Chevrolet P30 Postal Stepvan: Need help with the brakes.

[Mark Krieger]

I've been driving my retired 1988 Grumman/Chevrolet P30 USPS Stepvan for a few weeks now, between work and home, and I think everything is still looking fine.

I noticed that the hydraulic boost to the master cylinder is dripping power steering fluid where it attaches to the master cylinder. Does anyone have a good way for me to identify the boost hardware so I can try to locate a replacement? Has anyone ever had to re-build one of these? I'm not sure what's inside!

The master cylinder must not be in the best condition either. The brakes work fine and there's no noticable pedal fade. However, I've noticed that pumping the brakes once results in less travel and stronger brakes on the second application. I'm betting that the front or rear brakes aren't contributing much until I pump it once. Again, I need to learn how to identify the master cylinder so I can rebuild it or get a replacement.

The GVWR of this P-30 chassis is 11,300 so I'm not sure if it uses the same hardware as a pickup truck or suburban. Any help would be appreciated.

Did you know: My 2003 3/4-Ton Suburban has a 6.0L gas engine but doesn't use vacuum assist like normal light-duty trucks. It actually has hydraulic assisted brakes just like the diesel trucks do. The power steering pump does dual duty in the Suburban just like the Stepvan. Has anyone else noticed?

[arveetek]

Originally posted by Mark Krieger:

The master cylinder must not be in the best condition either. The brakes work fine and there's no noticable pedal fade. However, I've noticed that pumping the brakes once results in less travel and stronger brakes on the second application. I'm betting that the front or rear brakes aren't contributing much until I pump it once.

The GVWR of this P-30 chassis is 11,300 so I'm not sure if it uses the same hardware as a pickup truck or suburban. Any help would be appreciated.

I imagine your master cylinder is just fine. I'm sure that all you need to do is adjust your rear brakes. Every truck I've owned with front discs and rear drums will usually display the symptoms that you describe, at one point or another. What is happening is that the rear shoes are too far away from the drums, so that when you step on the brakes a second time, you're just taking up the slack. My Ford was doing this bad when I bought it. All I had to do was take out the slack by turning the wheel on the slack adjuster. Much firmer pedal, much better brakes.

With the rear brakes out of adjustment, you're actually only using the front brakes to stop. When you pump the pedal, the rear brakes come into action, and then you have a lot more braking power.

You should have nearly the same hadware as a 1 ton pickup. Although now that I think about it, a lot of P-30 motorhome chassis with 19.5 wheels have rear disc brakes. I would assume that your 88 model would have drums, though. I'm not sure. You'll just have to crawl under it and look.

GM has used hydroboost for years on many different vehicles. All diesel powered vehicles got hydroboost, as well as all 1 ton trucks, gas or diesel. They are very similar systems, but there are differences in the light and heavy duty versions.

Casey

[Mark Krieger]

Originally posted by arveetek:
I imagine your master cylinder is just fine. I'm sure that all you need to do is adjust your rear brakes. Every truck I've owned with front discs and rear drums will usually display the symptoms that you describe, at one point or another. What is happening is that the rear shoes are too far away from the drums, so that when you step on the brakes a second time, you're just taking up the slack. My Ford was doing this bad when I bought it. All I had to do was take out the slack by turning the wheel on the slack adjuster. Much firmer pedal, much better brakes.

With the rear brakes out of adjustment, you're actually only using the front brakes to stop. When you pump the pedal, the rear brakes come into action, and then you have a lot more braking power.
Casey Casey:

That's beautiful! It matches the symptoms exactly and I willing to bet you're 100% correct. I should have known...

Looks like I get my first lesson in removing dual wheels. They sure look big and heavy, I hope I don't need a crane to lift them. I guess my 2-1/2 Ton floor jack should be enough to get it airborne.

I know I can probably adjust them through a hole in the backing plate, but I better take a look to see what condition they're in. It'll be easier to adjust them with the wheel on after I've seen what I'm doing with the wheels off.

[NH2112]

I think a 2 1/2 ton floor jack will probably only lift one side of your P-van at a time. I know mine barely lifted 1 side of my 77 Dodge W200 w/equipment body! The duals aren't any different to remove than a regular tire unless they're Budds. If there's not a 13/16" square drive on the wheel studs, they're not Budds.