Caliper question

[zooropa1985]

About two months ago i replaced my front drivers side caliper, it was working really well until one day i noticed the car feeling very sluggish.

When i stopped the car i checked the caliper and it was hot, far warmer that the other side. I left it to cool down and when i came back to check it the caliper had free'd itself.

Checked the pistons and they were fine, yet when i take the car out she starts out fine but the longer i go on the more the caliper seems to start sticking again, only to free up when stopped for a few hours.

Any ideas what this could be?

[dansREV2turbo]

can only be the pistons or sliders. mine had the symptoms you describe and it was the piston.

[sticks]

same with mine.its the piston.prob the same with yours.

[peterv6r5]

Mate - if it sticks - you can only keep it goimg for so long.
Had my rev5 for 3 years - use to take alll 4 calipers off evey 4-6 months - clean regrease etc but got caught out when my mum got ill. rear got stuck on and cooked the disc. - So went for new set of discs all round and a new set of calipers all round. Sorted but cost me £600 + time etc. But now absolutly great.

[Peter Gidden]

Any ideas what this could be?

If your sliders are working correctly, sounds like a warranty claim to me.

[Will_bmx]

I may be completely wrong here, buy my drivers front is currently sticking and the first thing my experienced friend suggested wasn't the runners or piston (i know they're most likely), but air in the system heating up and sticking the caliper. Given your symptoms is this not possible?

[Peter Gidden]

I may be completely wrong here, buy my drivers front is currently sticking and the first thing my experienced friend suggested wasn't the runners or piston (i know they're most likely), but air in the system heating up and sticking the caliper. Given your symptoms is this not possible?

Your experienced friend needs to Google "hydraulic brakes" and if he does, he'll find that there will be no air in your brake system. If there was you would have a pedal issue.

Pistons and/or sliders are your suspects.

Alternatively, check whether your friend can get hold of a temperature compensated blow off valve for your braking system.

[Will_bmx]

No xxxx. He spends his life working with hydraulics on trains and he means a small amount of air in the system, ie, shouldn't be there but is and will expand under temp causing that piston to bind hard. No need to be rude and sarcastic.

[Si_Crewe]

Just had this issue on a mates motorbike so I thought it might be worth mentioning.

Turned out that the problem was the o-rings in the caliper were borked and were starting to melt!

What was happening, I think, was that the caliper was sticking on cos the o-rings were a mess and then, cos so much heat was being generated, the o-rings would go soft and the pistons could retract again.

Soon as it cooled down the o-rings would harden up again and ensure that the pistons jammed the next time you apply the brakes.


Thinking about it, I've seen o-rings go manky when hydraulic oil has been put in the system rather than brake fluid too.

Trouble is that, even if it's only the o-rings that are damaged, it's often a bu88er of a job to replace them without damaging them.


*EDIT*
Regarding the whole "air" thing, I guess trains don't do many track days.

If you've got any air in the system it'll expand under temperature and, as a result, you'll lose the pedal.

The brake system in a car isn't a closed system. It's open-ended so fluid can enter from the reservoir if neccesary.
If there's any air in the system and it expands it'll simply force fluid back into the reservoir, which is what makes your brakes more and more spongy as they heat up.

Air in the system is never going to pressurise anything (for longer than one pedal-press) because it isn't a closed system.

[Will_bmx]

Just had this issue on a mates motorbike so I thought it might be worth mentioning.

Turned out that the problem was the o-rings in the caliper were borked and were starting to melt!

What was happening, I think, was that the caliper was sticking on cos the o-rings were a mess and then, cos so much heat was being generated, the o-rings would go soft and the pistons could retract again.

Soon as it cooled down the o-rings would harden up again and ensure that the pistons jammed the next time you apply the brakes.


Thinking about it, I've seen o-rings go manky when hydraulic oil has been put in the system rather than brake fluid too.

Trouble is that, even if it's only the o-rings that are damaged, it's often a bu88er of a job to replace them without damaging them.


*EDIT*
Regarding the whole "air" thing, I guess trains don't do many track days.

If you've got any air in the system it'll expand under temperature and, as a result, you'll lose the pedal.

The brake system in a car isn't a closed system. It's open-ended so fluid can enter from the reservoir if neccesary.
If there's any air in the system and it expands it'll simply force fluid back into the reservoir, which is what makes your brakes more and more spongy as they heat up.

Air in the system is never going to pressurise anything (for longer than one pedal-press) because it isn't a closed system.

That's a more respecting reply.lol. cheers for that as it makes sense looking at it that way. Just cant stand rude responses that don't take the other points into concideration

[zooropa1985]

Thanks for all the replies.

Well yesterday was a nice sunny day so my dad and i stripped the caliper down and greased everything, bled the brakes and that seemed to free everything up.

Took her out for a spin last night and the caliper was nice and cool when i stopped... happy days.

However when coming home from work today i felt the car feeling sluggish again and so when i stopped i checked the caliper to find it was hot again...

Usually when the caliper is greased it lasts at least a few weeks before this happens again so im thinking could it be the brake hose itself?

This is the second caliper to do this in the last 13 months.

[Peter Gidden]

so im thinking could it be the brake hose itself?

This is the second caliper to do this in the last 13 months.

I can't think of any reason how it could be a hose.

Are you fitting old s/h calipers?

[zooropa1985]

Hmm i replaced the original one with a second hand one, it worked great for the last 2 months.

Funny enough it was this precise problem that meant i needed mine replaced.

Have i just got unlucky again?

[ashley]

When you say you stripped and regreased the caliper- do you mean you re-greased the sliders or have you stripped out the piston seals as well?

What kind of grease have you been using?


For what it's worth it sounds like you've been unlucky with the replacement units and may need to claim for warranty replacements

[Steve-O 2007]

did you fully remove the pistons?

My drivers front was sticking (so bad I could hardly spin the wheel by hand!!) and one of the pistons was solid!! Had a block of wood stopping the free one from moving and I had to realy force the pedal down just to get the piston to move! got it so far and decided to push them back in, had a compressing tool on them to push them back in and they were stuck solid!! wouldnt go anywhere! So I then had to tap it side to side with a hammer / screwdriver to free it and get it out! Other one came out ok.

Both pistons were a mess so I flatted all the crap off them with 800 wet and dry. I then flatted all the crap off the inside with 800 wet and dry. Put the pistons back in and good god what a difference, I could slowly squeeze the pistons back in by hand they were so smooth!!


Oh and dont use grease on the pistons, this can make them stick!. My Dad Rebuilt some micro ones ages ago and they were nice and smooth and then he decided to grease the piston, big mistake made the piston stick, had to take it out again and clean it all off!

Wont be your brake pipe... If it was the brake pipe you wouldnt have any brakes as you would just be pumping fluid out..

[Si_Crewe]

I dunno,
I'm always wary of writing things off to coincidence. 9 times out of ten you'll find another cause if you look hard enough.

I can't really see how a hose would cause this. I've seen something vaguely similar where a 2" hydraulic hose has delaminated internally and allowed oil to flow one way but then stopped it flowing the opposite way but I don't think that'd happen in a brake hose cos the internal diameter is so small.


Perhaps there's something else going on here?
Maybe the caliper mount is bent so the caliper isn't properly aligned or a wheel bearing is damaged so the disk is wonky in the calipers?
If something like that was happening it'd cause the caliper to heat up enough to cause damage to the o-rings.


What about the master cylinder and ABS unit?
I haven't looked at how the brake circuits in the MR2 are built but, particularly if your car has ABS, I assume (yes, I really should check this stuff out before guessing) it'll have seperate lines to each wheel.

In that case a dodgy seal, or something else, in the master cylinder (or ABS) could be causing the brakes to be applied unevenly.

Gotta say, from experience, mucking about with master cylinders can be a nightmare.
There's dozens of tiny o-rings which're easy to damage and you've got to do the work in a clean environment or and tiny lump of crud could cause a problem in the future.
Might be better to buy a master cylinder (or ABS unit) from a scrap car and swap it out.

FWIW, if the car doesn't have ABS this should be much simpler as, from looking at mine, it seems like it's a dual-circuit master cylinder that feeds into the ABS unit which then has 4 lines coming out of it.

If your car doesn't have ABS it's unlikely to be the master cylinder cos the same line should feed both front wheels...
...unless non-ABS cars use a different master cylinder with more than 2 output lines.