[1965cat]

I have a 65 Wildcat Conv w/power brakes. The brake pedal has full travel, but only engages brakes when near floor and does not return to top position. I have to drag it back to top by placing my foot on the backside of the pedal and pulling it towards me (not real safe [img]<>/crazy.gif[/img]). Their is plenty of fluid in the master cylinder, all brakes, lines, hoses, were changed when I restored this car and the brakes worked fine, no leaking fluid, blown seals at the wheel cylinders. This started to gradually happen, not overnight. I did remove the master cylinder and the pedal acts the same, so this leads me to believe it may be the booster. So, a couple of questions:

1. How do I check the booster to be sure it is functioning properly? If I press the brake shaft on the booster while its off the car, should it return to position without vacuum being supplied?
2. How about checking the check valve?
3. If I have to replace the booster, is it a good idea to replace the master cylinder?

Thanks in advance for any suggestions!!

[NTX5467]

I suspect there should be a return spring inside the booster itself. Not a strong one, but one in there to keep things positioned.

The vacuum is to assist the "apply" of the brake pedal, not the return of the brake pedal to "unapplied" positions.

The check valve is there to ensure a vacuum reserve when engine vacuum ceases to exist. There is supposed to be enough vacuum reserve to make 1 or 2 easy stops, less if the first one is a harder one. By the end of the second apply cycle, the vacuum would be depleted . . . at which time the brakes would still work, but with more effort (probably more than manual brakes on the same car). The check valve only works to keep vacuum in the booster when the vacuum source ceases or is lessened for some reason.

Many auto supplies (and their reman/rebuild vendors) will sell a rebuilt booster ONLY with a rebuilt master cylinder attached. Others, will do them separately. If the master cylinder is not leaking or "bypassing" (pedal drop under steady pedal pressure, as if you are at a red light for a longer period of time), no real reason to replace it.

MAKE SURE that the booster you might get back -- BEFORE -- you hand yours over for a core exchange IS EXACTLY like the one you have on the car now. Over the years, there were a few different booster and master cylinder vendors (i.e., Moraine, Bendix, and a few others) and they might not fully interchange on particular boosters. This can be a reason for a reman vendor to only sell a "matched set" so that such mis-match issues will not exist.

There might be a rebuilder somewhere near you. Hopefully, a local auto supply might have that information. I suspect there is something not right in the booster itself rather than in the master cylinder. You should have brakes in the first inch of brake pedal travel, typically, depending upon where the brakes are adjusted at.

Might make sure the brake shoes are correctly adjusted. Other than the method of turning the star wheel and testing for drag, you can also purchase a brake shoe adjusting caliper so you can match them to the inner drum diameter before you put the drums back on the car.

Regards,
NTX5467

[sledhead]

Per One of the brake booster retailers start engine after running to build up vacuum, shut of engine pump pedal several times to bleed of vacuum, hold pedal down start engine if pedal drops booster is ok.