w-body rear brakes

Shep,

Yep, '96 GP has disks in the rear.

Regards, Bill Bowen

"Shep" wrote:

Mike,

Your regular service brakes self-adjust themselves as the pads wear by piston movement in the caliper bores, just like the front calipers. The ratcheting device is used only by the parking brake.

Where the problem comes in with the parking brake is that if the parking brake is not used for a long period of time and the pads have worn, the piston will have traveled too far outward for the parking brake assembly to properly apply the parking brakes until it is applied and released a number of times (the ratchet mechanism has to "catch up" with the piston).

If you never use your parking brake your regular brakes will work fine, but your parking brake may get to the point where it will not hold the car..

Regards, Bill Bowen Sacramento, CA

"Mike" wrote:

Actually, no...this isn't what is happening. The ratchet mechanism (if working properly) does not have to "catch up" with the piston, it happens automatically. I've replaced numerous pistons on these rear calipers, have seen how they operate, and the big problem is that they simply stopped working. In fact, what usually ends up happening is that not only does the park brake not work properly, but the piston is unable to "stay out" against the rotor as the pads wear, and you begin to have a low brake pedal. In these cases, I've successfully "adjusted" the caliper so that everything works, but it doesn't last. The caliper then has to be manually adjusted every so often. But since the rear calipers on those cars were about 3-400 dollars each (GM), most people were happy to simply adjust them.

The second generation of W-body rear brake calipers had none of these problems. I believe they started in 1996.

Ian

Ian,

All I can say is that is how the action of the older claipers was described to be. So far (knock on wood) I've have zero problems with the rear calipers on my '94 Regal, but I do know of folks that have had problems (and all of them have lived in snow areas where various chemicals are used on the roads for snow control).

BTW, can the newer type calipers be retrofitted onto the older model "W" body cars without having to change the rear knuckle?

Regards, Bill Bowen Sacramento, CA

We had a lot of problems with those older style calipers up here in Canada. Actually, that's an understatement. I'd be surprised if there was one car from those years that didn't eventually experience problems with the rear calipers. Along with what was essentially a one way clutch inside the piston that refused to adjust properly, we had a lot more issues with the caliper slide pins seizing up. The inability of the piston to adjust properly was largely ignored as folks were not going to be replacing calipers on that scale.

No, totally different design. Wonderful calipers tho, even with tons of miles on the cars, you can screw the piston back into the bore with a pair of needle nose pliers. The older style, even when relatively new, were a real pain to retract.

Ian

In all respect, the older rear calipers didnt work that way either, Bill.

The parking brake on most four wheel GM disc brake systems was manually applied via a cable to the rear caliper piston assembly

( There WERE variations where there was a separate parking brake minidrum to hold the vehicle. Corvettes among others might have had such systems.)

Since there was a solid connection involved through piston to the pad, automatic adjustment was a necessity. The piston did not travel freely as it would in a front caliper.

The ratcheting mechanism provided, on those occasions when it worked, the adjustment to take the slack out.

If you didn't use the parking brake, the automatic adjustment didn't work. Even if you DID use it, they often froze up and had to be manually freed up.

When the rear brakes dont apply properly, all the braking energy goes to the front rotors and you are soon out of pads and have burned up rotors.

I have worked on a ton of these, starting in about 1989.

Just some clarification here. Your first sentence above says the ratcheting mechanism provides the adjustment, the second paragraph says the parking brake is what was necessary to make the automatic adjustment work. Am I reading this right? The two statements seem to contradict each other.

Ian

I get your point, Ian. Those old systems were conditionally** automatic;>)

Dusting off my brain, here is the way I remember it... The ratcheting system on the rear calipers was actuated by the parking brake cable. When you set the parking brake, it put some clicks on the adjusters inside the caliper assembly in order to remove the slack. Of course, if they were already tight, no adjustment was possible or even needed.

If you didnt activate the parking brake, the rears did not adjust properly on these models, IIRC. You could quickly get outside the range at which the rear brakes would apply.

It was functionally and conditionally automatic -if you used the parking brake. And if it weren't frozen..

The newer 4 wheel disc systems dont seem to cause the problems these old ones did.