Proportioning Valve Location?

[racenitro]

Need to know which circuit the proportioning valve should be located in.

I have 4 corner disc brakes. Dual master cylinder, 2psi residuals, brake light switch between master cylinder and residual valve. Front disc's are 1970 VW fastback and the rears are 1979 Lincoln Mark V.

The original system had the proportioning valve located on the front disc brake circuit, no residuals, single 1954 chevy master cylinder and 1957 rear chevy drum brakes.

Don't believe this was set up even close to right.

 

[Francis Blake]

The proportioning valve should be in the back circuit so you can adjust the back brakes, you want the front brakes do do more than half of the work. If you want anything in the front it would be a line lock so you can do big burnouts (I took mine out)some guys like to do this.

 

[ellis8500]

My front brakes have 2-3/8 dia pistons; rears are 1-7/8 dia. This results in 62% of braking force on fronts and 32% on rears. So far can not tell that any proportioning valve is needed. Rear wheels do not lock up during heavy braking.

 

[bobs66440]

It goes to the rear circuit.

 

[fordsbyjay]

The proportioning valve goes in the rear circuit. In a typical vehicle your front brakes do approx. 70% of the braking. Weight transfers forward when braking taking weight off the rear of the car. This causes the rear brakes to lock up hence the reason it goes in the rear circuit. A proportioning valve simply blocks off flow to the rear calipers or wheel cylinders.

Now, the reason I say "typical vehicle" is because when you start running tiny tires in the front and huge tires in the rear theory can go out the window.

 

[bigblk1177]

The proportioning valve goes in the rear circuit. In a typical vehicle your front brakes do approx. 70% of the braking. Weight transfers forward when braking taking weight off the rear of the car. This causes the rear brakes to lock up hence the reason it goes in the rear circuit. A proportioning valve simply blocks off flow to the rear calipers or wheel cylinders.

Now, the reason I say "typical vehicle" is because when you start running tiny tires in the front and huge tires in the rear theory can go out the window.

So are theories like opinions which are like !! Well you know what opinions are like!!

 

[Hotrod46]

Now, the reason I say "typical vehicle" is because when you start running tiny tires in the front and huge tires in the rear theory can go out the window.

I found out that my T has more weight on the rear than the front(60%). Big drum brakes in the front and little drum brakes in the rear, too.

The rear mounted proportioning valve did pretty much nothing. Even closed all the way, my rear brakes wouldn't do anything productive. Fronts locked up first. Finally solved the problem with a dual master cylinder/balance bar setup. No proportioning valve at all.

The old rule that says 75% of the stopping power is on the front wheels just doesn't seem to apply to my car and maybe all T's. I'm thinking that most are at least 50/50 front/rear and with their fairly low center of gravity, they just don't transfer that much weight to the front when stopping. When I finally got enough pressure to the rear brakes, the car stopped far better than the old 75% rule would suggest.

Mike

 

[bobs66440]

I found out that my T has more weight on the rear than the front(60%). Big drum brakes in the front and little drum brakes in the rear, too.

The rear mounted proportioning valve did pretty much nothing. Even closed all the way, my rear brakes wouldn't do anything productive. Fronts locked up first.

If you had your valve closed all the way, your rear brakes won't do anything because you are cutting pressure to them. And your front brakes should lock up first. Generally, it's more stable that way. If your rears lock up before the fronts, the car may swap ends real fast and you will lose all control. You want the fronts to lock up just before the rears. I test it in the grass so I'm not abusing the car on the road. That way it's easy to see at low speeds.

Of course, on a T with huge tires on the rear and little skinnies on the front, all convention may go out the window... But I still think I would want the fronts to lock first...

 

[fordsbyjay]

So are theories like opinions which are like !! Well you know what opinions are like!!

Well theory is based on a traditional car that is typically more nose heavy and has the same size tires all the way around. When you have skinny little tires on the front which are typically short have a very small contact patch. Then on the rear most people have wider/taller tires which are a lot heavier and have a lot more contact patch. IMO inertia and friction is why the rear tires don't typically lock up on our cars and the fronts do lock up for the same reason. I can't even do a brake stand in my car it just pushes the front tires because they have such little grip to the road.

I should have mentioned I do no have a proportioning valve on my car either.

 

[Hotrod46]

Actually, I didn't explain that quite right. You increase pressure by turning the prop valve in. Mine was turned in all the way, not closed.

My problem was a mismatch of braking force front to rear. The dinky little 7.5" S10 drums couldn't match the power of the 12" 39 Lincoln Bendix units I have up front. Even after swapping to smaller wheel cylinders up front and custom built larger cylinders in the rear.

The dual master setup allowed me to run a smaller bore MC on the rear brakes and get the line pressure high enough to make the rears work correctly. I spent quite a while adjusting the brake bias to get the fronts to lock just before the rears, but the stopping power increase was pretty dramatic.

 

[bobs66440]

Ahh, ok. Makes sense now. Good work! Too many guys just slap a car together and drive it without getting it adjusted properly...

 

[EX JUNK]

Ahh, ok. Makes sense now. Good work! Too many guys just slap a car together and drive it without getting it adjusted properly...

The last sentence is VERY true in a lot of builds, I'm sorry to say.

Jim

 

[racenitro]

Bobs...that is why I asked the question. I was aware of the 70% front figure but since this had the valve in the front originally, I was wondering if somebody knew something I did not know. I have built/restored way too many cars so it had me wondering.

There will be no half way on this bucket. If it is not right, it is not going on the bucket. This is why it is getting a ground up rebuild/restoration. Every bolt and item is being inspected and if necessary updated or improved right down to the last cotter pin and grease zerk.

 

[bobs66440]

Bobs...that is why I asked the question. I was aware of the 70% front figure but since this had the valve in the front originally, I was wondering if somebody knew something I did not know. I have built/restored way too many cars so it had me wondering.

There will be no half way on this bucket. If it is not right, it is not going on the bucket. This is why it is getting a ground up rebuild/restoration. Every bolt and item is being inspected and if necessary updated or improved right down to the last cotter pin and grease zerk.

Excellent. That's the way it should be done. That setup would have had me wondering too. I have never seen or heard of a valve going to the front...