Rear disc brake conversion

[xylorex]

check this out http://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf

 

[81cutlass]

check this out http://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf

I tried that on mine but I couldn't get it to work.

There are two main types of prop valves used, kelsey-hayes and Bendix. The style in that link (and the style you buy as replacement prop valves) are the kind that you can modify to be disk/disk. The ones G bodies were outfitted with are the other style, i cant remember which one is which.

 

[xylorex]

I tried that on mine but I couldn't get it to work.

There are two main types of prop valves used, kelsey-hayes and Bendix. The style in that link (and the style you buy as replacement prop valves) are the kind that you can modify to be disk/disk. The ones G bodies were outfitted with are the other style, i cant remember which one is which.

thanks for that insight. i've done my rear brake conversion, but the only things mounted on my frame right now is the rear axle and its suspension --- this is what i had planned to do on my prop valve when i got that point. interested to see other replies on this.

 

[69hurstolds]

I tried that on mine but I couldn't get it to work.

There are two main types of prop valves used, kelsey-hayes and Bendix. The style in that link (and the style you buy as replacement prop valves) are the kind that you can modify to be disk/disk. The ones G bodies were outfitted with are the other style, i cant remember which one is which.

KH is the cast iron POS. It has the non-convertible style and if not taken care of, can rust up horribly. It's got the proportioning part of the valve that points down in the back.

The newer brass replacements sometimes come with an extra plain plug to replace the front metering valve for the disc/disc applications. Otherwise it's the same valve.

 

[69hurstolds]

I'd get a Blazer master cylinder too if you're into replacing the parts. It has a larger bore diameter, meaning more volume. May not need it, but you never know. Amazon seems to have the best price for the GM unit at 65 with prime. GM wants 140 list price!!!!!!

https://www.amazon.com/dp/B000C9E5IW/?tag=gbody-20

 

[pontiacgp]

check this out http://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf

"This will disable the proportioning valve. "

Have you driven a G body without a proportioning valve whether it is disk disk or dish drum? You'll find the rear end really loose especially in the rain

 

[malibudave]

I just finished my rear disc brake conversion, but my question is what going on when my calipers seem so tight that the wheels will not turn unless I hit the gas. I bled the brakes and fluid is making it to the back although I'm not using a proportioning valve, it seems like I need to push da pedal almost to the floor to get it to stoo, but what do I need to get the wheels to move freely, it sounds like there is friction some where. I thought I had rear end issues. My calipers and brackets came off a 2000 Jimmy which fits fine. I'm working on a 81 Cutlass. This is while the car is on stands. Video was too large to load so you guys can see. No thread was if help!!

Installing a prop valve will not fix your rear brake issue. Volume and pressure come from the master cylinder only.
How did your car stop before the conversion?

Are you running the stock Jimmy emergency brakes? They might be engaged and causing the drag.
If you remove the rear calipers, does the rotor turn freely. You can remove one caliper at a time to see if it is just one caliper causing the issue or both.

What master cylinder are you running?

Does the master cylinder hold pressure? Plug both ports at the master cylinder and pump the brake pedal. The pedal should become rock hard with little to NO movement. If there is excessive movement in the pedal, you have air in the master, or a bad master cylinder.

 

[oldsmobile joe]

what do I need to get the wheels to move freely, it sounds like there is friction some where

My calipers and brackets came off a 2000 Jimmy which fits fine

lets start here, and lets assume all the parts are used. caliper pistons could be stuck, do they move inward when pushed with a c-clamp, channel locks or other devices?

one or all of the hydraulic hoses could be cracked inside, acting like a one-way check valve. fluid gets to the caliper but won't release. test by cracking the bleeder or banjo bolt loose at the calipers. rotors should turn freely afterwards.

master cylinder not fully releasing to its normal neutral position, causing fluid to not flow back to the reservoir. again, test by cracking the brake line loose at master cylinder for the rear brake line, rotors should turn freely. this could be caused by the faulty master cylinder, faulty booster, incorrect booster push rod, or brake pedal.

as mentioned earlier, are the rotors centered in the caliper brackets? if not centered, double check assembly, rotors, brackets, calipers, mounting flange, etc.

is the parking brake set too tight?

This is while the car is on stands

and this one sounds silly, but needs to be asked, is it a posi, if so, is the trans in park or neutral?

I'm not using a proportioning valve

i don't know how you got it to this point, but you definitely eliminated this as a possibility for this portion of your concerns.

it seems like I need to push da pedal almost to the floor to get it to stoo

this is usually caused by insufficient amount of brake fluid being pushed from the master cylinder. master cylinder bore size will need to be increased. there are many variables on which to determine which master cylinder size to pick unless you find someone with the exact same set up as yours, both front and rear.

 

[Mean_n]

lets start here, and lets assume all the parts are used. caliper pistons could be stuck, do they move inward when pushed with a c-clamp, channel locks or other devices?

one or all of the hydraulic hoses could be cracked inside, acting like a one-way check valve. fluid gets to the caliper but won't release. test by cracking the bleeder or banjo bolt loose at the calipers. rotors should turn freely afterwards.

master cylinder not fully releasing to its normal neutral position, causing fluid to not flow back to the reservoir. again, test by cracking the brake line loose at master cylinder for the rear brake line, rotors should turn freely. this could be caused by the faulty master cylinder, faulty booster, incorrect booster push rod, or brake pedal.

as mentioned earlier, are the rotors centered in the caliper brackets? if not centered, double check assembly, rotors, brackets, calipers, mounting flange, etc.

is the parking brake set too tight?




and this one sounds silly, but needs to be asked, is it a posi, if so, is the trans in park or neutral?



i don't know how you got it to this point, but you definitely eliminated this as a possibility for this portion of your concerns.



this is usually caused by insufficient amount of brake fluid being pushed from the master cylinder. master cylinder bore size will need to be increased. there are many variables on which to determine which master cylinder size to pick unless you find someone with the exact same set up as yours, both front and rear.

The calipers moved perfectly fine with a clamp because I had to use them when I put the calipers on, I do have a posi 3 73 and the car was actually running when I was testing it, I did shoot a video but it was too large to upload but when I hit the gas to get them to start turning I noticed a metal sound, but at one point the wheels would move then after a few pumps the wheels would not turn without hitting the gas. I am uploading video on YouTube, I will share it

 

[Mean_n]

lets start here, and lets assume all the parts are used. caliper pistons could be stuck, do they move inward when pushed with a c-clamp, channel locks or other devices?

one or all of the hydraulic hoses could be cracked inside, acting like a one-way check valve. fluid gets to the caliper but won't release. test by cracking the bleeder or banjo bolt loose at the calipers. rotors should turn freely afterwards.

master cylinder not fully releasing to its normal neutral position, causing fluid to not flow back to the reservoir. again, test by cracking the brake line loose at master cylinder for the rear brake line, rotors should turn freely. this could be caused by the faulty master cylinder, faulty booster, incorrect booster push rod, or brake pedal.

as mentioned earlier, are the rotors centered in the caliper brackets? if not centered, double check assembly, rotors, brackets, calipers, mounting flange, etc.

is the parking brake set too tight?




and this one sounds silly, but needs to be asked, is it a posi, if so, is the trans in park or neutral?



i don't know how you got it to this point, but you definitely eliminated this as a possibility for this portion of your concerns.



this is usually caused by insufficient amount of brake fluid being pushed from the master cylinder. master cylinder bore size will need to be increased. there are many variables on which to determine which master cylinder size to pick unless you find someone with the exact same set up as yours, both front and rear.