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becida · 09-25-2013, 09:42 PM

I have a 1987 Winnebago class "A" on the P-30 chassis with the 454 engine. It has been sitting for almost 6 months and we plan on leaving next week so I started it today.

Other than having to charge the battery there was not problem with that. The brakes on the other hand have problems...

Pedal goes slowly all the way to the floor & the brake light comes on.
The master cylinder was half way down in the rear chamber & 3/4 down in the front and there are no obvious leaks. I filled the MC & pumped it up, it never felt 'right' but for a moment the brake light went out then came back on, went out and came back on, maybe 3 times as I pumped the brakes (by hand) then stayed on.

No change in the feel with the engine running or not. I pulled up the shop manual for this and read up on the brakes.

Tomorrow I'll make sure the power steering reservoir is full then crawl under and look for leaks that didn't make it to the ground in the 6 months it's been sitting. Then I'm not sure, maybe try to bleed it....

I've had some car & small truck brake experience (5 yrs at a front end shop). I don't think the MC is the problem (when it's the MC it usually comes back to normal with the second pump) but I've never messed with the hydro-boost.

I'm open to suggestions....

kewag · 09-25-2013, 10:00 PM

I owned a 1987 Winnie many years ago. Just a fun MH. I had a simular brake problem as you describe. Brakes would lock up also, turned out to be the booster cylinder. A PIA to replace, but fixed the problem.

becida · 09-26-2013, 03:41 PM

I ordered a new master cylinder & a remanufactured hydro-boost today.

Chuck48 · 09-26-2013, 03:55 PM

If the master cylinder got that low, air got into the lines. Breaks both front and back will have to be bled. Hard to do on a motorhome because of the long lines. Take it to a good shop that has a power bleeder. Might not need a new master cylinder. If master cylinder is bad, break system will still have to be bled. Breaks are a closed system, has to be a leak to be that low. Usual suspect rear break cylinders. Hard to detect. Good luck!

becida · 09-27-2013, 06:30 AM

The master cylinder was not empty, just low so air from there shouldn't be a problem.

This is a simple system (booster, master cyl, lines & 2 calipers & 2 drums. If the fluid was leaking (not seeping) at a drum slave cyl it would show up, it didn't. The fluid had to go somewhere...

I'm "guessing" the MC is leaking into the booster so I'm going to change them both.

Yes I will bleed the brakes when I'm done...

Nick-B · 09-27-2013, 01:54 PM

Hi Bob,

Replacing the master cylinder is a good call. Your symptoms were classic.

Unless you know the rest of the braking system parts are much newer than 1987 you should consider replacing all the hydraulic components - those being the calipers (w/pads), wheel cyls and hoses as well. If they are still original parts or at least of unknown age, it would be wise to freshen up the entire system. Since one component failed the remainder may not be far behind.

Ray,IN · 09-27-2013, 06:19 PM

According to the GM mechanic in Whitehorse who replaced the rear disk brakes on my 02 Chevy dually, with the hydro-boost system you can slowly push the pedal to the floor while stopped. He said it is the way it works.Don''t know if he was right or wrong, I just know after he worked on my truck the brakes worked normally.

Don and Barb · 10-16-2013, 05:31 PM

Sounds like you need to bleed your brakes, if that doesn't correct it then it's your master cylinder. There's a rubber plunger that pushes the brake fluid to the wheel cylinders, it can degrade over time. When it does the brake fluid goes around the plunger so no pressure goes to the brake, you won't see a leak because it's not leaking to the outside only around the plunger. You can buy rebuild kits at the auto store to rebuild it or buy a new master cylinder. I haven't seen too many boosters go bad, it usually the master cylinder.