I need some help with an issue I'm having with the brakes on my 1952 GMC 354-24. For some context, I bought this truck a few years back from a farmer in Montana who was using it to haul grain all the way up until the fall of '23. When it was pulled out the next spring after being stored for the winter, the brakes would not work.
Here is what I have found:
- the brake pedal goes all the way to the floor when initially pressed - pumping the brakes builds pressure allowing the pedal to become firm, however after a minute, the pressure bleeds off and the pedal goes to the floor again - with the engine running, doing the above procedure would cause the motor to bog down a little bit before returning to idle - there does not appear to be any brake fluid leaking from the brake drums, lines, master cylinder, or booster
This leads me to believe that it may be a vacuum issue. Mostly everything mechanical-wise appears to be original and the motor is a 248 ci. I have not taken the wheels off yet to inspect the wheel cylinders. This is the first restoration project that I've owned and are learning as I go along. I wanted to see if anyone has had a similar issue or knows what may be happening before I start throwing parts at it.
The brake pedal going to the floor usually indicates that the master cylinder is leaking internally (bad cup seal). It could also be a leak somewhere in the system. Your motor bogging down when the brakes are applied could mean that the vacuum booster is leaking, but could be something else. Compare the brake effectiveness with the engine off with engine on. If there isn't much difference, a leaking vacuum diaphragm in the booster could be the issue. With the engine off, pump the pedal till it gets firm, then hold it and start the engine, if the pedal goes toward the floor (but not all the way down) then the booster is working as it should.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Welcome to Stovebolt! Before getting too much deeper into your question, I think it will help to move your thread to the Big Bolts forum as that's the best place for help with your particular truck and brake system. Lots of other"Big Bolters" to chime in and offer the best help for your truck as the brake system is different than the 1/2 to 1 Ton trucks.
Will catch up with you in the "Big Bolts" forum.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
Hy 52GMC35424JD, welcome, I'm afraid I'm going to advocate for a complete braking system overhaul, including all hard and soft lines. I know this is throwing you in the deep end, but you will know when you are done you and everyone around you on the road can count on your trucks braking system. Keep coming back with any questions you have , we're here to help.
Don't imagine the old farmer spent a lot of time on maintenance or money on new wheel cylinders. The missing brake fluid has to have gone somewhere. It really is a good idea to go through all of it at this point. Brakes are cheap, accidents are expensive.
