Pedal gets hard half way down, little front brakes
Clues in color, click to expand
Hi I’m having some trouble with my car 1970 dart 4 wheel drum. I recently had the front end apart for about a month rebuilding it. The drums were off the whole time. Finally got it back together and now my front brakes don’t seem to be doing much.
The rear tires lock up first
and the pedal seems to get hard
half way through travel.
I readjusted the front shoes. Gave it a quick bleed at the wheel cylinders. And cracked the lines at the master loose. I did get a couple bubbles from the line going to the front brakes. But
the only thing that helped any was re adjusting the shoes. Still locking up the rear tires and only slight nose dive and have
hard pedal half way down. 12” vacuum at idle. Thought the hoses may have gotten collapsed internally but they seemed to bleed ok. Is it possible my master cylinder went bad while sitting? Or the hoses are bad but bleed ok? I was going to take the drums off next and check wheel cylinder movement. How much travel should I expect? Any other ideas?
Thank
This is a toughie
but you supplied some great clues;
The
hard pedal seems to indicate that the hydraulics are OK, keyword "seems"
The
halfway down tells me it could be a slack-adjuster adjustment problem
The
rear lock-up seems to confirm this
But the statement about having adjusted the front shoes already is a bit of a puzzler
So I'm gonna guess that the front wheel cylinders are running out of piston travel, and hitting a mechanical stop, before pushing the shoes out, or just not moving far enough in the first place. The latter could be because the pistons inside the master are not hydraulically linked,and the front system is actually waiting for the rear to link up mechanically. Thus,it is operating in failure mode.
I suggest to watch the compensating ports one in each reservoir, while a helper slowly applies the brake-pedal,holds it when it gets hard, and then slowly releases it back to the start....ALL the way.. You should see the fluid roiling at the beginning of the application, and a more roiling at the very end, as the fluid returns;watch out for a geyser at the end . If there is any air in the system it will cause the fluid to return in a hurry, and the geyser is the proof of it. I have seen the geyser hit the hood, so protect your paint accordingly, and make sure your helper knows to stop when you yell STOP !!!!!!!! There must be roilings or geysers to prove the C-ports are open. Without compensation, there might not be enough fluid moving out to the Wheel Cylinders to affect meaningful brake action.
Ok so assuming the ports are both open,or that you have mechanically opened them; then I recommend to bench-bleed the M/C, to fill the inter-piston area with fluid. Sometimes/usually, you can get away with doing this on the car. But in your case,you may have to lower the front of the M/C , lower than the rear.
That's all I got
