S4R front brake issues

[enbee23]

Went out to the bike for an after work blast today and the front brake lever is pretty much going to the bar. The lever has been a little soft since I got the bike two months ago but was still usable. Now it isn't.

There are no leaks and reservoir is full of clean fluid. Bike is a 2004 S4R with unmodified brakes. My thought was internal failure of the master cylinder but happy to hear any suggestions.

If it is the master, are seal kits available for these bikes or would I be needing a new cylinder? Or is there even an upgrade path available?

[Mr Gazza]

First thing you could check is the span adjustment on the lever. Just push the lever away from the bar and rotate the numbered dial.
Then check that the little pipe from the reservoir to the master cylinder body is not kinked.

If neither of those things make any difference you're going to need to bleed the system. If it were my bike, having owned it for such a short time I would change the entire fluid as you can't be sure how old it is.
I have seen it turn to a jelly in the reservoir and pipes and when it does that it's extremely difficult to clean out of the entire system properly. You'd really need to strip the master and callipers, replace the seals and either flush out or replace the brake lines. That would be a very worst case scenario indeed but not unheard of!

For master and caliper seals Moto Rapido or https://powerhouse.uk/

[enbee23]

I have fiddled with the span adjuster and even with that fully out, the lever comes back to the bar.

I will bleed the system as soon as I get hold of a bleeder kit but am assuming that something internal has deteriorated to the point of effective failure. No external leaks or anomalies so prime suspect so far has to be the master. The fluid in the reservoir is clean and normal viscosity so hopefully I'll avoid the worst case goopy scenario!

[conquistador]

Have you bled it from the lever? It needs doing more frequently than the calliper bleed.

[enbee23]

I have a vacuum bleeder kit incoming so will bleed it every which way as soon as that arrives. If that doesn't fix it a new master is going on.

[350TSS]

Bleed it as best you can until you have a firm brake then put an elastic band/bungee cord around the lever and leave it under tension overnight. If, in the morning, when you take the band off, the brake is rock hard and the right distance from the bars - the job is done.
If the lever is not rock hard or worse than you left it the night before then the master cylinder seals have had it

[conquistador]

The brake lever bleed is the highest point in the circuit so any air will collect there.

[enbee23]

MityVac kit arrived so I bled it today, from the master. Tons of air. Lever much better than it has ever been in my ownership. But... I did a few other jobs on the bike after bleeding it and in that time the lever had become slightly softer again although firmed up after a couple of pumps. Will keep an eye on it.

[Luddite]

MityVac kit arrived so I bled it today, from the master. Tons of air. Lever much better than it has ever been in my ownership. But... I did a few other jobs on the bike after bleeding it and in that time the lever had become slightly softer again although firmed up after a couple of pumps. Will keep an eye on it.

If you still have air in the system, consider applying PTFE tape, (or even some grease), to the nipple thread to create a good seal - it may be that you're drawing air in past the threads when you loosen the nipple

http://www.ukmonster.co.uk/monster/showthread.php?t=58090

[enbee23]

If you still have air in the system, consider applying PTFE tape, (or even some grease), to the nipple thread to create a good seal - it may be that you're drawing air in past the threads when you loosen the nipple

http://www.ukmonster.co.uk/monster/showthread.php?t=58090


Thanks. I'd seen that thread already, was one of the things that steered me towards getting the MityVac. I thought I had ptfe tape to hand yesterday but of course it hid when I went looking for it. I will go back and re-bleed fully, including ptfe tape.

Has anybody fitted stainless bleed nipples? Good or bad reports welcome.

[Darren69]

I've had no issues with the stainless bleed nipples on my S4. I always put a very small smear of copper grease on the thread, just a tiny bit.

So do you rate the Mityvac? I've been considering one or something similar for a while, especially when fitting new lines.

[Mr Gazza]

I've got stainless and some Titanium bleed nipples. All good, but do make sure and buy the correct thread for your bike, there are two thread rates available.
I now always PTFE tape the threads after Luddites typically excellent tip and it works every time with no tears.

Now you've got the machine and a bottle of fluid open you might as well change the fluid completely for peace of mind, unless you already have done of course.
(Do the clutch and rear brake too if there's enough fluid as it's pointless storing it once opened.)

Sounds like your master seals should be okay though if you can get a firm lever. If they go it's almost impossible to get anything at all. But don't rule it out yet.

[enbee23]

I bought the MV 8500 kit with the metal-bodied pump. The pump itself seems a decent thing but the included plastic parts are a bit basic. It works though and certainly makes bleeding brakes easy for one person. The cheaper MV 8020 kit comes with a plastic bodied pump without a gauge and would probably work fine too.

[enbee23]

I've got stainless and some Titanium bleed nipples. All good, but do make sure and buy the correct thread for your bike, there are two thread rates available.
I now always PTFE tape the threads after Luddites typically excellent tip and it works every time with no tears.

Now you've got the machine and a bottle of fluid open you might as well change the fluid completely for peace of mind, unless you already have done of course.
(Do the clutch and rear brake too if there's enough fluid as it's pointless storing it once opened.)

Sounds like your master seals should be okay though if you can get a firm lever. If they go it's almost impossible to get anything at all. But don't rule it out yet.


Yesterday's bleed was just a first explore really. The lever improved but I'm not convinced it will stay good. I will revisit for a full bleed with ptfe and maybe stainless bleed nipples too. The fluid reservoir lid is looking its age as well so there will be some sprucing going on. I've got the fairing off anyway to replace a mangled bracket so now is the time to get in about the fiddly bits. And yes, I'll bleed as many of the systems as my bottle allows.

[enbee23]

Bleed nipple dimensions...

From what I can see, the three brake caliper nipples are M8 x 1.25, 15mm length.

Does anyone have equivalent numbers for the brake master cylinder and clutch slave?

Bike is a 2004 S4R.

tia!

[conquistador]

Watch out for galvanic corrosion if using stainless steel although ptfe tape should give protection

[Mr Gazza]

A stainless nipple is not going to make the slightest impact on galvanic corrosion, when the Aluminium calliper body already has steel or stainless steel pinch bolts and mounting bolts as well as a banjo bolt, probably brass, with copper washers on the steel, brass or stainless steel brake line.
The zinc on the original fittings is going to be way the first thing to go.

[enbee23]

Just finished putting it back together. The ptfe tape makes a massive difference to the ease and quality of the bleed, makes for a very neat job with the MityVac.

Complete change of fluid for Motul 660 and the lever is good. Did the clutch as well even though the lever was fine on that, cleaned out some gunk from the reservoir and flushed it completely through. The rear brake will have to wait until the wheels come off for new tyres soon.

I reused the original nipples as the hexes were sharp and the threads were still shiny despite some weathering to the exposed parts.