4x4 low pedal

cobraman809 · Jul 8, 2015

Hey guys. I have an 1986 ford ranger 9in rear 302 bored .30 over power vacuum assist and i have all new wheel cyl, drums, calipers, lines, master cyl. I have bled many times, adjusted the rear. I still have a low pedal. HELP!!!!

RonD · Jul 8, 2015

Generally low pedal after new parts, especially rear drums, indicates rear shoes need adjusting, they are too far away from drums so more fluid is needed to get equal pressure at the 4 wheels.
The "star wheel" adjusters on the rear shoes do have a left and right, so can be reversed by mistake.
E-brake will tighten the rear shoes, as will backing up and using the brakes.
So Pump the e-brake and see if it gets higher, indicating it is adjusting the star wheel.

There is an adjustment on the push rod between master and booster, this usually doesn't need to be adjusted for stock to stock swap of the master, but............

cobraman809 · Jul 8, 2015

Thats the thing man i have adjusted to where the drum would barley move at all and still the same. The booster is fine. Im thinking im getting too much vacuum pulling too much assist. Im just looking for more possibilitys or someone who has had the same issue

billpac4u · Jul 8, 2015

I'm no expert . . .

But . . . the guys who are always say to be sure and bench-bleed the MC properly. Worth a try? :dunno:

RonD · Jul 8, 2015

If vacuum was the issue you would get "grabby" brakes, i.e. touch the pedal and brakes are on full, so too much assist

Assuming there is no air in the system and push rod has no play, then you are simply using/needing more fluid to the calipers/slaves than you did before.
Also assuming calipers and slaves are the same size as before.
Larger pistons in the calipers and slaves require more fluid for same distance traveled, so with stock master it may required more pedal travel to get the same braking.

If the 9" axle has bigger slaves that may be where the extra fluid is going, it isn't much but you would feel the difference.
The comparison is the smaller the master piston the lighter pressure on the brake pedal is needed but longer travel is needed.
Bigger master pistons require less travel but more pedal pressure.

So if you increase the size of the slave or caliper pistons you are, in effect, making the master piston smaller in the comparison, so more travel is needed.

Big Jim M · Jul 8, 2015

YES! What Ron said! The piston travel is measured in CC's normally. Search and find the CC's the master puts out and the amount of CC's needed to accommodate the present pistons in all four wheels.
Like Ron I'm thinking you will need a larger master to go with those 9 inchers.
Big Jim

Andy D · Jul 8, 2015

Try a gravity bleed of the RR If it doesnt gravity bleed with the cap off the MC and the bleeder open on the brake cylinder, there is air in the system. When I was replacing the brake lines on the Rat, I followed the leaks from the MC to the wheels. One coupling after another until the bleeder started bubbling

.

Spott · Jul 8, 2015

Andy D said:
Try a gravity bleed of the RR If it doesnt gravity bleed with the cap off the MC and the bleeder open on the brake cylinder, there is air in the system. When I was replacing the brake lines on the Rat, I followed the leaks from the MC to the wheels. One coupling after another until the bleeder started bubbling .

First, you need to ask him if his brakes feel squishy. If they're good and firm, then there's no air in the system and bleeding can't improve anything.

cocoasranger · Jul 9, 2015

If all else fails try this. The power brake unit has an adjustable push rod. The adjustment end can be seen when the brake master cylinder is removed. There is a standard measurement (0.995" rod tip to face of chamber iirc) called out in the Ford manual. You can always try threading the rod tip out to see if this is the problem. Just be sure to count the number of turns and you can return it to the original setting if no improvement is noticed. Hope this helps. :icon_idea:

cobraman809 · Jul 10, 2015

Ive bench bled, ive gravity bled, im thinking its the wheel cyl, how can i tell if the wheel cyl are too big?

cobraman809 · Jul 10, 2015

Also if i change the master cyl will it change the way my front calipers work because its a stock twin i beam front end and factory calipers and rotors

RonD · Jul 10, 2015

Original ranger axle with 9" or 10" drum would have 13/16" slave piston diameter.

Look up the year of your 9" axle and see what the piston diameter of those slaves are.

cobraman809 · Jul 10, 2015

I dont know what year rearend it is i think its a late 70's but not sure its a 10inch drum

Spott · Jul 10, 2015

Big Jim M said:
Search and find the CC's the master puts out and the amount of CC's needed to accommodate the present pistons in all four wheels.

RonD said:
Look up the year of your 9" axle and see what the piston diameter of those slaves are.

You need to look it up yourself. Try auto parts stores websites, like rockauto, and look for descriptions for parts fitting the donor vehicle. Also try forums and websites for the kind of truck that axle/brakes came from. Also look in our own tech library.

cobraman809 · Jul 10, 2015

They are ranger wheel cyl the guy at Auto ran the numbers on my old one and my new one both are ranger wheel cyl

4x4 low pedal

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