Master Cylinder leaking?

[mopar73dge]

I have in my 73 Charger with 318 power front disc brakes, At stop light the pedal slowly goes down with pressure on the pedal and then the red brake light comes on, if I press down on the brake pedal hard after it comes back up the light goes out and I feel a bump. There are no leaks anywhere and the level in the master cyl has not dropped. Good braking other wise. This mstr cyl is 15 years old which was a Bendix, new, at the time. I think it is the master leaking, Chiltons has a good trouble shooting chart, I want to be sure. The factory manual is a little vague for these symptoms. What do you think fellas?

 

[Zeppelin264]

Sounds like either a vacuum leak at the booster or a small small leak at one of the wheel cylinders.

 

[mopar73dge]

I checked the booster, it holds correctly as stated in the testing section from the manual. The light does not stay on and there are not any leaks at the cylinders.
I remember now back about 25 years ago the pedal would slowly go to the floor and we replaced the master cyl. the light did not come on though.

 

[Yatzee]

Well if the level in the reservoir is not going down, we can eliminate a leak downstream. If you pump the pedal and the firmness comes back, I'd think that there's an internal leak in the master between the cups for front and rear circuits. After 15 years it's probably worth changing and really, they're not worth that much. If after the change you still experience the same systems then I'd look at the vacuum booster. Perhaps after 15 years, both the master and booster are on their way out. The light indicates low pressure in the system not low level in the master.

 

[mopar73dge]

Thanks, I would agree most likely the master, and yes pressure warning. I will order a new one now.52.00 through a car quest store in town.
I think since we do not drive these cars too much wit this one having only 16000 miles on it, sitting and less use would make it corrode and not last, well obviously. Thanks

 

[rlem1977]

Thanks, I would agree most likely the master, and yes pressure warning. I will order a new one now.52.00 through a car quest store in town.
I think since we do not drive these cars too much wit this one having only 16000 miles on it, sitting and less use would make it corrode and not last, well obviously. Thanks

You buy a MC rebuild kit and save little. Probably only the seals on the piston are the problem.

 

[Ranger16]

At stop light the pedal slowly goes down

Sure sounds like a bad MC to me.

 

[mopar73dge]

I pulled it back and it is leaking has been for a while. Still connected to the lines until the new one is in and I will install it on Monday,

 

[mopar73dge]

All set the re-engineered master cylinder is installed. It has a significantly tighter bail and it has fine grooves on the edge where the cover gasket makes contact for the reservoir. I painted it with Duplicolor cast grey engine paint 500 deg with ceramic, which is an excellent color match.