I put a new brake booster/master cyclinder combo on my truck a couple of months back. The brakes work well...much better than previously (Not spongy), but I seem to have inconsistent brake pedal return. Half the time the brake pedal won't return to it's original position, and consequently, my brake lights stay on. I think it returns mostly at idle when vacuum is highest, but I'm not sure. any ideas? Is the linkage adjustable? It didn't seem to be. I have vacuum running off of the manifold directly. Do I need a check valve? Maybe my vacuum is too low because of the modified engine? I'll check it and see what it is.

Truck details: 1978 F150, Modified 460.

thanks for any advice anyone can provide!

-Pete

 

I suppose it could be low vaccum but are you sure you have the correct setu fort the pedal you have? I had a similar problem because the rod length was not exactly right so I too had the the brake light on. It was a pain.
You could always put a vac gauge on it and see what ya got.

 

I didn't change anything. The reman setup I put on was an exact match with the original...I'm pretty sure all the parts are right. Vacuum gauge soon.

 

Yea I think I would check the vac then. I was fixing problems I created by going with a disc brake setup needing a different style mc and going to a dual diaphragm booster.

 

I don't think it'd be a problem with vacuum if the pedal is returning best when vacuum is high-that would make it easier to fall down.

How does the fluid look in your MC? Is it low? If you pump up the brakes do you get good return? Also, you say high vacuum, like maybe high idle when you first start the truck? This is when everything in the truck is cold. Maybe if you have brake line too close to exhaust you could be suffering from brake fade.

 

1973/79 F100/350: There are TWENTY TWO different brake pedals / NINETEEN different P/B boosters / SEVENTEEN different master cylinders / SEVEN different clutch pedals...I kid you not!

Differences: Years / Series / 2WD vs 4WD / Manual vs Power Brakes / Disc vs Drum Brakes / With/without Speed Control / Before/from specific serial numbers.

Because there were soooo many different pedals, they have stamped numbers (one example of 22: D7TA-2455-MA) used to ID them.

 

Wow, I feel like a real member...number dummy posted to one of my threads! Looks like I need to do some more differential diagnosis. I ordered the setup over the phone and we worked through all of the specifics, so I'm pretty confident I have the right stuff, but you never know I suppose.

Fluid levels are normal, brake fade is a possibility I guess from my headers, but the return issue happens from the get go when the engine is cold too. It seems to get worse I think over time, but something isn't right beyond that. Maybe my remanned booster from A-1 cardone is bad? I hope not. What a pain that would be! Is there supposed to be a return spring under the dash that I'm missing? There also seems to be quite a bit of travel before the brakes engage. This travel is through the area that the brake pedal doesn't return through if that makes sense. Although, I know the brakes are on ever so slightly with even a little bit of pressure, because when the brakes don't return, I can feel resistance until I pull up on the brake pedal with the top of my foot.

I just don't want to throw parts at it. Thanks!

 

Also, I don't really have great return with the engine off either. I don't seem to be able to pump up the brakes until they're hard as rocks like I expect to be able to when bleeding. What does that mean?

 

What year is the truck ? Older ones have kind of like a linkage set up in behind the booster and sometimes the pivit points can get froze up.