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Discussion Starter · #1 ·
OK, there has been lots of discussion about trying to "adjust" front/rear bias on your standard TD. Using conventional means, this is impractical due to the diagonal split on the brake systems. It's not as simple as adding a single adjustable brake prop valve, as you have to control two lines, and they have to be identical.

While playing with my 89 turbo mini, I noticed that I can adjust the rear brake bias via a nifty little valve attached to the rear suspension. Setting the valve to add more rear brake made a very noticeable difference (and white knuckles in low traction conditions!). For those not familiar with this, it is essentially a mechanical valve that reads the deflection of the rear leaf spring, and adjusts brake bias accordingly. It adjusts both lines to the rear simultaneously, 2 lines in, 2 lines out. A heavier load in the rear will give more brake bias to the rear.

What I don't know is exactly how it works. More specifically, how does it work in conjunction with the primary proportioning valve. I am assuming that adding the adjustable valve to a car with the "correct" proportioning valve would only allow you to decrease rear brake pressure. I presume the minivan prop valve must have a steeper slope, or no split point on it's own? Does anyone have split/slope specs on minivan proportioning valves? Does this adjustable valve control the slope, with the split controlled by the prop valve?

One of these adjustable valves would be an easy enough install, and rather than tie it into the suspension, a simple manual adjustment could be made to tune brake bias. Can anyone shed any light on this? I don't yet have a FSM for my mini, so I am flying blind right now.

william
 

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Discussion Starter · #2 ·
Having done some more reading, it seems that many people that swap to SLH2 & SLH3 in Omni's are reporting premature rear lockup with the correct 4 wheel disc MC and prop valve... so would adding one of these adjustable valves be just the ticket to reduce the rear brake pressure just a hair?
 

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Having done some more reading, it seems that many people that swap to SLH2 & SLH3 in Omni's are reporting premature rear lockup with the correct 4 wheel disc MC and prop valve... so would adding one of these adjustable valves be just the ticket to reduce the rear brake pressure just a hair?

Way to many people bolt on 11" rear disks with 10" front disks on L bodys. They also use solid rear disks and 54mm front calipers with an L body and wrap there cars around phone poles. People just need to use the right front and rear brakes together. Will the back end still skate on my SLH 4? Sure a little, but the front end is still doing much more work. My car doesn't spin when I hit the brakes and I use just a pro valve for the 11" disk car. Another thing everyone should be doing is adding SS front caliper pistons and removing the plastic things. The stock caliper pistons crack and get too tight, then more brake pressure goes to the rear, at the pad. The answer is not adding a rear pressure control valve, the answer is doing the brakes right the first time. Which also means not reading dempseys page and going to boosted mopar and reading in the faq sections. Done right L bodys sit down flat, compressing there rear suspension lowering the rear of the car as well as the front. Then the car is low and planted into a corner, not butt up in the sky. I can rotate my car on the brakes to a level I thought was impossilbe. Rotating just right and hitting the gas at the right time you can make a tron bike 90 at 40 MPH. Next dangerous thing with the brakes working right? DON'T stick your kids in the 40 lb booster seats. They fly right out of them when you turn hard. In regular lap belts the kids are safe, no matter how hard the car corners. Think those boosters are safe? Better keep your windows rolled up, that includes if your car gets T boned. The GLHS just corners unreal at 40 MPH, and my boys have learned you never leave home with your seat belt off. I guess the law thinks the only time a kid needs a seat belt is when you get in a head on wreck.:confused:
 

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Discussion Starter · #5 ·
Rob,
I agree with what you are saying. No amount of adjustment in the form of a prop valve is going to make up for a fundamentally mismatched brake system. I was thinking of a properly balanced system to begin with, and simply adding the ability to reduce the rear brake pressure to suit driving conditions. The minivan valve appears to be a reasonably easy way to do this, as it adjusts both sides equally. Obviously you would have to be very close to begin with in order for this to be of any value, not a substitute for having the proper prop valve, or mismatching front and rear components. If there was a factory spec prop valve for 4 wheel disc L bodies, I wouldn't be giving this a second thought. Once I get the brakes installed, I will see how close to "right" it is, and go from there. Good point on the SS pistons, the stock ones are trash. Not sure what plastic things you are referring to?
 

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I would use a rampage rear valve before a mini van rear valve and hook it to the end of the swing arm by the brakes for a full distance adjustment. With a 11" rear brake though as the back end squats from hard braking it'll engage them more, making the back lock a lot hard than the front. So that valve would make the car stop even worse. Another idea you rarely see is just use the 11" fronts with the solid 10" rear disks, that would solve a lot on an L body for those more worried about it. The stock pistons in the calipers are "basically" plastic, not steel. They can freeze in the caliper and drag your brakes, I have had the front then the back of my CSX have this problem. But if you do only the fronts with SS pistons then you add a little more front bias breke power =)
 

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Discussion Starter · #7 ·
Yes, if you were to connect it to the suspension, it would almost have to be opposite the installation on a rampage or mini. I wouldn't bother tying it to the suspension, but build a manual adjuster for it. If I find my rear brakes are too much, I might try this setup out. I am going to run the 10" minivan fronts, and 10" solid rears, so it should be pretty well balanced out of the gate. I might bump up to 11" front when I redo the control arms/K frame next winter, but not likely in the rear, although I have a nice set to go on.
I have been reading mixed info in what prop valve to use though. I have valves for both the 10" and 11" rear disc setups, but it seems like many people are using the factory disc/drum prop valve without problems. It looks like with the low crack point and .27 slope, it wouldn't be putting much power to the rear. I can see where with the prop valve for the vented 11" rears, there would be WAY too much rear bias for a 4dr L body. The 11" vented rears would probably work better with the factory L body prop valve in an omni than with the disc prop valve, but why haul those big brakes if you aren't really using them. Anyway, will rear discs really "work" with the disc/drum prop valve? Seems like you would be missing out on some of the benefit that way, but no scary oversteer either. Thanks for the info Rob, I am trying to get a crash course in brakes, without the crash part.
 

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For 99% of the people out there the 4 wheel 10" brakes with mini fronts are more than enough. The Daytona struts and 11" fronts make it more difficult to install on an L body because you should do a coil over to use them. So most going though the trouble of adding the big fronts just add the 11" rears too. Doing the opposite of Demseys page, adding 11" front disks and the solid 10" rear disks would most likely be best for most. You really need expensive tires and you need to be running on a track or near 100 MPH to really use my setup. My car has 325 lb front and 250 lb rear eibach coils and Daytona konis up front and L body konis in the back. Then I have a solid 1 1/8" addco front sway bar with poly and polybushings.com 1" rear bar. ALL rear disk L bodys should be upgraded to the polybushings.com rear swing arm bushings for no reason other than a larger rear bolt to hold the swing arm on. On my car the rear rubber bushings deflected so much that the car had a longer wheel base nearly hitting the rear tire on the fender. Nitto 555s or RT-615s are needed to use any good 4 wheel disk on an L body too. The last thing for safety is drive everything else you own like your on ice, I blow through stop signs not thinking lol. Casual stops from 60-70 MPH. Where there is no nose dive or tire scratching, rear end skating, thowing you around in the car. Just a nice sit on the ground and slow to a stop, less than 150 ft from 70. Panic hard stops and your close to 100 ft from 70 but your really working the car on the edge of lock. I have brought men to tears because they said a car can't stop that hard without rolling over. The way the suspension is on the TDs make the whole car front and rear sit flat on the ground. With weaker springs they may scrape lol. The rear disk and rear swing arm really kill weight transfer making all 4 tires really work hard. thats my driving experiances =)
 
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