The Stovebolt Site Forums The Parking Lot Big Bolts 1953 6400 brake system troubles

Hello, I need some advice. I have bled the hydrovac and brake system as per the factory manual. After bleeding the system we had a decent feeling brake pedal. When the truck was started the pedal went down and just kept on going. We see no evidence of additional leakage from any lines or bleeders. We also see no fluid loss in the master cylinder. The truck will idle fine and I can hear no evidence of vacuum leaks around any of the hydrovac vac lines.
I would appreciate any help.

Thanks and best regards to all!!!

Hy plasticman, Welcome. Have you test driven the truck? Hydrovac equipped trucks take a bit of getting used to, one of the tests you do to check that the booster is functioning is to step on the brakes a couple of times with the engine off, then hold your foot on the brake pedal and start the engine, the pedal should go closer to the floor with the engine running. Are your brakes properly adjusted? If your brakes need adjusting it will give you a low pedal. If you had a solid but low pedal without the engine running then it should be lower with the engine running. Hope that helps.

Hi 3B,
Thank you for your reply. I have not test driven the truck. The pedal feels like mush. However, at the last inch of travel, there is a little resistance. Perhaps this is normal? I'll go fire up the beast and try out those brakes. I'll let you know how it goes. Once again, Thanks for your reply.
Stay tuned, I'll be posted pics of my "bolt" in the next few days.
Best Regards,
Phil Stewart
"Plasticman"

Hi 3B,
Just tried those brakes. No luck. I must still have air trapped somewhrer in the system. I'll try to bleed systems again to see what happens.
I'll let you know howit goes.
Thanks
Phil Stewart
"Plasticman"

Hy plasticman, You said in your first post that you bled the brakes according to the procedure in the manual, so you bled the hydrovac before you bled the wheel cylinders, is that correct?

Is the master cyl. new or rebuilt? The master cyl. can have an internal leak & the pedal drops under light pressure. If not that you have air in it yet. Some of the large trucks had the rear wheel cys. at an angle & are hard to get the air out.

I swear by power bleeding but you have to make sure the shoes are adjusted up properly. I like to adjust them tight so I know there's no excessive play then back them off when done. If after all the air is out, then you may need to adjust the pedal to master rod to get the freeplay needed,
Scott

I would be suspicous of the master cylinder, like wrenchbender as already said. If you are not getting any bubbles, I think something isnt right though. My Chevy is my first truck with a hydrovac system, but my system gives a good ferm feel, good luck - interested to hear what you find.

plasticman

I have the same year truck Model 6400 and I bled a quart of fluid through it and came up with the same result, no pressure until the very end of the stroke or lots of pressure after a couple of pumps? Then after doing what I should have done first and read the manual. I jacked up each wheel and adjusted the brakes unil they started to drag a bit and then backed them off a tad! I went from a little pressure at the end of the stroke or pumping the brakes, to about 3-4 inches of trvel and rock solid on the pedal and plenty of stopping power!!!
Set of your brakes and then give her a try.
Good luck
DS

i have a 1950 6400 and after several days of laying in a rocky drive way bleeding in several ways, i did the adjustment thing and solved the low pedal problem . at least they are easy to get under..