'94 TC Rear Brake Issue

[Ornery]

What are the chances the ABS Hydraulic Unit is at fault here?

I've installed new rotors, calipers, pads, master cylinder and vacuum booster. The rear right brake (and possibly left as well) is sticking closed on occasion. The rear calipers were originally replaced because they were seized open. After replacement, the rear right was chattering when brake wasn't applied. I replaced the pads and the chattering stopped, but I can still feel the brake applied once in a while. (The pads that came off were pretty singed.) The engine strains to overcome it, until it finally lets loose.

Could a section in the hydraulic unit be causing this? Since the rear calipers were frozen for so long (years), it may have allowed corrosion in that segment of the unit. I'll probably just throw another caliper at it, since it's under warranty anyway, but I thought I'd ask if anyone else has faced this problem first.

Thanks.

 

[dRock95MarkVIII]

Have you lubricated the caliper slide pins?



Do you have optional Electronic Traction Assist?
Do you hear a 'buzzing' sound under the hood when this happens?

 

[Ornery]

I'll be darned, I didn't expect to ever get a response at this point, but I was going to post the results when I finally solved this.

Pins were all lubed with hi temp grease, and I replaced the pins in the rear right caliper last time it was removed.

I don't have Traction Assist as far as I know. There would be a button on the dash if it did, right? Mine's an Executive if that makes a difference.

There is no sound when the brakes start to seize, but the pedal is higher and harder when it occurs. Otherwise, my pedal is a tad mushy and low no matter how much it's bled. I've never bled the ABS unit, which is probably the cause of this mushy condition. This "seizing" seems to come and go at random, whether the pedal is depressed or not. I can feel it come and go by the "seat of the pants". Engine lugs and coasting is poor. It doesn't seize so tightly that the engine can't easily overcome it, but it's dragging bad enough to notice. On the 27th I found both front brakes are seized at the same time this happens.

Replaced the right rear caliper again on the 26th and all four hoses on the 29th & 30th. Didn't help. On the 1st, I finally turned it over to my mechanic, who gets all the jobs I can't handle or figure out. No word yet. I will update this thread when the issue is resolved.

Thanks for the help,
John

 

[papa bear]

to much lube on slide pins causing air not to release sucking them in and not releasing them or rear emergency brake hanging up

 

[Ornery]

The rubber the pin passes through is open on the end, and they aren't very long or complicated:

Seems unlikly both brakes would be affected simultaneously due to suction in a pin's bore.

The E-Brake is completely non functional:

Edit: Hold on, the fronts are more complicated and the end is sealed I think:

If that's what's causing the trouble... I'LL SCREAM!

 

[Ornery]

My mechanic called this morning to report all four calipers were grabbing at the same time, and that tapping the master cylinder released them. The master cylinder was replaced on the 4th, along with the booster, both front calipers and all four pads. Rear calipers were replaced the following day and the trouble has been ongoing since.

I told him to install whatever brand master cylinder he thinks is best. The master cylinder I bought from AutoZone was actually warranted out when I got it. I only replaced it because of the mushy pedal. Not sure what they'll do for me when I ask to be reimbursed for it. Take this as a head's up for the wondrous crap sold by AutoZone. Warranty doesn't mean squat when you tally all the lost time and headaches!

 

[papa bear]

proportioning valve was my next guess let us know if the new master cylinder was the fix

 

[Ornery]

Well, $180.58 later, I'm back to my low, mushy, pedal but without the sticking calipers issue. My wife picked up the car, and he tried to explain the poor pedal, but she glazed over and simply told me to call him about it. I assumed it was due to not bleeding the ABS, but she said that wasn't mentioned.

A nice fellow at AutoZone (the manager) told me he'd reimburse me for the master cylinder and even the core charge for my current unit, so I'm OK with that. Hope this helps somebody else down the road, but I really doubt these same circumstances will crop up again.

Happy Motoring,
John