C30 - grabby power brakes

[ncoonen]

I have a '65 C30 283 4-speed that has a strange behavior. The factory power drum brakes seem to work okay but come on all at once after a long push on the brake pedal. The brakes take almost no effort to lock up. The truck has what looks like the original master and booster.

At some point I will switch to a dual circuit drum system so if the issue with the grabby brakes I have now is the old booster, well now is the time to make that swap. Any tips on that swap would be appreciated also.

Thanks...ned.

[AcampoDave]

When my stock set up did that, I yanked the booster converting to manual and it fixed the problem. Not knowing why it grabbed, I put the booster on the shelf hoping to figure it out later as it looked fairly fresh. After a while, a buddy tried it on his truck and it still grabbed so it went in the trash. Wish I was more help but thought I'd at least relate my experience.

[dtkarst]

I know the master cylinder is less than a year old, but also wasn't driven daily. But sounds like a vacuum booster to me especially being the original one

[ncoonen]

Thanks Dylan and Dave. A faulty booster was my guess but I have not seen this mode of failure before. It's good to know the master is pretty fresh.

...ned.

[ncoonen]

Followup for future thread searchers: a Cardone reman booster #54-73535 solved the problem. Brakes might need some adjustment but the pedal feels pretty good now and you can modulate the brakes to smooth stop. Been a while since I have driven power drum brakes. They have a different feel than modern brakes and I think a majority of the remaining pedal effort would go away if I cleaned and lubed all the linkage bushings! A light touch is all you need.

Thanks oldtruckguys...ned.

[wahl4m]

these old 64-66 power boosters are easy to rebuild ! the tricky part is disengaging the two halves /ive done mine in a press .Twist the two halves in opposite directions then clean & check the insides and rubber diaphram -90 per cent of the time the diaphram is OK.THEN BLAST OR CLEAN UP THE HALVES OR CAD PLATE or powdwer coat them and reinstall with a new boot -which can be bought off e-bay or cheaper at the chevy dealer {using a newer part #} also cleaning up all mounts and the aluminum wedge and lubing all pivoy points /should work as good as new /if cleaned it looks better thaN that off/shore booster kits on evil bay- GOOD LUCK MIKE

[old cool]

Dear ncoonen, I'd like to hop on your post. I have a half ton with a power booster and dual circuit upgrade. It's prob been on there for 5-6 years. The booster appears to be a Cardone. The brakes have a light touch but I got used to it.
A few points for your consideration or input.
1. Did you have to adjust your push rod or did you keep the longer pedal?
2. My brakes are grabby if I need to make an abrupt stop. Otherwise they are ok. Have you made any sudden stops yet?
3. My master cylinder looks contaminated so I plan to change. (awaiting a suggestion as to type of unit to buy- posted a thread yesterday)
4. I learned on this site, and also research, you don't need a proportioning valve with drum-drum brakes. I initially thought that's why they were grabby but apparently not.
5 Lastly, I put a hose up to back of power booster from inside the truck (where push rod enters) and here a faint, continuous hiss. Same air sound whether brake is depressed or left out. Pedal is not hard to push so I'm thinking a little air sound is acceptable. Can you hear a slight air sound from back of booster inside truck?
Since we both have Cardones, I would greatly appreciate some feedback on #1 and #5. Thanks