new brakes + dual piston caliper + seized piston = trouble

[JHZR2]

Hi,

Our 94 toyota previa with 196k needed new front pads. THis is the second time the pads have needed replacement since we bought it new. It really hasnt needed a thing other than tires gas and oil... just standard PM. So we decided to replace the pads and put new rotors on.

We started by flushing the rear calipers (those pads and rotors were replaced about 25k ago), the went to the fronts. The stuff was pretty badly rusted, in terms of bolts (wow, it took a lot of force to get the ones that held the brake carrier' off!) and the surrounding metal. However, we got the right front done and then bled the fluid.

We then went to the other side. it turned out that one of the slider pins was so badly corroded that we could barely tilt the caliper up to service the pads, and then when we went to push the pistons in (this vehicle has singe piston rear calipers, dual piston front calipers), and the one piston went fine, the other didnt budge. We nearly broke a c-clamp trying to compress the one piston. Even with the master cylinder open, bleeder screw open (and leaking fluid), the piston wouldnt budge.

So, we had to put that side back together with the old pad and rotor (though the other side had new pads and rotor), and then bled that side to get the air out. The problem was that we were at our home in PA (vacation house), and so we had to get back (yes I know this was very stupid...). So we drove, minimizing the use of the brakes. All the way the van rode fine, no signs of a hanging pad (the side with the bad caliper didnt have odd wear patterns on the pad or anything when we removed it), and it stopped fine, though with a very soft pedal. We drove very slow and catuously, but since stopping ability was maintained, all was OK.

When we got home, we realized that the wheel on the side with the replaced pad and rotor (rt front) was VERY hot to the touch, and smelled slightly of overheated pad material. The van rolled fine, and didnt yaw, pull, etc when brakes were applied.

Why would the one side get so hot? WOuld it be because the side with the low old pad needed a lot more fluid and pressure to contact the pad to the rotor, and that made the good side squeeze that much harder? Once again, the van didnt pull or do anything odd at all. Could it be that the stuff was so rusty that the 'good' side wasnt sliding properly when the new pads were put in, and so they remained a little too close to the rotor, especially when the brakes were applied a few times in succession (stoplights and local streets)?

I hope the new pad/rotor werent ruined. What is the sign? discoloration from silver to black?

Any ideas why the pedal was so soft (Im hoping it was just excess air that somehow we didnt get out), and why the one side with the replaced pads got SO hot? Ive never had any problems like these, and have dont a lot of brake pad and rotor replacements...

Thanks!


P.S. does anyone have any knowledge of toyota remanufactured parts vs. small shop rebuilders? Are rebuilt calipers that failure prone? Right now were leaning towards replacing both front calipers with toyota rebuilds at $148/ea. There are neww dual piston calipers for the previa available, but theyre $450 each, and it seems that a toyota remanugfactured ought to be of high quality, and in rality the only diffeence being the casting date.
Comments?? Thanks!

 

[JHZR2]

Yeah I saw those... I have to wonder who does the rebuilding...ACEI??? if theyre any good. AC compressor rebuids in my experience have a relatively high failure rate... Id hate for brake caliper rebuilds to be the same.

Toyota rebuilds would at least be a little bit more quality assured, right?

Thanks!

 

[Willy_G]

They are rebuilt by Automotive Caliper Exchange Inc. out of California.

In my experiance I've seen many "Japanese" caliper slides/pins sieze, but have never seen a piston sieze unless a boot was damaged, the car sat for a looooong time, or the car was sunk.

If this were my van and I took it to my trusted mechanic's shop for calipers...these are the exact units he would order.

As long and the cyl bores are poished and new seals installed, there really isn't much 'improvement' in quality to be made.

 

[JHZR2]

Ok, thanks...

Yeah the slider in that was not removable (one side has a removable bolt the other has a permanently sealed pin, unline the rears, my BMW and chevy truck where both sliders are servicable and regreasable) was severely seized up... couldnt slide or tilt upwards. The piston looked fine! A little rusty at the pad interface, but so was the good one... The seal looked perfect and everything seemed OK. But it just wouldnt go in!

I tried with the bleeder valve open, with the reservoir to the master cylinder open, etc. It wouldnt budge with a c-clamp pushing evenly on both pistons, with direct force, even with big channel pliers, which can exet a LOT of force... the other piston went in fine... Do you think I may have done something wrong?

If ACEI is a good rebuilder, than maybe we can save the $75-100 each over the toyota ones... Ive just read that sometimes generic parts or lower quality rubber seals are used... not my cup of tea in a brake caliper...

Thanks for the insight!

 

[kenw]

I got Wagner rebuilts for my Camry and the part markings and machine marks were identical to the core (factory) caliper I returned.

 

[labman]

Rubber parts do not last forever. As boots age, even if they don't show any damage, they loose their elasticity and fail to keep out moisture, grit, salt, etc. Eventually it gets to the part of the piston outside the seal. If the piston doesn't easily push back in, it is going to leak, stick, or both. The calipers need to be rebuilt or replaced at least every few pad changes. The anal, every pad change. As long as the piston is in good shape, a rebuilt caliper is as good as a new one.

The hardware all needs to be cleaned up, replaced if damaged, and lubricated to ensure good operation. I slather everything except the pads and rotors with Sil-Glyde when I do a break job.

You may as well plan on rebuilt calipers. Likely the pistons are shot. A rebuild kit plus a piston is about as much a rebuilt caliper. Might be interesting to pop out the pistons before turning them in and look for corrosion on the outer part.

 

[Tosh]

quote:

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Originally posted by labman:
Likely the pistons are shot. A rebuild kit plus a piston is about as much a rebuilt caliper. Might be interesting to pop out the pistons before turning them in and look for corrosion on the outer part.

---

If I were younger and more inquisitive (been there, done that), I would try to polish up that piston and bore and see if it worked again. But it isn't really an area to fool about on, especially on the family minivan. I think you'll do fine with just one rebuilt caliper.

 

[JHZR2]

I thought so too... but after 196k, likely its not hurting anything to replace both. Id hate to only replace one then have the vehicle yaw as we braked... At the prices they go for, I figure we might as well.

 

[kenw]

if you do replace only one and it "yaws as you brake", then you probably should have replaced both....

but if only one is bad, only replace that one. You may do it again soon on the other, but ony time will tell. replacing them both is probably a good idea at that mileage but i don't/didn't at ~160k.

no yaw-ing yet.

 

[andyd]

Uhhmn, maybe apples and oranges but Ive had success rebuilding single piston calipers for my 528es. Ive freed up stuck pistons by peeling back the dust cover and giving them a small squirt of penetrating oil. I've used a vise and a socket to free a really badly stuck piston The O-ring is in the outer most end of the piston. The only pitting I saw was in the base close to the bleeder. This is well beyond of the travel of the O-ring on the piston. Rebuilding the calipers is pretty easy except for fitting the dust cap properly. Your comments re the difference in price is well taken, I keep a rebuild kit around only because I have 3 identical cars. and its much more convienent to rebuild than to find a rebuilt caliper at night or on a Sunday afternoon. A rebuilt GM caliper for my Grand Wagoneer is only about 15$ at A-zone. I dont mess with them at all.

 

[labman]

Actually, when I worked in the brake shop, I polished off a lot of rust on pistons and put them back together, as long as the chrome plating wasn't flaking off. Even if the piston corroded again, as long as the corrosion was outside the seal, it would work fine for at least one set of pads, maybe more with a good coat of Sil-Glide. I had one Lincoln owner ask if we could replate the piston. I said yes, it would have to be stripped, plated, machined, and polished, and we could buy a new one for $20.

When the guys came in and talked about how hard they had to work pushing the piston back, I knew they were shot.

 

[Willy_G]

$55/Ea. at www.bimmerparts.com

I have bought bunches of VW & Audi stuff from this outfit w/o any problem. Many things ship same-day.

(It is really just on of the many storefronts for Worldpac...supplier of OE parts to many independant shops.)

[ October 11, 2005, 01:17 PM: Message edited by: Willy_G ]

 

[labman]

As far as protecting parts outside the seal, flushing is a waste of time and money. I am still waiting for an explaination of how it gives immortality to the boot that never touches the fluid until the seal leaks.

 

[JHZR2]

whats to say that this caliper failed because of parts outside of the seal? IMO the seal looked AOK, and the issue was internal... perhaps due to a fluid issue, perhaps not...

Unless we tore it down, which we cant because its a core, I couldnt say.

 

[AcuraTech]

IMO brake calipers can and will fail sometimes for no apparent reason. Sometimes the slides stick, sometimes the pistons get stuck. It happens and some cars seem more prone to it.

BTW Brake Fluid flushing is definetely a good idea if you want to keep your ABS happy.

 

[Winston]

I am curious. Did you ever replace the brake fluid on that minivan? Or is it the same fluid that it had since the last pad change?

 

[JHZR2]

We have it flushed with each bigger serivce... maybe every 60k.

Until I got my MB, BMW and saab, I never really thought about brake fluid. The manual doesnt give any changeout interval.

The fluid was slightly darkened, but when squeezing it out, there was nothing abnormal, no particulates, etc. noticable.

Likely should flush it yearly in all cars like my BMW reccomends.

 

[labman]

I have torn down hundreds of leaking calipers or with a stuck piston. Most of them had a big gob of rust on the part of the piston outside the seal later in the life of a set of pads. Many of them were working fine until the rust was pushed back through the seal to accommodate a new set of pads. A good way to have to pitch the pads you put in yesterday.

Calipers fail for a reason. It could be they were run so long the seal wore out or lost its elasticity. They are cheap and easy to rebuild. You are blowing smoke about safety and preventive maintenance if you run more than 2-3 sets of pads between rebuilds.

Clean up the hardware good every pad change and apply a silicone grease. Rebuild/replace the calipers every second pad change. You should never have a caliper problem. Don't let the hoses go too long either.

 

[Schism]

As for the pad and rotor you put on that got burning hot, it would be best you just replaced them.

 

[JHZR2]

labman, thanks for the info...

The pistons were both quite rusted on the outside (~200k of rain and dirt will do that!), but the one didnt push in at all from its original position. It was already seized up, as was the slider pin that is not servicable (one is a greasable bolt, the other is permanent). 2-3 sets of pads was about what we had -though we were at 196k. I guess we were due! Ill be puting in rebuilds as PM from this point on every so often!

Thanks,