NP208 and proportioning valve issues?

[mstockton]

First of all, I need to know if anyone knows of a good rebuilding manual for an NP 208.

Secondly, I've got a brake issue. The truck used to pull to the right a bit when you'd get on the brakes hard, now thats gone away and the truck pulls to the left an incredibly dangerous amount when you just apply the brakes. I'm assuming my right caliper was not functioning so I tried to bleed the right caliper with my vaccum pump. The bleeder just kept sucking air with very little fluid coming out, it would never hold pressure at all, I just kept pumping and pumping and it never stopped. The left brake was working so I'm assuming the problem starts at my proportioning valve to my right caliper somewhere. I can not see where I have any leaks at any of the fittings, and I have not messed with them in quite awhile. So all I'm left with is a busted caliper or a busted proportioning valve. Anyone had this happen to them? I also developed a squeal out of that right caliper just before this problem developed. My brake pads are fairly worn, so it could be just that, but I'm not sure if the squeal and failure are unrelated.

Any help clearing this up would be much appreciated guys..


-Martin

[Robyn]

Best book is the factory truck manual

The prop valve regulates pressure to the rear brakes and not side to side.
You may have an issue with the master cylinder.

You need to clean the whole system out from the master cylinder to the calipers and rear wheel cylinders.

After you clean it all out (Pump fresh fluid through) replace the master cylinder, rebuild your calipers and the wheel cylinders.
Replace the prop valve with a fresh one.

Bleed the entire system out and you should be good to go.

Make certain the brake rotors are good as well as the pads.

I bad pull can also originate in the rear brakes.
Be sure the brakes dont have grease from the rear axle on them.
Adjust to tight then back of untill just spin easy (rear)

Brake systems have a way of slowly going south without really having a catastrophic failure.

Hope this helps

Robynq

[Cat 920 Sweden]

Does my -91 k 2500 truck have that proportioning valve ? I have more brake pressure on rear than front, not so good in the winter , I have to run 4 wd all the time or the rear wheels keep locking...:confused:
Could the prop valve be the problem here ?

[RoverIIa]

Be careful taking apart a 208. Bearings go everywhere, it is a real mess to get them back.

If you e-mail me off-list natersxj6@hotmail.com, I have a used case for a good deal. I could send you photos.

As far as brake proportioning: It sounds to me like your left caliper has seized. If the inner pad is worn worse that the outers, you need to clean the pins that they slide on, and maybe replace the sliders, o-rings, and rubber grommets. These are called "brake hardware kits" and are available cheaply at most parts stores.

Sometimes a complete failure of a proportioning valve will cause it to stick in one position or another, and significantly reduce braking pressure to the front or rear. It needs to be reset, consult the factory manual, or a haynes book. Sometimes simply bleeding the whole system will fix this. I've always hated the factory proportioning valves, and had a similar problem, where my front brakes would lock, and my high idle would push me through icy intersections unless I locked in the 4x4.