Brake Problem Help Needed (revisited)

You said that you had the Brake system on the Car & it was OK until you Changed over
to Power Brakes?
Did you Change the ROD which is Different from Standard
The Power Brake Rod is Longer than the Standard
just my 3 cents

 

The rod is the same length on the master I have. I just got back from the parts store I got the master from. They gave me another one to try. I also had them check the specs on it and it is 1 1/8 bore, for disc drum. So hopefully the new one will work...

Oh yeah, the calipers are mounted correctly...

 

I bench bled the new master and got it mounted up. I also replaced one of the hard lines that had a loop in it with one the correct length. Hopefully in the next few days I will have a chance to bleed it out and see where I am at...

 

pressure bleed.............

 

tommy is dead right. adjust rhe rear shoes properly and see what happens.

 

Absolutely! This should get all the air out, leave it hooked up, start the car and push the front pads out and give it another shot all around to ward off evil spirits.

Bob

 

There is a wonderful kit out there that mounts on top of the master and uses tire pressure to pressurize the system, one man power bleeding. You may be able to rent one from a parts store. It will make replacing the bad master cylinder (my vote) much easier.

 

Its $45 to rent a pressure bleeder from the local store. Or I can get one from Summit for $65. I think for the $20 its worth having one. Unless there is somebody local that has one I can borrow...

 

Ok here is an update. I manually bled all the lines. Then I clamped off the rear and took the car for a spin. With the rear clamped off the brakes are at about 40%, not too good, but its way better than before. I need to figure out how to get more of a pedal.

Then I undid the clamp on the rears and the brakes are pretty bad again. So this tells me that the shoes are probably not adjusted correctly, and there may still be a bit of air in the system.

So once I get the rears a bit more dialed in, I need to figure out how to get the whole system to have a better pedal. Does it matter if I bleed the car with it running or not? Does the power booster need to be on to bleed it right?

 

If you have not done already: Jack up the rear so it spins freely with your hands and then adjust your shoes out until you hear them just start to drag. Should give you more pedal...

 

Thanks, that was going to be my next question.

 

OK I'm no expert, but here's my 2 cents....these kinds of problems are super frustrating for me...and hopefully by trying to help I'll put out some good karma for my 4wdb conversion I'm in the process of doing

1) I'd adjust the rear shoes on the tight side. Everybody has their own opinion but I like the tire to rotate like half a turn when I give it a spin. 9 times out of 10 this solves my low pedal problems.

2) I'm talking out my *** here but I'll bet that MC is meant for a firewall mounted 11" booster. Does that make as much boost as a 7" dual? I don't have the answer. I know you need at least 1,000 lbs of pressure for those discs in front. From this catalog it says you need 18" of vacuum. It says with a smaller 1" bore you should get abouit 1200 psi. Another website says you need 1000-1200psi to lock your brakes up. FWIW I think your MC is a little large.

3) pedal ratio. I don't think this is a factor, but ? Your pedal ratio with stock non power drums should be around 6:1 I guess, and as I understand it a PDB pedal is around 5:1, so you ought to be fine, but something to consider. Theoretically your brakes should be a little too sensitive.

4) how big are your brake lines? are they 3/16" in front?

5) is your booster hooked up to the right port on the carb and do you have 18" of vacuum?

6) is your bleeder screw located on the top in the 12:00 position?

7) is your MC a deep bore or shallow bore? As I understnad it, deep bore (about 1 or 1.5") is common in non-power master cyl because you need the pushrod deeper in there so it doesn't fall out. My guess is that your booster is setup for a shallow bore, which should be just about flush with the booster face.

***BOOM that's my guess that you need this piston adaptor, that looks that its just a 1.5" or so piece of rod. ***

I'm no expert, I've just been reading on the net and copied that info from here

hope it helps!!!

 

Thanks for the info. The piston adapter isnt the problem, there is about 15 thousanths between the booster pushrod and the master, that should be pretty good.

The rear shoes definatly need to be adjusted.

I think the pedal ratio is good because the aftermarket brake pedal is for power brakes.

The front lines are 3/16, put does that matter?

The bleeders are up.

But I dont think the car makes much vacuum, its god a pretty hot cam for a 235.

Again thanks for taking the time to help out.

 

make sure you adjust the rear brakes, even if they are a little tight, i had a problem like that with my conversion on my truck..not enough brake pressure for me...because of the rears, just my opinion..

 

Vacuum has nothing to do with your problem. Do adjust the rears though. If the pedal can be pumped up, you have an adjustment issue. But you should still get a better pedal than what you have unless they're grossly out of adjustment.

I always bleed the brakes with the engine off, but give it one last pop at all 4 corners with the engine running. Manually push the front pads out before you start it up, once you have a decent pedal.

Bob