I'm getting a slow weep type leak that seems to be coming from between the cylinder flange and the booster. I have a dual remote res. system instlled with an alum. dual fitting cap. In looking at pictures of the MC I noticed a small hole on the bottom of the mc flange. If the mc is overfilled above the cap line would this be some sort of weep hole for the excess fluid? Although this is a new mc I'm also wondering if the front seal is leaking. Although the mc is new it sat for about 3 years with fluid in it before use. Anyone had a similar problem?Thanks for any insight in advance. Bill

 

That m/s is leaking out the back end. and I am pretty sure the hole on the power booster is in fact just for that reason, so you know it's leaking. Sounds like you need to either rebuild or replace. bummer! hopefully somebody else will chime in and agree or correct me.

 

Jeff when you say the back end do you mean the flange end that bolts to the booster? Thanks Bill

 

bump to see if there are any brake pros out there.

 

Been there: I'm with Jeff. On the vette 1965-82 cast m/c usually has a metal cap with a rubber gasket. You can back off the two nuts without disconnecting the lines and use a flashlight and small mirror to look at the back end for a leak. Some restorers use a m/c that is not matched with the booster. This series m/c must be mounted level. Since you haven't used the m/c, I would guess the orings gave up and you need a kit. Two problems come up with mismatched m/c and booster that causes a leak. There are different bores in the m/c back end and some rods between the brake pedal and the m/c are to small in diameter and will slide off center enough, with many max pressure on the brakes, to scratch the bore edge and each time you brake, a drop of fluid will pass by the orings or sometime the area will crack the rod cup and leak. So the m/c rod needs to match the booster and the pedal to m/c length needs to be adjusted so not to exceed bottom in the m/c. If you do a kit, change the cap gasket. chuck

 

I had one of those vette style m/c on my 57 chevy, brand new and a complete POS from the start. I suspect they are made in China, so say no more i guess.
I replaced it with different style M/C with the same internal dimensions and problem solved. Just sayin.........John

 

My '51 utilizes a MC from a 1976 Blazer and I recently had the same issue. I replaced it with a remanufactured MC (from Carquest Auto Parts, only $23. with core exchange) and within three days that one leaked from the rear as well. I ended up returning that one and buying a new MC, no leaks so far. The MC was $45. (made in China...) and if you bench bleed the unit before you install it, it will only take you about ten minutes to install. You can bleed it from the lines on the unit with the assistance of someone inside the vehicle. Make sure you lay down some plastic before you perform the job because DOT3 brake fluid will ruin your paint if it gets on it. You can neutralize it with soapy water if you do but clean it asap. It's an easy repair, let me know if you need any other advice on performing the job.

Wally

1951 F1 - "Lucille"

 

Sorry I missed this Bill! But looks like others stepped up where I fell off!
But yeah thats what I meant. Go get ya another master cylinder.

 

Thanks guys..It's a complete booster kit I bought from Mid Fifties which I suspect came from CPP. I'll take it out and check. The push rod length idea has got me thinking. As I recall I adjusted it dry for about 1/2" free play before it contacted the cyl piston. The brake shoes may have been too far from the drum and caused too much piston travel before they seated on the drum. Got the right rear shoes centered and adjusted but the left side star wheel won't move and the drum doesn't want to come off. Shoes don't sound like they are touching. Thought the drum would just pull off. I'll keep trying to fix the shoe adjustment problem then move to fix the MC leak problem. 2 steps forward and one step back right? Bill

 

Well finally got the damn brake drum off. Had to heat it around the flange stub and it came right off. Brakes look good. I'll put it back together and recenter the shoes and adjust. Then on to the leaky MC. Your responses have really given me some ideas and a fix plan. Thanks guys I'll keep you posted. Bill