Prop. valve upgrade with LS1 front brake swap?
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Car: 92 Z28
Engine: LB9
Transmission: 700R4
Axle/Gears: 10 bolt/2.73
Prop. valve upgrade with LS1 front brake swap?
My 91 Z28 came stock with single piston front brakes, and drum rears. I first upgraded my rears from drums to the PBR discs when I swapped out my rear end. I bled the system after this and the brake pedal felt normal.
However, I recently upgraded my front brakes using the ebmiller (or fly-n-bye) 4th gen LS1 brake swap kit. On my first attempt to the bleed brakes, I noticed a gurgling noise from my brake fluid reservoir. I immediately knew what it was and ran over and began to add more brake fluid. Brain fart.
After that happened, I began a second attempt to bleed the system. The fluid from the front was coming out a little milky, but after a few bleed cycles, it was coming out perfectly clear. I then stopped the bleed process and tried to drive the car. The pedal was extremely soft and I nearly had to press the pedal all the way to the floor to make the car stop. I figured I still had a lot of air in the system, so I saved the work for another day.
Third attempt. I spent about 30 mins with a helper running around and bleeding the brakes again and adding more fluid as needed. Pedal feel is now improved, but is nowhere near what it should I feel like, and definitely unsafe to drive, nevermind trying to stop in a performance-like matter.
I am now starting to doubt my problem is from air in the lines. Do I need to upgrade my proportioning valve? I was told that on the later cars such as mine, that the prop valve didn't really need to be changed, but I'm starting to think otherwise. I am also using the stock brake lines (for now).
Thanks for any advice or info you can share.
However, I recently upgraded my front brakes using the ebmiller (or fly-n-bye) 4th gen LS1 brake swap kit. On my first attempt to the bleed brakes, I noticed a gurgling noise from my brake fluid reservoir. I immediately knew what it was and ran over and began to add more brake fluid. Brain fart.
After that happened, I began a second attempt to bleed the system. The fluid from the front was coming out a little milky, but after a few bleed cycles, it was coming out perfectly clear. I then stopped the bleed process and tried to drive the car. The pedal was extremely soft and I nearly had to press the pedal all the way to the floor to make the car stop. I figured I still had a lot of air in the system, so I saved the work for another day.
Third attempt. I spent about 30 mins with a helper running around and bleeding the brakes again and adding more fluid as needed. Pedal feel is now improved, but is nowhere near what it should I feel like, and definitely unsafe to drive, nevermind trying to stop in a performance-like matter.
I am now starting to doubt my problem is from air in the lines. Do I need to upgrade my proportioning valve? I was told that on the later cars such as mine, that the prop valve didn't really need to be changed, but I'm starting to think otherwise. I am also using the stock brake lines (for now).
Thanks for any advice or info you can share.
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Car: '90 Trans Am-12.45@110.71
Engine: 355 w/AFR 195's Elem. 400/430 HP/TQ
Transmission: Tremec T-56
Axle/Gears: 12 Bolt 3.73
Re: Prop. valve upgrade with LS1 front brake swap?
No need to change is correct.
Is the brake light out?
I'm sure you must still have air in the lines....just been thru this myself.
Bleed the front one farthest from the master first.
Same on the rear.
Is the brake light out?
I'm sure you must still have air in the lines....just been thru this myself.
Bleed the front one farthest from the master first.
Same on the rear.
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Re: Prop. valve upgrade with LS1 front brake swap?
In searching I've found that 89-91 shows the same Cylinder, Brk Master GM 18014286. Earlier years show different masters for J50 and J65. GM, however, pretty much made them interchangeable (All have the 'quick take up' master):
https://www.thirdgen.org/forums/susp...fferences.html
There are different combination valves (if only one was needed, why would GM design valves for different applications?). For exampe:
Valve, Brk Combo (1989 2nd Des) (J50) (1990 [and also 91]) (J41, J42) GM 10136839
J41 - BRAKE SYSTEM, POWER, FRONT DISK, REAR DRUM, CAST IRON
J42 - BRAKE SYSTEM, POWER, FRONT DISK, REAR DRUM, ALUMINUM
Valve, Brk Combo (1989 1st Des) (J65, 1LE, Y82) GM 14089496
J65- BRAKE SYSTEM, POWER, FRONT & REAR DISK
1LE - PERFORMANCE PACKAGE, SHOWROOM STOCK RACING
Y82 - MERCHANDISED PACKAGE, FORMULA
EDIT: BTW, did you allow the master to run dry? If so, you'll need to bench bleed.
JamesC
Last edited by JamesC; 11-23-2011 at 07:13 AM.
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Car: 1987 IROC-Z Z28 Convertible
Engine: LB9
Transmission: 700R4
Axle/Gears: 3.23
Re: Prop. valve upgrade with LS1 front brake swap?
The prop valve ONLY distributes the pressure front to rear....so for a given brake pedal input, you'll get say 500 psi on the front and something less ddepending on the prop valve criteria (say 300 psi). YUou might have air trapped in there (especially since you ran the master dry), but should be able to bleed it out.
One easy and robust method I use is to crack the bleeders at all corners, remove the master cap and let it gravity bleed. Be sure to put a heavy rag under each caliper since the fluid will drip out on the floor.
One easy and robust method I use is to crack the bleeders at all corners, remove the master cap and let it gravity bleed. Be sure to put a heavy rag under each caliper since the fluid will drip out on the floor.
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