Brake caliper seized....but it isn't!

[Alex O]

Strange thing happened today.

Front right brake seized on at around 70mph and of course had lots of wheel wobble. Stopped and smoke pouring off the pad.

So, took the wheel off and the caliber wasn't seized, everything moved freely. Tested the brakes and as normal the pads engaged and released.

Have done a further 70 miles since and no problems.

Any idea what may have caused this? ABS issue? Is there a way to test this using my paperclip? Should I bridge the normal T1 and E1 ports ( or whatever letters they are)??

Thanks

[alanmr2turbo]

there is a way of doing a diagnostic using the papar clip but its a different config which i cant remember at the mo. Will look it up and let you know if someone doesnt post it before

[alanmr2turbo]

Tc and E1

and a link to show what error codes are

http://www.stephenmason.com/cars/mr2abscode.html

[Alex O]

Alan, you're a star.

Thank you. I'll get to this over the weekend and see what happens.

Thanks again
Alex

[alanmr2turbo]

no probs, hope you get it sorted

[JeffD]

I'm assuming youve tested the caliper by checking the pistons go back in ok and youve also checked the sliders slide?

If so have you checked that the pads themselves arnt sticky? Try removing caliper out if the way and take the V shaped springs off (if you still have them) and just check that the pads themselves move freely on the little clips - had it a couple of times now where everything is in good order but the pads stick.

If the above happens remove the pads and also remove the clips - the hub carrier goes rusty underneath the the clips - particularly the bottom ones - and scrape away all the rust/yak etc. Clean the clips and out the pads back making sure they move freely :-)

[2tmike]

that must have been a scary moment, and under the wrong road conditions .....!!!!
It should be almost impossible for an ABS unit to malfunction in that way...brakes are safety critical items and go through quite severe failure mode analysis during design...
Sometimes you can get a sticking piston that will seize the brake on to that wheel although I've never experienced it to be an 'emergency stop' level of braking. End result is pads smoking and disc, caliper and hub seriously hot...but, when it all cools down the piston has freed itself. I had exactly this today driving up the M5, the NS front stuck a little and it got worse the longer I drove for obvious reasons. Then after parking on the drive for an hour the piston has released

[Alex O]

The pads aren't that old, about 2000 miles. The sliders and metal clips are all free and happy. Good thinking though.

I haven't checked the pistons yet, however, this caliper seized proper only 200 miles ago and I cleaned and rebuilt using new seals/rubbers etc. even if I was a total muppet (quite possibly) it should last longer before seizing again.

The 70 miles I have done since were also fairly quick ones and no issues (that would have given the brakes a chance to fully heat up again).

If I don't get any error codes I'll take everything apart and investigate a bit more thoroughly than I was able to at the roadside.

[John145]

Cannot be an ABS fault, ABS only removes brake pressure it does not apply it.

Good luck finding out what it is though.

[Nic]

What pads do you have fitted? sounds like a pad is loose, twisted in the spring clips and jammed onto the disc.

[Alex O]

What pads do you have fitted? sounds like a pad is loose, twisted in the spring clips and jammed onto the disc.

They are carbotechs.

You're saying the same kinda thing as JeffD I think.

Could be right, I'll have to take a closer look....when everything is not 2 million degrees!!!

John145, yup! But worth a look anyway.

Final thought is corroded rubber brake lines, however, they seem to work fine again so there again, maybe not.

[JeffD]

When you disassembled them to inspect them did you notice any parts that seem stuck ie. pistons didnt go back in easily or the pads were difficult to remove from the carriers (which would point to what I suggesed)

[Alex O]

When you disassembled them to inspect them did you notice any parts that seem stuck ie. pistons didnt go back in easily or the pads were difficult to remove from the carriers (which would point to what I suggesed)

No, but as it was still very hot, I couldn't fully dig around.

The only thing that is 100% Ok is the sliders. The rest I shall need to take. Closer look at.

I'm hoping sticky pad as you suggest-easiest fix!

[marshiboi]

I had this exact same experience, turned out to be a seized caliper and needed replacing, I ended up just getting a new one instead of getting it reconditioned.

Not worth the risk, especially considering what a seized brake could suddenly do at 70mph

[Alex O]

So, upon investigation I have to conclude that those who suggested a stuck pad must have been correct.

The abs showed no error codes.

The newly refurbed caliper is good as gold (go me!) but there was a lot of dust around the clips.

I can't remember for sure, but I guess that after the caliper first seized I must have repaired and replaced without properly cleaning all the old dust off....hence the latest issue.

Good day for a thrash so I'll go on a proper shakedown now and hope for the best!!

Thanks for all the suggestions.

[Alex O]

Still screwed!!

Not losing my patience at all!!!!!!

The caliper is certainly not seized but the brakes don't retract off the disc. Only occurs when hot.

They are in certain need of a bleed (no question).

Could air in the system cause this? When hot, the air expands and doesn't let the pads back off the disc.

When cooled down it seems ok again.

[Nic]

It won't be air in the brake lines causing the issue.

Still think from your description of what happened it's a pad that has moved in the spring clips and jammed itself onto the disc.

The only way you're going to cure the issue is to remove the calipers and refurbish them, I'd also fit new springs clips for the pads. I've just refurbished all my brakes and it's made a massive difference to the braking - http://www.imoc.co.uk/forums/viewtopic.php?t=159506 Alternatively you could get them refurbished by a company such as http://www.biggred.co.uk/

[Alex O]

Think I may have got to the bottom of this:

One of the rubber boots over the piston has split (after 2000 miles!!).

The undamaged booted piston extends and relaxes as it should, however, the one with the damaged boot will extend but not relax. So....not properly seized but enough to keep the pad against the disc and cause problems.

New boot ordered and hopefully this should be resolved early next week....

[Nic]

A torn seal and sticking piston wouldn't cause a brake to suddenly lock up.

[JeffD]

theres also a little rubber ring over the other end of the slider bolt which can cause problems too so check that as well plus whether the bolt is rusty too