New Brake booster / hard pedal

[Stanglover]

I have just completed an upgrade by adding an original remanufactured brake booster to my 71 Mach 1 which was a manual drum/drum car. I added 4 piston discs on the front back in 2010, which have work well, but still needed the booster. Long story, not going there right now, but yesterday when I finally got to fire up my newly rebuilt (again) motor. The cam is only just slightly better than stock so my vacuum should be around 17"hg (Not checked it yet). What I got was very aggressive brakes and a hard pedal, no slight softness at the start as one expects with a booster.

I don't want to get into a long process here, but is there something I can do to get the right feel? A friend suggest too much vacuum. Of course, I could have a badly reman booster (Cardone).

Anyone got a quick fix???

Geoff.

 

[73pony]

Mine is stock system front disc rear drum and they are pretty aggressive as well with a hard pedal. You hit the brakes and you know it right away if your not careful. I just thought it was normal.

 

[c9zx]

Did you check the length of the booster driven rod that engages the master cylinder? The rod being too long may cause this problem. The rod is adjustable. Chuck

 

[turtle5353]

Did you check the length of the booster driven rod that engages the master cylinder? The rod being too long may cause this problem. The rod is adjustable. Chuck

+1 YEP!

 

[72HCODE]

there is a different brake pedal assembly for the drum verse disc brakes.

The disc version has a different fulcrum and brake force that goes to the adjustable rod through the booster is suppose to be higher.

i forget the details another member should chime in. i never dealt with it directly because my car had power disc from the factory.

if i remember the Disc and Drum front spindles are different also.

 

[Stanglover]

Did you check the length of the booster driven rod that engages the master cylinder? The rod being too long may cause this problem. The rod is adjustable. Chuck

Yeah, I set it to have a gap of about .015" (The ball of plasticine method), but that was before I could put any power to it. This issue has been discussed before and I think someone said .015 was about right. I can change that quite easily if necessary.

 

[Stanglover]

there is a different brake pedal assembly for the drum verse disc brakes.

The disc version has a different fulcrum and brake force that goes to the adjustable rod through the booster is suppose to be higher.

i forget the details another member should chime in. i never dealt with it directly because my car had power disc from the factory.

if i remember the Disc and Drum front spindles are different also.

Yes, that was all done. I had the pedal support out to add ball bearings to the clutch pedal shaft. What a difference on that issue!

I have posted before and added a picture of my modified brake pedal. The new position for the pin is 2" lower.

I changed my front brake to discs in 2010. I used the SSBC Kelsey Hayes 4 piston setup. One does NOT have to change spindles with this kit, a reason I chose them.

 

[c9zx]

Do you know the "new" brake pedal ratio? Is the master cylinder for a manual disc/drum or a power disc/drum? Chuck

 

[Stanglover]

Do you know the "new" brake pedal ratio? Is the master cylinder for a manual disc/drum or a power disc/drum? Chuck

Well, that's the interesting part. The M/C that was supplied with the brake kit is disc / drum and 1" bore. However, with a power brake m/c, there is not a groove on the back end of the outer collar(??) for a dust seal as there is on a manual m/c. I queried this point with SSBC, but got no response to that question. If needs be, I will order a m/c that I know is for power brakes. I'm assuming the one I have IS by the fact that there was no dust seal groove. That is easily changed.

Since I posed this question. I have had chance to drive the car and the brakes do seem to be working. I have a separate rear brake circuit which is adjustable and I can back them off a bit. I am taking the car in to my garage tomorrow and have a mechanic look at them.

I don't know what the ratio is, but the pin is where it is supposed to be.

Thanks for the help,

Geoff.