Strange vibrations
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
After the brakes cooled the wheels turned freely. I've added a spacer between the M/C and booster but the same thing happens. As noted earlier this is my second M/C booster combo (1" bore, 8" duel diaphragm). What to try next? Ideas?
What master cylinder are you using? Do you have e any kind of proportioning valve at all? Just helped a buddy with a 72 truck that the proportioning valve messed up and would lock the front brakes after pressing the pedal. Are you sure the residual valve is plumbed the right direction? When the wheels are locked up, you could loosen the line at the residual, brake caliper side, and see if that releases the pressure. If it does, you know that from there on back to the caliper is fine. If it doesn't, then unhook the other side, if that doesnt loosen the brake, it would tell me the valve is bad. If unhooking either of those doesnt loosen the wheels, go to the master and unhook that line. At that point it has to be a bad master, but if you already changed it, I doubt that will be it. Could possibly have a residual valve built into the master and you are doubling it with the external one though.
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
I don't have a proportioning valve in the system. Only think between the M/C and brakes is a residual valve and a "T" with brake light switch. Had to make the "T" by drilling out one of the inverted flares and tap to 1/8" pipe. Pulled it out and all was good inside, no teflon tape or brass chips. Shimmed the M/C again and went for a short ride. Same results but this time I thought to shoot the temp of the rear rotors. They were at 135 degrees which tells me the pin between the MC and booster is way off. How can this be, used the special tool to set it to .020". Will pull the MC and booster and recheck the clearance and see if I can find something wrong. Small fortune in brake fluid!
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Here is a brand new twist to the brake problem that may help others. No matter what I did the problem kept coming back and noticed the wheels would unlock after cooling or if I loosened the M/C from the booster. Trevor at MPB thought I should take a closer look at the booster. Researched on line how to bench test a booster. Got my old booster out and applied vacuum to it, then pushed the pedal rod. Pin at the other end of the booster came out fine BUT did not retract. Hand pushed and pulled several time and it started to act normal. Pulled the new booster out and tested it. The new booster acted worse than the old one. Sometimes the pin would retract and others it would find some random place to stop. Trevor said he had seen this before on 7" and 8" booster. Now for a solution. Any ideas? Can' just keep buying boosters 'til one works. Going to try and oil the pin when it's out to see if I can get consistent and smooth operation.
From my post #16 -- ".......Turned out that there was an internal failure in the vacuum booster. Had the booster rebuilt - problem solved."
Maybe not just lubricate it -- but also see what you can do to smooth/polish what I'm imagining is a pin/bore. And check alignment -- is something putting some lateral force on the pin causing it to jam somewhere.
Maybe not just lubricate it -- but also see what you can do to smooth/polish what I'm imagining is a pin/bore. And check alignment -- is something putting some lateral force on the pin causing it to jam somewhere.
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Never thought a booster could have a problem other than a hole in a diaphragm but, I suspect, some of the off shore units may not be up to an operational standard.
I've set up a test station so the booster can be cycled and checked for smooth operation and consistency. If it's cycled say 20 times and smoothly goes back to "zero" each time I'll feel better about reinstalling it. Got a small show this weekend and would like to go.
I made sure the pedal return spring is pulling on the same axis as the pedal travel just to make sure there is no lateral force. Hope this helps others that have gremlins in their brake system.
I've set up a test station so the booster can be cycled and checked for smooth operation and consistency. If it's cycled say 20 times and smoothly goes back to "zero" each time I'll feel better about reinstalling it. Got a small show this weekend and would like to go.
I made sure the pedal return spring is pulling on the same axis as the pedal travel just to make sure there is no lateral force. Hope this helps others that have gremlins in their brake system.
