Brake Booster issue?

Carmen Marchesani

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I have a 1964 barracuda. I just installed front disc scarebird kit. rear are factory drum. I installed new M/C and booster. I haven't done a road test yet. I've started the car a I shut it off and hear air escaping from the booster area. My question is should I install an in-line check valve on the hose coming from the carb to booster? or am I missing something else.

Thanks
 

BillGrissom

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A missing check valve isn't your problem since the check valve is stop air flowing the other way (into booster), but you do need one so the booster can store vacuum in case the engine dies and you need to stop. First, insure your pedal is coming up all the way. It shouldn't bottom out on the brake lamp sense switch. Amazing how many people don't understand that, and the switch is adjustable. If the brake pedal were pushing in a bit, then it would leak air since that is what the air-valve does. If the pedal is all the way out, then sounds like the booster is bad - either a bad air-valve or a torn diaphragm.
 

AJ/FormS

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Did you measure the pushrod extension before you bolted on the M/C? If the rod was much too long,I suppose it could possible that when you mated them, the pushrod was driven backwards breaking the valve.
 

Carmen Marchesani

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Did you measure the pushrod extension before you bolted on the M/C? If the rod was much too long,I suppose it could possible that when you mated them, the pushrod was driven backwards breaking the valve.

At first the pedal would not return so I did some reading and sure enough it was out of adjustment. I lengthened it a bit and I have better pedal feel. I only drove the car out of my garage about 20 feet and new something wasn’t right. That’s when I noticed the air escaping after shutting the engine off. Weather has been crazy here on the east coast. So a few more weeks before I can get it on the road. Thanks for the response.

A missing check valve isn't your problem since the check valve is stop air flowing the other way (into booster), but you do need one so the booster can store vacuum in case the engine dies and you need to stop. First, insure your pedal is coming up all the way. It shouldn't bottom out on the brake lamp sense switch. Amazing how many people don't understand that, and the switch is adjustable. If the brake pedal were pushing in a bit, then it would leak air since that is what the air-valve does. If the pedal is all the way out, then sounds like the booster is bad - either a bad air-valve or a torn diaphragm.

I did notice the pedal not returning and I needed to adjust the rod length. I do have better pedal return but the brake light is not adjustable. One think I didn’t look at is if the new rod coming through the fire wall is rubbing on the brake pedal. And I’ll look at getting a check valve and see if that does the trick.

Thanks for the response.
 

BillGrissom

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... I did notice the pedal not returning and I needed to adjust the rod length. I do have better pedal return but the brake light is not adjustable. One think I didn’t look at is if the new rod coming through the fire wall is rubbing on the brake pedal. And I’ll look at getting a check valve and see if that does the trick. ...
I'm lost on all of above.

The brake pedal should swing freely when not attached. When you attach it to the booster rod, it will just follow the MC piston's motion (via the booster). The piston returns w/ a spring and MC has stops built in. Those stops should determine the extents of your pedal motion. Not sure what rod you adjusted since Mopar boosters have a flat, fixed rod (as I recall). Perhaps your booster is an after-market GM-based type which has a threaded rod, to which they install a Mopar pedal adapter. Regardless, that will change the pedal's resting position, but not its stroke length.

My 1964 & 1965 A-body and 1965 C-body have adjustable brake lamp switches. Sure, you can't adjust the light itself, other than can change the bulb. Newer Mopars have non-adjustable pedal switches, and that can cause problems.

The rod should attach to the pedal and pivot freely. Does your "rub" = "doesn't pivot freely"?
 

Carmen Marchesani

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Found the leak. It’s where the booster spilts in half. Seems to be leaking from the seal near the bottom of the booster. QC must have missed it!
 
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