I'm a little confused about this one: prop valve adjustment

[bull]

Today was pretty nice so I decided to take the wife out for a ride and have her help me adjust the Wilwood proportioning valve. I found the center point and drew a line on it so I could keep track of the turns. Full adjustment is 6 turns so I put it in the middle and started there. The rear end locked up first, and so it went every time until the valve was turned all the way out. With it adjusted as far as it will go the rears still lock up first. It's better, and pretty close to even now, but it still isn't right. Any idea what's going on?

[John_Kunkel]

What size rear brakes and what diameter is the wheel cylinder?

[bull]

10" drums, 15/16" diameter wheel cylinders.

One factor I can think of that may effect this is manual brakes with discs in front and drums in the rear, which we talked about in that other thread I started. I think most people agreed that drums may do better than discs initially because thay have the advantage of better leverage. But then I see no real advantage to brakes that lock up easily in a panic stop situation, which defeats the purpose of the immediacy. Still, all that said, I would think there should be enough adjustment in the prop valve to accomodate this situation.

[b5blue]

You should be closing the valve not opening, you want to force fluid to the larger bores. 

[bull]

You should be closing the valve not opening, you want to force fluid to the larger bores.  

I went both ways and it got worse when I closed it. And before you ask, yes, I've got the out/in ports going the way they're supposed to go.

[b5blue]

The answer is here some place! http://www.moparaction.com/Tech/archive/disc-main.html

[b5blue]

Hummmm......with it closed all the way the rears would not work......?  Air in the front lines? 

[bull]

Hummmm......with it closed all the way the rears would not work......?  Air in the front lines? 

With it closed (righty-tighty all the way) the rears worked too good. They locked up immediately. Well, actually I didn't even turn the knob all the way closed because the rears were locking up so bad with 1-2 turns left I didn't see the point.

[b5blue]

  I would test, in/out all the way (Full stop to stop.) to see if one position blocks the rear brakes off completely.  Your dealing with a very small differential of fluid volume, be certain the fronts are fully bled and set snug to the front rotors so the pistons are fully extended. 

[John_Kunkel]

If the rear drums lockup first with full proportioning, the only way to cure it is to go to a smaller diameter wheel cylinder; problem is, this also reduces the braking force during normal stops...might not be desirable with manual brakes.  

I wonder if different prop valves might have a different percentage of proportioning. 

[bull]

I wonder if different prop valves might have a different percentage of proportioning.  

My thoughts too. I'll check some other prop valves and see what's offered. Most I've seen are all the same with a max line pressure decrease of 57%. I did see one that was a 2000 psi unit where most are 1000, but it didn't specify the max line pressure decrease %.

 I would test, in/out all the way (Full stop to stop.) to see if one position blocks the rear brakes off completely.   Your dealing with a very small differential of fluid volume, be certain the fronts are fully bled and set snug to the front rotors so the pistons are fully extended.  

Yeah, I'll check them out.

[b5blue]

With a swap in my future I'm interested in what you find. I "went out of my way" to find the old school large brass Mopar adjuster for my swap. 

[bull]

Now I'm wondering about the push rod.

[Sublime/Sixpack]

With it closed (righty-tighty all the way) the rears worked too good. They locked up immediately. Well, actually I didn't even turn the knob all the way closed because the rears were locking up so bad with 1-2 turns left I didn't see the point.
[/quote]

FWIW
On the proportioning valve (ssbc kit) that I just installed on my Coronet, when you turn the valve to the right (clockwise) you are actually opening the valve which allows more pressure to the rear brakes.

[bull]

You would think it would be like any other valve, like a faucet really. Opening it up would increase the flow to the 'out' port.

It's supposed to be nice on my days off next week so I'll head out and try it again.

[Dino]

Do you have a residual pressure valve in the system?

[bull]

Do you have a residual pressure valve in the system?

Yes, inline to the back like it's supposed to be. I'm wondering if it or the prop valve might be getting stuck. I bought them way back when I first bought the car 9+ years ago when I was just farting around trying to get it on the road temporarily before deciding to tear it down. When I get some time I'm going to go over the front brakes again and make sure they're working right and then maybe order a new prop valve and residual valve. Everything bled out correctly so I'm pretty sure that part of the system is fine.

[b5blue]

What about the doo-dad (By the proportion valve.) that needs to be centered. It directs pressure away from and open (failed/unbalanced) front or rear and turns on a brake warning light. (In some cars.) 
http://www.ebay.com/itm/Mopar-Chrysler-Brake-Proportioning-Valve-P-N-4131254-/281067960473
See the pin on the end? You push/pull to center.

[bull]

What about the doo-dad (By the proportion valve.) that needs to be centered. It directs pressure away from and open (failed/unbalanced) front or rear and turns on a brake warning light. (In some cars.) 
http://www.ebay.com/itm/Mopar-Chrysler-Brake-Proportioning-Valve-P-N-4131254-/281067960473
See the pin on the end? You push/pull to center.

Ah, you may be onto something. Never messed with it other than to clean it up and reinstall. Something to try anyway.

[bull]

What about the doo-dad (By the proportion valve.) that needs to be centered. It directs pressure away from and open (failed/unbalanced) front or rear and turns on a brake warning light. (In some cars.) 
http://www.ebay.com/itm/Mopar-Chrysler-Brake-Proportioning-Valve-P-N-4131254-/281067960473
See the pin on the end? You push/pull to center.

My propertioning valve does not have that pin. There's just a plug in the bottom and lines to every other port.

[Dino]

Bull do you have a link to the prop valve you have?

[bull]

Bull do you have a link to the prop valve you have?

I'll try to find it when I get home. It's just a common Wilwood proportioning valve.

Just to clarify some definitions here, as I understand it some factory distribution valves include proportioning valves and that together in one component is called a combination valve. Mine is apparently not a combination valve but rather a simple distribution valve, which shouldn't be a factor in all this.

[Dino]

Bull do you have a link to the prop valve you have?

I'll try to find it when I get home. It's just a common Wilwood proportioning valve.

Just to clarify some definitions here, as I understand it some factory distribution valves include proportioning valves and that together in one component is called a combination valve. Mine is apparently not a combination valve but rather a simple distribution valve, which shouldn't be a factor in all this.

Ok, then I know which one you have.  I have the same one.  It was part of the Wilwood kit that came with the car.

I was advised to not use it because of problems you describe so I ended up buying a combo valve instead.  It seems that in order for this to work, you need a metering or hold off valve as well.  That's why I bought the combo valve as I didn't have any separate metering valve either.

Good reading here:
http://www.mbmbrakeboosters.com/index.php?option=com_content&view=article&id=6:proportioni..

[bull]

Ok, that must have been my mistake. I wrongly assumed the Wilwood proprtioning valve would cover the metering too.