This is in regards to my 95 F-150.

This truck does not have a normal proportioning valve under the master cylinder. I'm not exactly sure how it's taken care of but I'd like to change it if possible.

My truck is obviously lifted and the trouble I have now is that the rear brakes lock up too soon because of the weight transfer change when lifted.

I found an adjustable proportioning valve from Summit for about $40, that taps into the brake lines under the master cylinder like a normal old school one. I wanted to get that so I could dial in my brakes and have it adjusted properly so I don't lock up the rears too soon. I want to add brake pressure to the front and subtract it from the back.

Can anyone educate me on how the proportioning bias is setup on these trucks? Can I just put that valve in the brake lines and sort of over-ride the factory proportioning system?

Thanks for any info.

 

Your probably going to have to eliminate the RABS,if your talking about changing the whole prop. valve.Another option is a residual valve,which would restrict/hold the pressure on 1 or the other (front/rear).They're about $15-20 each from summit,jegs,etc.Have you thought about backing the rear adjustment down a bit.

 

I assume your refering to the Height Sensing Brake Proportioning valve. If so check to make sure that the linkage is the correct height on your rear axle, I know when I lifted my first truck up 4in it always locked up.

Also, check and make sure your front pads are good. Your pads might be shot and you are pressing harder which is causing your tires to lock up. Remember that the front is supposed to do around 80% of the stopping.

 

My brake system is properly functioning, it's just that the proportioning bias is incorrect now that the truck is lifted and I'd like to change it.

Why would I have to eliminate the RABS? I am not trying to change out the stock proportioning system. I'll try to explain more...

What do you mean by backing the rear adjustment down a bit? You can't adjust the rear drums as they are self adjusting - an adjustment in the star wheel would be changed when you hit the brakes in reverse.

Height sensing brake proportioning valve? Elaborate on what that is if you could. What linkage on the rear axle are you refering to?

Is a residual valve what I am refering to when I was talking about the adjustable proportioning valve from summit? Or is it different?

The proportioning valve I am talking about buying can be seen on jegs.com as part number 950-260-8419

http://www.jegs.com/webapp/wcs/store...0165&langId=-1

I'm just simply trying to change the proportioning bias front/rear....decrease braking in the rear and increase braking in front by changing the fluid pressures. I don't know how I could do it and am trying to learn how, since this truck doesn't have your normal old school proportioning valve in the brake lines under the master cylinder.

 

The brake height proprtioning valve senses when your trucks back end goes up from braking. Front brakes do 80% of braking so when you hit the brakes usually your front dips down. This valve is connected on most trucks (including these fords) to the rear axle and then usually the truck bed. It adjusts brake pressure to the rear brakes by linkage connected to the bed and the axle. When the bed goes up on the brakes from the font going down it puts more back brakes on, if you lifted the bed off of the axle from a suspension or body lift then it might be giving your back brakes more pressure when you are stopping. If you lifted it 6 inches, I would put 6 inches of extra linkage like I did in my chevy truck. I wasn't sure if our Fords had this valve because I haven't been under mine in a while but my Chilton's Truck manual from 1991-1995 says our trucks do so I hope this helps.

 

I have never seen any kind of linkage from my axle to the bed of the truck. The only things attached to my axle are the leaf springs, brake line, e-brake cables, VSS signal wire, my locker electrical wire, shocks, and my traction bars. I don't know if this exists. I've never heard of that and don't feasibly understand how that system would be in place on this truck and I don't know it. Thats just plain weird to me I don't think I have that.


The proportion of the braking doesn't feel like it's changed. It's just that since it's lifted, more weight is transfered to the front of the truck under heavy braking. The rear tires have less traction with the decrease in weight, and lock up easier. The front brakes have more traction and are harder to lock up. It's almost like I have two independent brakes because they're not matched up and it's unsafe.

 

I don't know if my 1994 has it either, but like I said its in the Chilton's manual and its on my 84 Chevy thats why I am familiar with the system.Where the number 2 is, the arm above that is the linkage mounted to the bed, and where the 3 is is where it is hooked into the valve. Thats how this system works when the valve is connected to something such as the frame or rear axle as Chilton says it is, I will look under my 94 tomorrow in the day light and try to help you out.

 

I don't think our year F150's ever used the height (load, ultimately) based proportioning valve in the rear. I don't see any reason why an adjustable proportioning valve in the rear line wouldn't work, when placed between the master cylinder and the ABS valve. You would limit the line pressure to the rear brakes this way so they wouldn't lock up. I wonder why the abs is letting them lock anyway.

 

Cause these ABS systems are not all that great...I'd rather not even have it if I had to choose but it's a stupid design.

I can say with 98% confidence that I do not have that system in my truck.

So for sake of simplicity, lets forget about that system.

How is the proportioning between the rear and front brakes handled on these trucks? Is it internal of the master cylinder?

I don't want to just limit line pressure to the rear - I want to limit line pressure to the rear AND increase line pressure to the front.

 

I checked under my truck today, and it doesn't have that valve so I don't know what Chitlton's is smoking but thats a different situation. I don't see any reason why it wouldn't work either as EPNC stated. I am not 100% sure but I belive that the master cylinder applies the same amount of pressure to all brakes. The only way that I know how to increase front brake pressure would be to use Pascal's law which is P=F/A. So for more pressure, you would have the same amount of force from the master clyinder, but you would have to increase the area. The only way to increase area is buy some different calipers that either used a bigger caliper piston or a dual piston set up to get more area/pressure to your front. Hope this helps.

 

The increase in front line pressure would come from increased pressure on the pedal with your foot. You can eliminate the abs entirely if you want to, and just run an adjustable proportioning valve in its place. You limit the line pressure to the rear so that with more pedal you get more pressure in the front. There's really no way to amplify one pressure without a master cylinder or caliper piston size change as 02Ford said.

 

OK, so I should just get that adj prop. valve like I linked and tap it into the lines and adjust away as planned....

 

Yep, that one at Jeg's looks like it would do the job

 

Ya that one looks like a nice piece, I am sure it will work. Let us know how it turns out because I might be lifting my 94 soon!

 

I'm going to get it within a few months. I've still got some other things to take care of first. But I'll let ya know how it goes when it happens.