VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 1938 Chevy Master Cylinder Leaking

I removed the filler hole to see the master cylinder. When I step on the brake pedal, I can see brake fluid being force out of the vent? holes in the filler plug. Why is this happening? Do I just need to rebuild the master cylinder?

Sounds like it's time for a rebuild. Sounds like your piston cup #10 here is bad.

I would think if anything, it is overfull. If you were to take the plug off and pump the brakes, you would have fluid all over the place.

Sounds to me the cylinder is overfilled. Level should be at least a 1/4" from the top. If it is and still does it you have a problem.

Overfilled +1. Have you adjusted the shoes up lately ?? this will force more fluid back into the reservoir

ollie

I went to NAPA and bought the master cylinder kit ($18). I looked up the part number on line, it was UP3. When I told them the part number at the store, they looked at me like I was crazy and said that was a bad number. After typing it into the computer, she said...Oh, ok, there it is.
The brass ring on the cup somehow seperated and was crushed inside the cylinder. I honed it out, and put it back together. The wife helped me bleed the brakes, and it has a great pedal now.

Nothing like a wife/helper

Nothing like good pedal!

That's fer shur! I was pushing my '40 up the incline into my back yard and told my wife to hit the brakes so I could rest a bit. The pedal went to the floor and I was very lucky to have a nice rock handy that I was able to get under a tire. The hand brake has parts missing, so that wasn't an option...

Nice work Mars

I just rebuild my master cylinder on my 38 chevy now my brake lights don't work and my headlights also not working I connect the two wire to the brake switch what seen to be the problem? thanks

Has to be a blown fuse, I would think.

On the back of the headlight switch?

Do you have a voltage tester or a voltmeter/multimeter? Will help to troubleshoot.

If you have 6 volts across the master cylinder brake switch wires, or 6 volts from one wire to ground, then your switch is suspect. If you don't have any voltage either way, then the problem is most likely a fuse or a loose terminal.

Most of my electrical issues after repairs are usually caused by my own hands, so.....

The '38 doesn't have a fuse on the lights. The only fuse in the car is on the back of the ammeter. Try touching the two wire that go to the brake light switch together. If the brake light comes on you have a bad switch. Those pressure switches are infamous for not working well. I finally converted to a later model mechanical switch on my '38 for that very reason. We'll need more info on your headlights before we can help you there. Were they working then stopped? Have they never worked? Have you used a multimeter to check the continuity of the switch?

I learned the fuse was on the back of the switch one night in Ohio while on a tour. The member lost his lights and I had a difficult time finding the fuse. For my '39 it was on the light switch.
The original fuse was a 20 amp. A 30 amp like a '39 uses works well also.

The headlights on the 38 sedan are fed through the fuse, as indicated on the wiring diagram. A blown fuse will affect the headlights and the brake light.

Sounds like the fuse...

With only one fuse on the '38, if it blows nothing will work. If everything is working but the brake lights I don't believe it would be the fuse. That is unless the OP has the brake lights on an in-line fuse.

With the fuse blown the ignition and the gas gauge will still operate and of course the starter.

thanks guys for your knowledge. it was a fuse now I see the light god bless you all