Soft Brake Pedal

[Logan]

When I press the brake pedal it goes about 3/4 of the way to the floor before it catches, but if I pump it once or twice it catches at about 1/3 of the way down.  I have recently rebuilt the entire system including master and wheel cylinders, new shoes and even replaced some lines.  Could there be a leak?  One more thing--and this was a real "oops" moment on my part, so don't laugh at me.  I was driving down the freeway, when I noticed my emergency brake was on and had been for about 20 miles.  The good thing about it is my EB only grabs on one wheel, and that not very tight.  Also, I had not pulled it out as far as it goes.  I got out of the car and could smell the brakes when I did.  I felt the wheel and it was hot to the touch, but it doesn't seem to have affected the brakes, except for the problem I noted above, but even that it was doing to some degree before.  Ideas?

[Kenn Evans II]

You may have boiled your brake fluid and the lines need to be bleed again. Check for any obvious leaks and for any funny smells like windex.  If you do you may need to rebuild the wheel cylinder. Also check the brake hardware for discolorization, they could have crystalized and will break under  stress. the heat can also distort the brakeshoes. I hope you only have to bleed the brakes. If this helps let me know.

[joefrazer]

You'll probably want to readjust the shoes too. KF brakes..except for a few 49-50 cars..are not self adjusting so the shoes do need to be manually adjusted every now and then. Pressing the brake pedal causes the wheel cylinder piston to push the shoes out and the action of pumping the pedal catches the piston before it's fully returned. This makes the shoes move further out and eventually making contact with the drum.
So, check your brake fluid and make sure it's topped off and then adjust the shoes at all four wheels. That should solve the problem.

[HJ-ETEX]

Logan:
Before your brakes can be bled properly, the shoes have to be adjusted properly. Adjust each shoe (there's eight) until the wheel doesn't turn, then back off on the adjustment just to the point that the wheel turns.
Now, before you proceed to bleed the brakes, get under the car and pull back the rubber boot on the master cylinder so you can see the end of the piston in the MC. Move the brake linkage by hand and note how much movement is required before the MC piston starts to move.
You mentioned that you had changed the MC. I think it is likely that you will find that the pushrod that goes into the MC piston is now too short. The bolt that holds the pushrod on to the linkage is eccentric, but I doubt it has enough adjustment to solve this problem. The solution is to find a longer pushrod and cut it to the length desired.
After all of this is checked, you can bleed the brakes and then back off on the shoe adjustment if desired.

[Logan]

Thanks, I'll try these suggestions and let you know what I find.

[51henryj]

Look at your rubber brake lines too.. they could be soft..

[Logan]

I finally got around to the brakes this weekend.  I noticed that on the wheel that got hot the wheel cylinder had leaked a little, so I got a rebuild kit, honed it out a little, rebuilt it and put it back in.  I also adjusted all four wheels, removing the wheels and using a feeler guage as directed in the shop manual.  Then I bled the brakes, but they are still soft.  They don't seem to be AS soft as before, but the pedal still hardens up if I pump it once or twice.  I think I bled all 4 cylinders pretty well--let a lot of fluid through, so I'm not sure why it's still soft.