Rear disc brake kits

[Bitterman]

I wonder if your buddy is calling the proportioning valve the combo valve. If so, I have not heard it called that before. Correct me if I'm wrong but i believe all cars use some type of proportioning valve in the brake system.

Will you be replacing the lines as well in your project or work with your stick lines?

 

[shawn1112]

I wonder if your buddy is calling the proportioning valve the combo valve. If so, I have not heard it called that before. Correct me if I'm wrong but i believe all cars use some type of proportioning valve in the brake system.

Will you be replacing the lines as well in your project or work with your stick lines?

I’d like to keep stock lines as they are fairly new.
He is calling the combo valve “a big aluminum block under the master”

 

[565bbchevy]

Combination valve and proportioning valve are same thing.

 

[Bonnewagon]

Since around 1970 they call it a combination valve because it incorporates both the proportioning valve and the limiting valve as well as the residual pressure valve for drums. My 1968 Firebird disc brakes used separate proportioning and limiting valves. They are as rare as can be and stupid expensive so everyone uses a modern type combination valve now.

 

[shawn1112]

Thanks and makes sense

 

[64nailhead]

So searched about these kits and found this thread. I’m also looking to convert my rears on my 83 Regal to a disc set up. I’m pretty handy around cars and not afraid to tackle a project. But when it comes to this, I’d rather be safe than sorry and if best left to a professional so be it. So with kit I’m linking below, would this just be pretty straight forward bolt on or more involved? I see mention of master cylinder, proportioning valve and possibly removing the axel. Would any of that apply with this kit, if so what needs to be done.
Thanks in advance

JEGS 630110: GM 10 & 12 Bolt Rear Disc Brake Conversion Kit for 1964-1972 GM A-Body [Premium Kit with E-Brake & Red Calipers] - JEGS

Get the Best Performance with JEGS GM 10 & 12 Bolt Rear Disc Brake Conversion Kit for 1964-1972 GM A-Body [Premium Kit with E-Brake & Red Calipers] 630110 parts at JEGS. Shop Now at the Guaranteed Lowest Price!

www.jegs.com

If the Jegs kit in the photos is the actual kit, then don't use it. You need the traingular piece woth the hole the size of the axle tube in the middle. Look at the Inline kits in the link https://www.inlinetube.com/pages/pr...l=6692521664942362587#?f=5020779022569191615|. G-body rear axles are somewhat odd in how the brake is mounted to the axle - the Inline kits use the correct method without any welding or alignment issues.

I second my recommendation to use the Inline Tube kit for the only reason of their customer support. Also, drilled and slotted rotors are unneeded on a street car, but they do look cool - lol. We spent plenty extra for them and they were unnecessary IMO . Good pads on the other hand, is a different story.

Buddy of mine mentioned possibly having to remove the combo valve? My car isn’t here to check, but he said most front disc, rear drum cars should have one.

Regarding the proportioning valve, if you have upgraded the front brakes via an S10, F-body or C5/C6 install, then the stock proportioning valve will work fine (it's already been answered that you have one - it's mounted on the driver side frame rail next to the transmission). IF, you have not done a front upgrade and install rear discs, then you'll need a new proportioning valve due to unbalanced braking you have. I would STRONGLY urge not to upgrade the rears to disc without upgrading the fronts.

 

[shawn1112]

If the Jegs kit in the photos is the actual kit, then don't use it. You need the traingular piece woth the hole the size of the axle tube in the middle. Look at the Inline kits in the link https://www.inlinetube.com/pages/pr...l=6692521664942362587#?f=5020779022569191615|. G-body rear axles are somewhat odd in how the brake is mounted to the axle - the Inline kits use the correct method without any welding or alignment issues.

I second my recommendation to use the Inline Tube kit for the only reason of their customer support. Also, drilled and slotted rotors are unneeded on a street car, but they do look cool - lol. We spent plenty extra for them and they were unnecessary IMO . Good pads on the other hand, is a different story.



Regarding the proportioning valve, if you have upgraded the front brakes via an S10, F-body or C5/C6 install, then the stock proportioning valve will work fine (it's already been answered that you have one - it's mounted on the driver side frame rail next to the transmission). IF, you have not done a front upgrade and install rear discs, then you'll need a new proportioning valve due to unbalanced braking you have. I would STRONGLY urge not to upgrade the rears to disc without upgrading the fronts.

Can I ask what your reasoning is on not converting the rear to discs without upgrading the fronts?
Also thank you for the other info.

 

[64nailhead]

Brake fluid volume requirements.

When you upgrade the fronts, all of the upgrades involve a larger caliper piston or groups of caliper pistons that require more volume than the stock. When you upgrade the rears to disc from drum - the same occurs. The function of the proportioning valve is to equalize the volume requirements to allow for 'even braking'.

If you upgrade just the fronts to an S10 caliper, then the change is small enough that the stock proportioning valve will still function very well. If you upgrade both the fronts and rears, then the stock proportioning valve functions correctly, but the master cylinder will not have enough volume to function art the same pedal height, so you will have a deeper pedal. The deeper pedal is uncomfortable in panic stop situations (leads to brown underwear moments lol.) Hence, the reason for upgrading to a larger diameter master cylinder if you've upgraded both the front and rears.

Now comes the issue, upgrade the rears and leave the stock fronts, now the proportioning valve cannot overcome the varying volume requirements and you have uneven braking. In a straight line it's not much of an issue, but a hard brake application on wet roads while turning will identify your displeasure with brakes that apply too much to the rears.

 

[axisg]

I disagree. Stock 1984 setup with the orig MC and Prop valve here. I am using the Blazer front dual piston calipers, and LS1 rear dual piston calipers and I have no issues. Pedal is actually a little higher than with the stock brakes and stock "new " rubber lines when I did the swap.
It does not lock up the rears, nor does it want to "come around", nor do I have brake dust from the rear disks "dragging" as I have read should happen due to residual pressure that the drums are supposed to have. Just my personal experience over the last 7 plus years now.

 

[64nailhead]

I disagree. Stock 1984 setup with the orig MC and Prop valve here. I am using the Blazer front dual piston calipers, and LS1 rear dual piston calipers and I have no issues. Pedal is actually a little higher than with the stock brakes and stock "new " rubber lines when I did the swap.
It does not lock up the rears, nor does it want to "come around", nor do I have brake dust from the rear disks "dragging" as I have read should happen due to residual pressure that the drums are supposed to have. Just my personal experience over the last 7 plus years now.

With no argument intended, you have upgraded both axles, so the stock master and prop valve setup will work. The stock master works quite well with S10 front calipers. The reason you can't lockup the rear is because you do not have enough volume to rears, but they are contributing to braking a bunch. If you put he C5/C6 or F-body calipers on the fronts, then you'd expect a deeper pedal.


I guess I should've included in my previous post that upgrading the rear to disc and using everything else in stock form is not much of any improvement. The front brakes do 70+% of the braking. The best money spent for brake upgrades is on the fronts (to Shawn1112).