1990 P3 braking issues

[ALO]

I have a 1990 P3 class A 27' Coachmen. This thing is nasty to stop. It has hydro-boost brakes on it, disk front. Both front brakes will lock up if I apply any amount of solid pressure. Consider the rear are ajusted as tight as I dare, all the brakes do function. In the rain it's impossible to stop, I can't trust it at all. If I tow my 4800 lb trailer, well forget it. The front is doing all the work even though the entire braking system is serviced. It's not that heavy a unit to have such issues stopping.

[Wallaby Dan]

Sounds like the diverter valve can get stuck when Changing pads and or have to bleed the brakes. They are supposed to be guided by the front and rear.If the rear brake or Front brakes leak down or one side it shuts down the defective side and give you enough o get you to a garage. If they didn't check it than that could be your issue. Does the brake light come on when you turn the key on?? how about when you start it ?? If you don't have a light,look under the drivers side and see the brake master cylinder. Near that you will find the diverter there should be seeing one wire and with someone inside see if that light works as it is coming off the ground side. If the light doesn't light up check the bulb. If that fixes the issue there get in the cab, foot on the brake and jamb as hard as you can see. That should fix the problem. I would do this before I did anything else, I'd try it and see. Dan

[Marty too]

Alo, I'm going to do a bit of guessing here based on two previous GM chassis Motor Homes.

Down below the master cylinder on the firewall was a little metal block that all the brake lines from the master cylinder went to. It's purpose was to equalize brake pressure between the front and rear brakes. You might take a look there just in case the internal plunger is gummed up. There is a set procedure for adjusting it according to the book I had at the time.

Marty

[Wallaby Dan]

Marty Too, Thats the diverter valve I was talking about. There is a sensor light wire coming out of that valve.

[ALO]

It is also called a proportioning valve, common on most braking systems. Some are front to back or diagonal. It has a dash light which is functional but no isssue there. All the brake hardware front and back are replaced in an attempt to solve this problem, also a complete fluid flush. I suppose master cly and proportioning valve are next. I'd like to find an adjustable valve to put in there. It's a great smaller RV except for this stupid brake issue.

[Max Hubrich]

Change the brake hoses to the front wheels. They have been known to collapse internally--- due to age.

It happened to me with my '86 Chevy P-30.

Also, my P-30 had an extra master cylinder under the coach, near the steps, to actuate the rear tag axle brakes.

[ALO]

Yes I've changed the hoses, I thought that as well.

[ALO]

Would anybody know the PSI rating on this RV braking system? I have found an adjustable valve that is rated up to 3000 lbs.

[Wallaby Dan]

Before I would change anything else I would go to the back Brake pads and rotors and see if when you have someone else press on the brake if the rear pads move. If it have been awhile since it ran there could be water or rust or collapsed brake lines, Yes they used something like the fronts, And like what was said above. I have ap-30 and the book calls for new fluid and flush every two years!! Have fun, Smokey

[Lamont]

the Proportioning valve---i got mine from them several years back-for my 84 Pace Arrow and yes on the Hoses---i got a bad one once---had to replace it again,
try LMC Truck they have lots of parts too
mill supply sell p3o parts too.
rich in Va.