Rear adjustable Proportion valve on 280zx brake system

[superduner]

Hey yall,i Looked all over for the answer to my question but no luck sourcing out directions. I recently swapped the ENTIRE 1981 280zxT brake line system along with the 280zx 15/16 MC on to my 70z. Everything is stock from the donor car. I recently swapped on the S12W 4 piston calipers and 300zx vented rotors as well, regardless of many saying its not technically an "upgrade" I've ran into other good reviews about the set up so I'm giving it a go. I'm in the midst of swapping the rear 280zx calipers and disk conversion to the 70z and read up on the recommendation for the adjustable proportional valve. Ive seen the info for swapping the adjustable prop valve for the 240z brake system. But I noticed the components and distribution is set up differently for the 280zx. Where's the stock proportion valve I need to remove/swap for the wildwood/aftermarket adjustable one? And is the block that goes on the rear passenger side block just a distribution block or does that need to be removed as well?

[Miles]

As discussed before, your brake setup (Toyota front - 280ZX rear)  will be biased toward the front.

 

A variable proportioning valve only reduces pressure. Therefore,  you do not need a variable proportioning valve.

 

Why would you want to reduce pressure to the rear on a front biased brake system?

 

 

For your other questions, do like everyone else (as recommended to you) and read the factory service manuals (FSM) for the 240Z and the 1981 280zxT that you got the brake parts from. 

 

 

Go here: http://forums.hybridz.org/topic/109702-hybridz-is-not-automotive-101/

Edited February 22, 2017 by Miles

[Chickenman]

Actually, you can get a significant improvement in rear braking effect by installing an adjustable proportioning valve hooked up to the rear brakes. The factory proportioning valve has a set point. It is usually set very conservative so that you always have considerable front brake bias. Lawyers consider that safe for Grandma and Grandpa.....

 

Standard valves may have a minimum set point of 40% to 50% reduction in pressure. FWD cars even higher.  However, an adjustable proportioning valve ( Hydraulic )  has a much wider range of adjustment. You can adjust them so that it always allows 100% of line pressure to the rear. So no pressure reduction at all.   Net result, more rear braking. 

 

However, you do have to remove the factory rear proportioning valve and replace it with a straight through coupler. You should never run two proportioning valves on the same circuit.

 

I've done this on many Autocross and Hillclimb cars and have  found that replacing the factory rear proportioning valve with an adjustable one ( WilWood or similar ) has allowed me to crank in more than enough rear brake bias to maximize rear braking. To the point of getting rear brake lock before front on stock systems. I like a lot or rear brake on my Autocross cars. Helps rotate the car on turn in and eliminates understeer. 

 

Adjustable proportioning valves do have limits. Exception being where larger brakes are installed on the front and the rear brakes are left stock. In that situation even 100% line pressure to the rear brakes ( no pressure reduction ) may be enough.

[Miles]

Actually, you can get a significant improvement in rear braking effect by installing an adjustable proportioning valve hooked up to the rear brakes. The factory proportioning valve has a set point. It is usually set very conservative so that you always have considerable front brake bias. Lawyers consider that safe for Grandma and Grandpa.....

 

Standard valves may have a minimum set point of 40% to 50% reduction in pressure. FWD cars even higher.  However, an adjustable proportioning valve ( Hydraulic )  has a much wider range of adjustment. You can adjust them so that it always allows 100% of line pressure to the rear. So no pressure reduction at all.   Net result, more rear braking. 

 

However, you do have to remove the factory rear proportioning valve and replace it with a straight through coupler. You should never run two proportioning valves on the same circuit.

 

I've done this on many Autocross and Hillclimb cars and have  found that replacing the factory rear proportioning valve with an adjustable one ( WilWood or similar ) has allowed me to crank in more than enough rear brake bias to maximize rear braking. To the point of getting rear brake lock before front on stock systems. I like a lot or rear brake on my Autocross cars. Helps rotate the car on turn in and eliminates understeer. 

 

Adjustable proportioning valves do have limits. Exception being where larger brakes are installed on the front and the rear brakes are left stock. In that situation even 100% line pressure to the rear brakes ( no pressure reduction ) may be enough.

 

You can also just gut the factory proportioning valve (PV) on the early 240Z that is located in  back of the storage compartments. Once gutted  the stock 240Z PV body just becomes a connector block and flows 100%.  However, many people have done this and then later said that it did not improve rear braking bias at all.  There have many threads on this subject discussing the pros and cons of variable PV vs stock vs gutting the stock PV. On the later Z cars the PV valve was moved to the firewall and it is of a different design than the early PVs. Search and/or look at the FSM for details.

 

If you want more rear bias start with the basics such as larger diameter rotors etc.

 

 

Edited February 23, 2017 by Miles

[superduner]

You can also just gut the factory proportioning valve (PV) on the early 240Z that is located in back of the storage compartments. Once gutted the stock 240Z PV body just becomes a connector block and flows 100%. However, many people have done this and then later said that it did not improve rear braking bias at all. There have many threads on this subject discussing the pros and cons of variable PV vs stock vs gutting the stock PV. On the later Z cars the PV valve was moved to the firewall and it is of a different design than the early PVs. Search and/or look at the FSM for details.

 

If you want more rear balance start with the basics such as larger diameter rotors etc.

 

 

STOCK PV AND T BLOCK.jpg

I want a an adjustable proportion valve for the rear for exactly that reason, so I can OPEN the flow more than is offered by the restrictive factory one and allowing me to max out the rear force and not have as bad a brake bias (even if it's still not that good maxed out). At least it would be an improvement from running oem prop valve but Yeah man I switched over everything from the 81 zx donor and noticed the routing and distribution is different on the set up. I'll definitely check out the fsm. As I have to find out if the rear block in the jack is a distribution block and not a prop valve and can just leave it as is. In comparison to the 240z one.

Edited February 23, 2017 by superduner

[Chickenman]

You can always add more rear bite with a more aggressive rear  brake pad compound as well. Or shoes if you have drums brakes. ( Carbon Metallic shoes ) 

[superduner]

Seems like the 280zx brake line system is definitely a beast on its own when it comes to adding an adjustable prop valve. The proportion valve for the rear is located in the passenger side fender. Problem lies that that same part feeds the passenger side wheel? So weird.... I'm pretty sure the wheel isn't getting mixed in with the fluid going to the rear. But that's definitely an inconvenience gonna have to figure something out

[Miles]

You don't seem to understand what you are doing.

 

In the interest of public safety I recommend that you study how your brake system works before making any more changes.

 

Actually, all you had to do was install the Toyota and 280ZX brakes and a 1 inch Wilwood brake master cylinder and you would have been done. Plus all of the information needed to do the Toyota - 280ZX brake swap is documented in the brake and FAQ forums.

[superduner]

You don't seem to understand what you are doing.

 

In the interest of public safety I recommend that you study how your brake system works before making any more changes.

 

Actually, all you had to do was install the Toyota and 280ZX brakes and a 1 inch Wilwood brake master cylinder and you would have been done. Plus all of the information needed to do the Toyota - 280ZX brake swap is documented in the brake and FAQ forums.

I'll look into that miles thanks