Adjustable Proportioning valve question - Chevelle Tech
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post #1 of 13 (permalink) Old Aug 27th, 18, 12:07 PM Thread Starter
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Adjustable Proportioning valve question

Hey there,

I have a mostly stock brake system on my 1972 Chevelle. Power disc front, drum wear. Stops well but I had to make a pretty hard brake last night and the rear brakes locked up quickly. I have pretty tall tires in the rear, the car is raked out a bit, lots of aftermarket suspension etc.

My master cylinder is leaking a bit on to the booster anyways, so I was looking at upgrading my MC and installing an adjustable proportioning valve at the same time. My question is: do I need to remove the combination valve as well, or is it OK to keep the combination valve in place and have an adjustable proportioning valve close to the MC?

Looking at this wilwood unit:

https://www.summitracing.com/int/par...0-bk/overview/

72 Chevelle Malibu
Muncie M20
SBC 406
KB Pistons
PW Aluminum heads
RPM Air Gap Intake
MSD 6AL2
Holley Sniper EFI
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Stainless Long Tubes to 2.5 Exhaust
UMI Suspension Stage 2
CPP Steering setup
10 bolt rear - 3.55 with Eaton Posi
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post #2 of 13 (permalink) Old Aug 28th, 18, 8:09 AM
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George
 
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Re: Adjustable Proportioning valve question

I'm using that same willwood mc that your looking at. I did get remove the proportioning valve and the round accumulator valve. Brakes are working fine. I also added a line-lock while I had it apart.

My biggest worry is when I pass on my wife will sell all my stuff for what I told her I paid for them.
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post #3 of 13 (permalink) Old Aug 28th, 18, 8:31 AM
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rick
 
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Re: Adjustable Proportioning valve question

I'm using a wilwood adj P valve & 68 corvette MC, stock type large booster with 4 whl disc nothing else in the lines, the valve adjusts bias between front & rear, I've just recently got my car drivable and having a little problem after 5-6 miles of driving with a caliper dragging but I think it's just a bad caliper, there's also a sticky on this subject if you do a search lots of good info there, good luck


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post #4 of 13 (permalink) Old Sep 8th, 18, 9:50 PM Thread Starter
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Re: Adjustable Proportioning valve question

Thank you for the feedback. I just ordered a wilwood adjustable prop. valve, along with a Wilwood M/C to replace my leaky stock style unit.

I plan on removing the stock combo valve, and replacing all of my hard lines while I'm in there since I will be moving the prop valve from the frame rail, and using the adjustable unit close to the M/C so I can dial it in. Probably about time, since the stock valve rubs on my headers a bit.

Question: the stock rear hard line on my chevelle is 1/4", whereas the Wilwood prop valve has 3/8 outs for both front and rear brakes.

Does anyone know of a suitable flex-line that will accept a 3/8 flare? I currently have the Russell braided hoses front and rear, but the rear line is a stock 1/4" flare into the flex line, which tees out into two 3/8th flares for the rear drums.

72 Chevelle Malibu
Muncie M20
SBC 406
KB Pistons
PW Aluminum heads
RPM Air Gap Intake
MSD 6AL2
Holley Sniper EFI
Holley Dualsync
Stainless Long Tubes to 2.5 Exhaust
UMI Suspension Stage 2
CPP Steering setup
10 bolt rear - 3.55 with Eaton Posi
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post #5 of 13 (permalink) Old Sep 9th, 18, 11:25 AM
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Pat
 
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Re: Adjustable Proportioning valve question

I installed a similar kit, may be the same I would have to find order to check part #. my prop valve isn't 3/8" and adapters are supplied for master to prop. I used 1/4" to rear and 3/16" up front with no issues. Maybe a different kit?
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post #6 of 13 (permalink) Old Sep 9th, 18, 4:28 PM Thread Starter
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Re: Adjustable Proportioning valve question

Quote:
Originally Posted by myrusty66 View Post
I installed a similar kit, may be the same I would have to find order to check part #. my prop valve isn't 3/8" and adapters are supplied for master to prop. I used 1/4" to rear and 3/16" up front with no issues. Maybe a different kit?
All of the outs on the prop valve are definitely 3/8 inverted flare (3/16th line).

I think I'll just run a 7/16th flare to 3/8th flare adapter at the rear flex line and call it a day.

72 Chevelle Malibu
Muncie M20
SBC 406
KB Pistons
PW Aluminum heads
RPM Air Gap Intake
MSD 6AL2
Holley Sniper EFI
Holley Dualsync
Stainless Long Tubes to 2.5 Exhaust
UMI Suspension Stage 2
CPP Steering setup
10 bolt rear - 3.55 with Eaton Posi
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post #7 of 13 (permalink) Old Sep 9th, 18, 8:18 PM
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Pat
 
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Re: Adjustable Proportioning valve question

That is correct. I put a hold off valve on since im running drums on rear. that was kind of a pain to convert size and having to have lines on motor side due to the way I plumbed it. worked fine but took some thinking. gotta love self made messes.
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post #8 of 13 (permalink) Old Sep 10th, 18, 12:18 AM Thread Starter
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Quote:
Originally Posted by myrusty66 View Post
That is correct. I put a hold off valve on since im running drums on rear. that was kind of a pain to convert size and having to have lines on motor side due to the way I plumbed it. worked fine but took some thinking. gotta love self made messes.
Is the hold off valve necessary? I’ve read some conflicting info on this. Can you link me to where you picked it up? I’d like to put some thought into the brake system so I only have to do it once.

72 Chevelle Malibu
Muncie M20
SBC 406
KB Pistons
PW Aluminum heads
RPM Air Gap Intake
MSD 6AL2
Holley Sniper EFI
Holley Dualsync
Stainless Long Tubes to 2.5 Exhaust
UMI Suspension Stage 2
CPP Steering setup
10 bolt rear - 3.55 with Eaton Posi
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post #9 of 13 (permalink) Old Sep 10th, 18, 10:17 AM
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Re: Adjustable Proportioning valve question

I'm not an engineer and don't have the car completely dialed in yet so I cant answer if it is really necessary. I talked with the guys at Wilwood and they claim that it is part of the system to operate as designed. Could be sales pitch, could be engineer overload, but for the actual cost it really isn't a big deal to install.


https://www.summitracing.com/parts/w...3784/overview/
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post #10 of 13 (permalink) Old Sep 10th, 18, 12:58 PM Thread Starter
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Re: Adjustable Proportioning valve question

Quote:
Originally Posted by myrusty66 View Post
I'm not an engineer and don't have the car completely dialed in yet so I cant answer if it is really necessary. I talked with the guys at Wilwood and they claim that it is part of the system to operate as designed. Could be sales pitch, could be engineer overload, but for the actual cost it really isn't a big deal to install.


https://www.summitracing.com/parts/w...3784/overview/
Cool, for 20 bucks its no big deal. So you plumbed this in between the M/C and the adjustable proportioning valve on the rear brake side?

72 Chevelle Malibu
Muncie M20
SBC 406
KB Pistons
PW Aluminum heads
RPM Air Gap Intake
MSD 6AL2
Holley Sniper EFI
Holley Dualsync
Stainless Long Tubes to 2.5 Exhaust
UMI Suspension Stage 2
CPP Steering setup
10 bolt rear - 3.55 with Eaton Posi
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post #11 of 13 (permalink) Old Sep 10th, 18, 3:17 PM
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Pat
 
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Re: Adjustable Proportioning valve question

no I plumbed it after prop valve. between the prop valve and line going to rear brakes.
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post #12 of 13 (permalink) Old May 6th, 19, 7:38 PM
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Re: Adjustable Proportioning valve question

You guys with disc/drum combos and adjustable prop valves....where did you end up with the adjustment? I am about to make the same change and want a good starting point. The instructions say start in the middle, but I think they are meant for disc/disc. Rear drums need far less pressure to lock up right?

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post #13 of 13 (permalink) Old May 6th, 19, 7:53 PM
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Re: Adjustable Proportioning valve question

You have larger tires on the rear and it's dumped in the front, still don't know why your rear brakes locked up ?? Try putting the same tire size on the rear as is on the front, and if your "dumped" front is from air shocks/shorter front springs or taller rear springs...in other words, return it to "stock" and your problem should resolve itself. You have successfully managed to unload the rear tires and being they now have less weight on them they lock up on you. Simple physics, return to stock, solve problem, save all sorts of money.
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