Update on International truck brakes

I sure don't have the experience of Allan or IAGary, but here goes....

1. I don't understand your comment, "...pedal got hard and has no brakes whatsoever." Are saying that you can't push the pedal down, and that the brakes are not applied (or locked against the drums)?

2. This truck has a hydrovac on it, correct? Is it possible that the vacuum line is attached to the wrong port on the hydrovac?

3. If you suspect the vacuum booster (what ever kind / model) is causing the problems, can you bypass the booster and verify that you are able to build pressure on the brake system?

4. Can you post a picture of the booster unit?

Keep at it, you'll get this one figured out.

Nathaniel

The way a Hydrovac works, if there is air in the system AFTER the hydrovac, AND/OR the brakes are not setup tight enough, the Hydrovac will reach the end of it's stroke before the brakes apply, then, then you'll get the HARD PEDAL feel.

This takes more than one "pump" of the brake pedal, though, and it's a DARNED SCARY feeling when it happens!

Last year, I rebuilt the hydrovac and all the cylinders and put enough fluid in the system to have "some" brakes, but still need to finish bleeding the brakes and get the engine running before I bring her home.

Nathaniel

If you are sure you have good vacuum it sounds like you have two problems, you still have air in the lines and/or your brake shoes need adjusted and your booster is leaking.

I'd start by puttung a vacuum pump on your booster (a shop can loan or rent you one). The one I borrowed was a little hand thing with a gauge that you pumped up and watched to see if it bleed off.

Had the brakes on a 1959 Cadillac drive me up the wall after doing the very same work you had done. Finally traced it to the "rebuilt" vacuum booster. Once I got it working right I moved on to individual wheel adjustments.

Bill

That's what I was just thinking.

Adjust 'em up 'til they lock and back off just a hair. Then, they'll probably still be too darned loose. :>)

Allan

I've read that they were a problem on the IH trucks.

Hope ya get 'er figured out,

Allan

That's what I was wondering since it is a '71.

Are you bleeding your longest runs first (right rear), then next shorter, next shorter and working back to the shortest (left front)? This is especially important in big trucks because you can dump air right back into a long run if you do them out of sequence.

Dunno, otherwise, I'd almost say the throw on the master cylinder is out of adjustment or like Gary says, maybe a bad booster/bad master cylinder?

Bad new parts will absolutely drive ya up a wall because it "plays" with your sense of reason.

There's got to be a culprit there somewhere.

Allan

Allan

Gary