BRAKE QUESTION 78KC

[way2fast78]

I have a 78 KC and recently the brakes are giving me trouble. Here's what is happening. The pedal feels ok when you mash the brakes but if you keep pressure on the pedal, it slowly goes to the floor. Would I be correct to assume that the master cylander seals are bad and not holding? The fluid level stays the same and I do not loose it anywhere, there are no leaks in the brake system. It is power brakes. I did check the vac line to the booster and it all seems to be tight and good. Any suggestions?

I have never replaced the master on this car, is it easy?

Any help or ideas would be greatly appreciated, I am going to fix it tonight.

 

[78CobraII]

Yup...sounds like the usual master cylinder seal failure. If the same thing happens with the engine off, you've eliminated the booster as the culprit.

The last time I did one the only hard part was getting the brake lines disconnected from the MC. I recommend brake wrenches to keep from rounding off the fittings.

I would also recommend opening the brake lines at the front calipers and rear wheel cylinders after replacing the MC to get as much old fluid out of the lines as possible, then pouring new fluid in at the top and pumping until it comes out the line at each corner. I've seen master cylinders that didn't last very long due to having junk in the old fluid.

 

[Wart]

The last time I did one the only hard part was getting the brake lines disconnected from the MC. I recommend brake wrenches to keep from rounding off the fittings.

And don't just turn the fittings off, if their in the least bit stuck you'll wind up twisting the line.

Break the fitting loose, work it back and forth until the fitting turns freely on the tube.

Don't get in a hurry.

I would also recommend opening the brake lines at the front calipers and rear wheel cylinders after replacing the MC to get as much old fluid out of the lines as possible,

I suggest opening the bleeders before removing the master.

This will drain the master and leave less in the master to drip down the inner fender.

Sure, you can put a rag under it, but you'll need lots of rags.

 

[Dano78]

The last time I did one the only hard part was getting the brake lines disconnected from the MC. I recommend brake wrenches to keep from rounding off the fittings.

Those are called 'Flare nut' wrenches. Sears (Craftsman) and Napa carry nice 3 pc wrench sets at a reasonable price.