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Proportioning rear brakes


Denisefwd93

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On this truck, (94, 4wd,4.0) after bypassing the rabs valve I've noticed the new front brakes are hardly wearing at all, either it's the master cylinder (I have another) or the proportion pressure to the rear versus front is way off. I've seen a number of adjustable and non-adjustable proportioning valves on the aftermarket just wondering which any of you have used
the new hoses pads and calipers on the front went on very well and bleed very easily so can I assume the master cylinder is still good?

I have a connection right by the master cylinder it would make it very convenient to install an adjustable proportioning valve.
https://www.jegs.com/i/JEGS/555/63022/10002/-1
 
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RonD

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By-passing RABS valve shouldn't effect proportioning, the valve was wide open, like a straight brake line, unless activated to reduce pressure at rear brakes to prevent lock up.

Generally if Brake Master cylinder has 2 brake lines coming out then it has internal proportioning, on Pickup trucks it would be 70/30, most cars and SUVs are 60/40

You can add the adjustable unit to send LESS pressure to rear brakes but not more pressure, because that line only get 30% of the pressure.

If truck dips down in the front on hard braking and rear wheels don't lock up easily then front brakes are getting good pressure, 70%, and rear is getting less pressure, 30%
If not then Master could have a problem
 

Denisefwd93

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stock, may get leveling springs in front "somday"
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Thanks Ron, no "Dip" can actually feel the rear brakes grabbing, about 700 miles on the new front rotors and pads they don't even have a shine on them and i can still see the machine marks from when they came out of the box.

I'm really thinking it's the master cylinder, also get a slight rise in the pedal after driving awhile, thinking the front is bypassing to rear internally can that happen?
 

RonD

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Try bleeding front again, you may have air between Master and splitter, so it won't pull to one side, it will just have weak pressure to both front brakes.

The master piston closest to the brake pedal is considered the primary piston so it is used for front brakes, farthest away is secondary so used for rear brakes, which is why the brake lines are hooked up the way they are :)
 

Denisefwd93

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Ford
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4WD
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stock, may get leveling springs in front "somday"
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235
That's always been my understanding of a dual master cylinder, it just makes sense to change it anyhow and do a good bleeding, although the pedal seems good and firm.
 

Denisefwd93

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4WD
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stock, may get leveling springs in front "somday"
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Well the new booster has to come out, the input rod (pedal rod) clicks in and out it's socket about a 1/2" what a PITA!
 

Denisefwd93

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South East PA
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1994
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Ford
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4.0 V6
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4.0
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Manual
2WD / 4WD
4WD
Total Lift
stock, may get leveling springs in front "somday"
Tire Size
235
Round 3! This booster doesn't clickiy click, bench bleeding the new mc took allot of pumping.

I had another OMG moment too, the rear brake line connector did NOT want to thread into the new MC tapping. Took about a 1/2hr of futzing but finally it went in. Whew!



Didn't bleed the system yet, that's the next project, maybe when the Sun goes down. pedal goes down about halfway and gets firm without the engine running.

Anyone other then me having failed photo uploads from tapatalk????
 
Last edited:

Denisefwd93

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Location
South East PA
Vehicle Year
1994
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Total Lift
stock, may get leveling springs in front "somday"
Tire Size
235
It's all back together! I just did a driveway Run 10 20 30 feet the brakes are definitely improved, even though the pedal is lower it's not very spongy will get the brakes bled tomorrow. It already seems like the proportioning is back like it should be! I can only guess the older master cylinder was not up to the task and the first booster wasn't working right,
 

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