Brake Line Question

When was the proportioning valve behind the rear stop light switch eliminated? The Factory Service Manual shows one for early model CJs. Is the proportioning done at the master cylinder on late models?

 

My '71 would be considered the "late model" if you're talking about Kaiser-era CJ5's, and it has the proportioning valve. If you're talking about "late model" intermediates (72-75), I know they had a prop valve in '74 b/c I just finished working on one.

Just so we're clear - there are actually two brake light pressure switches. One is right near the motor mount, on top of the frame, and the other is inside the frame rail, just behind the clutch tube. I only have the rear one hooked up, and the lights work fine (albeit only reading rear brake pressure)

 

I was only referring to Kaiser CJs and the rear brake switch behind the clutch tube. Do you have a proportioning valve near there? Also, are you sure you have a proportioning valve and not just a brass junction?

 

I'm not sure if what I have is a proportioning value (per se) or just a junction block. We've debated that before (seems like someone suggested cutting one open to see what's inside). The two lines from the MC run to it, then two lines come out of it for the front, and one to the rear. Seems to me that it would be a prop valve of some sort, b/c why go from the MC, forward to this valve, then back-track to the rear axle? I understand the the front line has to be split to two, but why just just use a simple 'T' fitting???

 

Tim - All good questions. I'll add one more. What exactly is the purpose of the proportioning valve?

 

Controls the amount of pressure going to the front vs. the rear. During braking the weight transfers to the front of the vehicle (about 60%) necessitating more braking on the front than the rear. Without the proportioning valve you would have the rear brakes locking up before the fronts really start working causing vehicle control issues. This is of course all on a 4 wheel drum braking system. Nickmil.