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Brake bias/proportioning


trhull

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Hey guys,

So I just got done installing my newest upgrade, a 2002 explorer 8.8 rear axle with trac-loc and disc brakes.

My question to any of you is if you know where the brake proportioning/bias valve is located. Is it taken care of within the master cylinder, or is there a separate valve after the master cylnder, possibly in the RABS pump or something like that? I as this because I now have the rear discs and would like a little bit better control over what they are doing (personally I would like to add a little more rear brake). I was thinking about installing a manually adjustable proportioning valve or setting up a load sensitive proportioning valve.

Any input would be much appreciated, as of now I am fairly convinced proportioning is going on in the master cylinder.

Thanks guys.
 


AllanD

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The problem is that any kind of valve, factory or aftermarket,
that you might add in, can only REDUCE the line pressure to the brakes.

MOST of what proportioning there is, is accomplished internally inside
the master cylinder, by a combination of choice in bore diameter and
by the springs inside the master cylinder.

a softer spring "up front" will cause the rear brakes to apply earlier
and with more pressure, but at the expense of delaying application
of the front brakes.

a softer "mid spring" will increase front line pressure earlier in the piston stroke
at the expense of less rear line pressure.

Compression of the "mid spring" applies the front brakes but also applies pressure
to the piston that drives the rear brakes, so...

You could also use a smaller bore M/C, the master cylinder in your 1994 almost certainly has a 1" bore diameter switching to the 15/16" bore of an earlier M/C will increase line pressure but slightly increase pedal stroke....

As I'm sure you can begin to see it's a rubik's cube of adjustments and ANY adjustment changes several parameters at once....

AD
 

trhull

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Ok thanks AD. As it is there isn't really a problem with the way the truck brakes so I'll just leave it and save myself a headache or accident.


Thanks again.
 

Natedog

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TRrhull,

As Alland said, it's all a trade off and can get quite involved.

What is your truck that you put the 8,8 in? Maybe able to swap the corresponding front brakes/axle and then the appropriate master cylinder. I've done alot of brake/axle swapping and it is difficult to get the front/rear brakes exactly as you'd like it, however you can usually get it pretty close.
 

CheapThrillB2

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i swapped my disc into my 93 sport with 4 wheel ABS, and when i brake hard the rear disc's lock-up before the fronts, same goes with my 87 B2. I put discs on that and same result, but that one does not have 4 wheel abs only rabs.
 

compleckz

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On explorerforum they talk about adjusting "the pushrod for the master cylinder. In order to maintain a good pedal feel after the conversion, the rod must be adjusted to push further into the master cylinder":


i didnt notice much of a braking increase after my explorer rear-end swap, should i try this, or will it cause premature master cylinder wear, or apply too much front pressure?
 

AllanD

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If your rears lock first an aftermarked adjustable proportioning valve
installed in the line to your rear brakes will by reducing line pressure
correct the rear lock-up problem.

the rears locking up first is BAD.

I'd get one of the ones with a knob and mount it under the hood
(on a homemade bracket) next to the master cylinder.

My first reason for saying to mount it under the hood is that it'll
basically eliminate the temptation to play with it while driving.

one of the lever actuated valves on the market (the Tilton for example)
is an unnecissary complication, and is limited by the distinct "steps"
of the seven detented positions.

AD
 

AKBroncoII

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Try swapping to a disk/disk master cylinder from a later model explorer or ranger. Should take care of your problem. Adjusting the rod will do nothing to help the problem you are having.
 

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