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Old 04-12-2009   #1
merc3065
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rear brakes

Couple questions...
Jacked up the rear end to help with pulling the rear axle.

So, to verify that the rear axle is warped, I decided to do some brake tests...
Mash the pedal hard, the driver's side works just great...sort of. I can stop the car's idle speed from 12mph to 4mph. Rear wheels still slipping.

Parking brake does almost nothing on either side.
Parking brake on, it causes the pass side posi to start slipping like crazy and make like a grinding noise, thats not good so those tests stopped in a hurry.

Anyhow, im thinking that both the rear calipers and the parking brake system needs to be overhauled. Can the rear calipers be rebuilt or are replacements in order? Are the 89+ PBRs better than the 88 cast irons?

Ideas?
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Old 04-12-2009   #2
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GTA Year: 1991
GTA Engine: 350 TPI Automatic
Re: rear brakes

I dont think that that test would be enough..........imo.

Imo, I would just pull the axles and see if they are bent that way.

As for the rear calipers, I would get new ones. hth
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Cliff Jones
1991 GTA Trans Am
w/305,231 miles
on the original motor!!!!
Time of Death on motor, 4:07pm on 05/29/2010.
Hp:211.2@4200rpms/Tq.328.5@2700rpms
Best et: 13.959@97.05mph
Best mph: 98.3
Best 60' : 1.875 on BFG Comp TA's w/ 32 lbs of air in them
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Old 04-12-2009   #3
merc3065
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Re: rear brakes

Im not sure the axle itself is bent, but the plate that the wheel studs are in is for sure bent.

I've got replacement axles regardless so thats not a problem. I think its easier just to pull the old one and get the "new" one in.

Will the newer PBR aluminum calipers work on the 88 setup? I've got access to a parts car from 92 so parts galore!
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Old 04-12-2009   #4
FearThisGTA
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GTA Year: 1991
GTA Engine: 350 TPI Automatic
Re: rear brakes

On that part I aint sure if they will or not.
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Cliff Jones
1991 GTA Trans Am
w/305,231 miles
on the original motor!!!!
Time of Death on motor, 4:07pm on 05/29/2010.
Hp:211.2@4200rpms/Tq.328.5@2700rpms
Best et: 13.959@97.05mph
Best mph: 98.3
Best 60' : 1.875 on BFG Comp TA's w/ 32 lbs of air in them
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Old 04-12-2009   #5
merc3065
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Re: rear brakes

yeah might be some different bracket or something.

I'll goto the parts place tomorrow to see whats up.
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Old 04-13-2009   #6
george88gta
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Re: rear brakes

Quote:
Originally Posted by merc3065
yeah might be some different bracket or something.

I'll goto the parts place tomorrow to see whats up.
They are not a direct replacement. Check out Third Gen Org website, they list all the different parts you will need. If you have a complete PBR rear axle, you are all set. I have the instructions on a CD around here, if you get stuck let me know. I checked my rear axle for warped/bent with a run-out guage. Removed the rear wheels and mounted the guage and let the car idle in gear. My right rear axle flange was out about .020", doesnt sound like much, but you could see the rotor wobble and in turn, the caliper would move around. Replaced the axle, brakes still lousy ( 1988 ). Only thing that really made a difference in rear brakes was to remove the little valve in the front of the proportioning block. Allows more fluid to be directed to the rear calipers .
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Old 04-16-2009   #7
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Re: rear brakes

Replaced rear calipers tonite, bled the system, watched it barf an airbubble out through the reservoir all over the engine bay.

That was fun cleaning up...

Can stop the rear axle on the pass side now super easy.
Driver's side still slipping ever so slightly. However mashing the pedal to the floor does manage to stop both sides barely.

On a side note I think the parking pin broke off inside the transmission. After placing it in park and turning it off, doing some more bleeding, then turning it back on and putting it in gear, the sucker was making a god awful grinding noise. Back in park and shut it off, power up again, but no noise this time. It's pretty sketchy...gonna take it for a low speed test drive around the block to see what it does.

Any more ideas for the crappy rear braking issues?
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Old 04-17-2009   #8
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GTA Year: 1991
GTA Engine: 350 TPI Automatic
Re: rear brakes

Upgrade, either to the LS1 deal, or to someone like SSBC. Thats about all I can think of that you might be able to do.
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Cliff Jones
1991 GTA Trans Am
w/305,231 miles
on the original motor!!!!
Time of Death on motor, 4:07pm on 05/29/2010.
Hp:211.2@4200rpms/Tq.328.5@2700rpms
Best et: 13.959@97.05mph
Best mph: 98.3
Best 60' : 1.875 on BFG Comp TA's w/ 32 lbs of air in them
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Old 04-17-2009   #9
george88gta
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Re: rear brakes

Quote:
Originally Posted by merc3065
Replaced rear calipers tonite, bled the system, watched it barf an airbubble out through the reservoir all over the engine bay.

That was fun cleaning up...

Can stop the rear axle on the pass side now super easy.
Driver's side still slipping ever so slightly. However mashing the pedal to the floor does manage to stop both sides barely.

On a side note I think the parking pin broke off inside the transmission. After placing it in park and turning it off, doing some more bleeding, then turning it back on and putting it in gear, the sucker was making a god awful grinding noise. Back in park and shut it off, power up again, but no noise this time. It's pretty sketchy...gonna take it for a low speed test drive around the block to see what it does.

Any more ideas for the crappy rear braking issues?
You can try this modification http://www.gofasst.us/brake_proportioning1.htm I did this and there was a definite improvement, still not great, but better. The tranny grinding is normal. Both rear wheels have to be stopped completely when you try to put the tranny in Park. Another option would be an adjustable proportioning valve. Master Power Brakes, Summit, etc. sell them. One word of caution, too much rear brake is dangerous. You are not the first one to upgrade to the PBR calipers and still have problems. That is why I didnt bother with the mod. Collapsed hose can cause this problem as well. Trouble with the rubber hose is that it can look good on the outside and be partially plugged on the inside.
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Old 04-17-2009   #10
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Re: rear brakes

I haven't upgraded to the PBR style, kept the older cast irons just reman'd calipers.

Definite improvement on the pass side which has the rubber hose.
Not much better on driver's side which has hard line all the way to the caliper.

I knew about the rear brake biasing, if you lock up those puppies you're in for a roller coaster ride at the wrong time...

I'll look at the adjustable prop valve as well.

The LS1 brakes seem like a neat idea but that is unfortunately going to have to wait.

I did some more reading last night and realized that since I don't have the return spring for the parking brake on the driver's side it may not be adjusted right.

The torx bolt was seized in the old caliper so I have to run around town trying to find the proper sized bolt to put the spring retainer back on.

Once I get that on i'll adjust the parking brake a little and then try it again and see how it does.

After that, it's off to the frame shop to get a guesstimate on the frame specs!
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Old 04-18-2009   #11
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Re: rear brakes

Quote:
Originally Posted by merc3065
I haven't upgraded to the PBR style, kept the older cast irons just reman'd calipers.

Definite improvement on the pass side which has the rubber hose.
Not much better on driver's side which has hard line all the way to the caliper.

I knew about the rear brake biasing, if you lock up those puppies you're in for a roller coaster ride at the wrong time...

I'll look at the adjustable prop valve as well.

The LS1 brakes seem like a neat idea but that is unfortunately going to have to wait.

I did some more reading last night and realized that since I don't have the return spring for the parking brake on the driver's side it may not be adjusted right.

The torx bolt was seized in the old caliper so I have to run around town trying to find the proper sized bolt to put the spring retainer back on.

Once I get that on i'll adjust the parking brake a little and then try it again and see how it does.

After that, it's off to the frame shop to get a guesstimate on the frame specs!
One thing I forgot to mention. There was a recall for rear brakes and parking brake issues. It only pertained to the factory 5 speeds. After all an automatic has park and doesnt need a parking brake ( at least thats GM's theory). The recall installed new pistons and actuators in the rear calipers. They used a rebuild kit ( part number 18019028). The kit contains new pistons, actuators, seals, springs and the clips that retain the pads to the pistons. They are discontinued, but gmpartsdirect.com has some stock. I rebuilt my NAPA rebuilt calipers with this kit. The NAPA rebuilds did not have the upgrades. I saved the parts I removed and if I have to replace calipers I will reinstall the NAPA parts and save the GM upgraded parts. Something else you need to know, if you dont use the parking brake regularly, the pistons do not travel out as far as they should and the pressure will not get them out to the required distance. There is a GM service bulletin out on that as well. If you want the bulletin. let me know and I will get you a copy.i.
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