Brake problems after the 5.0 swap.

[BucknEB]

My '76 Bronco just received a '91 5.0 EFI engine. The brakes worked normal before the swap. The brake system lines were never disconnected and the whole system was left completely intact during the swap without any leaks of fluid. The MC was disconnected from the booster to paint it but the hydraulic system was never opened.

During the first test drive the brakes were not performing correctly. I would press the peddle and I would not feel the brakes until I had the peddle almost to the floor, and then with added foot pressure I would get full brakes all of a sudden.(locking up the front brakes).

I then took the MC off and adjusted the stud on the end of the push rod from the booster 1/4 turn. Took it for a test drive and no change. Adjusted 1/4 turn again, test drive, no change. Made a full turn, test drive, no change.

Then we bled the brakes. Started in the R rear, pumped the brakes,hold, opened bleeder, peddle drops with out much pressure from my leg, and fluid steadily pours out without bubbles. Repeat the bleed on L rear. Same result.

Bled the R front. Pump, hold, open bleeder and not much fluid comes out, I push the peddle harder with the my leg and with the valve open and fluid starts gushing out. Bled the R front a few times and it showed the same symptoms. Tried the L front same thing happened, pump, hold, open- not much fluid comes out, push harder fluid gushes out.

I have a stock peddle assembly, booster,brackets and linkage, new MC, new proportion valve,new front calipers/pads, new front SS lines, rear is stock drums with a slight wheel cylinder leak in the left rear, and original steel lines.

Does anyone have any ideas on what would cause this problem and how to fix it?

[chuzie]

Did you check to make sure you are getting vacuum to the booster from the intake?

Crank it, turn off, and crack the check valve seal. Do you hear it queef?

[BucknEB]

Well we bled the brakes again, and again had the same results. Then we started to look at the proportioning valve. I redid the brakes about 2 years ago and we figured out that I plumbed the lines from the MC wrong. I had the small reservoir going to the front brakes and the large reservoir going to the rear brakes.:doh: After that We changed out the prop. valve with one that Chuck had on his parts shelf and we ran the lines correctly. We bled the brakes again and got good flow out all the lines. The I took it for a test drive and the brakes seemed a lot better. They are still a little soft and touchy at the bottom of the peddle but a big improvement from the night before. I've adjusted the push rod from the booster another 1/2 turn and it didn't seem to make a deference. After making the prop valve swap and correcting the lines we never did check for vacuum to the booster.

I think I may just keep adjusting the rod until I can find some type of change in the feel of the peddle. I'll start by taking it all the WAY back to the shortest measurement so that the rod is barley engaging the MC (giving me pressure to the brakes) and still allowing the MC piston to retract (releasing the brakes).

[SC74]

This still doesn't explain why they changed during the 5.0 swap. Did it not do this before, even with it plumbed incorrectly?

[BucknEB]

You're right it doesn't explain why anything changed. No, it didn't do this before. The brakes worked pretty good for an old truck and I had nothing to compare it to.

[broncosbybart]

Does the new engine have a big cam in it? Engine vacuum would be less with a bigger cam- ie- harder brakes. pedal travel shouldn't change though.

[chuzie]

I agree with bart. Make sure you give the vac enough time in between application and see if it makes a difference. All that intake crap they had makes me wonder about the cam.

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[BucknEB]

We started checking the booster out tonight. I was pressing the peddle and Chuck could hear a hissing sound out of the rear of the booster. Then we swapped the booster out for Chuck's old power booster. I started it up and I could feel a 100% difference in the feel of the peddle. The brakes are FIXED!!!!!:chili:

[broncosbybart]

Cool. The engine should run better now too!

[chuzie]

Hey dumb dumb. Glad you got it fixed after all that craziness. Remember a few posts ago when I asked if it queefed when you cracked the valve seal? Had you done that, you would have seen that likely would not and that you had a seal issue with the booster and could have saved yourself a lot of headache. I may be crazy but I ain't nuts!