By on November 12, 2012

Adam writes:


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?



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23 Comments on “Piston Slap: RV ready for Hydroboost Brakes?...”

  • avatar

    hydroboost only works when the engine is running and pressurizing the power steering system. If you’ve got no brake pedal with the vehicle not running, that has nothing to do with hydroboost. The fact that you’ve had to top up the master cylinder before indicates a brake or master cylinder problem.

  • avatar

    with brakes u dont wanna to screw around, get professional help.
    unless u really looking forward to spend indefinite time to a do memoir with son of sam. As u sitting upfront probably u the one could buy the farm too atleast u no need to face the inquest.

    aounds like is the master cylinder went, even if HB fails u still get pressure but take 3 guys to step on da pedal inorder to stop.
    unlike air brakes or those Citroen or RR ( hydro pneumatic ) which uses the hydraulic pressure to push the slave cylinder.
    thats the price of u not driving her every so often.
    your RV is many time heavier than a yugo, trabant where sticking a foot outside will bring her to a grinding halt.

  • avatar

    I had a Cadillac Eldorado from the 70’s with hydroboost, you needed it to slow down that beast. For the uninitiated, they work off the power steering pump instead of using engine vacuum.

    They aren’t that expensive to replace, my guess is a new or remanufactured unit is probably around $250, and it’s probably bolted somewhere in the firewall. It shouldn’t be a big deal for a technician if you can’t get to it yourself.

    • 0 avatar

      my 73 eldo came with reg vac booster. i take they do that to certain yr.
      i say vac may have some reserve pedals, even when eng died, but hydraulic system if eng dies u have nothing in a hurry!

      • 0 avatar

        The hydroboost had a fluid reserve that gave you a few extra uses after the power steering pump stopped.

      • 0 avatar
        MRF 95 T-Bird

        My 80 Olds Toronado Diesel had a hydro booster which worked off of the power steering pump since diesels are not able to generate vacuum. It started to leak fluid so I took it off and replaced it with a rebuilt unit and all was relatively well considering it was an Olds Diesel.

    • 0 avatar

      My local SCCA region had a GM cube van with hydroboost. You could brake or steer, but not both.

      • 0 avatar

        Do they use it as a hot lapping simulator? “Ok, your tires have a dollar worth of traction, which you can spend on steering or braking. Now take a 10mph lap in this van, which simulates the effect with hyrdoboost.”

  • avatar

    quite often u may have to take a saw saw to cut open the whole big enuf to change the master brake cyl.
    the hb is same as reg vac booster, the master cyl bolted infront of the HB.

    i heard of they had to do that on a xj6, cut out the fire wall inorder to change the heater fan, then weld her back and spray bomb her with blk paint.

    or access underneath, if there’s room.
    first time my merc 300sd had the tumbler frozen I had to cut a hole on the dash, since i had only an angle grinder to work, cut away the locking pod so i can free the steering.
    2nd time on another car I didnt have to make such a cosmetic mess, i had a saw saw, so the surgery was much neater, no scars mom.
    if u dont wanna to spend more $$, then cut away a hole big enuf to pull the master, or so the mechanic didnt have to do the surg on behalf for u. When they have do it will be more that simple.

  • avatar

    The GM Diesels from eighties used the power steering pump for brake boost.

    It was one of the issues,you ran into,if you tried to install a gasoline engine.

    • 0 avatar

      It’s not an issue at all and usually requires no changes, as the gas engine will still have a power steering pump and the rest of the hydraulic plumbing stays the same.

      There are plenty of gas-powered vehicles (mostly pickup trucks and 4x4s) that also use hydroboost brakes. For situations in which there is low manifold vacuum (racing cam, supercharged or turbocharged engine, sustained high RPM operation, high elevation, etc), it makes perfect sense.

  • avatar

    Get professional help. You don’t want to do a just-good enough job to make it look like the brakes to work in your driveway if you’re going to be descending for hundreds of twisty turny miles. Not over a few grand in furniture. You would feel like a total asshole in your last moments if you and your wife did a Thelma and Louise over a bedroom set. As a general rule I try to avoid putting myself in situations that involve ironic death.

    And I’m a bit confused about why you need to go through Mexico to go from Arizona to the Deep South, unless by Deep South you mean El Salvador. I bet furniture is really cheap in El Salvador.

  • avatar

    Why rent a truck when you have a giant RV? how much furniture can you fit in that thing – a lot I bet. might need to make some adjustments though to get anything large in it.

  • avatar

    Stop being cheap, there are more rvs in az then most any state. Go on a Winnebago forum find a local mechanic. In and out for less then $350

  • avatar

    “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.”

    Unfortunately, that’s what RVs often do. Since you’ve found a willing taker for this vehicle (hallelujah!), just pay a pro to fix the brakes. The furniture – and your safety – are both worth it.

  • avatar

    You survived Gary, Indiana. So did I (barely).
    How much luck do you think you have left?
    DO NOT skimp on fixing those brakes. Have a pro do it right regardless of cost.

  • avatar

    My mom had an ’84 Caprice wagon(my avatar) that had hydroboost. I never had the misfortune of working on it, but it was just about the most powerful brakes I’ve ever felt. That thing would stop on a dime and give you back 2 nickles!

  • avatar

    Owned lots of HB cars. Mostly turbo’d Buicks. OK pedal goes to the floor. It aint the HB. Most likely MC or some other component in the hydraulics. Confirm where the leak actually is before you pay somebody to fix it. If it’s leaking DOT3 than it’s the MC. If it is leaking PS fluid than it’s the HB.

  • avatar

    bonfire – take the insurance. I wonder what they’d make of something like this in Cuba? Assuming it could get on a boat.

  • avatar

    Not a job for someone who needs to ask how to do it. Get a mobile tech to come fix it. If I’m wrong and you know what you are doing–got to and look around until you find the stuff on repairing P30 brakes. Should help.

  • avatar

    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.

  • avatar
    19 Pinkslips

    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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