Rear brake trouble

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

I'm sure I read a thread like this a while ago but I can't find it. The rear brake on TDM went FUBAR today. There was suddenly no pressure on the lever when I pumped it I got pressure back then as I rode away and tried to use it again no pressure. The bike is going in for a service saturday hopefully it should sort it. But I am a little worried. The brake disc was boiling went I went to touch it so much so that when I licked my finger and trouched it it made a hissing noise! There is still plenty of meat on the pads.

Any ideas?
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Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
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Bezzer · World Chat Champion Joined: 14 Apr 2005 Karma :

If you haven't got a fluid leak then sounds like the master cylinder seal has gone, fluid goes past it so you're not getting much pressre. Pumping it eventually moves the pads in but they stick on as the cylinder won't draw them back that's why you have the boiling disc. If it's going in anyway let them know beforehand what's happening in case they need to get a master cylinder service kit in to sort it.
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skinny · Nitrous Nuisance Joined: 16 Jul 2007 Karma :

Sounds like the calliper is seized. the master cylinder does not draw the piston back the rubbers do if the fluid is old the heat generated will course the it to have no pressure.
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oops I did it again....

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

I'll take it to peices and give it a clean, I relly hope this aint gonna cost alot, the service is gonna cost me £450 (inc rear tire) Shocked

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Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.

skinny · Nitrous Nuisance Joined: 16 Jul 2007 Karma :

Give the calliper and pad sliders a good clean up and copper slip and force the pistons in then pump them back out do this a few times don't push them in as far as they will go or you can end up damaging the rubbers, Just enough to get them moving nice.
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oops I did it again....

Gazdaman · I did a trackday!!! Joined: 12 Aug 2004 Karma :

I'd say the heat is causing the lack of pressure.

The caliper pistons are crusty meaning they don't withdraw properly into the caliper meaning they stick onto the disk.

Causing a crap load of heat, which evaporates and water in the brake fluid. Which turns into gas which compresses easier than brake fluid leading to the sponginess.

OR the caliper seals could be shot as mentioned above.

Either way it's a fairly easy fix. Either it just needs a simple caliper overhaul (whip it off, clean up the pistons with a rag/cotton buds with brake fluid on, push the pistons back in and bleed it good.)

If the seals are knackered you'll have to remove the caliper, force the pistons all the way out, get the seals out, push new ones in, wet them with brake fluid, force the pistons back in (difficult, will need a G clamp or be careful with a vice). Then reconnect the caliper and bleed.

They'll probably do the former in a service but not the latter. A caliper seal kit will set you back about £20.

Gaz

Bezzer · World Chat Champion Joined: 14 Apr 2005 Karma :

skinny · Nitrous Nuisance Joined: 16 Jul 2007 Karma :

news to me not what I trained and at years ago or have worked with for years Rolling Eyes

never mind You can take his advise or mine. But I think you will find I'm right on it being seized and over heating. It will cost you nothing to find out Laughing

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oops I did it again....

Gazdaman · I did a trackday!!! Joined: 12 Aug 2004 Karma :

It's the vacuum effect of the fluid moving that draw the pistons back. The seals simply allow that vacuum effect to happen by keeping it sealed from the air.

The dust seals stop crap getting in there and messing up the seals.

Gaz

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

skinny · Nitrous Nuisance Joined: 16 Jul 2007 Karma :

Thankyou nice to know someone know what they are talking about.
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oops I did it again....

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Right I have taken them apart and cleaned them out and changed the pads. the pads where fairly new sub 3k miles and the piston was moderatly clean. I went down the road on the bike to post a letter and test them out. The brakes work fine (they did on the way home from work too) After getting back from my 1 minute ride I went to touch the rear disc but didn't I when my finger was about an inch from it I could tell that touching it was a bad idea, it was fucking hot! Does this mean a caliper rebuilt? the bike is easy to push and I cant here the brakes dragging at all. How much would this cost me from the dealers? I'm taking it in anyway so I might ask them to do it, depending on the cost.
____________________
Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

Did you take the seals out and clean behind them?

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Seen them (and got one). Remember that it uses a very low pressure (if you connect it to a fully inflated tyre then expect fluid everywhere).

All the best

Keith
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chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Tend to find that any way you try, you need to finish off with the conventional way. The conventional way works fine once there is some fluid through the system. Where it seems to be a real problem is from empty.

Some people use a syringe to push fluid through the bleed nipple and up to the master cylinder.

The Mityvac vacuum pumps are useful.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

Thom · World Chat Champion Joined: 24 Oct 2007 Karma :

back bleeding, this can even be done without removing the master cylinder cap as i've had to do it this way (although it takes alot longer!).

Simply assemble your brake system onto the bike, remove the master cylinder cap and undo the bleed nipple, now with a very large syringe full of brake fluid, attatched to a piece of tubing, connect the tube to the bleed nipple and force the fluid up into the master cylinder.

close your bleed nipple while the tubing is still attatched to stop any fluid escaping/air entering and finally add the cylinder cap back. now just pump the brake a few times until pressure develops.

Simple, ten minute job with no need for any fancy tools.
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Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Gazdaman · I did a trackday!!! Joined: 12 Aug 2004 Karma :

I use one of those one way valve bleeding things from Halfords. Always have. They work great. Very easy to use.

Gaz