1980 Bronco MC and brake booster

fordguy

blah.
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School me please, trying to fix friends ride

1980 bronco, pedal always went to floor and veey poor braking.

No worries, told him to change stuff because its been parked for 20 years. New front calipers and braided lines, new rear wheel cylinders and sprinfs, new distrivution block front and rear, and finally nee acdelco master, 1" bore as speciefied.

Bled bled and bled more. Measured boister pushrod, 100% correct. Rear brakes adjusted goo.

Same ****. Pedal goes to floor and stops very poorly.

Now we are going to try one more thing, to change the old rubber line from MC to front distribution valve, and take front calipers off and bleed them wit nipple pointing straight up.


Niw my question, I ordsred two different MCs for 80a F250/350 with 1 1/8 and 1 1/16 bore and NEITHER of them fit. The holes to bolt onto boister are too wide, and rhe round part that goes into booster is too big compared to original.

Whats the deal with this, I see forums me tioning dfferent bore sizes but they are obviously not fitting.

Any help is appreciated
 
Provience said:
Have you tried leaving the bleeders open and letting it gravity drain? Sounds like air somewhere. 1" bore shouldn't be an issue
Click to expand...

we bled it different ways and so many times, gravity bleed wont do anything more than what we did.

Where else could air be hiding ?
 
fordguy said:
we bled it different ways and so many times, gravity bleed wont do anything more than what we did.

Where else could air be hiding ?
Click to expand...
Sucking air from a poorly sealed fitting or some such. Gravity, being low pressure, addresses that stuff.

Basic hydraulic system, no reason for it to not to have resistance at the master without a leak or air
 
When you bleed is it moving fluid as you would expect? Will they pump up at all?

Did you bench bleed the master?

What do you mean take off calipers and bleed with port straight up? It already should be pointing up.
 
Are the rear drums adjusted properly. You might be spending all your pedal travel expanding them.
 
x2 on bench bleed master question. I had an issue where brakes would go soft after like 3 seconds. new master solved it.

what about brake booster?
 
fordguy said:
School me please, trying to fix friends ride

1980 bronco, pedal always went to floor and veey poor braking.

No worries, told him to change stuff because its been parked for 20 years. New front calipers and braided lines, new rear wheel cylinders and sprinfs, new distrivution block front and rear, and finally nee acdelco master, 1" bore as speciefied.

Bled bled and bled more. Measured boister pushrod, 100% correct. Rear brakes adjusted goo.

Same ****. Pedal goes to floor and stops very poorly.

Now we are going to try one more thing, to change the old rubber line from MC to front distribution valve, and take front calipers off and bleed them wit nipple pointing straight up.


Niw my question, I ordsred two different MCs for 80a F250/350 with 1 1/8 and 1 1/16 bore and NEITHER of them fit. The holes to bolt onto boister are too wide, and rhe round part that goes into booster is too big compared to original.

Whats the deal with this, I see forums me tioning dfferent bore sizes but they are obviously not fitting.

Any help is appreciated
Click to expand...
If your front caliper bleeders aren’t pointed up when installed, that’s your issue…
 
heres the caliper. could be some air hiding up there ?

prop valve is new, all that fluid being displaced to the floor is definitely not leaking out anywhere

gonna try to replace that rubber line from MC to prop valve and rebleed thr calipers out of the brakes

kinda stumped
 

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Caliper looks good to me.

Will they pump up at all? Or just keep going to the floor.
 
1980 was a first year there was some odd stuff on there.

Bore size doesn't matter.

We did all 4 wheels at the same time on my kids excursion. I have a hand held vacuum bleeder. I spent hours trying to bleed it. Test drove and they still not right, bled again. Still not right. Finally I bet I run at least a pint through each bleeder. When it finally worked it was amazing, but it was a struggle. He knew the second he sat in the truck and hit the pedal.

Another thing I had heard to do in these tougher situations, done this on ATVs, take calipers off, put C clamp on to hold the piston in. Adjust the drumbrakes as tight as you can get them. But that is a lot of work.

That will keep the pistons and wheel cylinders from "bouncing" air in the lines. e.g. you have a bubble, bleed the brakes, bubble moves 6", let up on the pedal as the caliper piston relaxes it pushes the air 6" back towards MC. Worked Great on ATVs, never had to go that far on a truck though.
 
Ok so weird ****ing ****, I was ****ing with it myself, no luck.

I started measuring strokes. Pedal at the MC rod only moves 3/4" before hitting a hard stop. Ok, lets troubleshoot. Removed MC, pedal goes all the way to floor, total of like 2" at the MC rod. So what I thought was the floor, because it was a HARD stop, was less than 1/2 of travel.

Put MC back on, 3/4" at the rod again. MC off, 2", pedal moves straight, no bindining or mechanical issues.

MC off, MC moves approx 2" on the bench. WTF, ok.

MC back on, 3/4 stroke again.

Unhook both lines (look bleed lines bsck in res), MC on, 2" stroke at rod, pedal to floor (literally). Ok, weird, maybe an obstructed line?

Most of the system is new, but next I told him to replace line going to the rear. If its blocked and not letting fluid move properly, it could be causing the limited stroke
 
fordguy said:
Ok so weird ****ing ****, I was ****ing with it myself, no luck.

I started measuring strokes. Pedal at the MC rod only moves 3/4" before hitting a hard stop. Ok, lets troubleshoot. Removed MC, pedal goes all the way to floor, total of like 2" at the MC rod. So what I thought was the floor, because it was a HARD stop, was less than 1/2 of travel.

Put MC back on, 3/4" at the rod again. MC off, 2", pedal moves straight, no bindining or mechanical issues.

MC off, MC moves approx 2" on the bench. WTF, ok.

MC back on, 3/4 stroke again.

Unhook both lines (look bleed lines bsck in res), MC on, 2" stroke at rod, pedal to floor (literally). Ok, weird, maybe an obstructed line?

Most of the system is new, but next I told him to replace line going to the rear. If its blocked and not letting fluid move properly, it could be causing the limited stroke
Click to expand...
Stop in the same spot regardless of engine on or off?
 
so whats this proportioning valve tripping rsetting nonsense? watchex a video, stil confused.

I am thinking just yank it out and install a T for the front, and just straight pkumb the rear?
 
Provience said:
Stop in the same spot regardless of engine on or off?
Click to expand...

I want to say yes, but I dint think I tested it engine on MC off because it had no resistance, but I will do specifically this

really stumped when it hits the end if thr stroke, 3/4 or 1" or whatever, its a HARD stop

but probably not a bire size issue because if its not getting more than 1" of stroke, wel that would do it
 
Do you still have the porportioning valve?

Did you hold the plunger down when bleeding? You kinda have to do that.

There are a few different styles, most vehicles with disc/drum combos had this in the 70's and early 80's. Usually doing one axle you didn't always have to screw with it, but doing all 4 I am sure the thing is tripped.



b86670122d959780d5e1365d6b3498b1.jpg
 
no did not do that. hell didnt do it on my pontiac either. yeah its still installed but its coming out
 
I've never done that. As long as the light does not come on it is centered. If it comes on a couple stabs at the pedal should recenter it.
 
No need to **** with the idiot light deal.

A line lock will set the brake warning light (as it should) and can be cleared with one press of the pedal. (after burnout is done).

I now bleed brakes with a cheap A/C vacuum pump and a moonshine jar. Works quick. One man show.
 
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