1977 P30 hydroboost questions

[mcarlo86]

The brakes on my motorhome have gotten quite sketchy so I decided to look into it since it is in the shop and it is too cold to do much of anything outside. I opened up the master cylinder and found that the rear section for the rear brakes is basically empty.

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I went looking for the leak and see that there appears to be fluid leaking from between the master cylinder and the hydroboost. I’m not sure if it is brake fluid or power steering fluid as it is kind of a red/brown color. The power steering reservoir is low on fluid. I don’t see any evidence of leaks at the power steering pump or steering box. The fittings for the lines going in and out of the hydroboost are also dry. I have not pulled the rear drums off yet, but there isn’t any evidence of brake fluid loss on the back side of the drums or along the brake lines anywhere.

I do think I will replace the master cylinder and was wanting to replace the hydroboost unit also, but it looks like the hydroboost units are out of stock everywhere. Can those hydroboosts be rebuilt?

 

[mcarlo86]

Here is a picture of the master cylinder and hydroboost from underneath. Not the best picture, but best I could do laying on my back under there. This shows the leaking fluid I am seeing. I’m assuming it’s brake fluid, but not completely sure.

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[AuroraGirl]

Here is a picture of the master cylinder and hydroboost from underneath. Not the best picture, but best I could do laying on my back under there. This shows the leaking fluid I am seeing. I’m assuming it’s brake fluid, but not completely sure.

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hows rust on the thing? does your truck have a rear disc but a prop shaft park brake? Or rear drum? if you have drum id still find it worthwhile to pull the drums or check for wetness on the backing plate on the back before assuming much about the hydroboost
But if you have some rust, wherever the brake pipe transitions for the rear brakes, im betting theres a threaded connection that allows for different brake/wheelbase setups and that it hugs the frame, and wherever its at worth looking at for corrosion

I know on my square thats where my rear lines failed , but worth checking. you could also put brake fluid in and just work the brake pedal, maybe even wipe the grime away as it is now to see if you can induce it to leak from there

May need a hook to pull the pedal back up if its that cold and want to speed up the diagnosis. You could start it but that would pressureize the power steering, and this way you can check it for just that problem at a time. Suppose you could do the same by starting and not using the brake to do the opposite.

 

[AuroraGirl]

Even if you just use a turkey baster or battery electrolyte or a 2 stroke mixing syringe (clean, no oil on it) or a brake bleeder tubing to siphon, you should change out that front fluid. Even if its just in the reservoir, getting that nasty out and refreshing will be better in the long run, whatever is left in system will slwoly contaminate the clean but even a little dilution with good stuff before you can fully flush and clean out will be wise

Old brake fluid becomes corrosive to the brake pipes, and new stuff mixed in should help extend the life of the brake lines even a tiny bit, and has a much higher boiling temp, and has less particles which can wear bores/seals etc

 

[fast 99]

small/front side is rear brakes. Likely a wheel cylinder leaking. Can be a master bypassing but if so the larger/rear side will be overfull. If you suspect master is leaking in the rear unbolt it and look. Should be able to pull it forward far enough without removing lines to inspect. While your at it crawl under the dash [inside] and inspect for power steering fluid leak at booster.

As suggested above brake fluid should be sucked out and replaced at least yearly. I have a dedicated turkey baster just for brake fluid.