Technical Brake Master Cylinder Lenghth

So I need figure how long my push rod needs to be. Any suggestions would be much appreciated.
It’s a disc/drum unit with no booster. 7/8 bore. Want to be sure I don’t damage it.
Thanks

 

Back up

 

long enough so the piston gets pushed in all the way as the pedal reaches the floor. Might require you to do some measuring, push the piston in all the way with a screwdriver (with the M/C disconnected, or the bleeders open), see how far it moved. Then set up the pedal and pushrod so you get that much travel.

 

Thanks @squirrel, I assume that’s with no fluid in the M/C ?

 

yeah, if there's no fluid it's easier, but if there is fluid, make sure something is open to let it out when you push the piston in all the way.

 

Thanks again

 

And you need to make sure you have some type of stop on the pedal return to keep the push rod from being able to come out of the mc.

 

Thanks, that’s not the problem, I have a return spring to keep pressure off of it. The problem is it’s leaking from where the push rod enters the M/C. Was thinking maybe the push rod is too long and causing it.

 

that's a leaking seal in the master cylinder.

 

Brand new, maybe it’s defective. The other issue is the push rod enters at a slight angle, thought maybe that was contributing to the leak as well ?
Thanks

 

We pumped the pedal to bleed it, maybe caused the seal to fail ??

 

no, pumping is not going to cause a seal to fail.

The angle thing, need more information. The pushrod should only contact the piston at the end of the pushrod, not the side. If it's binding, then you need to fix the issue. I still doubt it would cause a leak, though.

 

Just a slight angle to the push rod. The push rod was provided by Brookville with the chassis. It’s just a straight rod with a rounded end. The push ro the came with the master cylinder had a ball at the end with a rubber ring. Should I have adapted that push rod instead of the straight one ?

 

I was just pointing that out because you would be surprised how many cars are built where you can pull the pedal back and the rod will drop out of the cylinder, I was in a shop the other week and they where working on some pile and you could side step the brake pedal and it would pop out of the cylinder. Just thought I would share.

 

All suggestions are welcome, I appreciate the advice very much

 

The pushrod with the rubber ring at the end, is designed so it won't fall out...as TA DAD mentioned.

 

Thanks

 

And when you do the test push be careful using a screwdriver. It is easy to slip and score the cylinder wall. They make a bench bleed tool that does not have a sharp end.

 

Nice, I made this one, thanks

 

Slight angles aren't a problem. Most factory pedal assemblies vary angles depending on whether they're manual or power assist. The leaking is quite likely a defective master, and I'd get it warranted and not mess with it.
The pushrod needs to have slight play between the master piston, and pedal, or it wont ever bleed correctly. Too much play and it can drop out of the recess in the master. It should also have a rubber boot on the master to help keep the pushrod centered at all times.