Hydro-boost brake problems

[trukman1]

Hoping someone can help[ me. I have had hydro-boost for years w/o problem. One day while driving I lost brakes (literally) then on the way back to the house I have brakes again. Back home I bled the brakes, buddy system and gravity, no brakes then suddenly on third attempt I had brakes. Took for test drive, all okay. Drove later in the week, same old thing again, brakes working fine then NO brakes then brakes again on way home. Any ideas?

Needless to say I'm afraid to even test drive it at this point.

[Grumpy old man]

Trash in the proportioning valve .time to flush the system .

[davepl]

If you lost brakes it has nothing to do with the hydroboost. If you lost assist, it might. But those are two different things.

There could be garbage in the combo valve (mine has a combo valve, but I don't know about 1967, maybe it was in fact a prop valve) as mentioned. Either way, when you find it and fix it I'd consider an inline power steering filter. LMC has them I think.

You also need to treat your power steering pump, belts, and hoses with more scrutiny than you would otherwise since your brake assist is now dependent on it all working. But like I said, if it fails your worst case is really hard manual brakes.

Sorry I can't be of more help. If you lost both circuits of the master cylinder I'm stymied, because unless you ran out of fluid in the master cylinder reservoir either the front or rear should have worked. They are mechanically interlocked so if, for example, the rearmost circuit fails the piston will still go forward and mechanically (instead of hydraulically, if that's a word) engage it.

[trukman1]

Grumpy, I've bleed the brakes so much I don't know how much more I can flush through them. Is there a specific procedure for flushing the brakes other than lots of bleeding? Or do I need to have it professionally done at shop? Thanks, Trukman1

[trukman1]

davepl,

I just mentioned the hydro-boost so everyone would know what type system. I thought I'd get responses like diaphram leaking in the vacuum booster.

The proportioning valve is out of a 1977 K20 but the truck now has four wheel discs on D60 front and C14 rear so I went to hydroboost to up my stopping ability.

I thought, at one point, maybe the pieces weren't the right ones to work together (if that makes any sense) but it all worked great when installed over 8 years ago.

Also, I hardly ever drive the truck. That may have caused some problems by itself.

Thanks for the advice, Trukman1

[trukman1]

Just realized I needed to update this post. Hopefully my mistake can help somebody else. I purchased a rebuilt master cylinder when I first had the braking problem. Thought the problem was the M/C so I took it back (lifetime warranty.) Long story short, I did three M/C swaps so decided they couldn't possibly be all bad. Turns out I was wrong. Local mechanic said it was a bad M/C and that the bore was worn. He said this will allow the piston to moved back and forth and sometimes the fluid will bypass the piston and it will not move resulting in sporadic braking ability. He recommended I get a new M/C. I did and the problem disappeared. Turned out a new M/C was only another $24.00 (Used was $20.) I also removed the brake pedal to drill a new hole for the rod from the hydro boost so it would be in proper alignment. Moral of the story is I will never buy re-manufactured brake parts again. YMMV but I would never recommend buying a used M/C or any brake part. It is just too risky, IMO. Thanks to all who contributed to helping me solve my problem.

[snj8198]

trukman1, what did you do for an e-brake? what did you do for a booster bracket? did you mount the master cylinder right side up or up side down?

Have any pics by chance??

[Raleighswb]

Thanks for the update that information is going to help someone out there.

[trukman1]

Originally Posted by snj8198

trukman1, what did you do for an e-brake? Went with the 1978 Cadillac calipers withthe built-in e-brakewhat did you do for a booster bracket? Bolted directly to the firewall, seems plenty sturdy enough did you mount the master cylinder right side up or up side down? Seriously?

Have any pics by chance??

(Nope, someday maybe I'll to learn how to post pics.)

[snj8198]

did you mount the master cylinder right side up or up side down? Seriously?

Ya seriously, that's actually a legit question, although i should have asked whether you mounted the booster upside down or upside right. Some mount them upside down to clean up the brake line routing, but i obviously got my answer.

Thank you for the info.

[trukman1]

Steve,

Okay, the booster I get. (Had me scratching my head on the M/C part. Couldn't figure out how you'd get the brake fluid in.)

Truthfully never heard of mounting the Hydro boost upside down but I am going to give it some serious thought when I redo the truck next summer.

Thanks for the tip.

Gary