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Dark-Jon
24-04-2005, 08:39 PM
not as much fun as you may think ;)

I've finally gotten around to fitting my twin disc conversion on my bike but have run into a bit of a problem. Discs, callipers and master cylinder all on and bled through and seemed to be working fine, no leaks or furious pumping (back to those twins again :D )

However, took the bike for a spin, brakes seemed good and strong so all fine. On the way back to my house (only went around the block) the bike seemed to be braking of its own accord and got to a point where by slipping the clutch loads all I could get it to do was skid the front wheel or spin the back wheel (yay my first little burn out :lol: ) Had to take the pads out of one of the callipers to get it going, not fun in the middle of the road (literally). As far as I can tell, the near-side calliper is fine but on the off-side calliper one of the pistons is really stiff, would this be causing the brakes to stay on and indeed get stronger? I thought I'd checked them all before assembly and they seemed fine. They're not brand new callipers so I can't exactly take em back to the shop. Can you get replacement calliper pistons and seals or is the job a no no. I know I can with my Mini but that probably means naff all.

Anyone, need to get it sorted before Friday :confused:

DJ

Oh by the way, the miss' muttered summint about why tinker with it if it ain't broken? :rolleyes:

Scotty
24-04-2005, 08:53 PM
dismantal clean reasemble ,you know its the answer.
dont scratch bits dont break seals, check to see disk is not warped from your trip round the block check to see pads arnt now glazed (whatever that it)

Pedro
24-04-2005, 10:41 PM
DJ

get yourself to halfords and buy some brake cleaner then scrub around each piston with a tooth brush. Last time I did mine, I eased the pistons out using the lever but be careful not to over do it.

You can't buy seal kits for Brembo so if you take them apart, take care!!!

Ped
PS - you have a PM

slob
24-04-2005, 11:16 PM
check the condition of the seals, they deform when you apply the brakes, the 'memory' of their original shape helps to draw the pistons back into the caliper body.
As previously mentioned on the site, Italian liability law means you can't get many brake spares. However these guys seem to have wide range of bits http://www.yoyodyneti.com/SearchResult.aspx?CategoryID=164
Brembo calipers seem particularly 'delicate' in our weather, I take mine apart and clean them out at least twice-a-year.

bod
25-04-2005, 07:14 PM
Make sure you havn't got the brake flexi twisted around 180 degrees.

Dark-Jon
26-04-2005, 01:50 PM
Bit of an update

Stripped down the suspected caliper and cleaned out some debris etc. The seals seem fine and aren't cracked or otherwise knackered. The pistons themselves have a little bit of corrosion on them but were talking one or two specks. Just to be on the safe side took the pistons out of my original caliper and put them in and re-assembled. My dad, bless him, put everything back on the bike this morning whilst I'm at work. He says the brakes are still binding a little and the wheel rotates maybe half a turn before stopping. Now is this down to new pads or does it need a bit more force to get the calipers to back off? Continued use of the lever/brakes gets them to return to the same place as before but NOT stay on permanently. Also tried removing the brake lever to see if that was playing up but that makes no difference.

Is this sounding better or am I gonna have to revert back to a single disc for the weekender?? the calipers now seem ok and my dad can't find any trace of any of the pistons playing up (on both calipers), or should I start suspecting the master cylinder (although in my experience a dodgy master cylinder gives you no brakes at all)

so many questions

DJ :)

slob
27-04-2005, 07:18 AM
If I'm understanding what you're saying correctly, I'd have a good look at the disk, sounds warped.

Zimbo
27-04-2005, 07:22 AM
Phoenix had the same problem this week fitting twin calipers and a 916 master cylinder. Turns out the lever was not allowing the master cylinder piston to retract fully, leaving the brakes partly on. A little filing off the rear face of the brake lever solved it, allowing the master cylinder piston to extend fully when the brakes are released.

Dark-Jon
27-04-2005, 09:12 AM
well, I've ended up putting my original master cylinder back on and they work fine, if somewhat spongy and slightly vague, but it does an emergency stop from 30mph ok, even gets the back end squirming a bit. So it looks as though its the master cylinder. My dad's dismantled it and can't see anything obviously wrong with it or excessively worn. Is there any way to adjust these things as it feels as though it's always slightly 'on' if you get me, like it just needs backing off slightly? we've tried with and without the lever and it still binds either way so its not the lever applying too much pressure (i read phoenix's write up and thought of that :D )

stumped

DJ

Dark-Jon
27-04-2005, 02:02 PM
k, been doing some reading (see surfing the web) and it seems that early M750's had the coffin type master cylinder with the twin discs. A couple of reviews mentioned the spongy braking on the early bikes, so is it ok to run with the coffin type master cylinder, just that it's not reccomended?

honestly, at the weekender and a few ciders later I'll stop asking so may questions

DJ :bunny:

slob
27-04-2005, 03:07 PM
We're talking about your brakes here... I'd keep asking, until you're absolutely happy!