Proportioning valve

[ty166]

im getting my ty going after years of it sitting. i long ago switched it to four wheel disc but never finished. i searched but couldnt find exactly what i was looking for or many diffrent opinions. when switching to four wheel disc should you remove the proportioning valve in order to get rid of the risidual check valve. i want to do this right but i dont wan to do it over, should i run a adjustable ? no proportioning valve at all ?

 

[fauXGT]

Re: proportioning vavle

Re: proportioning vavle

I converted front & rear to LS1's three years ago. Haven't had a chance to run it hard yet, but from what I've read here, some have not changed the proportioning at all, like myself. At a semi-hard braking, the truck squats, rather than nose dives.:2cents:

 

[Blazin_Jason]

Re: proportioning vavle

Re: proportioning vavle

Planning on removing the "guts" from the stock combination valve if I can. Have a summit adjustable valve coming to plumb in for the rear. That's my plan.

 

[BoostedSUV]

Re: proportioning vavle

Re: proportioning vavle

I haven't changed mine but it feels like my back brakes don't work that well. They start pushing at 4psi

 

[blackty]

Re: proportioning vavle

Re: proportioning vavle

Left my stock one in. It's true, no nose dive. And I can stop alot faster than those with stock brakes. I don't drive it in bad weather so I couldn't tell you if the backs lock up first. I haven't had them lock up on dry pavement. I write this wearing my black Rockford Fosgate t-shirt, spooky...Jim

 

[Strykerblythe]

Re: proportioning vavle

Re: proportioning vavle

From what I was told from a GM specialist that the prop valves were the same after a certain year don't know how true that is but when I did a 4th gen camaro swap on my 3rd gen I didn't swap valves and braking hard and wet weather made it a lot easier no noise dive and grabbed better than the stock drums on a 92 camaro prop valve

 

[jollygreen1964]

Re: proportioning vavle

Re: proportioning vavle

I am not good at this computer info, but go towww. theherd.com our local 94 to 96 impala ss site, go to links then hotss web site, in the archives there are pages of easy mods to do to the proportioning valve, the 94 caprice ghad disc / drum set up, but the ss had disc/disc set up but gm never changed thp/m 9 prop/ metering valve,exact same set up. there are mods to the back and the front of the valve to make it work properly with disc/ disc.

 

[DaveP]

Re: proportioning vavle

Re: proportioning vavle

This intrigued me. I found the ImpalaSS site. Did a search ("proportioning valve" in the Brake Forum) on there, and came up with a thing that seems to be common-knowledge with Impalas is "Brake Bolt Mod". I've never heard of this.

Here's a couple of links. Interesting reading.

http://www.impalassforum.com/vBulletin/showthread.php?t=244367&highlight=proportioning+valve
http://www.proforged.com/tech-tips/Stealth-Bolt-Instructions

Here's an old post. 1998. The P/n for the vale is NLA. But explains the valve mod in more detail.
http://www.gofasst.us/brake_proportioning1.htm

Thanks, Jolly Green for the tip.

 

[dgoodhue]

Re: proportioning vavle

Re: proportioning vavle

I remember reading a mod on he SyTy mailing list about modifying the portioning valve for rear disc brakes.

 

[DaveP]

Re: proportioning valve

Re: proportioning valve

OK. When I first saw this thread, I thought "my SyTy's are stock. This thread doesn't have anything for me". I responded this morning because I was curious. Then tonight it hit me: DesertSy has a 14-year old Baer Brake rear disc conversion on it. I haven't really driven the truck yet, so I can't evaluate its brake performance. But if it's like everything else has been so far, it isn't right.

So now I have a vested interest in this thread and combo valve / proportioning valve issue. I did some more searching tonight and found this thread. Some of the following text are copy/pasted from the links I've posted above and here.

• If you mod the bolt on the combi valve closest to the radiator (on the rear brake hydraulic circuit), then you are doing the proportioning modification.
• If you mod the bolt on the combi valve closest to the firewall (on the front brake hyd circuit), then you are doing the metering modification.
• The proportioning mod removes the 90:10% front:rear proportioning needed on a disc/drum car (because rear drums are self energizing once applied, so you only need a little bit of force to get them working). You need something more like 70:30% front:rear on a disc/disc car.
• The metering mod removes the delay in activating the front brakes. The metering was included by GM because the rear drums don't instantly apply until the brake shoe return springs have been stretched. You don't want the metering (delay) function once you fix the proportioning because in a hard stop, it means the front brakes WON'T come on at the same time as the rear brakes. In an easy stop, you won't ever notice the difference with or without the metering mod because the metering orifice has no effect.

Here are some of the pictures from this thread:

The Brake Proportioning Valve mod removes the delay function from the combi valve and increasing the proportion of brake fluid pressure to the rear brakes. This is accomplished by removing 2 parts, a spring and a red aluminum valve, from the brake combination valve and replacing the vented cap with a solid cap (see "Bolt Mod").

Here's the metering mod. The chamfer on the 'replacement' bolt uncovers the hole in the combo valve to the front brakes, removing the delay in applying the fronts.

And here's the four parts left over.

During my reading today, I found a thread with descriptions of various Impala valves from the late 80's to the 97 SS. Evidently the threads on the valves changed. Between the early Impalas, and the SS's that had 4WDB. So I suspect the parts produced for the 96-97 Impala SS won't fit our earlier valves.

I'm going to think about trying these mods on an existing combo valve. TIG the hole in the front bolt to seal it, and remove the valve for the proportioning mod, and cut a chamfer on the existing bolt to uncover the hole for the metering mod.

But I have to get DesertSy on the road first to evaluate it. Thanks for reading, hope you found something useful.
DaveP

 

[BoostedSUV]

Re: proportioning vavle

Re: proportioning vavle

Thanks for that research and info Dave. I'm looking into prop valve options or mods to get my truck to stop better. To me it feels like the back brakes just won't hold and I'm doing all the stopping on the front after the disc/disc and hydroboost conversion. I like to try to modify or replace my prop valve to allow more breaking power to the rears.

 

[fauXGT]

Re: proportioning vavle

Re: proportioning vavle

Thanks DaveP for the write up. Now I'm affraid to slam on the brakes until I do this mod. Spent the morning trying to find a simple kit for this. The one parts link has changed to a different company, so the individual part link page is invalid. I'll keep looking.

 

[wildphil]

Re: proportioning vavle

Re: proportioning vavle

Would you take pictures and maybe do a write up when you do this mod to your truck Dave? I will be adding the LS1 brakes to my Ty in the near future. It would be helpful to to see it done step by step on one of our trucks.

 

[MRKING]

Re: proportioning vavle

Re: proportioning vavle

I voted and am not running a proportioning valve . I'm only running without one because at the time , I wanted to see what the ls1's on all four plus the hydroboost drove like . Now I would like to install one but have not pulled the trigger on it's purchase yet.

 

[DaveP]

Re: proportioning vavle

Re: proportioning vavle

The ideal front/rear proportioning ratio changes constantly because of traction available at the tires, vehicle loading conditions, and other dynamics, but can be calculated if you know the formulas and are an advanced math wizard. I'm not. So most of us are going to use "seat of the pants" feel to know if we got it right, or close enough.

The absolute goal is to have the fronts lock before the rears, particularly at higher speeds.

If you want to try to understand this "proportioning" thing a little better, check out this Master's Thesis. Beginning on about page 58 he describes the "optimum braking curves" and the dynamic forces at play that cause undesirable yaw-progression with the rears locked, but more controllable yaw with the fronts locked. The 5 minutes it took for me to understand this (why fronts must lock first) made this exercise in learning worth it for me.

We also have the advantage of the mechanical linkage of AWD. It is difficult to lock a rear tire, because it is coupled to the fronts mechanically. The ABS system for AWD dumps the rear brakes circuit to zero during an ABS-controlled event. So all the braking is on the fronts once the ABS becomes active.

Whether you have functional ABS or not, I feel an accurate assessment (road testing) of correct ratio resulting in front before rear lock up is only going to be valid with the front prop shaft removed, and the ABS defeated by pulling the 10-pin connector on the unit. If you can achieve front before rear lock up, and it 'feels' balanced under 2WD conditions, than it will behave optimally in AWD without the mechanical linkage masking a gross proportioning imbalance.

Some more food for thought.

 

[midnightbluS10]

Re: proportioning valve

Re: proportioning valve

Wow. You're an intelligent mofo, Dave.

 

[fauXGT]

Re: proportioning vavle

Re: proportioning vavle

I looked up to see if I could change the prop valve body to the newer threading so as to use the Impalal SS stealth brake bolt & metering bolt kit. I read that some have done this on full size cars, like Caddy's. I'm no machinist, and bolt on is more do-able for me. On my 91 it has rear abs and the valve body is alot different. It sets parallel to the fire wall and it has three of those black capped bolts, so I need more research. Might go to pull-n-save and grab one to tear appart... once I can drive.:roll:

 

[DaveP]

Re: proportioning valve

Re: proportioning valve

I'm no machinist, and bolt on is more do-able for me. On my 91 it has rear abs and the valve body is alot different. It sets parallel to the fire wall and it has three of those black capped bolts, so I need more research. Might go to pull-n-save and grab one to tear appart... once I can drive.:roll:

I too have a 91 pick-up with RWAL, so I know what you're talking about. The 4WAL systems still have the combination valve. The RWAL valve/solenoid block is aft of the combo valve in the line to the rear brakes. The modifications we're discussing will still be of value. Regardless of how you choose to implement them.

But the calibrations for the RWAL may not be optimum for rear disc brakes. AND your truck is 2WD, so you don't benefit from the mechanical coupling of AWD like the SyTy's do to prevent rear lock-up. You're kind of on a parallel path development to what I'm doing with an AWD Syclone. While there are similarities in the valves, and the mods needed, the evaluation and testing will be different for the two platforms.

Let's keep other posted.

 

[JaySS]

Re: proportioning valve

Re: proportioning valve

OK. During my reading today, I found a thread with descriptions of various Impala valves from the late 80's to the 97 SS. Evidently the threads on the valves changed. Between the early Impalas, and the SS's that had 4WDB. So I suspect the parts produced for the 96-97 Impala SS won't fit our earlier valves.

Yes - the change was implemented between '93 & '94 according to this:

http://www.impalassforum.com/vBulletin/showthread.php?t=244367

I'm going to think about trying these mods on an existing combo valve. TIG the hole in the front bolt to seal it, and remove the valve for the proportioning mod, and cut a chamfer on the existing bolt to uncover the hole for the metering mod.

We have also performed this mod by tapping the existing hole with a 6-32 thread and countersinking the face for a flathead capscrew, installed with thread locking compound.

The procedure was often done in the early days - pre-aftermarket bolt availability - but has been lost (at least for the time being) in the ISSF crash of 2009.

- J

 

[Throws]

Re: proportioning valve

Re: proportioning valve

...
The procedure was often done in the early days - pre-aftermarket bolt availability - but has been lost (at least for the time being) in the ISSF crash of 2009.

- J

Do you have a link to the thread? Archive.org tends to get all that stuff fairly intact, provided we can find it.

-P