[battlecat]

The rear brakes on my 1987 Cressida (disc brakes) have (all of a sudden) started failing to release completely. This means they are dragging and becoming red hot (the front brakes have no problem). Yesterday, I removed the rear calipers, inspected them, (did not disassemble them), and finding no obvious problem, pressed the piston back in, then replaced them, then replaced the brake fluid in the car, flushed the brake lines completely (bled brakes on all four wheels). I should note here that the brakes fluid coming out of the rear lines was quite dirty, (the front lines were not so bad)..I flushed them until the fluid coming out was clean. Then I drove the car again. The problem was still there! Now, I can go ahead and replace both calipers, but would this fix the problem? Why would both calipers start dragging AT THE SAME TIME? Could the problem be further up the line (either with the master cylinder or in the lines between the master cylinder and the rear brakes?) When I bled the brakes, the fluid flowed fine. I should also note this car doesn't get driven allot (it sometimes sits for as much as two weeks at a time without being driven at all...this problem started to occur immediately after a two-week period of inactivity). Anyone have any ideas???

 

[nitro's good 4u]

How is your handbrake cable? jack the rear up and see if the wheels turn freely (in neutral) with the handbrake off and check the difference with the handbrake on

 

[battlecat]

Thanks nitro ! Yeah, That was the first thing I checked. (I neglected to mention that). When I pulled off the calipers, the wheels were immediately freed (no dragging at all from the parking brake). Before I pulled the calipers, however, I checked the parking brake cable tension with the lever down and it was slack, no tension, then I planned to dismantle the hub to get into the parking brake hub (to see if perhaps the mechanism was frozen with rust, etc) When I popped loose the caliper and revolved it up, the wheel was freed to turn without any dragging whatsoever!.

 

[kamesama980]

the ebrake will wear through the pad and into metal which you'll hear long before it starts smoking. they just don't have enough friction/life. stupid disk/drum combo setup

 

[stepho]

Since both went wrong at the same time and the handbrake cable has been rules out, that only leaves the hydraulics.
I've had bad master cylinders before that pumped fluid into the brake lines but didn't allow it to return when the pedal was released.

Jack up the rear wheels, pump the brakes and hold the pedal down.
See if a friend can turn the wheels by hand.
Release the pedal and ask the friend to try turning them again.
If they are still held tight then it is probably hydraulic.

As a double check, put a tube on one of the bleed nipples and release the nipple.
If the fluid comes out under pressure then it is definitely a hydraulic problem.
If it just dribbles out then we're barking up the wrong tree.
Just in case air bubbles got in during the test, bleed the the brakes.

Another (remote) possibility is grit in the fluid causing the pistons to stick.
Disassemble, clean and put new fluid in.

I've had grit in the slides of the calliper (the sliding part that lets one piston press on both sides of the disc) which caused it to stop sliding.
A clean up, some axle grease (keeping the grease well clear of the pads and rotors) and reassembly fixed that.
But hard to see how both callipers could go wrong at the same time.

We ruled out handbrakes but I have had one of the pins that holds the shoe in place drop off.
Other small bits then fell off (washers, springs) and got ground down real good

- Stepho

 

[battlecat]

great suggestions, stepho! I WAS wondering if this could be a hydraulic problem (for example, I've heard of interior walls of brake lines becoming corroded or otherwise partially blocked and acting as a "check" valve - allowing fluid to pass only one way - which may contribute to the problem). The suggestion to open the bleeder valve at that point (as a diagnnostic procedure) is a good one...I'll check that out. I have inspected the slider pins and they appear fine, well-lubricated with no corrosion or sticking at all. I will also check out the other suggestions you made (don't think my problem involves any malfunction of the e-brake as it performs without problem and there is no noise from the hub when rotated by hand). Regarding grit in the lines, I am wondering if this might not be the problem...(as noted in my first post above) the fluid coming out of those rear cylnders was pretty dirty with some kind of trash in there....perhaps evidence of corrosion in the system. But I am wondering if this "trash" could cause both rear pistons to stick). If I can eliminate the hydraulic system as the problem, then that just leaves the calipers. I did have another car whose front calipers began sticking at the same time...changing the calipers fixed that one!). Thanks again!

 

[battlecat]

the ebrake will wear through the pad and into metal which you'll hear long before it starts smoking. they just don't have enough friction/life. stupid disk/drum combo setup

agreed (to both observations...why did anyone develop this disc/drum ebrake combo thing? My Subaru has a lever that acts on the caliper..and it works FINE! But that's just my rant for the day!)

 

[battlecat]

...just wanted y'all to know...the problem has been repaired...and it turned out to be the calipers after all. Replacing both calipers appears to have fixed the problem...thanks everyone for your help!

 

[Jeff Lange]

agreed (to both observations...why did anyone develop this disc/drum ebrake combo thing? My Subaru has a lever that acts on the caliper..and it works FINE! But that's just my rant for the day!)

There are problems with both types, but generally speaking drum brakes can lock up better than disc and as such are better suited to a parking brake, which should never be on while the vehicle is moving which means the shoes should theoretically never need replacement. I've never had to touch the e-brake mechanism on the Supra, but on my Corolla which has the e-brake as a part of the calipers, I've had the bearings fail and had to replace the caliper because of it. That being said I know people who have had the parking drum setup fail as well.

Basically my point is, no matter what you do, something can always wear out. I've found that it is usually cheaper to repair something in a drum-in-disc parking brake setup than in a caliper-actuated parking brake. It varies from brand to brand though.

Jeff

 

[battlecat]

Good points, Jeff.....makes sense...thanks!