Brake reservoir lid leak

[kev2809]

I recently put in a brand new booster and cylinder a few months ago. this one does lean pretty good. I tried to straighten it up and remove the top spacers, but my current hood hinge setup hits them, so for now I have to leave it angled down. my issue is the master cylinder cap just doesn't seem right at all. I even tried swapping my other cap back on and it still leaks. are there any good replacements I can try?

[basketcase]

Those bails hold those lids on pretty tight. They should take some effort to snap in place. The lid doesn't appear damaged, so if there is no defect in the seal and the top of the master cylinder machined area is not damaged, it shouldn't leak. Since it has leaked with 2 different lids, I'd take a good look at the casting. Do you have 4-wheel disc brakes? That master cylinder looks exactly like the one on my 81 Corvette. On the Corvette it is slightly high in the front. Also my booster on my truck is smaller than yours and sits level holding the master cylinder level. My booster is about the same diameter overall as the smaller diameter front section of yours and would probably clear the custom hood hinges you have.

Tom

[kev2809]

the old booster and cylinder were also "new". I bought it brand new but the truck sat for like 8 years. that booster was more original style and the whole assembly sat level. this one angles down. the seller told me I could use spacers to level it, but until I redo my hinge setup, I can't level it. these bails just don't hold it tight at all, takes very little effort to pop them loose. the old ones I damn near had to use a flat head to pry them so I can pop the lid

I tried with the old bails too but they aren't the same. old ones are taller

[basketcase]

You might try to bend them down a little in the center so they will snap on tighter. It shouldn't take much.

[Wrenchbender Ret]

I've taken those bails & bent them so they fit tighter. Take a good look at the lid. Sometimes they get curved.

George

[kev2809]

thanks guys I will try to mess with the bails and see what I get. I will eventually level this thing out but that alone won't stop the leak

[Stocker]

I had the same problem a few years back, can't recall exactly what started it. Maybe a new master cylinder, I don't know. Couldn't see any good reason for a leak. Anyway, I did what a mechanic advised -- doubled up on the lid gaskets. That fixed it. Good luck with yours.

[pjmoreland]

I installed a new master cylinder a couple of years ago 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

[BAD1916]

I had an issue on my 71 where it leaked as well. On mine the rubber appeared to have shrunk or was severely undersized. My local Napa had a replacement part in their HELP section. Haven’t had an issue yet and mine tilts down as well.

[kev2809]

oh wow, your link didnt work but i found it on summit. $45! that is pricey. ill try to bend the holders or double up on the gasket. if those dont work then i dont mind spending the $50 to stop this leak, it already ruined the little paint job i did on the master cylinder

[pjmoreland]

Originally Posted by kev2809

oh wow, your link didnt work but i found it on summit. $45! that is pricey. ill try to bend the holders or double up on the gasket. if those dont work then i dont mind spending the $50 to stop this leak, it already ruined the little paint job i did on the master cylinder

I fixed the link.

[damnyankee36]

Originally Posted by kev2809

...this one does lean pretty good. I tried to straighten it up and remove the top spacers, but my current hood hinge setup hits them, so for now I have to leave it angled down....

Since I am new to the 67-72's I discovered that apparently all master cylinder/booster assemblies angle down for some reason. I never have found an answer as to why.

[leddzepp]

Check the sealing surface of the Master cylinder. A lot of times the rough casting will not allow the seal to seat properly. You can use some sandpaper to smooth it out.

[Southcity]

In addition to all the fine suggestions already provided, make sure of the following before you buy anything new.

1.Clean the mating surface on the casting (just where the rubber gasket makes contact) really well. Wipe it down with a clean rag being careful not to push anything into the reservoir. Do the same on the rubber gasket.
2.Then place the lid on the cylinder being certain to center it so that the rubber gasket lines up really well to mating surface.
3.Now the somewhat tricky part, make sure the lid does not move at all before securing the clips.

It's normal for these to have a little tilt (forward or back) depending on setup. But having clean mating surfaces and ensuring the lid is not moving when securing the clips is a good place to start.

[72SB]

Over filling the MC can cause a leak out lid......

[kev2809]

Originally Posted by 72SB

Over filling the MC can cause a leak out lid......

definitely wasn't overfill. it's maybe a 1/4 full on both sides