Rear brake issue

[jk5blazer]

I have done a rear disc conversion on my 14 bolt, after the instsall I noticed the rear brakes were not compressing, I feel that I have blead the brakes enought (three times) and was woundering if anyone else has had this issue. Do I need to consider a adjustible pro valuve, or what? Thanks

 

[70jimmy]

When I did my rear disc swap I was told to get a 2 lb residual pressure valve and an adjustable proportioning valve. I have both but haven't driven the jimmy since I got them. Still need to get some brake lines and bleed mine.

The residual pressure valve keeps pressure in the line and doesn't allow the rear brake calipers to back off too far, which sounds like the problem you might be having. I hear you have to pump them several times to make them work.

I ordered mine from Jegs. Seems like the valve was like $16.00 and the proportioning thing was like $50.00.

 

[sweetk30]

those valves are for the master being lower than the calipers in the system. thay didnt install them from the factory in the fronts.


i would check flow to the rear possible bad master. and what master are you running? 1/2 or 3/4 unit?

 

[jk5blazer]

not to sure if they worked before, but pretty sure. The 14 bolt was out of a van in the junk yard. And I have a 1/2 ton master. If I go to a 3/4 ton master will it screw with the 44 up front. Its an 8 lug 44.

 

[sweetk30]

i would bump up to the 3/4 master. it should bolt up to your booster unit. but the 1 ton boosters run a diffrent size on the back of the master. the 1/2 ton one just wont have the flow needed in most times of use. my friend has 1/2 ton master with 3/4 ton axles and the big break drums rear and his pedel sucks.

 

[jk5blazer]

oh yeah and the brake light stays on. I'll check in the morning if the pedal is firm or to the floor, its a project and I don't drive it yet.

 

[70jimmy]

Valve goes in the rear. On mine I was told to put the adjustable proportioning valve closest to the master cylinder and then the residual pressure valve. I mounted both on the driver side inner fender.

You are correct that they are designed for when the master is lower than the calipers.

My mechanic also an avid chevy guy and 4 wheeler told me that the rear discs can back way off and you have to pump them a few times to get rear brakes and that they can also back off too far and then won't compress.

Sorry still 2nd hand info since mine isn't out of the tube bending stage yet.

 

[JEBSR]

I had the same problem when I installed my system and it was that the 1/2 ton master cylinder has a smaller piston. Therefor it did not push enough fluid to the calipers and I had to pump them to get pedal everytime I hit the brakes. Got the 3/4 ton cylinder for factory disc brakes and problem was solved. 5 months no problems.

 

[Mudstud]

JEBSR- You gonna tell us the application your MC is for? I'm looking at getting a 77 K30 MC today to get mine right. It has the 1 5/16" bore and same size reservoirs. Half ton chevy bore size is 1 1/8" and has the small/big reservoirs. So JEBSR- how is your system configured? What year/model is your rig? Where do your lines go after the MC? Use any prop valve at all? You do have rear discs, right? Thanks.

 

[JEBSR]

I can't remember off hand what the model was, It was listed as a (3/4 ton without drum brakes). It didn't say with disc just without drum so I assume that it was for disc. Anyway I do have the receipt in my wide collection of unauthorized purchases (according to the wife anyway) I will look up the part number and post it.

I do have rear disc using front 3/4 ton calipers. I am also using the stock proportioning valve, with no residual valve ( it is not needed in my opinion). I will put an adjustable proportioning valve in eventually however my rears lock up only a fraction before the front so it really isn't a problem since I changed master cylinders.


Oh yea the body is 87,frame 77, axles 14 bolt ff/d60 from an 86 k30