1968 Brake question

[DLedin]

I'm noticing when I apply continuous pressure to my brake pedal, say while at a stop light, that the pedal is slowly sinking toward the floor and then the dash brake light will come on. When I release the brake pedal the brake light goes out.

Braking seems to be OK, it doesn't feel unsafe. At first I thought that it might be an issue with the brake booster but then I recall some folks in the past mentioning that a stiff/hard to press brake pedal may be a sign of a brake booster problem and that's not quite what I'm experiencing.

Any thoughts?

 

[cmacias24]

I experienced that and the culprit was the brake master cylinder. It was shooting the brake fluid through the sides when I applied the brakes. I’d check to see if there’s fluid stains around the cylinder.


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[DLedin]

Thanks for your reply. The fluid level in the master cylinder looks good but I'll have someone apply the brakes while I look at the mc to see if I can spot any leakage.

 

[franklinair]

Unless you see SEE any external leakage, the Master Cylinder is bypassing inside. Then replace the Master Cylinder.

Neil

 

[cmacias24]

If you don’t see any leakage around the master cylinder, the next thing to do is to check behind the rear wheels for drum cylinder leaks. Those things are notorious for leaking.


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[DLedin]

Unless you see SEE any external leakage, the Master Cylinder is bypassing inside. Then replace the Master Cylinder.

Neil

Thanks for your response Neil. So are you saying that if I don't see a leak (at the MC or elsewhere) that the Master Cylinder is "bypassing inside" and needs to be replaced?

Thanks,
-Doug

 

[DLedin]

If you don’t see any leakage around the master cylinder, the next thing to do is to check behind the rear wheels for drum cylinder leaks. Those things are notorious for leaking.


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Thanks for the tip. I'll check that as well.

-Doug

 

[franklinair]

You mentioned that the fluid level remains OK in the MC, so chances of external leakage is nil. I've seen this hundreds of times in my youth when I worked for my dad in his garage. The seals in the MC leak internally allowing the brake pedal to slowly sink to the floor.
Trust me on this- you've got a bad Master Cylinder. (By the way- they are repairable if you have a hone to clean the internal bore, and replace the two seals- that cost $1.00+/-).

Neil

PS: Be sure to bench bleed the new MC before installing it.

 

[DLedin]

You mentioned that the fluid level remains OK in the MC, so chances of external leakage is nil. I've seen this hundreds of times in my youth when I worked for my dad in his garage. The seals in the MC leak internally allowing the brake pedal to slowly sink to the floor.
Trust me on this- you've got a bad Master Cylinder. (By the way- they are repairable if you have a hone to clean the internal bore, and replace the two seals- that cost $1.00+/-).

Neil

PS: Be sure to bench bleed the new MC before installing it.

Excellent. Thanks for your expert advice.

-Doug