Need some help (intermittent hard pedal) on my 68! I have Baer 13" tracks on the front and 12" Sports on the rear. Engine is a 555 (700hp). After trying a couple of "tuff stuff" boosters (had issues with bore size) went with an MP Brakes power brake booster with an SSBC electric vaccum. No issues for about two months. Now, after about 5-10 minutes I am getting a hard pedal again! Not 100% of the time but off and on.

Ordered a vaccuum resevoir from Jeg's, installed and am having the same issue. Press on the brake pedal, vacuum assist motor comes on, vacuum pressure reads 25 on the resevoir but still have a hard pedal.

Am I missing something here? I replaced the vaccum switch and the relay thinking that may have been the issue. The engine I purchased as a crate engine and cannot find the spec on the cam. Do I need to go to a hydroboost setup?

Any ideas would be greatly appreciated.

I don't think you NEED a hydraulic brake boost setup. I was always curious about my buddies Chevy 3500 but the plumbing to the power steering didn't look pretty.

Just trying to narrow it down. The engine shouldn't have any thing to do with the brakes anymore. I assume you've checked the pads to make sure that brake fluid hasn't leaked on them.

Where along the line is the vacuum resevoir? Is the vacuum line going to the vacuum pump a big enough diameter? Might check for leaks or pinches.
Also, some resevoirs have a check valve. Make sure it's working and in the right direction.

Does the lack of brake boost occur stopping at a light or maybe when the wheels are turned? Does the car ever pull to one side? That can be an internally collapsed brake hose. Do the flexible lines have smooth radii and no kinks?

What is the proportioning valve do you have? Combo? 2lb residual valve/s?
Rear bias? I once had a Corsica that would every once in a while lock up like mad at the slightest touch.

I'm just throwing out questions. They may not be the key, but they might give you a similar lead that works out in the end.

I don't know the system, but don't think the pump should turn on every time you step on the brakes. Maybe the resevoir is not big enough. Try two and see what happens. :)

Tubergonz,

Checked for any pinched lines, thought one line seemed a little "soft" and replaced it. I had a local competition shop install the set up ( very well known shop in Indy, Steve Schmidt Competition Racing). Is at it's worst when I coast up to a stop sign or light. No fluid leaks. I think the hose(s) came with the resivoir.

The thing I find odd is that they did not install a proportioning valve when the did the original Baer conversion. They stated that since the set up was already a disc/drum they did not need the PV.

Time for a second opinion?

Thanks for your response