Piston Slap: RV Ready for Hydroboost Brakes?

by Sajeev Mehta

Updated: May 16th, 2014 Published: November 12th, 2012

piston slap rv ready for hydroboost brakes

Adam writes:

Sajeev,

I have a 1989 Winnebago Class A motorhome that’s built on a Chevy P30 chassis that’s been sitting out on the side of my house basically since I moved to Arizona about 5 years ago. Before I brought it out here I lived in it for about 6 months as a newlywed in a garage on the side of 80-94 in Gary, Indiana; I have no idea how I am still married but that’s beside the point.

Anyway, when it came time to move out to AZ I found that the brake pedal went straight to the floor and had no pressure whatsoever. I managed to find the master cylinder, which is only accessible through a small opening in the wheel well, pry off the master cylinder cap and fill the brake fluid. After about 10 pumps of the pedal the pressure built back up; since I was only going cross-country with all my worldly possessions loaded in a trailer behind me, and I didn’t have much choice, I embarked on my journey wrapped in confidence that the brakes would not fail me.

So now we fast forward to the present day and “Winston” has barely moved in years, mostly because I have no fond memories of it. I have been talking about selling it for a while now but going out and dealing with a vehicle that’s been sitting this long is daunting.

Well we recently bought a house in the Deep South as a vacation home and have realized that furnishing the place is going to be a hassle as we are limited to what we can take across the border since our car is small and renting a truck that will be going into Mexico is next to impossible. Somehow it came up that we have this Winnebago and the person we are buying the house from offered to trade the furniture in the house for the camper but we have to be able to make sure it gets down there.

I have everything working in Winston but the brake issue has reared its ugly head again. I climb in and there is no brake pedal pressure. I live on the top of a mountain and rolling down it then driving 100 miles to Nogales and then 200 miles into the middle of Mexico with only the emergency brake to slow me down is not an option. I’m pretty sure that my problem is the master cylinder leaking out the back seal. I can’t see this because the laughably small access hole in the fender well is the only way to see in there but I’m pretty sure I’m right.

The question is, how do I get the master cylinder out of this thing? I can’t get it out from the access hole, I can barely fit my mitts in there to get the cap off let alone remove the bolts and then get a wrench around to get the lines off. I can’t even see the stupid thing from underneath but even if I could the suspension is in the way and I’d need arms like Plastic Man to get a wrench up there. I’m down to cutting a hole in the floorboard as I think that would be the easiest way to do things. I can’t believe there isn’t some trick to getting this done.

Sajeev Answers:

I do my best to answer these Piston Slaps, but how do I say this correctly? Dude, I don’t know shit about RVs.

I know enough to get in big trouble, and Googling for some advice didn’t help matters. But then I looked a little deeper and found something else I understand: Hydroboost systems. The one perk to being a Lincoln fan since the 1980s is that I already know how this system works. And, unless your diagnostic pointed otherwise, I think your pedal pressure has more to do with hydroboost and less with brake fluid leaking from the master cylinder.

That said, the Hydroboost unit is probably in the same nightmarish location as the master cylinder on a Chevy P30 chassis. And while I have no clue how to get to it, I know you’d get the answer if you post on the RV forums.

How’s that for not answering your question?

#Hydroboost #MasterCylinder

Sajeev Mehta

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2 of 23 comments

Nikita on Nov 13, 2012

Sounds like the real issue here is access to the brake MC, HB or not. The RV builder took a P30 chassis and then built a body with no regard to serviceability. What a surprise. I worked for a plumber that had a Step Van (P-20). It was noisy and uncomfortable, but easy to service because the front of the body was built that way.

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19 Pinkslips on Nov 20, 2012

I have a similar vintage Class A motorhome on a P30 chassis. After is sat for a few months last winter I had the same issue. The seal at the pedal end of the master cylinder leaks fluid out as it sits, if you refill it and bleed the system again they'll work fine...until you park it again. The rebuilt master cylinder is available in stock at any major autoparts store for ~$50. That shield in the wheel well keeps the exhaust manifolds from melting your tires, it unbolts fairly easily, remove the half dozen bolts, undo the brake lines, swap in the new MC, hook up the brake lines and bleed away. You'll be back on the road in no time. The P30 chassis is less than perfect, but it's really not that hard to work on and for a HD chassis the parts are pretty cheap.

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