TAC Tech > Tires, Brakes & Suspension
1981 Rear Disc Brake Parking Brake
TATurbo:
Thanks, Blackbird!
I finally found the appropriate page in the manual. I was annoyed that there's no info about the lever in the parking brake section. Turns out...that info is over with the caliper / section of the brake chapter. I found this in my good old Chiltons manual, circa 1992...
79 - 81 GMRear disc brake by Tom Sherer, on Flickr
It says to compress the caliper with a C-Clamp, just like a 'normal' disc brake caliper...
79-81 GM rear disc brakes by Tom Sherer, on Flickr
I got it to push in about 1/8 on this old caliper...But somethin' aint right 'cause I ruined my biggest C-Clamp in by having to use a prybar on it.
79-81 GM rear disc brakes by Tom Sherer, on Flickr
This C-Clamp had survived several prior brake jobs. I'm sure I wasn't blocking the post on the back side while trying to clamp down. I guess I just hope the ones on the car will be more cooperative. IDK, this whole setup seems to be a PIA. If you look at the exploded view above, you can see there's a washer and seal that have to go on first...They are about 1/8 thick, then the lever itself is another 1/8 After all that clamping my 'test' calipier still isn't seated enough...
79-81 GM rear disc brakes by Tom Sherer, on Flickr
That's even enough for JUST the lever...which is 1/8 thick...
Untitled by Tom Sherer, on Flickr
On top of all of that, that hexagon shape in the lever is a very tight fit over the hex on the caliper actuator/post. The stock one shows evidence of perhaps being 'coaxed' on with a screwdriver/hammer at some point in the past. The hext shape in the NEW lever seems to measure just a tiny bit too small to fit over the hex on the actuator/post...I can't get it to go on...even on the bench. Honestly, the new pieces appear to be too precise and may require some 'fine tuning' to make them less precise?
I'll keep at it...At least I now have the information someone might use to complete this job.
81Blackbird:
Also, if the piston bottoms out and it is not full retracted, just turn the adjustment screw in one turn or two but not so far that it pops out of the O-ring. They are a PITA. I hope the ratcheting system works.
TATurbo:
You can say that again, 81Blackbird! These are a pain.
I think I sorta figured it out. And, I'll write it out here in case it might help someone in the future. But something funky is going on with the left (LH) side caliper.
Does anyone have a pic of an original set?
I think the LH calipers are rare for some reason. Core charges are 3x what they charge for RH calipers. Some places have only the RH part listed. Some say LH is discontinued. The places that list a LH caliper show either an unmarked unit or one with an R stamped on it. I cannot find a picture of a caliper marked 'L' anywhere.
I purchased the calipers installed on my car in 2015. They are ACDelco replacements. There is an "R" stamped on the caliper body and the actuator post for the RH caliper. The LH part has no markings. I went back to pics I took when I disassembled the car in 2015. And found this...
P9240061 by Tom Sherer, on Flickr
TWO RH Calipers?!
The car was 10 years old when I bought it. I have no recollection of changing the calipers back in the day. But, there is no way GM would stamp an R on one caliper and leave the other one with no markings...right? And, GM definitely wouldn't have a Left side caliper with a big R on it...right?
So, WTF is up with these LH calipers?
The reason why all of this matters is because the spring bracket and lever only install onto the caliper one way. And, when installed that way on my unmarked "LH" caliper, the lever turns the actuator in the wrong direction.
Turning the actuator post CLOCKWISE engages the parking brake. If you look at the pic below you can see that when the cable is pulled toward the front of the car by the parking brake pedal (compressing that spring), the post will turn COUNTER CLOCKWISE.
Untitled by Tom Sherer, on Flickr
So, I think one of the following must be true about the real (correct) LH calipers of this design.
Either:
A) The bolt hole that determines how the spring bracket is clocked (And maybe the position of the lever stops)
are in different positions then a RH caliper. (Allowing the lever to be mounted at say 2 o'clock instead of the 7
o'clock position shown above).
or
2) The actuator post in a 'real' LH caliper turns in the opposite direction? (COUNTER CLOCKWISE to push
on the caliper piston in, thus engaging the brake)?
Do any of you guys have any thoughts on this?
I haven't fully tested things yet, but the RH caliper is installed, adjusted, and engaging as expected. So, things are 50% functional I suppose. I'll share my experience getting things adjusted in this thread in order to close the loop on things. But, I wanted to see if anyone has any experience to share regarding the LH caliper issue noted above first.
Thanks again TAC!
Take care.
-Tom
TATurbo:
Ok. This is stupid. I spent about 6 weeks fiddling with the stupid parking brake. Spoiler Alert...It still aint right.
But all the parts are together and they should pass the PA State inspection.
Anyway, I figured I'd close the loop on this thread.
I finally found a picture of an actual marked, LH Caliper:
GM Left Rear caliper by Tom Sherer, on Flickr
As I suspected, the unmarked caliper on my left rear is wrong. You can see in the pic above how the park brake lever is up around 1 O'clock vs. 7 O'clock on the unmarked caliper I got when I ordered Ames PN FR218EB (now discontinued).
Untitled by Tom Sherer, on Flickr
The orientation of the lever is determined by a metal 'stop' on the back side of the caliper + the hole that mounts the spring retainer.
Reviewing old GM Parts catalog info, combined with some notes I think came from a pre-crash TAC post from someone more familiar with these parts, I found the GM PN's for these calipers are:
18006748 Caliper Rear(LH)
18006749 Caliper Rear(RH)
And, These calipers were also used on Cadillac Seville's and El Dorado's of the era.
So, to have a properly installed and fully functional e-brake, I need to replace my LH caliper with the correct one.
Finally, I wanted to try to write something about adjusting the parking brake. 'Cause the instructions and video's I found seemed contradictory in some places. Maybe its just how my brain works. Here's how I'd describe the adjustment process:
Caliper is on the car. Pads installed.
When turning the post/actuator via the inner hex shape, the post will move in and out. There is some sort of ratcheting/clutch voodoo going on inside there. While the post can push on the piston, it is not directly connected to it.
Because of the way the post moves in and out, you need to install the lever retaining nut onto the post while turning it with an open-end wrench. The nut prevents the post from pulling too far in so you can't reach the inner hex shape...Like my first problem in this post.
Untitled by Tom Sherer, on Flickr
Turning the post clock-wise pushes the piston outward, clamping the pads to the rotor / actuating the brake. Keep turning Clock-wise and eventually, the piston will clamp the pads on the rotor. It'll get tight and wont turn Clockwise anymore.
Turning the post counter Clockwise backs the post off the piston. but, remember it's not connected. So...it doesn't actually pull the piston back in. Turning Counter clock-wise works the adjustment mechanism. Because of magical, self-adjusting clutch/ratchet in there, a person could spin and spin and spin Clockwise and not notice any change. But, there's some sort of ratchet that is the key to adjusting the park brake actuator/lever.
OK, so...With the nut installed on the post, put a wrench on the inner 9/16 Hex and turn clock-wise until it wont turn anymore.
Here comes the 'trick'. The lever needs to fit onto that inner hex shape in a position that leaves no more than 1/8" gap between the lever and the stop on the caliper. Tighten down clock wise, then turn the post counter clock-wise. Just a 1/4 turn or so. You will feel the post try to pull in (but it can't 'cause you have the nut on there) you'll feel some resistance..push past it. That's the magical adjuster doing its job. Now...turn back CLOCKWISE. You should notice that your wrench doesn't return quite as far as where you started at before you feel it back to that tight position.
Repeat this...Turn to tight...Turn 1/4 counter clock-wise...then back to tight.
This ratcheting action moves the inner hex around. Repeat until is it clocked at the EXACT point where the lever will fit on with no more than 1/8" movement off the stop before it feels tight.
Good Luck!
-Tom
firebirdparts:
I'm just making this up, but the right hand caliper could be shared with cars that didn't use staggered rear shocks, and the left caliper can't be. I think that explains the difference in rarity. There used to be a ton of downsized Eldorados, Toronados, and Rivieras on the road with front wheel drive and rear 11" disc brakes (let's say 100,000 cars a year for 7 years). They did not have staggered shocks, both calipers were behind the center. A Trans Am is the only car, I think, that uses that left caliper, unless maybe the 1970's rear drive Cadillacs used it. They were rare, though, with rear disc. Really rare.
In terms of the bleeder location, on a trans am, both calipers are the same. The parking brake mechanism is the curious part.
when we were parting out cars, I used to get lots and lots of requests that I break up a disc posi axle to give them either one e-brake lever, or else one of those little brass blocks that was drilled for the end of the brake line. I never did.
I've never pushed one in without screwing it in, and I really didn't think you could due to the ratchet. But then I never tried. I just screwed the piston in every time I had to work on one.
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