Help with rear disc swap
 

I just finished swaping out my drum brake rear for a disc rear
The rear has new calipers on it. My problem is i cant seem to get a firm pedal or much for brakes. I am positive all the air is out of the system, after verifying this by taking it to a shop. The "Brake" light is on in the car indicating uneven pressure on each side of the proportioning valve i believe. I did swap out the m/c and proportioning valve to that of one with discs.

Is there any way i can test both the m/c and prop.valve to see if either or is bad. I dont really want to get both replaced if i dont have to.

Thanks in advance
Jon

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88'Camaro
305 TBI

No easy way to test either. There are no self adjusters on the rear calipers. Try pulling the park brake handle a few times. That's how you're supposed to re-adjust the rear calipers.

The proportioning valve may be forced over to one side. To reset it, have someone step lightly on the brake pedel. Crack a rear bleeder screw. As the pedel "slowly" goes down the brake light should go out. Stop when it does and close the bleeder screw. If it the light doesn't go out then try the same thing on a front bleeder screw. What you're trying to do is force the valve back to the center.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!

Member of the Calgary Drag Racing Association

I just did the same swap of a 9-bolt 88 Iroc rear end into my 90 RS. I also had the brake light on syndrome. OK, good news it is an easy fix. Unfortunately a 2 man job though. The brake fluid needs to be changed out a minimum of every 2 years, so take the opportunity and do it now. Then bleed the front starting at the master cylinder, then front brakes and last the rear. To bleed them open the bleed screw then SLOWLY press down the pedal to the floor, then close the bleed screw and SLOWLY release to the top. Keep repeating until no air comes out. The switch should re-set itself once the brakes have equalized. Then you will have a solid pedal. BTW, did you have any problems hooking up the parking brake cables? I ordered new cables (they are different from drum brake ones. Unfortunately in my case the parking brake mechanism on my 90 is completely diferent than the 88 Iroc was. The 88 Iroc has a threaded rod at the equalizer, my 90 has no such adjustability provision. I will have to swap out the entire PB mechanism, which requires the removal of seats and carpet. I will wait until my T5 swap. Good luck, Lon.


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90 RS Convertible
S&B #77-1403/D High Flow Air Filter, Jacobs Ultra Coil, Mileage Master Energy Pack & 8mm Energy Core Ignition Wires, Champion Copper Core Spark Plug, Mac Prod. 2 pc Underdrive Pulley set, Jet Fan Switch, TD Perf. Products Injection Riser Plate, Red Line Water Wetter, Flowmaster 3" Mandrel Bent Tubing, MagnaFlow 3" Single In Dual 2-1/2" Out Muffler, Random Tech. High-Flow Cat., TH 700R-4, Aluminum Driveshaft, 9 Bolt 3.45 Posi Disc Brake Rear End, Edelbrock 3-point STB (modified to 4-point), Alston SFC, SSPE Adj. Torque Arm &
LCA Relocation Brackets, ES Graphite Impregnated Urethane Sway Bar Bushings & Transmission Mount, Global West Del-A-Lum Front LCA bushings, 1LE 36mm Hollow Front Swaybar, 1LE 24mm Rear Swaybar, 1LE Swaybar Links, SLP Rear LCA's & Panhard Bar, Steering Brace AKA "Wonder Bar", Bilstein HD Shocks & Struts, Eibach Pro Kit Lowering Springs, Falken P245/50R16 tires, Pontiac WS6 16 X 8 rims, Power Stop Drilled Rotors, PFCM brake pads, Carbon Fiber Dash Dress Up Kit, Pedal Dress Up Kit, Black Velour Dash Cover, Calif. Car Cover Co. Interior Cover, Sylvania "XtraVision" Xenon Gas Headlights, NANE 9000 Series 55 W Ion Coated Fog Lights, Draw-Tite Sportframe Hitch Receiver, Pontiac Trans Am Door Pockets with Cupholders, Kenwood KDC-601 10 Disc CD Changer, Kenwood KCA-2FM CD FM Modulator.

Real cars don't have plastic doors & fenders!

You are suppose to bleed from the back to the front.

You are suppose to bleed from the back to the front.

I followed the instructions that came with my MIghtyvac I just purchased. It states to start with the master cylinder, followed by the wheel cylinders closest to the master cylinder and working out to the farthest one. I didn't check the Helms manual to confirm though. They do have a paragraph stating that wheel bleeding sequences vary among mfg's. I will have to check the manual.

thanks, i'll try the idea of trying to get the proportioning valve equalized and let you know how it turns out.

Does anyone know how to check the m/c??
I've heard that if its done, you'll get no-pedal at all and will know its done. Is this correct??


Oh..by the way, i did not hook up the parking brake cable yet, i dont have the correct cables. On my mechanism, there IS an adjusting rod with a nut which can be moved, im not sure if this will work or not.
my car is an 88

Does anyone know the price of a new prop. valve if mine is bad?

Thanks again

[This message has been edited by farm-kid/88camaro (edited September 14, 2000).]

Oh wow, I went thru this same hell with my 3.73/posi/disc swap. I could not get a brake pedal, and kept getting the "BRAKE" warning light. Turned out i had a bad rebuilt master cylinder.

I think I remember reading somewhere that when using the Mityvac vacuum pump, you're supposed to go from "closest" bleeder screw to the "furthest".. and yeah that's opposite of the normal rotation.

Want to pressure bleed your system yourself? I built a pressure bleeder, but only bled from the prop valve "down". You can make the bleeder work directly on the master cylinder by buying a spare m/c cap. Visit these websites:
http://www.ubscc.org/Tech1.htm http://www.eskimo.com/~dalus/bmw/all..._bleeding.html

Note that in the first one, he recommends against an air compressor. I think he means don't use the tire-inflator type of commpressor. Shop Air should be fine (and is what I used)- just make sure you have an air/water separator type of filter on your air line.

I can't do a powerbrake yet (brakes won't hold the car), so I think I have some air left in the m/c somewehre. I plan to rig up a spare cap to my bleeder this weekend, and bleed the m/c. Oh for a bottle I used one of the 7 empty quarts of brake fluid I had lying around.

-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards

Thanks Tom, I'm gonna try to get around to it this week sometime. I'll let you know how i make out. I think my first step is gonna be a rebuilt M/c and go from there.

Thanks again
Jon

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________________________
88'Camaro
305 TBI

A word of advice to anyone who does a lot of brake stuff.. i bought a thing from MAC tools called a Vacula. its a power brake bleeder.. it is pricey, like 175 bucks, but i love it. just make sure you keep fluid in the master !!