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proportioning valve for rear discs

Cornfield creations

Cornfield creations

1/2 ton status
Joined
Oct 19, 2005
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Location
Jasper, Indiana
So when I put the rear discs on my 14bff, I could never get a pedal. So I tried a new master for my 79 blazer. Didn't help, so after some research I found I have the JB7 front calipers on the rear, because those are what came with my front axle, I didn't want to pay core charges.

So I put on a 79 3/4 ton JB7 master cylinder, but what I didn't like was it swapped the lines front to rear. Well now I have a good pedal, but my rear is doing all the work. It stops fine and all, but the fact the front isn't doing much concerns me.

So my question is, should I put my old master back on, and change the proportioning valve for the disc/disc, or just take it out and put 2 adjustables in there and correct the front/rear setup.

Either way it will cost about the same.
 
I did not change my master or prop valve when I did my disc swap. The only issue I remember was trying to bleed the system.

What does it mean when you say "you could never get pedal"? Straight to the floor? Spongy? Feels good, but not stopping power? etc?

Did you brakes work before?
 
It would be really low, and barely grab. I drove it a couple days very carefully hoping that it would break the pads in some and get better but it never did.

I have heard that some people never had to do anything, maybe I should have had the smaller calipers on the rear. I could try swapping calipers front to rear and putting my old master back on.

Right now it has the larger piston calipers in the rear and the smaller 1/2 ton calipers in the front.

Before I did the axle swap the brakes were amazingly good.
 
I would think that you would want to run the smaller calipers in the rear as thats what sets your pedal height mostly. I'm gonna try the swap out real soon myself too and plan to run the same calipers front and back with a prop valve if needed.
 
I have dual piston calipers in the front of mine, they are factory and really big, so not sure if my input works, but I put your run of the mill front disc's on the back and haven't had any issues.
 
When I put my disks on the rear I added a $45 adjustable inline proportioning valve, and I needed it, otherwise the rear would lock up well before the front, but I have a truck. If you put it on make sure you put it on after the factory proportioning valve. Also, I had the larger piston calipers in front and the smaller piston calipers in rear.
 
I did the rear brake swap and put the TSM rear disc on. I've never had a good pedal feel, IE spongy. I've bled the brakes more times then I can count.

The parking brake doesn't work very well and when adjusted to the point that it does work the pads are so tight on the disc that it over heats them while driving.

I'm sure it's a master cylinder and prop valve issue. They were not designed for 4w disc.
 
i ditched the stock valve.

tee fitting front and adj valve in the rear mounted by the master for easy use and reach.

then run stright threw the new adj valve to rear.

blead out and then few test drives workes great.

i had 1 ton master/hydroboost and dana 60 / 14ff with disk rear. used 1/2 ton calipers i had at the time.

when i was done i could lock all 4 almost exact same time on panick stop from 45mph. and wow was it much better than the drum's full of mud.
 
On the K5, I've used a prop valve for rear disk brakes, bolted to the stock location. Stock '85 master; good results w/ 8-lug 10b front (with the 'big' caliper) and now w/ the 60; rear are Caddy Eldorado. Pedal feel is soft, but I prefer that over an on/off feel. Good control, even on nose-in-the-ground descents. On the road, the brakes are probably more than the suspension can handle...

On the FJ40 (which was converted to disks and Monte Carlo calipers in the rear), we used a Wilwood adjustable valve in the rear line at the master, and adjusted so that the front locks up first.
 
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I am getting close to setting up my rear disks. My master is the stock 1/2 ton for disc front and drum rear. Purchased the disc/disc proportional valve from Inline Tube & TSM Cady Calipers with Ebrake. After reading all the posts I have found in the forums I am still unclear as to the best approach to take initially. With so many knowledgeable people who have already done this upgrade I'm sure there is a someone who can help.

Does anyone have or seem a diagram, in the forums, for a successful installation?
 
Well I agree with the larger pistons in the front. Essentially, when you do the JB7 master cylinder swap, the sizes are backwards for the lines compared to the 1/2 ton. So I swapped the lines front the rear to get it going. So all the work is essentially done in the rear, which has the larger piston calipers.

So I am thinking, maybe swap out the masters to correct the front/rear line issue, plus swap the larger piston calipers to the front, and the smaller to the rear and see where it stands.

I have heard of lots of people not having to do anything after the disc swap. So maybe I'll try that.

I just don't understand why the line sizes were backwards on the JB7 master, which is the heavy duty brake setup.
 
skidog1us said:
I am getting close to setting up my rear disks. My master is the stock 1/2 ton for disc front and drum rear. Purchased the disc/disc proportional valve from Inline Tube & TSM Cady Calipers with Ebrake. After reading all the posts I have found in the forums I am still unclear as to the best approach to take initially. With so many knowledgeable people who have already done this upgrade I'm sure there is a someone who can help.

Does anyone have or seem a diagram, in the forums, for a successful installation?
Click to expand...

I have the InlineTube disk/disk prop valve. It simply replaced the stock one. I installed the calipers/brake lines first, then the valve. While you're swapping the lines over to the new prop valve, make sure the master cylinder reservoir doesn't run dry. Don't bolt the new prop valve to the crossmember just yet, just leave it hanging from the lines. That valve likes to trap air bubbles, and what worked for me while bleeding the brakes was to apply/maintain hydraulic pressure, hit the body of the valve a few times with a wrench (essentially to generate vibrations and such to dislodge air bubbles - this works better if the valve is not on a solid support), and then bleed at the caliper(s). Repeat as necessary as you bleed all four corners. Once you have a firm pedal (with the motor running - i.e. brake booster working), then it's time to bolt the valve back to the crossmember.
 
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