Technical Brake problem

Brake problem. Disc front, drum rear. 11" rotors, calipers from Speedway. Floor mounted pedal with dual 7 " booster under floor. Proportional valve, 10 and 2 lb. check valves. . I have bled the system a number of times and I just don't get the feel of a good grab. Just somewhat finished the 1935 Ford panel delivery, breaking it in . Haven't driven over 35 mph , but when I come to a stop sign , I can't relax my foot on the brake and not feel like it wants to move . Once I took it to a real garage to get the mechanic to bleed them . I bled them by vacuum myself and another time had a buddy help pump the pedal .
Thanks
Rick

 

Automatic, rev’s too high?

 

Motor not pulling enough vacuum? Power brakes really **** at idle with a rumpy cam not pulling enough vacuum.

 

If everything else is right and you have vacuum, those aftermarket boosters can be borderline useless. Including having compromised diaphragms from new (you know where rubber.)

Not saying this is the problem, but just to be aware.

 

Have you properly adjusted the rear shoe drag?

Many pedal feel, grab point issues can be traced back to improperly adjusted rear brakes.

 

This is true on my daily driver GM pickup.

 

TPI with vacuum 15-17

 

Going to look at those next. My real garage/service guy was suppose to check that.

 

About 750 in gear, but I'll check that again.

 

Not everyone knows about doing it in the disc brake age.

Every few clicks of the adjuster, go step on the pedal, to make sure that the shoes are still properly aligned, and not giving you a false impression of drag.

 

At idle? With stock cam?

 

I suspect it is not a stock cam. If it is, then it might need new gaskets up top.

I have seen these at 19-20 at idle.

 

Ah, the much loved brake guessing game!!

Pedal ratio?

Master cylinder diameter?

Master to booster clearance?

Pedal free play?

Pedal return spring present?

Plus all previous questions as well as those not asked yet!

To be fair, if it was easy everyone would be doing it, besides, what would we talk about!!

Chris

 

Your panel is a beauty, very nice!
I'm no expert but like to try and help when I can. Providing your pedal ratio and master cylinder bore is sufficient, sounds like things are correct. I like to adjust drums by tightening up the adjuster until the drum is tight and can't be turned by hand, then loosen until it can just be turned with a slight drag. Doing that will insure the shoes are centered, all parts slack is removed and minimum shoe clearance is achieved. Depending on the brake lining material, it can take some driving until the shoes/pads bed in completely and work like you expect them to. Good luck!

 

Lots of good info Agree on rear brake adjustment. 15" of vacuum is borderline I think. 18+ is good

 

Have you bled the master on a bench?

 

I really do not understand why guys try to use those worthless things. A properly matched manual system works great to stop these cars.

 

I avoid power brakes especially with in my case, since I run a steeper cam. So manual it is, disc up front, drum out back. No self adjusters, so I give the drums a few clicks twice a year and it brings the pedal up. It stops like a stock '72 or so Chevelle with a manual disc/drum combo.

 

I've on occasion found that even after bench bleeding the master, and bleeding all wheel cylinders, I still had similar issues with the brakes not feeling right. Re-bled, and no matter how much fluid came out it didn't help. I finally got a buddy to pump the brakes and hold the pedal as I opened each fitting coming out of the master, and I got some air from each of the two fittings! After that the brakes worked perfect. So you might give that a try.