1970 challenger brakes

[walt1800]

Anybody ever had a problem with not being able to get brakes no matter what you do? I have an entirely new system from front to rear. Started with an MBM conversion to disc drum. Installed all new lines...brake wheel cylinders...shoes. Talked to MBM and over the course of a couple of months they sent me two replacement master cylinders when we could not get any more than 250 lbs at the master. Changed ratios at the peddle...still nothing. Finally I ordered and installed the new trapezoid booster...linkage...and master cylinder that is out now and still the same problem. I have bled the brakes many times and the peddle is hard and can not be pumped up. I have done many brakes in my time and never saw anything like this and it's getting old FAST!! Any help or suggestion would be appreciated.

[Cuda Cody]

Are you using the stock proportioning valve?  I've never had any issue getting brakes to work with the stock set ups? 

[walt1800]

I bought a brake pressure gauge and tested the pressure and I have 250psi at the master. It is not a stock proportioning valve but it is a disc/drum valve. Testing at the master takes the valve out of the loop though.

[Roadman]

           Had a similar problem once. 4 wheel disc conversion, could never get a pedal. One day I was looking at the rear calipers and noticed that the bleeder valves were positioned so it looked like some air could still be trapped at the top of the calipers. So I took them off, them gravity bled them with the bleeders pointing straight up. Bolted it back together, problem solved.   

[walt1800]

 I have drum brakes on the back and good flow out of the bleeders. I have heard of people having trouble with bleeder position on calipers so I was sure to have the bleeders pointed up on the front. Great flow there too.

[Rich G.]

Did you bench bleed the master cyl before you put it on? Is the master cyl pushrod adjusted ( if adjustable ) so that the M/C piston goes all the back when the pedal is all the way released?

[walt1800]

Yes I bench bleed the master cylinder until there was no air bubbles and good fluid flow. There is an adjustment on the booster pushrod. I believe it is adjusted properly. When I received the master cylinder there was a retaining ring held on with two bolts that held a rubber boot which I assume is used when there is no booster for a manual brake set up. I removed this ring because the cylinder will not sit flush with the booster with it installed. When you remove the ring the piston will stick out appx. an eight of an inch which is about the distance from the booster before you tighten the nuts that hold it to the booster. So I am thinking it is about flush with the casting when seated on the booster. If this right then it is adjusted properly. But not sure.   

[Cuda Cody]

That might be the issue.  I think the 1970 boosters have a diamond shape so the master cylinder would fit.   

When I received the master cylinder there was a retaining ring held on with two bolts that held a rubber boot which I assume is used when there is no booster for a manual brake set up. I removed this ring because the cylinder will not sit flush with the booster with it installed. When you remove the ring the piston will stick out appx. an eight of an inch which is about the distance from the booster before you tighten the nuts that hold it to the booster. So I am thinking it is about flush with the casting when seated on the booster. If this right then it is adjusted properly. But not sure.

[Cuda Cody]

This is a 1970 cuda challenger ebody brake booster.

[walt1800]

I bought the setup from MBM and the master cylinder can be used with manual or power setups. I sent an attachment of the setup along.

[walt1800]

A better pick...

[Cuda Cody]

I've never had to removed that clip so it seems odd to me that you had too.  Have you contacted MBM and see what they say about the clip?

[walt1800]

These are the parts removed I believe that are used with a manual setup. And a pic with it removed to install it on the booster....mine is black.

[walt1800]

These are the parts removed so it would install flush. The pick above shows the piston sticking out of the cylinder. It is pushed in appx. flush with the casting when bolted to the booster.