1990 Chevy Lumina rear brake help

[ChrisW]

In my auto 53 class (adv brakes, steering, suspension), out group is workign on a '90 lumina. We got the fronts all said and done (dual pistons is fun! to compress back into the caliper).

But, we are having trouble resetting the pistons in the rear disc calipers. I looked in the Mitchell OnDemand program (great program by the way) and it says to use a C-clamp to push them in, but the piston is just NOT going back in.

I have used a special tool (from harbor freight that I personally brought with me to class) to both apply force and rotate the piston at the same time, but it is going nowhere fast.

Anyone know how to push em back in? Would the foot operated parking brake pedal spring&pawl mechinism not working have anything to do with not being able to compress the pistons back in (I dont thin it would because the parking brake doesn't even work (because the pedal mechanism is broken so i dont see how it could be holding the piston)? The fronts went in fine....

 

[kevm14]

Maybe apply the brakes gently and see if the piston will even move out. It might just be completely frozen. Do the rear pads look like they've been used much?

 

[paulo57509]

Don't use the c-clamp. The pistons need to be screwed back into the caliper.

Getting no where fast? The calipers are most likely hosed. Most people with this vintage w-body will just go out and get rebuilt/new calipers rather than have to hassle with dealing frozen, non-functioning parking brake mechanisms and frozen pistons.

 

[Mike_dup1]

It should be noted that the early Lumina W style bodies have rear disc brake problems, frozen rear caliper sleeves..This problem affecting the front brakes.

Brake Manufacturers Council ?? Tech Tips

quote:

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We receive many calls regarding General Motors "W" Body brake problems. These include poor stopping, premature front pad wear, hard pedal feel and premature rotor wear. We are now getting calls on one or both front calipers contacting the inner circumference of the front wheel. This results in thumping, grinding or vibration when the brakes are applied. Although the symptoms listed above seem to suggest a front brake problem, you will probably find that the vehicles experiencing one or more of these problems are equipped with rear disc brakes.

The cause of these symptoms is frozen rear caliper sleeves. These sleeves will not allow the caliper movement necessary to apply the outboard brake pads to the rotors to become a supporting part of the total brake system. The lack of full rear brake function causes the front brakes to do more vehicle braking than they were originally designed to do. This causes undo stress on all associated front caliper parts and mountings.

The problem of caliper contact with the inner portion of the front wheels is caused by the upper caliper adapter mounting hole becoming oval shaped allowing the caliper assembly to be forced outward, away from the rotor axis.

Repeated braking with poor rear brake assist overcomes the clamping force of the adapter bolts that go through the front strut flange. These bolts have a torque specification of 148 ft. lb.. The strut flange is not strong enough to stop adapter movement when the front brakes operate under these conditions.

The correction for this symptom is to thoroughly inspect the rear calipers for proper sleeve movement and rebuild or replace as needed. Then service the front brakes and front suspension as listed below.

• Replace front strut housing.

• Check front rotors for run out due to overheating.

• Check front pads for excessive wear and/or glazing.

• Replace front caliper hardware.

• Replace front calipers if there is any indication the piston seal has been damaged due to overheating.

Unless both rear calipers are replaced with units that contain updated sleeves and hardware expect continuing problems of this nature to occur.

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[ February 01, 2005, 10:41 AM: Message edited by: Mike ]

 

[kenw]

"Don't use the c-clamp. The pistons need to be screwed back into the caliper."

???? so how the heck do you compress the piston to remove it? You have to do this before you can remove anything or even get to the piston.

 

[labman]

Rear disks are a pain, some more so than others. Unless the piston is completely frozen, you should be able to create enough clearance with a C-clamp to remove the caliper. Quit as soon as you can drag the calpier off. Any caliper that has been in service over 10 years without being rebuilt, the piston is likely shot. The casting should be reusable, but the price of a kit, plus a piston may run more than a rebuilt one, even without labor.

Once you have them off, the class should disassemble them as a learning project. If you jammed a corroded piston back with the C-clamp, it may not yield to the standard shop air. Likely you do not have the nifty, ancient machine we had at the brake shop that could pump brake fluid into a stuck caliper and force the piston out. I have heard of good results with a grease gun, but you would need to adapt to a Zerk. Once apart, you can see how the piston is corroded out from the middle where the seal wears the plating. You can also see how the parking brake bolt screws into the piston.

I question whether rear disks make good sense on FWD with ABS. More so as wheel sizes have grown. There is plenty of room in there for a big enough drum for all the more work it has to do, and ABS will keep the braking even. Of course, marketing demands disks and independent suspension, even if they add much more expense than benefit. I will stick with my Cavalier, its 5 speed, rear drums, and beam suspension.

 

[labman]

More thoughts on this. OK, you already have the caliper off, and are trying to return the piston to make room for new pads. It will not push all the way in if the adjuster did its job keeping the parking brake working. You should be able to push it in a ways and then finish by turning it, or the parking brake bolt. As long as the piston is in good shape, it should go in without too much trouble. If it won't, even in California, chances are the piston is corroded. Same story on conventional calipers. Pistons don't move very far with each application, but the seals do wear the plating as the piston moves out past it as the pads wear. Other pistons besides the chromed steel have other problems. Moisture, grit, and maybe salt work their way past the boot and corrode the piston. As long as the corroded part of the piston remains outside the seal, the caliper works fine. Time after time, we sold somebody a set of pads, and they were back in a day or 2, saying the caliper, that was working fine before, stuck or leaked. Even if you manage to push a corroded piston back through the seal, it either hangs up or leaks. This is why, whatever else you may do, the piston must be cleaned up, fresh lube applied, and aged, worn rubber parts replaced. Besides being cheaper, if done in time to save the piston, I prefer to rebuild because that way I know the outer part of the piston has a good silicone on it rather than brake fluid or some other hygroscopic crap.

Oh yes, I found this link on another forum. I have seen better versions elsewhere, but it does show the difficulty of understanding what the other one is saying, http://sethglassman.com/Cartoon.jpg

[ February 01, 2005, 04:19 PM: Message edited by: labman ]

 

[slalom44]

In addition to Labman's excellent advice, take advantage of the thermal expansion characteristics of the metal.

Heat up the caliper with a propane torch, and put the piston in a freezer. The heated caliper will have an ever-so-slightly larger cylinder, and the piston will shrink a little, making the fit easier. If the piston is aluminum (I doubt it), then the difference could be quite significant due to the high thermal expansion coefficient.

 

[ChrisW]

Thanks for the replies guys, they went in today. We had to turn the pistons quite a number of times to retract them, also with a downward force at the same time. I'm used to the few turns needed on rear disc brakes on hondas, and the few turns needed on audis/vw.

Its odd that the left rear capliper needed counter-clockwise rotation to go in, and that the right rear needed clockwise rotation to go in.

Perhaps we should have rebuilt the rear disc calipers, but today we only had two out of four of our group members, it was a short work day, and, the parking brake mechanism is built into the piston; its not the usual plain piston type which would be much easier to work on and rebuild.

Our instructor wants us to eventually learn to do a rebuild on both wheel cylinders and disc calipers, but if we do customer's [or personal, but on personal, i'd be more likely to rebuild for the sake of enrichment] cars as lab work, we're most likely to just buy a new or rebuilt unit [loaded or unloaded] for the overall ease.

The fronts had no binding/troubles whatsoever when they were retracted. I only wish this were the newer w-body with the non-integrated parking brake piston.

Tomorrow we are going to pressure flush/bleed the system, old fluid tested at 0.20v.

 

[paulo57509]

"???? so how the heck do you compress the piston to remove it? You have to do this before you can remove anything or even get to the piston."

You don't "compress" the piston to remove it. You need to unscrew it from the parking brake actuator screw. The screw pushes it out of the caliper bore.

1. Remove the nut retaining the parking brake lever.
2. Remove the parking brake lever.
3. Remove the lever seal and washer.
4. Rotate the actuator screw (in the brake apply direction) to work the piston out of the caliper bore.

[ February 01, 2005, 11:36 PM: Message edited by: paulo57509 ]

 

[labman]

''Its odd that the left rear capliper needed counter-clockwise rotation to go in, and that the right rear needed clockwise rotation to go in.''

Not really. That way when the lever is pulled forward on either side, the piston is pushed outward.

So who remembers Chrysler products having left hand threads on the lug nuts on the left side?

 

[Matt_S]

Let's not let one bad design influence our whole view of disk brakes. I'd rather do a disk brake job over a drum brake job any day of the week, even if it included a caliper replacement. Let's keep in mind, too, that the later W bodies don't have that complicated rear caliper any more, they use a miniature drum setup for the parking brake. The caliper is just a standard caliper now, making this problem a thing of the past. Thank goodness.

 

[Gary Allan]

quote:

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Our instructor wants us to eventually learn to do a rebuild on both wheel cylinders and disc calipers, but if we do customer's [or personal, but on personal, i'd be more likely to rebuild for the sake of enrichment] cars as lab work, we're most likely to just buy a new or rebuilt unit [loaded or unloaded] for the overall ease.

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What your instructor is allowing you to do is make more money for the job.

Example: Toasted starter drive.

Slap in a reman on a Ford (two bolts and a wire)
($ and time figures are pulled out of my ar$e but TIFWIW)

Labor: .75 hour
Parts $ xxx.yyy

Replace starter drive:
Labor 1 hour
Parts $13

Your paycheck is bigger. Putting in the reman helps the parts manager/service writer/service manager/owner/parts store more than it does YOU.

 

[labman]

With the right tools, it isn't much of a job to rebuild a wheel cylinder or caliper. As long as you don't have to replace the caliper piston, the kit plus a reasonable labor charge is less than a rebuilt. If you have trouble retracting the piston, or the boot is damaged, go with an exchange, a new piston is almost as much.

It still might be good to dismantle it, just to see what a used caliper looks like inside. I hope the instructor is teaching the art of freeing frozen bleed screws too. Another time consuming task you avoid with a rebuilt.

 

[kenw]

quote:

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Originally posted by Gary Allan:

quote:

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Our instructor wants us to eventually learn to do a rebuild on both wheel cylinders and disc calipers, but if we do customer's [or personal, but on personal, i'd be more likely to rebuild for the sake of enrichment] cars as lab work, we're most likely to just buy a new or rebuilt unit [loaded or unloaded] for the overall ease.

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What your instructor is allowing you to do is make more money for the job.

......

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not really. I do think it is important to learn the underlying mechanism instead of just learning how to replace parts.

 

[paulo57509]

quote:

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Originally posted by labman:
So who remembers Chrysler products having left hand threads on the lug nuts on the left side?

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I do. GM full-sized cars used to be that way up until the mid-60's.

 

[Mike_dup1]

quote:

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GM full-sized cars used to be that way up until the mid-60's.

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Say What?

Never heard of that. I had a 1959, 63, 64, 66 Chev full size cars and none had left hand thread. Also has a 1949, it did not either.

 

[labman]

Not my 57 Chevy. I don't think the various other older Chevies, Pontiacs, Buicks around did either.

 

[Gary Allan]

quote:

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not really. I do think it is important to learn the underlying mechanism instead of just learning how to replace parts.

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The concept of a brake caliper is simple enough to have an old one sitting there torn apart. Cut in half even. Unless you want to learn the technique of rebuilding one ..the exercize would be worthless.

We learned caliper rebuilding. It was an aquired skill. You could be shown it all day long and still not get it right until you did it enough times yourself. We even developed using air to help expand the boot around the piston. You could become quite quick at it.

In a homey environment I would never do one ..nor would I rebuild a starter. In a private shop I wouldn't do it either. Not when $800-1200 bucks is in the parking lot waiting for my attention and I'm zipping (and zapping) the parts markup and the labor to the customer. In a dealership environment ..where the labor determines my paycheck???