Hitman's Pontiac Trans Am Forum

Trans Am Information => Trans Am Tech => Suspension => Topic started by: mattblack84 on September 14, 2011, 12:18:22 PM

Title: Help with rear disc brakes!!
Post by: mattblack84 on September 14, 2011, 12:18:22 PM
my 79 trans am has been sitting for a while and i finally got it back from the body guy and am going through the car slowly what are my best approaches for repairing the rear brakes there is no leaks but there def not grabbing and i was thinking new pads and rotors but isn't there somthing with the calipers on these i'm looking at the service manual and am a little confused any help would be greatly appriciated!!
Title: Re: Help with rear disc brakes!!
Post by: Tin Indians Rule on September 14, 2011, 12:59:56 PM
I'm going to hold off responding and see if Evan jumps in here. I know he just went through the wringer with his so I'll see if he or others pony up advice first.
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on September 14, 2011, 01:14:30 PM
well let me know so I can get my baby fixed!!!
Title: Re: Help with rear disc brakes!!
Post by: eroc022 on September 14, 2011, 01:42:17 PM
yup, these are a headache.... they have to be so accurately set with the emergency brake in order to get a good pedal feel...  I think Renovations has the link or pdf file that describes how to do it the best... its in the service manual as well... basically you will have to get the emergency brake as close as possible to engaging then you can bleed the brakes normally, to get the emergency brake set right you have to take off the inside lever and manually adjust the depth that the inside pad sits... by turning the shaft clockwise or counterclockwise the pad will move in and out... get it to where it touches the pad, and then just barely back it off of it so you have no drag.... then reinstall the lever, and bleed the brakes as normal... new pads and rotors are always a good idea too.....
Title: Re: Help with rear disc brakes!!
Post by: jjr on September 14, 2011, 01:52:01 PM

 From what I've seen and experienced the rear calipers are kinda
suspectable to corrosion from "not" using the parking brake every
time.

 Most folks buy rebuilt units rather than to do them themselves.

 You have to follow the very detailed instructions on setting them
up correctly, something I have to review each time I do a set.

 The rear discs work both by fluid and by mechanical means and so
setup is special.

 You'll need a few tools, a special one to be able to get the piston
at the proper depth, do you know which one I mean?

 Then there is a trick to the bleeding, if you aren't careful you
may create a difference in system pressures and trip the proportioning
valve to lock out one or the other system (front/back). Often the
old friend in the car pumping the pedal procedure does this.

 How where you planning on bleeding the system?

 Joe

 
Title: Re: Help with rear disc brakes!!
Post by: eroc022 on September 14, 2011, 05:44:18 PM
Joe, I reverse bled my system by feeding the fluid in through the caliper into the master cylinder... no air is in the system, but yet I still have a horrible pedal feel... whats the trick for the rest of it? its about to just go to the shop...
Title: Re: Help with rear disc brakes!!
Post by: jjr on September 14, 2011, 09:15:31 PM

 While I love and have used the reverse method, it's not 100% either.

 The thing that works is a obscure tool that holds the end of the pin
on the prop valve in place keeping the shuttle from moving. On the
aftermarket valves, a temp replacement for the differential switch
has a solid tip that prevents the shuttle from moving.

 Have you seen this?

 Joe
Title: Re: Help with rear disc brakes!!
Post by: eroc022 on September 15, 2011, 02:07:15 AM
my disc brake valve doesnt have a pin on the end..... solid brass but I do know what you are speaking of....
Title: Re: Help with rear disc brakes!!
Post by: kc79ta on September 15, 2011, 05:28:29 AM
Joe, I reverse bled my system by feeding the fluid in through the caliper into the master cylinder... no air is in the system, but yet I still have a horrible pedal feel... whats the trick for the rest of it? its about to just go to the shop...

Eroc, That might be your problem. Unless you pulled the MC back off and bench bled it after. I no pro on brakes, but I remember hearing that reverse bleeding a system with a tipped back MC can trap air in it that can only be bled out with it level on a bench. Just a thought before you spend some $$$ at the shop.
Title: Re: Help with rear disc brakes!!
Post by: jjr on September 15, 2011, 09:31:08 AM

 The brass one... then:

(http://www.301garage.com/78ta/PV-Tool.jpg)

 Joe
Title: Re: Help with rear disc brakes!!
Post by: eroc022 on September 15, 2011, 10:58:47 AM
aha well I found out I have a leak somewhere too. front brake resivoir is much much lower now than when I did this... I think its all coming off and hydroboost is going on.....
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on October 13, 2011, 02:55:49 PM
well i found out today it is my rear calipers no adjusting, the screw moves a little i'm thinking i might be able to fre them up been spraying pb blaster and working the ebrake.
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on July 28, 2012, 11:51:37 AM
Well got the e-brake to move every thing there ok, but the levers in the calipers themselves don't want to move much should i rebuild or try and free them up?
Title: Help with rear disc brakes!!
Post by: eroc022 on July 28, 2012, 04:19:48 PM
They shouldn't move much except for to clamp down on the rotor..... Very tight tolerance with them
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on July 29, 2012, 11:45:31 AM
ok but how do u get the piston to come out so i can put it against the rotor?
Title: Help with rear disc brakes!!
Post by: eroc022 on July 29, 2012, 12:28:30 PM
Take the emergency/parking lever off and rotate the std with a 9/16 wrench, then put you lever back on with the lever in the "released" position and reconnect everything
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on July 30, 2012, 12:23:50 PM
ok and if the 9/16 nut is not turning or hard too is there a way to sort of loosen it?  Or is it time for a rebuild?
Title: Help with rear disc brakes!!
Post by: eroc022 on July 30, 2012, 12:29:50 PM
Should turn one way or the other, one will back the pad from the rotor the other will push it towards the rotor if it's not turning, I would say new calipers or rebuild yours
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on September 07, 2014, 01:18:18 PM
ok so an update bought new rear calipers, pads.  everything went in ok but still soft pedal and after fighting to get it adjusted the brake light comes on radomly.  Does anybody know how to even get this damn thing adjusted or have the procedure I read the one in the service manual and it dosent make sense so im kinda getting confused and frustrated at the same time........
Title: Re: Help with rear disc brakes!!
Post by: Angelo on September 07, 2014, 01:42:05 PM
I suspect the prop valve, hose ballooning or a leak.
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on September 08, 2014, 09:10:50 AM
Checked this morning no leaks or hoses ballooning do you think there might be air in there ?  I'm going to try bleeding the car again and let you know.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on September 08, 2014, 10:36:00 AM
Air would make your brakes spongy, you would notice that right away. The reasons that cause the brake line to come on:

* Emergency brake set
* Leak in system
* brake line taking up too much of the pressure (brake hose ballooning)
* A lot of air in the brake system somewhere (if it's excessive to one of the front calipers, you would feel the car pulling to one side or the other during braking, this will at least narrow down this particular symptom to the front or rear brakes.)
* Proportioning valve not working correctly.

The prop valve is what turns the brake light on (other than the emergency brake). I would not suspect the booster or master cylinder, though others with more experience may if they have encountered some weird situation that could explain it.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on September 08, 2014, 10:39:29 AM
Do you trust your friend who checked that the hoses were not ballooning when you pressed the brakes? Or did you have a friend press the brakes and you observed that the hoses were not ballooning? Not saying whom ever is helping you can't be trusted, but they may not understand what you are looking for with the hoses. It is not going to balloon out like a kids balloon, you're looking for the hose changing shape (getting larger) when the brakes are applied.
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on September 08, 2014, 04:08:57 PM
Well me and my dad bled the brakes and found the emergency brake on the passenger side wasn't working right took off the caliper reworked it got it to ratchet out rebled the brakes and the car is stopping great got a nice pedal looks like problem solved.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on September 08, 2014, 04:30:34 PM
That could do it. BTW Make sure you use the emergency brake regularly, it is required for the rear caliper pistons to adjust.
Title: Re: Help with rear disc brakes!!
Post by: randr on November 15, 2014, 07:44:58 PM
  I think I'm having the same problem with my rear calipers.  No matter what I do the brakes feel spongy. No leaks, Vacuum bled 4 times and bench bled 4 times. I'm sure it's not recommended, but someone tried telling me to eliminate the e-brake and that front calipers should bolt right on to the rear? Anybody ever hear of this? Also anybody have a link to the proper procedure to adjust e-brake? Could it also be that I vacuum bled my brakes without using that PV bleeding tool that was show earlier in this thread? If so how can I re-center the proportioning valve and where can I get one of those tools? Thanks.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 15, 2014, 09:00:24 PM
80's s10 front calipers bolt right up to the rear. Same brake pads as well. You will have no e brake, so if you plan on doing any racing that requires it like autocrossing you will want to keep the ebrake.

If swapping to non ebrake calipers solves your problem then either your ebrake calipers aren't ratcheting properly or you never adjusted them before bleeding. Its pretty easy though, first you get the ebrake working then you bleed the brakes. If the ebrake is never adjusted though then those calipers will never be close to the rotors and would explain a lot with the braking condition.
Title: Re: Help with rear disc brakes!!
Post by: randr on November 16, 2014, 09:30:49 AM
Thanks. I'll try adjusting the e-brake again before I do anything rash. It's an automatic and I don't plan on  racing.  As matter of fact I don't think I ever even used the e-brake. What about bleeding without using the prop tool? Could that be causing problems?
Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 16, 2014, 10:16:59 AM
Prop valve?

'Prop tool' there's no specific tool needed to bleed brakes, There are many ways which seem specific to every mechanic. I use name brand speed bleeders myself, its a bit voodoo to most.
Title: Re: Help with rear disc brakes!!
Post by: randr on November 16, 2014, 11:01:55 AM
Sorry. Maybe I wasn't clear. I was talking about the proportioning valve tool that there is an image of on the 1st page of this  subject.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 16, 2014, 12:23:39 PM
Oh got it, I bought one but never used it. You only need that if your brake light gets stuck. Basically if there is more/less pressure on the front or back then your brake light will go on by that port in the prop valve. If you have your brake light wiring hooked up correctly your brake light will go on if that is not centered in the prop valve.  Its a safety feature to indicate if there is a loss of pressure to the front or rear. Is your brake light on? Is it wired correctly?
Title: Re: Help with rear disc brakes!!
Post by: randr on November 16, 2014, 12:50:51 PM
I believe it's wired correctly. Light isn't on. I was wondering if using a vacuum bleeder could cause it to shift back and forth and therefor give me a problem bleeding brakes. Any link on showing exactly how to adjust e-bake? Thanks for all the help.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 16, 2014, 01:55:43 PM
I referenced the service manual (I don't think the Chiltons type books will explain how to do it right). You can now get a USB thumbdrive with the entire service manual on it from this site.

I can give you a quick run-down though, assuming calipers are already on the car with rotors and pads in place.

1. With the ebrake lever off of the caliper, ratchet with a wrench (turn in the direction the caliper is pulled when the e-brake cable is pulled) until the caliper pads make contact with the rotors and stop them from spinning by hand. Repeat with the other caliper. Remember, one ratchets  clockwise, the other ratchets counter clockwise.

Just a site note, when you loaded the calipers (put the pads in them), you had to push the caliper piston back, turning counter clockwise while pushing the piston in. If you simply use a c clamp and compress the rear piston, you more than likely damaged the ratcheting mechanism inside the caliper.

test ratcheting the caliper also gives you the ability to test that it is working.

Just another comment, you can clamp down on the ratcheting mechanism with a wrench until it snugs up the pads on the rotors, but as soon as you turn back off a 1/8-1/4 turn, the piston can flex back enough to allow for the rear rotor to spin again.

2. Once you have the caliper adjusted with a wrench, re-assemble the emergency brake lever parts to the caliper. You will position them so when pulled they will lock the pads against the rotor (as you did with  your wrench). When pushed back you should be able to turn the wheel.

If your lever parts are bent or damaged, I highly recommend getting a set from scarebird on ebay, they are way stronger and plated: http://www.ebay.com/itm/Pontiac-Trans-Am-Seville-WS6-rear-disc-brake-caliper-parts-spring-lever-bracket-/371086849463

When all said and done the ebraake brackets will be bolted onto the rotor with the spring loaded pushing the lever back enough that the pads are not locked against the rotor. You should be able to lake a large pair of pliers and pull on the ratchet lever (compressing the spring) and manually tighten the rear pads to lock the rear wheel.

Tip: I used 3 zip ties to compress the spring I got from scarebird's kit. Once in place, I cut the zip ties. Don't think that's necessary for the factory springs.

3. Attach the emergency brake calipers (make sure they move freely before doing so), then adjust under the drivers side of the car (remember to adjust with the emergency brake of)

4. Here comes the fun part. Engage the emergency brake, then check to see if both wheels are locked. As I recall, the first time I did this it didn't lock, I had to release and readjust after one pull as everything got stretched into place. The second time was the charm, I only had a very small amount of adjustment to make after that.

5. Repeat engaging and unlocking the emergency brakes a dozen or so times, this firms up the ratcheting mechanism in the calipers.

6. Bleed the brakes with the emergency brake set.
Title: Re: Help with rear disc brakes!!
Post by: randr on November 16, 2014, 03:07:52 PM
Think I may have found my problem. The cable going to the right rear is binding up between the exhaust and body. When I apply the parking brake it doesn't compress the spring on the caliper. I put headers and true dual exhaust and there doesn't seem to be a clear path to run the cable. Would this even have anything to do with my spongy brakes?
Title: Re: Help with rear disc brakes!!
Post by: RENOVATIONS on November 16, 2014, 03:26:56 PM
I've posted this before but I'll put it up again in case someone else needs it.

(http://i113.photobucket.com/albums/n236/79ws6resto/1-1.jpg) (http://s113.photobucket.com/user/79ws6resto/media/1-1.jpg.html)

(http://i113.photobucket.com/albums/n236/79ws6resto/2-1.jpg) (http://s113.photobucket.com/user/79ws6resto/media/2-1.jpg.html)

(http://i113.photobucket.com/albums/n236/79ws6resto/3.jpg) (http://s113.photobucket.com/user/79ws6resto/media/3.jpg.html)

(http://i113.photobucket.com/albums/n236/79ws6resto/4.jpg) (http://s113.photobucket.com/user/79ws6resto/media/4.jpg.html)

(http://i113.photobucket.com/albums/n236/79ws6resto/5.jpg) (http://s113.photobucket.com/user/79ws6resto/media/5.jpg.html)

(http://i113.photobucket.com/albums/n236/79ws6resto/6.jpg) (http://s113.photobucket.com/user/79ws6resto/media/6.jpg.html)

Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 16, 2014, 05:58:24 PM
That rear disc brake article is interesting. I think GM abandoned this ratcheting caliper setup, Honda's use it, albeit without the problems.

If the caliper on one side is not positioned then yes. When I mean positioned, I mean the emergency brake ratchet system is ratcheted down enough to allow the caliper to press the pads onto the rotor.

Does the car pull to one side when you drive it and hit the brakes?

I'm not sure of the situation under your car, but under mine the cables go under the exhaust system. You would think this is not a good idea, but that's how the factory did it. As long as the cables are not running along something where they could bind you should be ok.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 16, 2014, 06:02:55 PM
Just to clarify, the factory ran the cable below the exhaust, not above (in between the exhaust and body). If you're looking under the car, the first thing you see are the cables, then the exhaust, then the body.

I'm going to have to deal with this when I get frame connectors, the sub frame on the drivers side has a designed dent where the cable should ride in. Frame connectors will make this disappear I believe.
Title: Re: Help with rear disc brakes!!
Post by: randr on November 16, 2014, 08:18:28 PM
My cables we're run between the exhaust and the body. I moved them like you described and they seem to be much better although they definitely rub along the exhaust.  Cable will now ratchet down on both sides although it still seems to pull tighter on driver side.  The e-brake now seems to work. Can apply e-brake and put car in drive and it doesn't move. Rebled the rear calipers and the brakes seem 10 times better.  Still feel a little spongy to me but maybe I'm just used to modern day cars.  Not sure though.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 16, 2014, 08:34:41 PM
RENOVATIONS posted the article with a couple reasons for spongy brakes. They should not be spongy.
Title: Re: Help with rear disc brakes!!
Post by: randr on November 16, 2014, 09:08:20 PM
When they say the e-brake should be " ratcheting" is that literally?  When I pulled off the cable and the spring at the right rear caliper and tried putting a wrench on it to manually adjust it I did not hear anything but it would definitely apply brake pressure. This week I'm going to try to do every thing 1 more time from scratch. From bench bleeding on back. If  still  the same results I think I'm on to putting the S10 calipers on the rear and going without an emergency brake. And thank you Angelo for spending your Sunday helping me out.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on November 17, 2014, 07:04:56 AM
It does not make clicking sounds like a Craftsman ratchet, it's smooth. Ratcheting may be the wrong word to use for this, but it's what I've herd others refer to it as in the past. If you put the caliper on a bench, and compress the piston (compressing it and it rotates back into the caliper), then take a wrench and turn the ebrake shaft, you will see the piston slowly come back as you turn it one direction. When you turn it the opposite direction, the piston does not move. You can compress it back a little bit at any point if you turn back the ratcheting action a little, this demonstrates how it relieves a little pressure when you disengage the e-brake.

I'm not saying which way you ratchet because each caliper ratchets one way or the other. When you go the opposite direction it doesn't reverse the piston position. The only way to do that is to compress back in the piston. Once the piston is compressed back in, you have to rotate the piston to get the D lined up for your pads. The piston needs to be able to rotate though it doesn't rotate once the pads are loaded into it. Confusing I know.

No problem, this needs to be discussed, these calipers are not that complicated but when you start trying to explain it takes a lot more words than it should, which means it is complicated.
Title: Re: Help with rear disc brakes!!
Post by: randr on November 22, 2014, 04:12:54 PM
  OK. Re-Went through everything. Bench bled and the rebled the old fashioned way with somebody pressing the brake. I was using a vacuum bleeder. Brakes seem to be much better. Finally have a nice feel to it. Thanks for all the help.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on August 20, 2018, 04:19:52 PM
For reference details how to use front 80's s10 calipers on a 79-81 rear disc brake TA car: http://transamcountry.com/community/index.php?topic=34085.0
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on June 02, 2019, 11:35:50 AM
Well here is an update:  My brother works at inline tube I replaced everything in the brakes, new stainless lines, rubber lines, master etc.  Still had the sinking pedal so I said screw it removed the emergency brake cable, zip tied the brake lever up inside the car and bought a new floating style kit for the rear.  Worked perfect brakes are awesome cost me 200 to do the rear.  They also sell ones with emergency brakes but i didn't want it.  My advice to anyone having trouble with the rear disc brakes is to call inline tube buy a new set and ditch the old ratchet style.  Save yourself the headache and money messing with them.  I lubed my old ones and put them in a box for originality sake if i ever sell the car.  Thank you all for your responses and help.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on June 02, 2019, 03:09:33 PM
if you donít need the emergency brake or are young to run drum emergency brake inside a rear disc your all set.

My brakes have always has some pedal before they engage as well. I think it has something to do with the design. The rod out of the booster had a bit more gap between the booster and master, not sure if that was by design or because the aftermarket master is a little deeper, unsure. I had a brake booster leak, ever so slight but it drove me nuts. I am almost done with hydro boost swap, which for a Pontiac 400 is not easy to get the ps lines plumbed with the clearance between pump and head. I can already tell a difference bleeding bakes, but I also got an adjustable wilwood prop valve this time I will dial in the rear brake pads as I believe the factory prop valve has them barely come in during heavy braking.
Title: Re: Help with rear disc brakes!!
Post by: mattblack84 on June 03, 2019, 09:47:16 PM
I always had what seemed like a low pedal with air in the lines with the stock discs, now its a really nice feel only thing I did was the kit.
Title: Re: Help with rear disc brakes!!
Post by: Angelo on June 03, 2019, 10:50:23 PM
Right, it is definitely something with the caliper design. I suspect its a combination of the prop valve and the rear disc ratcheting calipers, the prop valve GM part number in the catalogs is very specific, one part number for 79-81 Firebirds. The one prop valve fits all the aftermarket sells I am sure is not exactly tuned how GM intended.

I will know soon if an adjustable prop valve and/or hydroboost makes the brakes behave better.