Rapido, Just a matter of eating some humble pie and speaking very nicely to Craig.

I am much more interested in the pad backing plates now. I seem to recall seeing them on replacement Brembo pads, but I have never had them on my brake.
If anyone has a pair on an old set of Brembo pads I would gladly buy them.

[Mr Gazza]

Sorry didn't see your last post until after I posted Jeff!

I don't think the pistons are, or were retracting to far. My initial thoughts were that they were not pulling off enough, but I am happy that all is working well hydraulically.

This business must all be down to the sloppy bush allowing the calliper to twist and so wearing the pads unevenly.
I am a little dissappointed at only getting about 4000 miles out of a bush. Maybe I should have used something better than LM grease when I assembled it?
I am thinking in terms of fitting a grease nipple on the calliper bracket, so I can give it a pump every now and then.

It could also be that everything had got a bit gummed up with it's own dust, as it seems to work perfectly now it's all clean, albeit with no greases anywhere at the moment.

[utopia]

I don't think the pistons are, or were retracting to far. My initial thoughts were that they were not pulling off enough, but I am happy that all is working well hydraulically.





Strangely the pistons keep returning to the more retracted position after every lever application, where as I thought it would pump back to where it was?


Ok.
I was reading the second quote above as saying that the pistons were retracting too far.
But maybe I have the wrong end of the stick .....?


I did clean up the actuating rod soon after I got the bike, as it had considerably corroded. I haven't re-checked it yet, but the lever action apears to be satisfactory and has the all important free play which I often check.


The mention of "considerable" corrosion is ringing alarm bells.
How does it look now ?
If the rod was binding somehow then, although you appeared to have free play at the lever the hydraulics may still have been under a small residual pressure, closing the path to the reservoir and so on.
Your bench test of the hydraulics has not confirmed the function of the mechanical actuation, ie lever to rod to master cyl.

Not being picky, just trying to be thorough.
And anyway, we do love a brain teaser. :biggrin:

[Mr Gazza]

Sorry, I did kind of contradict myself there with the retraction thing.

I initially thought that maybe they were quite tight to the disc, but in fact the wheel turned perfectly normally forwards, so it was releasing okay.
After pushing the pads back and re-assembling dry I thought there was more pad disc clearance as I could not reproduce the original fault...The wheel was nice and free in both directions.
So confusing myself a bit there too as it is all so difficult to see in there when assembled.
Everything except the wear in the bush (and pads) is checking out okay so far.

I am sure I have free play at the end of the master..The rod was clean as a whistle, as I left it, so no probs there either.

I am blaming it all on a build up of brake dust at the moment, although that might not really explain the bush wear?... Could you suggest a better grease?

It is still just possible that there is some crud in the master that would block the 'ole when mounted, as the 'ole is at the bottom...I tested it inverted with the hole at the top.
I will do a fluid change in pretty short order and re-check everything so hopefully that will shift anything in there.

[Mr Gazza]

Re-test this morning and I now have an MOT...:biggrin:

I spent some time cleaning the calliper properly, extending the pistons and drowning them in brake cleaner resulted in being able to push them both back easily with finger pressure.
Where I had used Coppaslip, it had blended with brake dust to form a gum that must have been resticting the pad free movement.
These organic pads do produce a lot of dust, so I am resigned to more frequent and thorough cleaning to keep things sweet.

I replaced the bushes that let the calliper float and the new ones are nice and tight, with no perceptable play at the calliper end whatsoever...The calliper was moving just over a millimeter in and out before, but it was the twist that was the killer. The bush had lasted 6232 miles and still had grease in it when I removed it..The tester suggested Graphite grease, so I will try some quite soon. He also persuaded me not to fit a grease nipple for fear of grease dropping onto the disc when it exuded.

Luke kindly looked up the fitment of backing plates on the pads when I rang him to to sort the return of my new master. He confirmed that they are not an original part and are not listed for my model.
My pads had both worn on the leading edges and as a pair were about 2mm narrower at the front than the trailing edge...It was actually a very effective brake.
I still don't understand the mechanism by which it was locking in reverse, but it was definately doing it...Just a combination of wear and muck I assume....All sorted now...:biggrin:

As a bonus, my new spark plugs have tranformed my Monster back to it's silky smooth self again, having gotten a bit groggy around the 3000rpm mark.

A second bonus was meeting emzedder just heading out for a ride on his lovely 250 Ducati...Great to catch up and have a nice little ride out again.
250 looking absolutely superb with new ally tank and a red racing seat that I made for emzedder's dad about forty years ago for his Honda racer. (CB72 I think?) :thumbsup:

[Flip]

I've been reading this thread with interest so thanks for posting everything in detail.

But as I haven't got the fully floating rear brake set up and have no experience of it I didn't comment but I think I would have done as you have and taken it all apart and cleaned it all and replaced what I thought necessary.

Glad you have got it sorted!!

Now we just need Emzedder to post up some pics of his 250!!

[Nottsbiker]

I had a similar issue on my old 996

The master cylinder seized up resulting in slight pressure being constantly applied to the rear brake unknown to me. When slowing down for a junction it somehow sheared off the mounting bolts causing the caliper to drop into the wheel and then to make matters even worse ripped out the valve core giving me an instant flat as well as a heart attack.

Keep an eye on your rear brake ;)

[Darren69]

The problems made worse on the 916 style bikes because the master cylinder is bolted to the engine case. I've see a couple fail from the engine heat, the fluid expands and drags the brake pads. No such problem with the Monster but worth keeping an eye on, its easy to cook the rear caliper if its dragging.

[jerry]

i dont understand the floating caliper ??? none of my ducatis have floating calipers so am i missing something here ???

[Flip]

A floating rear brake assembly was an option available on many of the early bikes and came as standard I think on the 888 and then later (presumably to use up stock) when Ducati did the 'S' model Monsters.

This is from the accessory book that came with my 1997 900 when it was new:

http://i1372.photobucket.com/albums/ag329/fluke900/IMG_6235_zpskuqbsxio.jpg (http://s1372.photobucket.com/user/fluke900/media/IMG_6235_zpskuqbsxio.jpg.html)

[Mr Gazza]

Flip..Agreed that emzedder should put some pictures up...I've sent a request.

Jerry.. Flip is correct about the floater..It was also an option and kit for SS models, and standard on the SL (I think).

Nottsbiker, Darren..Yes so true, it's all too easy to ignore the rear brake and take it for granted..I've had my wake up call and I would urge all owners to just take the trouble to drop the calliper off every now and then give everything a really good clean and check over.
Dealers can be guilty of not paying enough attention to the rear brake too.
I lost a pad from my first Monster as a result of the pin not being passed through the hole... It had been dealer serviced by the PO prior to my buying it.

The rear brake has actually been the most troublesome thing on my Monster so far.
I had it lock up due to fluid expansion on my very first ride out on it..I had adjusted out too much free play at the lever...I run it with about 3mm free play now.
I later had to change the disc due it warping..and now this.!

[Dukedesmo]

Had a problem on the 916, dealer adjusted the brake pedal position at the first service and left too little play in the lever.

After 3-4 miles the bike started slowing and eventually the rear wheel just seized at a roundabout, when I looked around the pads were on fire and the paint on the rim of the disc had burnt off.

A couple of years later the caliper started leaking which, I assume was a hangover of the burning incident?

The mounting of the master cylinder to the engine cases causes the brake to go bad after time presumably due to the heat (needs bleeding despite there being no apparent leaks) and is very a poor design, but the fitting of the rear master cylinder support bolt to the same bracket that holds the exhaust to the engine is an absolute masterstroke in heat management! :eek:

The odd thing is that the 916 uses the same master cylinder and caliper setup as the Monster yet the rear brake is crap whilst that on my Monster is good and I don't think it's all down to the slightly smaller (10mm less) disc, rather just to poor setup.

I also have the floating caliper setup on the monster but, claims of transfering load to the engine under braking etc. apart, IMO the only real advantage is less drag...

[utopia]

Hmmm.
To be honest, my (non-floating) rear disc has been getting rather warmer than it should for quite a while now.
I regularly check that there is free play, even when "warm", and all seems fine there, but I'm starting to think that I should be more stringent and get to the bottom of it as a matter of urgency.
Nottsbiker's report of a seized caliper shearing the bolts and dumping the caliper into the wheel is making me rather nervous .. particularly now that said rear wheel is a £1k carbon jobbie.
All has been cleaned a couple of times and the pistons retract easily.
I'm thinking that increasing the free play is a next step, followed by new seals to ensure that they have enough elasticity to fully retract the pistons.
I will report back in due course.

I will investigate the backing plates further too.
They were fitted to the pads which came with my yr2000 750 which I bought at 2,000 miles old.
I'm pretty confident that the pads had not been changed from new.
I replaced them eventually at maybe 14,000 miles-ish.
They had worn to wafer thin but had not yet touched metal anywhere .. exactly the same both sides and even thickness (thinness) all over. (yes, I know !)
This kinda gave me confidence that the "lob-sided" backing plates were probably doing a decent job.
I hadn't seen them before, so I was curious.
Maybe an email to Brembo is in order.
I will also get a photo at some stage (I need to fit new seals anyway, so I'll be in there) and then maybe start a thread to see if other forum members know anything about them.

I'm never sure about copperslip, for the very reason you describe.
Last time I did use a tiny amount on the front pads .. but little more than a trace, and just dabbed it on the circular "witness marks" left by the pistons on the back of the used pads.
I'm still not sure about it though.

I'm a big fan of black, molybdenum disulphide grease (for the bush, and general stuff .. not pads obviously, dear other readers).

Hopefully, you've cured the root cause of the problem, BUT its not a certainty.
I'd recommend that you inspect it frequently in the future .. but I'd be wasting my breath because I'm certain that you're already well primed there.

What's the bush made of ?

Cool about the seat.

[DrD]

I now use a fine touch of high temp ceramic grease (http://www.dirtbikebitz.com/putoline-ceramic-grease-100g-tube-p-66459.html?gclid=CjwKEAjw26C9BRCOrKeYgJH17kcSJACbH NAbFEr1drSDNtu2CzBB1A941JVv6fN4doQz_iFjhCpUhoCsXDw _wcB&utm_campaign=products&utm_medium=BaseFeed1&utm_source=GoogleBase1 ) rather than coppaslip on the pad rears.
It seems to hold up better.

[Mr Gazza]

Glad I'm not the only one with rear brake problems. Also glad that this thread is being sensibly picked up and hope that folk will be inspired to give thier rear brakes a little service.
It wouldn't be too much of an exaggeration to say it might even save a life.

Utopia, I wonder if the heat conductive properties of Carbon Fibre has anything to do with your disc warming up...It's normally bolted to a large three spoke alloy heat sink....No idea if your wheel has a metal hub or insert of some kind?

Very interested to see what you can find out about the backing plates..As mentioned, Luke found them absent on his parts list for the 2000 M900Sie, but that doesn't mean to say that Brembo didn't supply pads with backing plates at the time.
I think they were fitted to cars to prevent squeal?

I am also starting to have grave doubts about Coppaslip after a lifetime of useing it...Talking to my Dad about it, he said it was probably better to leave everything dry to let the dust fall off. I might just wash it all off when the Graphite grease arrives for the bush.

I plumped for Graphite grease for the bush in the end, but the choice is quite bewildering. It is blended with Lithium, Molybdenum Disulphide, Copper and even Calcium!! Not knowing which would have any particular advantage in my application I went for a basic Graphite grease. I think frequent grease changes are going to be the key anyway.

I am thinking in terms of about a 2000mile service interval, given that the previous bush only lasted 6000miles I am sure non-floaters would go longer and overhead mounted callipers, longer still.

The fixed, inner, "Top hat" parts of the bush are steel. The bush pressed into the bracket is a split steel tube with a coating of a brassey/bronze type material on the last new bush (now the old bush!) the newest bush has a dark charcoal or Graphite coloured coating...I wondered if it might be Teflon?

Thanks for your comment on the seat...It gave me a very warm feeling to see it used again.

[utopia]

The carbon wheel has an alloy hub.
Not that I would expect it to make much difference.
The contact area between disc and hub is very small and I can't see it providing a significant heat path.
And the problem was there with the old wheels anyway.

[rbt1548]

I am afraid I am going to have to revive this thread.

On a particularly wet and dirty few hours on the bike, 2000 M900Sie, I thought I could hear a slight noise from the front brakes taking off from a standstill so I decided to give the brakes, F&R, a thorough clean, usual, off with callipers, pads out and into them with a toothbrush and brake cleaner, refitted and bled fronts no problem, discs ok too.
When I moved onto the rear, the wheel was very reluctant to turn backwards like Mr Gazza's. The calliper seems to be the floating type with the torque arm like the one in Flip's post , No.18 in this thread.

I removed the calliper to give it a clean and noticed the front and rear edges just before the pads on the outside half of the calliper, (the side furthest from the wheel), look as though they have been scored, see pic, possibly touching the disc, the disc looks fine and is 4.1 mm thick, so plenty meat on it.

I did notice, however, that the calliper mounting bracket could be moved on the spindle a bit, so I took it off and held it in a vice and with the bushes in I could get a .5mm feeler gauge between the top hat bush and the bracket when moving the bracket.
I take it that there should be NO movement between the bushes and bracket and they should be a snug fit?, if this is the case I would imagine it is possible that this movement caused the scoring on the calliper and I need to get a new set of bushes?

The parts book for a 2000 M900Sie lists another rear brake set up, but '98 900SS F.E. looks the same, can anyone tell me if I'm on the right track and enlighten me on the parts I may need?

Cheers


https://i.postimg.cc/1R7Hg4sd/DSCN3304.jpg (https://postimages.org/)

[Nickj]

The metal bits are anti rattle shims, you usually find them where you will have some lateral float in caliper or rotor. If you look at these they usually cover the piston area and they are often slightly offset and need to be positioned relative to the rotors rotation.
You want the trailing edge of the pads to hit the disc first or you get a brake that feels really on/off. It will be just a few thou rather than a few mm
Floating caliper or floating disc ... in either case the pads will float over the rotor and maintain clearance
UNLESS the pads or a pad don't float back properly then as soon as one edge touches the disk rotor when the float in the rotor/caliper allows a pad surface to work like an auto hill start device. typically just one pad (If it's both then something is actually broken). Rotate the correct way and it clears itself. If there is some rotation in the caliper mount then it is easier for this to occur
Often there's some friction in the system that isn't helping, often just a layer of scrubbed off pad material stopping the rear face clearing properly (symptom is wedge shaped pads). The old pad material will build up and be quite hard as it gets bloody hot.

Probably a good idea to clean the caplier(s) when using soft pads on a more frequent every so often basis and ensure that any dust is shifted and any heavier 'baked' on stuff is too. The pins need to be round and smooth with no rough corrosion or wear steps, surface damage will stop the pads moving properly and if the pad is left with a little clearance with the piston it can start to rotate as the brakes applied and start to wedge.

I've found disc systems much easier to sort out than stuff like fontana 4LS drums... another story there are you can get a bit of auto servo effect enhancement when there's wear which is fun

[Nickj]

Rbt ..
A very little lateral movement relative to the rotor is going to be OK, Rotational movement isn't. Ideally you'd have none of either unless you have a floating caliper where you should only have lateral.
Lateral movement makes allowance for tolerances in build, if it wasn't there you'd be having to shim the caliper/rotor.
The caliper can also take out a little lateral offset but you want this to be as small as poss.

[rbt1548]

Hi Nickj,

Thanks for that info, but I don't have any rattle shims at all on either the front or rear pads, the bits that are scored are actually parts of the calliper casting.
The pads are worn even, I bought a new pair just in case but when put side by side there is very little wear on the ones that were on.

I will check on the rotational movement and if there is any maybe need to adjust the rose joints a tad. They seem also to be in decent nick and well greased.
Thanks

[Mr Gazza]

Robert, I'm going to have a go at answering your query, but first let me bring the thread up to date.
The MOT that followed the last one mentioned here, showed up that the rear brake problem had not completely gone away. The rolling road brake meter showed that the rear brake was hanging on a little after release. Instead of the needle dropping when the brake was released, it just slowly fell with a damped sort of action. The tester commented on this.
So. I changed the master cylinder for a new one and did a fluid change. The new master has transformed the rear brake. I should have done it in the first place when I originally ordered a new master and ended up sending it back...Mistake!!
Do not dismiss a draggy master. All appears to be working well but the slow return of the master causes a lot of problems.

So to answer your post Robert.
The ratchet like effect of not being able to turn the wheel backwards may be caused by wedge shaped pads, which in turn is caused, I believe, by a draggy master, or in your case it could be caused by foreign matter everywhere just making a nuisance of itself.

Check the pads for even front to back wear.

The calliper bracket is supposed to move in and out on the bushes about half a mm or so, ( a little more should not be a problem) that is the way in which it floats, as well as moving radially on the bushes when the suspension moves.. adjusting the torque rod ends will achieve nothing.
What you don't want is any twist in the bracket, which will allow one edge or other of the pads to lead. So get hold of the calliper and try to wring it on it's bushes, there should be no play in this sense.

The damage to your calliper does not appear to have been done by contact with the disc, if it was it would be even, flat and probably shiny. It would also match marks on your disc. The calliper body should clear the disc by about 2mm either side (float not withstanding).
I would suggest that the calliper damage has been caused by very hamfisted maintenance by a previous owner.. Maybe that half of the body has been gripped in a vice, or hammered when split? I think it's unlikely that the damage would have been caused by stones or whatever on both forward and rear edges of the calliper... The leading edge only, maybe, and then it would be matched by deep scores in the disc.

Can you check the calliper to disc clearance? Even with the natural float pushed towards the disc.

If the calliper is contacting the disc then there needs to be a serious investigation as to why, as something is badly out of order. A mis-placed spacer or bent bracket perhaps?

At the end of the day the noise and "hill start" effect could just be caused by dirt... At this time of year it comes with salt too, so is extra evil.
Have you tried rotating backwards after cleaning it all down?

Hope you get to the bottom of this sooner than I did.

[slob]

It’s normal to have more wear at the leading edge of a pad. The friction of the disc causes a turning force on the pads, drawing the front in with more force. Thats why on multi piston calipers you often have different sized pistons, front to rear, evening out the wear.

[Mr Gazza]

[QUOTE=slob;570923]It’s normal to have more wear at the leading edge of a pad. /QUOTE]

Maybe so. But I think that wedge shaped pads have something to do with the wheel locking going backwards phenomenon?

Looking again at the calliper picture, and zooming right in to the damaged area, I can see what might be marks from an engineering vice or metalwork vice, but as mentioned these could only be made when the calliper halves are split.
If you look below the red ringed area, to where the body halves meet, you may notice an abrasion which looks consistent with contact with the edge of the disc. It appears to be on the same plane as the ringed damage.
If these marks are caused by contact with the disc, surely they must have been made, either with no pad present or with extremely worn pads, as the pad pictured appears to be higher than the damaged area whilst being hard against the back of the calliper body? So the pad is preventing the disc from touching the damaged area.

Howsoever caused, if it is the disc that has contacted the calliper to make these marks then something is seriously amiss. I suggest that maybe the wheel has been turned with no pads and the calliper bolts only very loosely in position, or with the wheel spindle not tightened up... Hopefully it was not ridden in this (presumed) condition!

[rbt1548]

Thanks guys for all your input.

I am not so concerned now about the small lateral play in the mounting bracket as it has been explained there should indeed be some movement and on mine there is a bit less than the 2mm mentioned.

Both pads are flat with no wedge shaped wear on either, there is a chance that it was dirt that was causing the reluctance to move, as after I had cleaned it it is moving freely in both directions, but I will keep an eye on it as suggested.

The damage to the bodies could have been caused by putting the calliper half in a vice at some point previous to me getting the bike. What I did notice when I had it apart was the calliper to mount Allen screw had been cut short for some reason, was 15mm should be 20mm with, no washers fitted, I will replace that with the proper size. Maybe something did happen with the rear brake before I got it and I have just noticed it during cleaning, maybe a good clean more often may help?

The brake seems to function fine now after cleaning and bleeding, and if anything I have less pedal travel, the only way to tell for sure is on the road which will not be for a week or two due to stuff going on... now if I only could get my foot to touch the pedal with out contorting it that would be a bonus!!!!

The disc itself shows no sign of wear or having been in contact with another metal surface and with a thickness of 4.1mm seems hardly worn.

Anyway thank you all very much for your help and advice , it's much appreciated!

[Capo]

Full floater

https://i.postimg.cc/sX7tjRQd/P1020982.jpg

https://i.postimg.cc/v8jVFF7H/IMG-0104a.jpg

[ledheadlamp]

Thank you all for your contributions to this thread, the remarks are worth it.

[rbt1548]

Ok, guys an update, and it's not too good for me!

With the mounting bracket on the bench I decided to give it a good clean, only to discover that one of the calliper mounting holes, the rear one that does not hold the torque arm, has been helicoiled and not very well done at that!, so for some reason, something definitely has been messed about with in the past.

I have helicoil kits in the garage but because it's the mounting for the rear brake calliper I am reluctant to redo it. I have looked for the bracket online and they are not cheap but it looks a though I may need to bite the bullet and get one.

"C'est la vie" as they say or in my case "Bollocks, don't need this just now!"

[slob]

Personally I wouldn’t worry about helicoiling or timeserting it. The end result will be a stronger thread than the original. We used to ‘pre-helicoil’ the brackets on DD bikes, to reduce the chances of stripping the thread during frequent tyre/wheel changes at the track, where engineering is more difficult than the workshop.

[Mr Gazza]

Well there you go. It might explain how the calliper drifted onto the disc at some point if the bolt let go.
I had to get a replacement bracket for mine when the powder coaters lost my original!

If I recall, it was about £60-£70 from Moto Rapido with 10% UKMOC discount. Note that you have to buy the bush in the bracket separately and press it in yourself.

Luckily for me the powder coaters footed the bill, but they probably wouldn't buy you one? :rolleyes:

As Slob says, nothing wrong with a properly done helicoil. So long as the calliper is still pulling down flush to the bracket and not being held out of line in any way.
2V cam belt tensioner bolt thread holes are helicoiled from new btw.

[rbt1548]

Great guys, thanks for the info and reassurance. I will take out crap helicoil , clean it all and see if I can re insert a new one, hopefully it will take a new one.

If necessary I will keep an eye out and see if I can get an undamaged bracket, I'm sure they'll come up from time to time.

Cheers

[Mr Gazza]

Do check Moto Rapido's price for the bracket and bush, as my memory does play tricks on me.

Also worth noting, apparently there is a Wurth insert available that is over size from Helicoil and can be used sometimes if the 'ole is too big to helicoil successfully.. I have been told.

[slob]

the wurth one is called a timesert, it’s a steel threaded sleeve that expands into the oversize hole.
https://images-na.ssl-images-amazon.com/images/I/51c4L7hBq6L.jpg

[rbt1548]

I'll try the helicoil first as I have an M8 kit amongst others, if it doesn't feel right I'll look at the Wurth Timesert.

Cheers