Technical disc brake conversion

I did a front disc brake conversion with power booster. At this point I don't have a lot of pedal. I have bled the system I cannot pump up the brakes, so I believe there is no air in the system. I adjusted the rear drum brakes. Any suggestions would be appreciated.

 

Do you have the right master cyl disc drum and a combnation valve in your system

 

Just what slim39 said. Was this a kit or something you made up? Do you have the rod from the pedal adjusted to where it needs to be?

 

I’ve had that problem more than once. Posting the kit/parts/ etc. will help. I’ve found that just because you bought a “kit” from a well known vendor doesn’t mean the various components all work together. Pedal push rod free play and push rod between the master and booster have been prime suspects for me. Same with the master/combination valve combo as mentioned by Slim above.

 

Got the correct piston diameter (or close) piston in the master cylinder ?

Mike

 

I made an aluminum plate that fits over the master cylinder with a cork gasket. In the middle I tapped threads so I could plug in a standard air hose fitting. To that I put around 3 psi. On the hose. Start at the farthest bleeder and refil the master after each wheel is blead. This worked great on my chrysler with disc brake conversion and also our MGB which are notoriously difficult to get right.

 

It is a kit from leed brakes. It is a GM style dual master and GM style bottom mount proportioning valve, 1 1/8 piston. The rod locates the pedal as was before. Should the pedal rod have any free play before it makes contact?

 

You can actually use more pressure than 3psi if you want, i have a motive power bleeder that i use for OT work and i usually hit the bottle with 7-15psi to bleed a system. If i fill the motive with fluid, i don't have to pull the pressure bleeder to fill.

There should be a very small gap, you don't want to loose a lot of travel.

 

Are the bleeders for the calipers on the top? If not switch the calipers side to side.

 

Did you remove a booster from this system, before you installed the new one?

If so, can you post a picture of it?

Or tell me if it looked like this:

 

I removed it and bench bled it.

 

This was a new conversion. It did not have a booster. It is on a 1953 for vicky.

 

That is a "Corvette style" master cylinder. Did you bench-bleed it before you installed it?

I have known them to hold on to a lot of bubbles, especially if it is a dual-sided one, with outlets plugged on the other side.

 

How far down does the pedal go before you get resistance?

 

The booster control valve/input push rod normally does not have any free play adjustment, but you have to make sure the pedal can move farther than necessary when the rod is disconnected, ensuring full booster return.
The booster output rod or pin normally can be adjusted. Unless specified, check for a clearance of around .040" pin-to-master cylinder primary piston, with full (+/- 20" Hg) vacuum applied to the booster.

 

I have this exact setup on my 52 Merc. Are you using the ECI kit with GM calipers with Ameristar rotors? After reading many post about problems I expected some but I have a solid brake pedal that stops well. I expected a little better stopping but I'm only using a single diaphragm booster. At any rate, I did have to bleed the hell out of the front brakes using a hose and a jar of brake fluid and I spent 15 min to bench bleed the master cylinder just to be safe. I used the 1"diameter master cylinder. I bought the master cylinder and proportioning valve and brackets from Pirate Jacks. My mount bracket came with 2 different pushrods and bellcranks I chose the ones with the longest throw. Don't know if this helps but thought I might mention it since it is the same application.
Rob


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Thank you all for your insights and suggestions. They have helped me resolve my issues