Jump to content

Brake proportioning valve


Recommended Posts

I have an '89 Mustang that's been converted to disc rear with a Baer kit. Part of the process was the partial removal of the proportioning valve guts when installing an adjustable bias valve. I'm not sure if the remains of the stock proportioning valve is doing anything more than acting as a 'T' for the front brakes at this point.


I'm wondering if there's anything that would prevent me from replacing the proportioning valve with a simple 'T' since I have an adjustable bias valve?


For ref, there's two ports out of the master cylinder both going to the proportioning valve. A single line goes from the valve to the rear brakes (Y's to left/right at back axle), and each front brake comes directly off the proportioning valve. The plan would be to run one port from the master cylinder through the adjustable proportioning valve to the rear brakes and to use a 'T' fitting to split the other port off the master cylinder directly to both front brakes.


Anyone have any thoughts on this?

Link to comment
Share on other sites

  • 3 years later...

I am hoping someone else will chime in on this as this thread has gone cold.


I have heard conflicting answers on this subject.


I am searching for info regarding how to deal with the routing of lines for an A1 VW GTi that my brother is prepping for the track.


There are 4 ports on the master cyl, one for each corner. The rears go to a prop valve that adjusts with axle beam movement.


We are curious if we can plug one of the ports feeding the rear and run one line to a bias valve at the drivers seat and then to a "T" block to then go to each rear disc brake.


What is the best option for a VW with this set up?

What is the best option for the Mustang above?

Link to comment
Share on other sites

My SHO has the same rear prop setup (as do many pickups in single channel form), which allows variable rear bias based on load in the back/forward weight transfer. When the rear rises on the spings, the valves reduce the rear pressure. You can replace the rear external spring prop valves with a manually adjustable valve, BUT... The reason for 2 separate lines and prop valves is because of the 4 wheel ABS system. Someone told me the system on my SHO is a split diagonal setup, but I'm not sure I believe it. If so, that would also require maintaining separate lines/prop valves. Teeing them together in that situation would effectively turn the hydraulic system into a single circuit. Lose pressure anywhere, and you've lost it everywhere.


No idea what the specifics are for the VW, sorry.


I notice the abs on my '96 Mustang is a 3 circuit system, since there is only a single line running to the rear brakes, so a single manual prop valve in that line would work fine.


The distribution block below the MC on the Fords used to provide both rear bias and a shuttle valve that completely blocks the MC connection to one side if there's a significant pressure difference between the front and rear circuits. Many people have said they experienced no such action on modern Fords/Mustangs (pressure bleeding only one side would cause the shuttle to block the other side). The brake light used to be connected to this valve on the older blocks as well. Now it's just a low fluid level warning connected to a magnetic switch in the MC reservoir. I believe a Ford braking engineer stated in a thread on another forum that the shuttle valve no longer blocks off the failed circuit. For a track only Mustang, the consensus seems to be that the block is not needed (just use a tee) if you're running a separate manual prop valve.


For a street car, messing with the braking system in a highly visible way like that could *potentially* put you at a liability risk in the event of a serious accident due to brake failure. So the advice I've seen given for a street driven car is to use the stock block (even if it is just acting as a tee) with the FRP plug to defeat the internal bias valve.


If I remember correctly, the Baer kit doesn't include the plug, does it? I had already done the mod to my prop block since I was running the SSBC T-bird rear brakes before stepping up to the Baers.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...