brake woes

[metalneverdies]

Hey guys, I installed a set of 85 k20 axles into my CJ7 (its the beater, the K5 is the pretty one ). I have installed the master and booster from an 85 k20 with the 13" rear brakes as that's what the axles have. I am having issues with the rear brakes locking up almost immediately with pedal pressure. The front hard line from the master is slightly smaller than OEM GM. But it does match the size of the standard Chevy lines at the brake hoses. Is that possibly causing the front brakes not to work as well as they should?

I do definitely feel like the rear brakes are massively overactive. Would I be better off not using the proportioning valve at all for the front and installing an adjustable valve on the rear to dial them in? Any better suggestions or things to try?

For reference, they are 8 lug Corp. 10 bolt front and 14BSF rear with JB7 13" drums. Running 37" military beadlocks with run-flat inserts.

 

[dremu]

Did you install the combo (aka prop) valve from the donor K20? The brake system isn't, well, a system, without it.

-- A

 

[diesel4me]

I tried using a master cylinder on my '82 K2500 from another square body,and made the mistake of screwing the two brake lines into the ports they happened to fit in,which required putting the line that formerly was in the front port into the rear one and the rear one up front..

I found later that basically I had hooked the front disc brake portion of the master to the rear drums...it was dam near impossible to drive it,a feather touch on the pedal would instantly lock the rear tires up..(It has 13" rear drums)..

I came THIS close to hitting a cop that was at a traffic detail when my brakes were like this !--he stepped right out in front of me while going 30 mph and puts his hand up,like he was Superman,and didn't move out of the way--I skidded for a good 100 feet and the truck never slowed down much,in fact,I think it sped up,despite one rear tire being locked..if I had not downshifted into 1st,I probably would have run right over him..
I got a good reaming and came close to being written up,and my truck towed away for having "defective equipment"..

Two $1.50 brass brake line adapters allowed me to install the brake lines to the master in the correct position (the 3/16" line to the front brakes,the 1/4" one for the rear),and all was well again...

This might be whats going on in your case--or perhaps you do need a proportioning valve to reduce the amount of pressure to the rear drums..

 

[dyeager535]

If your fronts aren't bled properly, the rears will lock up simply because they are doing more work than they should be.

Not ruling out other causes, just a thought based on personal experience.

 

[metalneverdies]

Did you install the combo (aka prop) valve from the donor K20? The brake system isn't, well, a system, without it.

-- A

I am running the stock jeep prop valve. I read on pirate and other sites where tons of guys were using the stock prop valve with E350 MC's, Dodge MC's, and other random MC's and had no issues. I though I would try my luck before messing with changing the prop valve.

Could I bypass the prop valve, put a T fitting to the front lines and run a adjustable prop valve for the rear? I was thinking of something like what is linked below.

http://www.summitracing.com/parts/sum-g3905

I do not see a stock GM proportioning valve on Rockauto or oreilly's. I was afraid to go with the GM one because I had to remove the load sensing valve on the rear axle when I removed it from the doner truck.

 

[dremu]

I am running the stock jeep prop valve. I read on pirate and other sites where tons of guys were using the stock prop valve with E350 MC's, Dodge MC's, and other random MC's and had no issues. I though I would try my luck before messing with changing the prop valve.

Could I bypass the prop valve, put a T fitting to the front lines and run a adjustable prop valve for the rear? I was thinking of something like what is linked below.

http://www.summitracing.com/parts/sum-g3905

I do not see a stock GM proportioning valve on Rockauto or oreilly's. I was afraid to go with the GM one because I had to remove the load sensing valve on the rear axle when I removed it from the doner truck.

You can do the tee, yep, and then the adjustable valve for the rear. I've only done it on a disc-disc conversion which was a nightmare, but I suspect for disc/drum you'd be in good shape.

Trying to source a stock-type combo valve is tricky, as there are many variations or OE, but the replacement ones tend to be lumped into "disc/disc" or "disc/drum" categories. I'd try the tee and adjustable option first.

-- A

 

[metalneverdies]

You can do the tee, yep, and then the adjustable valve for the rear. I've only done it on a disc-disc conversion which was a nightmare, but I suspect for disc/drum you'd be in good shape.

Trying to source a stock-type combo valve is tricky, as there are many variations or OE, but the replacement ones tend to be lumped into "disc/disc" or "disc/drum" categories. I'd try the tee and adjustable option first.

-- A

Sweet, I will try that route.