Uneven Braking

Leon · Postby **Leon** » Wed Mar 26, 2008 10:27 am

Have noticed on a couple of occasions the car pulls sharply to the right on braking.Its not there all the time however,after a few miles the brakes even up and stop well.Im suspecting its a caliper issue,its not used as much as it should unfortunately

and it all looks original stuff under there.Anyone experienced similar?

1991 Coupe Le Mans 5.3 Sportspack with ABS

Hosier77 · Postby **Hosier77** » Wed Mar 26, 2008 1:58 pm

If its under light braking, then it could be that the left caliper is sticking slightly, possibly needing new seals. If you brake harder, the pistons are forced past the seals resistance and you may be able to brake in a streight line.
The other thing to check is the disc run out, ie how flat it is. If the disc is slightly warped it gently knocks the pads back, so the first time you brake after a run you dont get much braking, the pedal moves a bit further down as the pads are pushed back out.

Leon · Postby **Leon** » Thu Mar 27, 2008 10:10 am

Thanks hosier.Ive had the wheels off and checked the calipers,everything moves the way it should,think I will go down route of replacing seals etc in each caliper.Have checked run-out on each disc and they look fine.

ptjs1 · Postby **ptjs1** » Thu Mar 27, 2008 11:17 am

Leon,

Without wishing to confuse you, I'm really not sure that I would replace the caliper seals just yet. Changing all the seals and bleeding the brakes is a pain, particularly as it is more likely that you'll have corrosion on the pistons which would then ruin the new seals anyway. If you've got no leaks and you really believe that the pistons are moving freely on both sides, then I would be looking elsewhere for the problem.

My first thought when I saw your problem was that you had a piston sticking, but this is usually caused by slight corrosion on the piston itself, not a failure of the seal. If your seals need replacing, then I would expect you to have fluid leaks. I would be more inclined to take out the pads, insert something thinner about the size of the backing plate of a pad and then very carefully (with the help of someone else) press the brake pedal until the pistons move towards the disc. Then retract the pistons fully and do that a couple of times until you're absolutely sure that the pistons are moving fully. Then grease up the piston with some suitable grease and replace the pad. Do one side of the caliper at a time. Then see if the problem is still there. I bet it will have gone. If not come back on the BB and I'm sure more knowlegeable souls than me will have some ideas!

Good luck

Paul

Leon · Postby **Leon** » Thu Mar 27, 2008 5:16 pm

Thanks for that Paul,just what I needed

I will check all this at weekend and report back,thanks again.

poprivet · Postby **poprivet** » Thu Mar 27, 2008 5:23 pm

While you're in there, have a good look for wheel bearing play or wear on the stub axles. Most likely to be a sticking piston though as already mentioned.
Pop

Leon · Postby **Leon** » Thu Mar 27, 2008 9:53 pm

Checked those last week thanks Pop,it went for MOT,and passed again

another 12 months of bliss !!!!!!!!
I agree with you I think it could be pistons,looks a bit rusty in there.

dogbitedavie · Postby **dogbitedavie** » Sat Mar 29, 2008 12:57 am

i had the same problem with mine, due to lack of use. but as Paul says, with the pads out, move the pistons in and out and they soon free up.also like he says, dont let the pistons pop out, there a swine to get back !!

Leon · Postby **Leon** » Sat Mar 29, 2008 6:34 pm

Thanks for all your responses.Ive had the pads out,the locating pins above and below on the OSF caliper were well rusted in situ.I think it may have been a case of the pads sticking to the pins as the pistons moved in/out pretty well but..........noticed that some moved out quicker than others

,this may be due to the constant in/out movement during the test and the fluid movement?
Ive ordered a pin/spring set for each caliper from JDHT and hopefully this will sort it.I will keep you all posted.

Leon · Postby **Leon** » Sat Apr 05, 2008 2:48 pm

New pin and clip sets fitted,piston ends lubricated,cleaned up all faces and jobs a goodun.Thanks for all your help.

ptjs1 · Postby **ptjs1** » Sat Apr 05, 2008 8:36 pm

Leon,

Great to hear that the problem is sorted! Well done!

Just to clarify, make sure you put some caliper grease on the side (cylindrical) surface of the pistons. It helps to both stop the cylindrical surface corroding and also helps to protect the caliper piston seals.

Paul

Leon · Postby **Leon** » Sun Aug 02, 2009 9:57 pm

The uneven braking is back.Swapped both front flexible hoses,and fitted new bleed nipples.
Ran plenty of fresh DOT4 through,bled and took for a run.First 10 miles great,thought it was over,then,under relativlely light braking,the car pulled sharply to the right

No damage done thankfully,its one thing knowing what may happen!
Ive read on Jag Lovers that problems with the rear brakes could cause this!Oil may leak from the rear drive seals on the diff and effect 1 x side.This may also answer the question why it doesnt occur when cold.
The other point Ive noticed is that when the car has stood for a week or so,when started the ABS warning light doesnt go out until the pump has stopped as it should,but this may take 60 - 90 secs.
Another interesting thing which may be coincidince,other vehicles reporting this seem to be around 1990 1991 when wading through the threads.

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