Hey all.. I think I'm missing a part here.

I have a W250 that I'm working on and from the master cylinder that goes to a brake valve which feeds the front brakes. From that valve it goes right to a splitter and into the rear brakes? Wouldn't there be a brake proportioning valve for the rear or no?

The issue is this.. the brakes work but will not hold when the engine is running. With the engine off you can push the pedal and it's rock hard. Weird as hell but I think that is due to there only being one valve. The SM shows only one but I think there needs to be two.

 

The splitter is the proportioning valve. I don't think it's adjustable. Have you had your rear drums apart? Left unserviced, my rear auto-adjusters like to grenade.

Have you replaced/bypassed/bled the air from the RWAL in the back on the frame? This is a common failure point.

 

I've been into my rear brakes so many times I'm wearing out the nuts on the axle and wheel. You have to get the kits to replace everything in there including the cylinder. Springs, self adjusters everything. Take a picture of it before you take them apart so you'll have a chance of getting the new stuff back in right. run the adjusters out until the shoes drag then drive around the block stopping a few times then adjust them again. Try a few stops in reverse helps settle things also.

Someday I may get gumption enough to look into rear disc conversion.

Edwin

P.S. I think the fellow who designed this system is in an asylum somewhere.

 

Anyone have a diagram of what the lines are suppose to look like? There is an electrical plug that is just hanging with electrical tape. I think I'm missing parts here.. LOL

 

I thought that "splitter" is the ABS valve? The star wheels need to be taken apart, threads cleaned, anti-seize put on them. After you get the brakes back together I do them to where there is quite a bit of drag. When you back the truck and hit the brakes is when the adjusters work.

Take pics before tearing them down.

Some people remove the ABS valve as they are $250-$275+ to replace if you can find them. They may be rebuildable. Some O-rings and a good cleaning(?)

 

A picture of what you're talking about would be helpful.

 

The 91.5-93 trucks (alum prop valve) have an extra junction block at the frame below the steering column. AFAIK, it has no guts.

None of my trucks have the same brake feel. I blame it on the vacuum booster and/or vaccum pump, D vs W calipers, and whatever combo of shoe size and wheel cyl size thats ended up in them. But they do basically stop. Its just bandaids and maintenance until i get hydroboost going. I've hoarded a few complete disc brake axles because i'm not into the cost of a 'kit' that features a parking brake.

 

Crawled under another truck and it looks like there is a front and rear proportion valves. I found one on ebay and got it ordered, the RC has the same setup but at the front it looks like it's a manual valve or something. I didn't want to mess with it as the brakes are pretty dang good in that thing. On my truck there is nothing for a proportioning valve so I wonder if they just ran one to the rear to give the front 100% power and the rear about 30%

 

The valve above the rear axle on the frame (with wiring connector) is for ABS.

 

Is that activated by the box behind the dash?

 

The RWAL (Rear Wheel Antilock Brakes) Computer is the box behind the glovebox on my 89. It's currently unplugged because the Dump Valve by the rear axle is bad and makes the light on the dash stay on. The valve is unobtanium AFAIK.

Edwin

 

I think Autozone, or something else hand them. Like I said $275+ IIRC. I was reading elsewhere, take them apart and clean them, new O-rings from Harbor freight. They may work.

 

Here is a rebuilt unit (out of stock) https://www.partsgeek.com/catalog/19...ulic_unit.html Its for a single rear wheel truck. Nothing at Autozone.

 

I plan to bypass my dump valve and then I can tear into it to see if it's repairable. I stopped looking for a rebuilt one because they're always out of stock if they're listed at all. Forget N.O.S.

Waiting for the fall when temps are more tolerant. Fixing up the garage little by little of the Okie homestead.

Edwin

 

When I had braided stainless lines made up at the Hydraulic shop, I cut and re-flared the frame line and ran a braided line directly from the frame to the axle. No RWAL valve at all anymore.

I'm a pretty easy driver, but I've yet to lock them up.