Wow!! Look why my brakes have been working so poorly.
10-19-2010, 01:38 PM
#1
Wow!! Look why my brakes have been working so poorly. Most of you all know I have been chasing a brake problem for some time. The brakes work well when the motor produces high vaccum but not when the motor is producing low vaccum. I have been blaming the cam as a result of lesser engine vaccum and still do, but to a much lesser degree now.
Again as most of you know, while chasing the problem I bought a used brake vacuum pump and once it was installed, the braking under low engine vacuum conditions greatly improved but I noticed the pump was cycling on every 25 seconds or so. Figured that was a bit strange. Turns out the pump has become an invaluable diagnostic to ultimately find what I now believe is the root of the problem.
I bought a new reman booster to do comparitive tests on to see how long the booster can hold vacuum before the pump cycles on, which occurs at 16" of vacuum and kicks off around 20" of vaccum. Again my stock booster would cycle every 25 seconds clockwork and when I stuck my head down near the booster, I heard the faint sound of air leaking into the booster. Bingo, that aint supposed to be happening.
I pulled the original booster out of the car and removed the master. Behind the master is a beefy rubber sealing grommet and a plastic pusher shaft that pushes the internals of the master cylinder. This plastic pusher shaft has four large grooves cut into the surface at least .030" deep and .030" across and up to an inch long. As a result of these grooves, it is impossible for the sealing grommet to provide a tight seal and thus the booster is going to slowly bleed off vaccum.
Here is a shot of the grooves on the plastic pusher shaft:
Here is a shot with the pusher shaft slid into the grommet. See that bright spot, thats sunlight passing through one of the holes where leakage is occuring:
The time I notice the braking problem the most is when I am steady cruising and the engine is at low vacuum in the neighborhood of 10" or so. If the booster where working right and not bleeding off vacuum, it would have a much greater supply available. But since it has a generous size leak in the form of the four grooves in the pusher shaft, at best it is going to equal the vaccum being supplied by the motor at the given time and thats all that is available for braking.
Right now I am painting the new booster and look to have it installed soon. I am also going to retain the vacuum pump and do some more road testing to see if it is really needed. The way I see it now, the pump will ensure that booster vacuum never drops lower than 16" regardless of what the vacuum is producing.
The other funny thing is the original booster passed all of the diagnostic tests I could find on line. I guess those tests can indicate a badly busted booster but not one with a slow leak like mine was having.
Just wanted to share this with you guys.
Again as most of you know, while chasing the problem I bought a used brake vacuum pump and once it was installed, the braking under low engine vacuum conditions greatly improved but I noticed the pump was cycling on every 25 seconds or so. Figured that was a bit strange. Turns out the pump has become an invaluable diagnostic to ultimately find what I now believe is the root of the problem.
I bought a new reman booster to do comparitive tests on to see how long the booster can hold vacuum before the pump cycles on, which occurs at 16" of vacuum and kicks off around 20" of vaccum. Again my stock booster would cycle every 25 seconds clockwork and when I stuck my head down near the booster, I heard the faint sound of air leaking into the booster. Bingo, that aint supposed to be happening.
I pulled the original booster out of the car and removed the master. Behind the master is a beefy rubber sealing grommet and a plastic pusher shaft that pushes the internals of the master cylinder. This plastic pusher shaft has four large grooves cut into the surface at least .030" deep and .030" across and up to an inch long. As a result of these grooves, it is impossible for the sealing grommet to provide a tight seal and thus the booster is going to slowly bleed off vaccum.
Here is a shot of the grooves on the plastic pusher shaft:
Here is a shot with the pusher shaft slid into the grommet. See that bright spot, thats sunlight passing through one of the holes where leakage is occuring:
The time I notice the braking problem the most is when I am steady cruising and the engine is at low vacuum in the neighborhood of 10" or so. If the booster where working right and not bleeding off vacuum, it would have a much greater supply available. But since it has a generous size leak in the form of the four grooves in the pusher shaft, at best it is going to equal the vaccum being supplied by the motor at the given time and thats all that is available for braking.
Right now I am painting the new booster and look to have it installed soon. I am also going to retain the vacuum pump and do some more road testing to see if it is really needed. The way I see it now, the pump will ensure that booster vacuum never drops lower than 16" regardless of what the vacuum is producing.
The other funny thing is the original booster passed all of the diagnostic tests I could find on line. I guess those tests can indicate a badly busted booster but not one with a slow leak like mine was having.
Just wanted to share this with you guys.
Last edited by wrd1972; 10-19-2010 at 02:00 PM.
02-13-2012, 07:36 AM
#4
I know this is an old thread, but how did the new booster work for you wrd1972?
I'm having similar issues with a new baer setup I installed, and it's better than the stockers but the braking is still not there. I'm wondering with my 108LSA is causing a Vaccum issue or if my booster is to blame as yours.
I'm having similar issues with a new baer setup I installed, and it's better than the stockers but the braking is still not there. I'm wondering with my 108LSA is causing a Vaccum issue or if my booster is to blame as yours.
02-13-2012, 08:55 AM
#5
Village Troll 
iTrader: (2)
Are you completely positive all of the air is out of the brake lines? How is pedal feel? I am running on 11" of vacuum and my brakes do just fine. Are you still running the ABS block?
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02-13-2012, 09:26 AM
#11
To check the booster, start it, stop it and press the brake to determine if the booster is holding vacuum. My damaged one would be out of vacuum in 2-3 minutes. The new one holds vacuum overnight. Unless you have recently replaced the brank master, I doubt you have the damage that I had as sgown in this thread. The damage was due to the wrong type of retainer clip in the MC bore and it carved the grooves in the shaft becasue of it.
Also cam LSA plays a role to some degree. My old 107LSA made 12" of vacuum and my new 110LSA cam makes closer to 15" of vacuum.
I still have the brake vacum pump installed on the car but it really provides no more benfit to me and I will be pulling it in the spring to sell on the board as a copmplet kit.
Again the heart of my braking problems were the damaged booster.
Also cam LSA plays a role to some degree. My old 107LSA made 12" of vacuum and my new 110LSA cam makes closer to 15" of vacuum.
I still have the brake vacum pump installed on the car but it really provides no more benfit to me and I will be pulling it in the spring to sell on the board as a copmplet kit.
Again the heart of my braking problems were the damaged booster.
