I've been screwing around now for 3-4 weeks trying to get my brakes working the way they used to. I'm getting a high, hard pedal and really have to stand on the brakes to get it to step. I installed a new brake booster a few days ago and then discovered that it was defective. This after struggling for 2 hours to get the brake lines to line up again with the master cylinder. What fun. At least Summit pays for return shipping and refunds the full price with no questions asked. Great company.
We checked the old booster with a vacuum pump and vacuum gauge. It worked flawlessly - holding 20" worth of vacuum without loss. The plunger was much easier to depress when it was holding vacuum, so it was working as designed. Upon checking the manifold vacuum at idle, it's 6", which my engine guy thinks isn't enough to work the booster. He suggested I try an electric vacuum pump, which will supply 20" of vacuum.
They're expensive though - $270. Has anyone used these to fix a low vacuum problem caused by a big cam?
Thanks,
Hutch
Well at least you seem to be on the right trail.
No, I have not used an electric vacuum pump - maybe someone else can chime in with their experience.
But what choice do you really have ...
Great idea Steve O!
I like the possibility of an alternator backed vacuum pump.
We should probably give Rod a shout and see what he ended up with.
Just to follow up on this (because I hate researching something just to discover a dead-end thread)...
I did end up buying the vacuum pump from Summit, figuring that it would be here by the time I put the functioning booster back in - and it was. I also figured if it didn't solve the problem, I could return it.
During the course of putting the booster back in, I decided to measure the push rod that sticks out of the booster in relation to the depth of the piston in the master cylinder. The push rod should just touch the piston in the master cylinder while there is no pressure at all on the brake pedal.
I ended up having two push rods of different lengths - one about 1.5" longer than the other. I wasn't sure which one to use, so this prompted my decision to measure. The rod is adjustable by about 1/2 to 3/4 of an inch by screwing the little cap screw in or out of the rod. The rod I was using needed adjusting by about 1/2". In my case, it should stick out of the booster - as measured from the face of the aluminum piece that goes over the studs on the booster - by exactly 1". It had been sticking out about 1.25". I'm not sure if that was causing my problem, but after putting everything back together tonight I now have good brakes without ever having to even try the electric vacuum pump I bought.
That's a good thing not only because it saves me $270, but also because the vacuum pump is about as big as a power steering pump and would only fit in one location - right behind the windshield fluid bottle on the inner fender well. Everyone that would look under the hood that was vaguely familiar with a Mustang would be likely to say "What in the world is that thing?"
All's well that ends well I suppose. I think I could now swap out the booster, master cylinder and assorted brake lines with my eyes closed. Now I just need to adjust the rear brakes because the right rear is locking up first and causing the back end to slide out sideways when slamming on the brakes.
Tremendous!
Glad to hear that you were able to sort it out.
Thanks for letting us know.
Good deal I love it when I figure out something and it all starts working like it should. Glad you got it fixed. JTS 71 Mach1