Archived '92 D250 Brakes ABS Bleed Valve?

[Dobrien]

HELP! I'm swapping to rear Disk Brakes on our '92 D250 CTD. All the new stuff is connected. The system has been bled, but I cannot get enough pressure to the rear brakes to stop them from turning while under power. (Rear tires are still off and jack stands holding truck up) I have to pump the pedal several times to get them to stop. I have a "MOTIVE POWER BLEEDER" and have pumped well over a quart of fluid through both rear brakes. All the old stuff is out, only new brake fluid, no bubbles. The manual states to bleed the RWAL Hydraulic valve. I CANNOT find the valve. I know it's there because it has worked for us. HELP please.

 

[Missouri Mule]

I'm looking at 96 service manual. In the manaul the RWAL valve is located near or under the master cylinder.

It is the valve closest to the engine the other valve which would be closer to the fender is the combination valve.

There is a brakeline going into it looks like there is bolt or screw above line.

 

[Dobrien]

Thanks Missouri Mule, I went out to the truck and found the EWAL Valve, but no "bleed valve" like on the brakes. I ran about another quart of fluid through the MC using the POWER BLEEDER, bleeding from the rear calipers. No bubbles come through and I still need to pump the pedal 3 or 4 times to get good pressure and keep the pedal from bottoming out to the floor. I'll hit it up again tomorrow and see what I can do.

 

[Sticks]

Different animal here, but when I have had to replace master cylinders on the chevy pickups at work, I run into the same problem. What I have found works is to bleed the abs unit like you would the calipers/drums by loosening the outlet lines. The really cranky ones I have to remove the outlet lines and apply a vacuum pump (MightyVac) to the outlet ports to suck the air/fluid through.

 

[Dobrien]

Sticks, Thanks. I'll give that a try. The '92 service manual states there is a "bleed valve" on the RWAL valve, but mine does not have one. I'll remove the brake lines from the RWAL Valve and try the vacuum pump on it.

 

[PToombs]

The rear wheel ABS valve is above the rear axle, bolted to the frame. The best thing you can do is remove it and go straight to the hose connection. There is a valve inside that fails, so when you hit the brakes, all you are doing is charging the accumulator, thus the spongy pedal and lack of braking power.

Most of us 1st gen guys have removed it and have the best brakes since the truck was new. Don't forget to unplug the ABS brain behind the glovebox, or the lights will stay on.



I know you posted in the 911 forum, but next time you will get a better response if you post in the 1st gen forum. We kinda stay to ourselves over there, it's the "Old school is still cool" attitude. :-laf

 

[Dobrien]

PToombs, Thanks for the info. I may just go ahead and try to disconnect the lines from the RWAL Valve bleed the RWAL Valve. If that fails, I'll probably bypass it. I'll hit it up when I get home this evening.

I certainly understand the "Old school is still cool" attitude. Computer controls lead to less hands on. I like the hands on approach, hence "Old school is still cool".

Thanks again, I'll get back online and update after I work on it this evening.

 

[Paul Herioux]

The rwal valve is pretty easy to test for internal leakage. There is a rubber plug in the end of the accumulator. Remove it and stick a straightened out paper clip in the hole until it bottoms against the back of the accumulator piston. Have a friend step on the brake pedal. If the paper clip moves the dump valve in the Rwal valve is leaking.

 

[Dobrien]

Didn't get a chance to work on it this evening. I bought WH 7917 and WH 7828 fittings from NAPA (per this forum and other forums) to by-pass the RWAL Valve. I'll check the valve and see if the accumulator dump valve is leaking. Paper clip, There's a simple and very useful little tool. I'll check on the truck in the morning and try to get something done. I need to get this back on the road. I need to get the cars back in the garage. My wife's getting a bit anxious to get it fixed and back on the road.

 

[PToombs]

Paul, that's a handy tip, I'll try to remember that. It won't do my truck any good, my valve has a new life as part of somebodies Toyota. :-laf

 

[Dobrien]

***UPDATE***
I by-passed the RWAL Valve tonight. All I have left to do is bleed the system. I hope to get that done tomorrow (If I don't work OT). There is all the wiring for the 2 trailer connections that 'hide' the RWAL Valve. Yes, it's behind the fuel tank, but it's also rear of the differential (mounted on the frame) as well. I only have the one side-saddle fuel tank, no second rear fuel tank where the spare tire is mounted. If I had removed the spare tire, it wouldn't have taken me as long to by-pass it. I'll update again when it's back on the road. I also have the front brake calipers and disks to change. I should have it completed an on the road some time Saturday. Thank you everyone that has replied (above) and for all the advice. It has been appreciated.

 

[PToombs]

Glad you got it working.

 

[Dobrien]

It's on the road. I've been driving it for the past week. Stops well. One thing I noticed is that the brake pedal goes down a little more than before, but stops great. ... also, if I press a second time, the pedal doesn't go down quite as far. (No air in the lines). The rear caliper holds a little more fluid than the stock rear D250 drum brakes. Seeing as the D350 rear drums have wider (3" wide) shoes, does the D350 MC have a larger piston for the rear? IF it does, I'll swap it out some time in the future with a MC from a D350.
Again, thanks every one for your help.

 

[PToombs]

Do you have the rear brakes adjusted up just touching the drum? If they are out much it will do that. One of the weird things these trucks do. You need to keep them adjusted up close too.

Pretty sure the MC is the same on both trucks.

 

[Dobrien]

Yep, rear calipers are adjusted correctly. I believe they are off a late '70's, early '80's Cadillac Eldorado. The parking brake lever on the calipers comes off to adjust the piston. They are a bit touchy to adjust but the parking brake works good. I can lock up the rear as well as the front with one good "stomp" on the pedal. The truck stops much better with the rear disk brakes than with the rear drums. It feels like there is better control than with the drums.
Thanks again...

 

[PToombs]

I didn't realize you had put on disc brakes. The pedal being off is probably just the difference in the amount of fluid needed to apply the bigger pistons in the caliper.