Leaking master cylinder cap.
 

Hi all, I have a '66 C10 with a leaking master cylinder cap. It is not over full. For some reason all the fluid came out the rear port. This is a new master that got all ugly from the fluid. I refilled and bled. Now I see why it is getting emptied. Has anyone else had this problem? Any ideas? Thanks in advance...

Re: Leaking master cylinder cap.
 

New cap and rubber gasket? Tightening the wire hold downs is a pain but took care of the leak on my cap.

Re: Leaking master cylinder cap.
 

I have a similar master. I went a couple years of driving before checking the fluid again. When I did that, a little bit of crustiness had built up on the seal. When I put the cap back on, I noticed that it started leaking. Took it off again, cleaned the crustiness off the rubber on both sides, then took a razor blade to the sealing side on the master to make sure it was clean and flat. I haven't had a leak since doing that

Re: Leaking master cylinder cap.
 

I installed a new master cylinder last year that is the same style as yours, and the cover leaked right from the beginning. I ordered a MCAK012 cover from opgi.com, and it hasn't leaked since. This cover is overpriced, but it did solve the problem.

https://www.opgi.com/brake-systems/m...l-mcak012.html

Re: Leaking master cylinder cap.
 

Thanks all, new cap, gasket and tightened the hold downs. No more leak!

Re: Leaking master cylinder cap.
 

Right on!!

Re: Leaking master cylinder cap.
 

@grubsster.....

Thank you for updating the status.
Would you care to share the p/n or any specific info related toward the 'fix' that can be used for future reference should others see this thread?

Re: Leaking master cylinder cap.
 

Sure, I used the original cap from my old master cylinder which seemed to be of better material than the new master. Installed the retaining clips upside down in the vise and bent both sides inward, at the point where they go in the master, about 1/8th of an inch to "shorten" them a little. Used a 42071 dorman gasket.

Hope that helps.

Re: Leaking master cylinder cap.
 

That's good info for the next guy that has a similar issue. Appreciate the feedback.

Re: Leaking master cylinder cap.
 

Thanks for the update. My brand new MC looks like it is seeping from under the cover but only when I fill it all of the way to the top with brake fluid. I will look into these fixes.

Re: Leaking master cylinder cap.
 

When you are filling, make sure you are allowing room for expansion. I fill mine as in the picture. Others may do differently, but that works best for me.

Re: Leaking master cylinder cap.
 

Those type of caps always leak. Mine was the same way. I spent the $150.00 and purchased a Wilwood MC. Best money spent, but I hate leaks.

I get that you would need to bench bleed the new MC prior to installing then re-bleed your brakes. I know that's what I ended up doing and it was still worth it (to me).

Marc