'75 scout BAD brakes, help?

E

estock

New member
Okay, pads/ shoes are good
calipers/ wheels cylinders good
new "autozone" master cylinder
bled mc and all lines
when braking: rear locks up, but not much grabbing in front
peddle low/ at floor

replace booster?
Replace proportioning valve?
What am I missing?

Thanks!
 
Did you bench bleed your new mc? Also, reman mcs are known for being junk right out of the box. Get all the air out of this one, bleed the fronts again, and if its still an issue, call Jeff for a "new" mc. I once took 3 back to o reilly's and still had no love.
 
I agree with deal...getting a workable master cylinder these days is a crapshoot. Doesn't matter if "new" or a reman.

Based upon your description, if you rig a high pressure gauge on each mc port in turn, you will find "normal" pressure on the rear brake port with very low pressure on the front circuit. That means the master cylinder is "bypassing" internally.

Also...anytime you screw around with swapping out master cylinders that were not originally mated to the vacuum booster being used, the pushrod length between the booster and the master cylinder piston must be "corrected" for proper length. If it's too short by a hair, you loose travel of the master cylinder. If it's too long by a hair, the brakes will be permanently applied!:

http://www.forums.IHPartsAmerica.com/brake-tech/4262-pushrod-between-mc-booster.html

And:

http://www.forums.IHPartsAmerica.co...aster-cylinder-original-booster-question.html
 
Alright.

Bench-bled the mc, bled all cylinders/ calipers.

Brakes are better, but pedal is still low and and doesn't really stop, it just slows down in a hurry...

Adjust the rod from booster to mc for more pressure?

Replace booster?

Thanks!
 
Alright, I purchased a remanufactured wagner booster/mc from scoutparts.com. Also a new proportioning valve from IH onlynorth.

I bench bled mc with booster attached.

Installed prop valve, installed booster/ mc.

Bled all brakes.

Brakes are slightly better, but now are super hard and I don't feel like the booster is doing anything. But at least they are not sinking to the floor like before.

Thoughts?

Thanks
 
If your m/c and power booster is new, you have good firm pedal ,but its hard to push, you need to check your vac signal to the booster. If your engine is not producing a nominal 15 in vac at idle , it aint gonna function properly. Also the the vac hose should be plumbed off the fitting on the intake directly behind the carb or on the rear of the carb. Depending on which set up you have. And as always the adjustment of the booster rod is very critical. You need to check it regardless if its a reman unit or not.
Remans are assembled in a factory by folks who dont give 2 flyin shits if you can stop. Double check everything and you'll find the issue. Trust me on this.
 
Yeah, I just got a vac meter and it's at a steady 20 pull.
The vac line is new with hose clamps at both ends pulling from intake manifold location behind carb.

Not sure how I should adjust the booster push rod.
Should I even attempt it based on the fact that vac pressure is good? How would I go about adjusting it?

Thanks!
 
If you have a hard brake pedal after changing out the booster then chances are you got a bad booster.
 
As Jeff said, chances are you have a bad booster, but to check the rod length. Remove the m/c from the booster,this can be done without removing the lines, then measure the length of the rod from the mounting face of the booster, write this measurement down, then measure the depth of the hole in the piston on the m/c from the mounting face of the m/c, you will have to do some figuring due to the lip sticking out on the m/c. Then figure the difference of the 2 measurements. If the rod comes up short. Adjust it so you have like .005 clearance to the piston. This allows for heat expansion, if it comes up long, turn it in to get it off the piston. If you look back at the thread m/m wrote in his response , there is a file in it that explains the factory adjustment procedure, this will give you a good idea where to start, but due to the fact you are not using factory issue parts you must do the adjustment procedure.
My 74 had brake issues also, it would stop, had good firm pedal but way too much travel, after adjusting the booster rod, it will throw you thru the windshield, skids all 4 33 tsl swampers on dry pavement. This lil adjustment took me all of fifteen minutes. All I used to measure the rod was a dial caliper and a calculator.
 
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Yes, it was a bad booster after all. Still kinda funny braking, feels like the back is grabbing first,

thoughts?
 
I failed to mention that I ran out of steam, and brought it to a shop that declared the reman booster not working. They put in another booster/mc set up, and now have stopping power. It is still weird. Feels like the rear is engaging before fronts. Replace front calipers?
 
I just put a hydro-boost setup in mine. Best thing I ever did. Stops like it has real power breaks.
 

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