Gutting Brake Bias

**cannonball** · 18-02-2009, 11:25 PM

What is confusing the issue is that you are tackling 2 problems at once.

1) Going drum to disk on the rear
2) Upgrading all 4 brakes (RX7 front and RT142 in the rear)

I know that if you upgrade the ADM drum brakes to JDM (or similar size) disk brakes on the rear, then you will need to change the proportioning system.

But as you are going for an RX7/RT142 setup, the differential between front and rear bias is an unknown (unless someone has done this before and calculated the requirements), it might require the same valving as the stock ADM valve, or it more likely will need something completely different.

This is what I had at one stage.....note the stock valve is gutted.

The front fluid goes into the block, and out to left and right fronts, the rear fluid goes into the proportioning valve, then through the gutted stock valve, and off under the car to the diff. You dont have to run it through the old block, its just an empty shell, I just did this so it would be very easy to "downgrade" the car back to the old S type diff if (and when) I broke an axle. The only new brake lines I needed were from the master to the Willwood, and from the Willwood to the old P valve block. About 50-60 cm of brake line in total.

Also, this is a diagram I did of the stock setup a few years ago...pretty much the same as yours.....

**cannonball** · 18-02-2009, 11:33 PM

Originally Posted by newbien

in the top pic i have put up, is that all that needs to be removed from the bias block?

Leave out everything, the spring, the valve, everything, just screw the plug back in.

**newbien** · 18-02-2009, 11:36 PM

ok...so the front section is completely sealed off from the rear...no worries...

what i will do is whack the diff in without anything touched, then gut my spare proportion block and compare the results...if im not happy ill grab the wilwood adjuster...

but just so im totally clear, is this all i need to take out of the stock proportion block for it to be "gutted"? assuming that i just screw the bolt back in

cheers to everyone who has given input, much appreciated

**mikie** · 19-02-2009, 10:53 AM

is it safe to run the proportioning valve before the factory bloc or does it have to be after? im still a little unclear.

Cheers Mike

**Tom86** · 19-02-2009, 04:39 PM

What is the braking performance like now? are you getting front or rear bias?

The reason I ask is I've done similar thing before I installed big brakes up front and was getting heavy front bias so I figured that I need more pressure to the rear to improve rear braking. So I gutted my ADM proportional valve. The results is no change gutting ADM valve does nothing for me.

**cannonball** · 19-02-2009, 10:34 PM

Originally Posted by mikie

is it safe to run the proportioning valve before the factory bloc or does it have to be after? im still a little unclear.

Cheers Mike

It doesnt matter. If the factory block is gutted, its just an empty shell, does nothing except give you somewhere to bolt your lines into.

**cannonball** · 19-02-2009, 10:36 PM

Originally Posted by newbien

but just so im totally clear, is this all i need to take out of the stock proportion block for it to be "gutted"? assuming that i just screw the bolt back in

any parts inside should be removed, so there is nothing left.

**cannonball** · 19-02-2009, 10:52 PM

Originally Posted by Tom86

What is the braking performance like now? are you getting front or rear bias?

Is this directed towards me?
When I started, I had way too much front bias, the fronts were doing all the work, and the disk rears were not even having enough pressure pumped into them to take the freeplay up so the handbrake would not work. This turned out to be because the stock valve had 20 yrs of crud plugging it up, so very little pressure was getting through.

I then gutted my valve, and took the car for a short brisk drive, and afterwards the rears were extremely hot, but the fronts were cool to the touch, also the rears would lock very easily.

Next step was to install the adjustable, and on a dry, clean, level stretch of empty, quiet road, basically jump on the brakes again and again, adjusting the bias one way, the the other, then find the "happy medium" that gives you the braking you like. You want the rear brakes to help as much as possible, without locking. Good bias can decrease stopping distance by about 25%, but if the rears lock, they can become more harmfull than helpfull.

Originally Posted by Tom86

The reason I ask is I've done similar thing before I installed big brakes up front and was getting heavy front bias so I figured that I need more pressure to the rear to improve rear braking. So I gutted my ADM proportional valve. The results is no change gutting ADM valve does nothing for me.

Mabey your ADM valve was not operating correctly to begin with? Dunno.....
Remember though, brake performance also depends a lot on suspension setup, wheel/tyre choice, alignment etc. A poorly set up car could lock up the fronts every time, regardless of what the bias is.

**bigmat** · 19-02-2009, 11:16 PM

your rears should do between 10 to 15 % of your braking and in essence should come on just before the fronts do to change the wait distribution so when the fronts come on they bite down harder.

cheers mat

just like a good woman. get her from behind .........you know the rest