Okay brake gurus-Here's one for ya I have a 11/8th vette MC with a 7 inch single diaphram booster -mounted under floor -have the usual 10 and 2 lbs residual valves -m/c was new this spring-new front calipers and pads at the same time -Dot 3 fluid-drum rears -everything has been working perfectly all summer -the other day-I hop in to drive home fron work-the pedal sticks when I depress it-comes up with a flick of the toe-but when it sticks-the brakes including brake lights are on. -the brakes function as normal-pedal is good-activation is good-does not pull one way or the other -yes I have a return spring on the pedal-I even put another one on it -pedal stll sticks part way down(or up) -I disconnected the rod from the booster to the pedal-the M/C seems to function okay-press it in and it pushes back -no fluid leaks -M/C does not leak at the seal Will a bad booster cause this problem??
I've not heard of that before, but it does sound like the booster could cause this. I'd first check that all the pivots are working smoothly and that the linkages are not draggin/bent and if all is well there I would try removign the booster and inspecting it. Seems like if it's the culprit you could replicate the problem with it removed and isolated.
The brake pedal runs through the floor-doesn't hit anything or rub -where the pedal stops after you depress it-there is nothing touching it-no bind when the rod from the booster is dis-connected.The pedal has complete free travel.I hooked up a second return spring because I thought the in-line one might be weak-didn't make any difference-pedal still sticks It seems worse when the engine is running-when the engine is off it doesn't seem to hang up quite as bad- but there is still a little resistance at the wheels.
What is the angle from the linkage to the booster - especially during travel. If it's not optimaized I could see it being a source of premature wear on the booster and causing this type issue. I ***ume your return spring/s are pretty beefy then? Here's a pic of my return spring on a very similar setup.
turf the booster ! its rusted up inside and the va***n boot is dragging on the shell casing when it returns
I'll post a pic in a little bit-but I am leaning towards turfing the booster -everything was working good before
Here is a pic-The small inline return had worked good-I put the larger spring on to see if that helped-but nothing changed
I had this experience. I had the pedal to booster linkage set where there was a little play like it should be. The pedal was slow to return to complete rest. Checked the linkage, etc, all was OK. I adjusted the linkage to depress the pushrod further toward the booster and the problem was solved. Boosters change shape once the vacuum is applied, perhaps that is the explanation. Of course do not pre-load the booster in the adjustment.
That booster looks like its in a wet area, if so it should have an 'concertina ' rubber boot over the input pushrod end. keep in mind it was designed to only see 'inside vehicle' climate at the rear side.could it be getting water splash from wheels ?( not good for it )
It had a boot on it-but it had gotten ratty so I trimmed it off-you can see the base of it is still there- I haven't run in much rain this year-but other years-lots of it. This is the 5th summer for this car with almost 25,000 miles so far. Booster was one of the first parts I bought when I started the build so it is likely 10 years old or more now. I tried the adjustment procedure blackout suggested-no difference-pedal still sticks doesn't matter if I adjust the pedal "tight" or "loose" definitely sticks down when brake applied with the car running-so I am going to try a new booster. Jim
If you have a MightyVac, you can test the booster to see if it holds vacuum, should hold 20 inches. You can also test the check valve, it should only work one way, and check your vacuum lines. If the booster is rusty inside, it is a bad sign, but it may have a leaking diaphram anyway. Because the M/C returns OK, it points to the booster.
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