Hey everyone, Im going to be ordering a new rear end from Moser soon (ford 9 inch) and I've been debating on getting their drums or their economy discs with the parking brake. I was wondering if i go to discs do I need to change the proportioning valve to get them to work properly or can I still use the one I have. I don't know a lot about brakes and how to set them up and I've been trying to do my own research but haven't gotten very far.

 

What year is your car

 

Your prop valve controls braking pressure by controlling the volume that gets compressed into that channel. The spring and plunger controls this. Your prop valve should be fine, just need to get the proper spring. This will depend on the calipers and how active you want the rear brakes to be. Changing the spring will require some calculation or pressure measurements after install. Refer to this thread here: Calculating Brake Torque

Maybe saying compressed is the wrong term since the fluid doesn't get compressed, but the volume of fluid being moved into the channel compresses your pads against the rotors. Less volume in the channel, less compression force on the pads. Cylinder diameters in relation between the caliper and MC play a role in determining the pressure. It's all well put together in the thread I linked. Plus more in depth explanation of how the prop valve is controlling the pressure based off the spring.

 

86 trans am

Ok, Right now I'm only going to upgrade the rear brakes because I'm getting the moser rear end and I want to have something that I know will work with them. The fronts I will probably upgrade later on I just dont know what I want to do. The wilwood brakes are really nice but for nearly $800 I think I would get the economy discs and upgrade when I need. Thats good to know about having to change the spring because I know about how the hydraulics work but Ill have to see what works with the setup I want

 

I may just run it in its stock form for now assuming that will be ok and when I upgrade the front to something nicer is when ill change everything I need to be where its supposed to.

 

I think the beauty here is, you can change the spring multiple times. You could have one now for the rears and then change again when you change the fronts if need be. You could put in an adjustable one and just turn the dial as you need too. Then you wouldn't have to do calculations and could just dial it in by testing. Probably get a more "ideal" setting.

Just remember, the rears on the 3rd gens didn't do a lot of the braking. Being light in the rear, you have to protect from the rears locking up before the fronts. If not, in emergency braking the rear could come around on you.

 

Then you probably have the NC code prop valve. I would be interested to know the actual measurements of the piston and spring if you take it apart.