The Stovebolt Site Forums The Parking Lot Big Bolts Fresh brake perspective

SO I have been driving my 1960 C60 quite a bit this spring and summer and I need some ideas on my brake performance. Backstory, restored truck, relined shoes, new wheel cylinders. new master. Wheels all adjusted to the GM spec in the factory manual. I made a cap that I clamp to the top of the master to bleed with pressure after banging my head on the floor trying to bleed with a vacuum bleeder, works good. It just seems I always have to give it a pump for top brakes. I put 200 miles on it on Sunday and I decided I need to track this down once and for all. The thing I haven't done is to remove and rebuild my hydrovac. It seems to bleed but I'm having a feeling I'm losing pressure there? There are no leaks or drips that I can see. Any insight here would be great.... Little things like this make me crazy and I have a feeling its something simple. The hydrovac is the only thing I haven't broken down so its kind of staring at me right now... or is just in my head??........

If you have a good firm pedal after the second quick pump then it sounds like the shoes need to be adjusted. Jack up each wheel and spin it by hand, it should not spin freely there should be some drag to where it almost takes two hands to turn the wheel.

The Hydrovac can be tested as you start the truck for the first time that day. Put medium pressure on the brake pedal and start the truck, if it's working you will feel the pedal fade as the vacuum from the engine builds up (happens quick).

The Hydrovac requires a small amount at 10w oil to keep the leather seal lubricated...see your service manual for more info.

Mike B

Hello Bee, I went through the same thing and got a lot of good advice on this site, which led me to remove the hydrovac on my 58 Spartan and have it professionally rebuilt. Note that the unit I had on my truck was a brand new old stock unit from a circa 1980 truck which I adapted onto my truck, but it leaked just enough that it caused that chronic low pedal (the leak was internal, so difficult to assess). There could be other problems, including the master cyl and shoe adjustment (which needs to be VERY tight - honestly, I tightened mine tighter than the specs, based on Mike B.'s recommendation). But considering that there are MANY reports of booster issues, I would be suspicious of it.

Thanks for the input. I have been delayed in breaking this open due to family obligations..... I was moving it today to a better area to work and as I pressed the brake i heard a couple of little pops and now when I press the brake I can hear constant vacuum sucking at the vacuum vent in the cab and the engine roughs up so I'm gathering my diaphragm has been compromised........ On that note.... does anyone have a recommended booster parts supply house? My normal avenues have told me its obsolete. I would like to rebuild this unit myself to better understand the system. Thanks again for the collected knowledge of this forum.

Thank you tclederman, I appreciate the tech direction....

Bee, I used Rebuilders Enterprises in Illinois. They can help you with professional rebuilding services and my understanding is that they can supply parts for the DIYers. Ask for Bill, as he is the one I dealt with and I had a good experience and results. Their phone number is 708-430-0030

Igot a lesson on those 6400 brake boosters from Mr. Jim Carter himself ,had called his tech person about Bendix vacuum cylinder oil . He didn't know but said: Mr. Carter is in his office ask him about it! Mr. Carter said go buy hydraulic jack oil ...same thing! Give the booster 2 oz. shot of this oil twice a year ,like the service book says. My two boosters now work fine both are around 70 years old ! ! filled a 1.5 wheel cylinder cup with that oil set it out on the bench for a week . It never hurt it at all !