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Gutting the proportioning valve.

6K views 40 replies 13 participants last post by  randedge 
#1 ·
So... has anyone done it?

Did it make the rears work a bit more?

See, this is tempting to do, but also dicey in that I'm a little scared that it might prove to be too much bias for the rears. I just want them to work harder, not lock up the first instant I hover my foot over the brake pedal.
 
#3 ·
now if bill was to make several of those and sell them at a decent price .. i'd buy one, especially if the fittings and lines coming from the original toyota proportioning valve were to fit straight onto this unit.
 
#6 ·
I have a tilton 7 way valve. I bought it with the foolish idea i'd be hopping in and out during races and adjusting it for changing conditons. Now, I have it set so it reduces as little rear pressure as possible, and it still has alot of front bias. I never play with settings, because reducing more pressure would only make front lockup worse, and it still has the standard mr2 lock up the front and plow syndrom. If i had an opportnity to do it again, i'd just gut the thing. Would have saved 70 bucks, 2 hours in the install and given even more improvement than what i have now. The mod has been done before. Its not all too common, but people have done it and no ones ever gone back, to my knowledge. The way the master cylinder and calipers are sized, you'll still get front lock up before rears with it gutted. When i was puttng mine in, i had people (not mr2 owners) telling me that the pedal would be so touchy i'd lock em up all the time. Its not true. The pedal feel doesnt change at all. It just accepts more pressure before the fronts lock. Either way, i'd recommend this mod to everyone if this wasn't such a touchy and important system.

If you want even more improvement, you can try a prop valve inline to the front. Its not recommended by any of the valve manufactuers, but i think its the only way to get into the adjustment range of where a prop value can be for rear lockup before then fronts, then backed off. Other than that, you're just getting as close as you can, but never full getting there. I believe this is the case for everyone mk1 with a valve plumbed into the rear lines. Someday i'll get around to doing mine like this and trying it.
 
#10 ·
I'll try. Take the 3SGTE. It would appear that 84% of the line pressure is transmitted to the rear wheels. Actually that is only true at one point. The proportioning valve tranmitts 100% at low pressure and something less than 84% at higher pressures. To plot the exact relationship we would need to know the flex point. For example, it MIGHT transmit 100% up to 60 kg/m squared and 60% above that. Or, it MIGHT transmit 100% up to 75 kg/m squared and 36% avove that.

You might take some asprin and ask yourself - Do I want the same front/rear bias under trail braking as under straight line braking? Randy, you met my son, Owen, at Nationals. He has pestered the heck of out the guys at Tilton about this.

Hope this helps,
Mike R
 
#12 ·
twoina2 said:
Here are the 91 specs -
5S-FE -- linear to 30kg/m squared with 60 to rear at 80
3SGTE -- linear to 60kg/m squared with 84 to rear at 100
OK, so on the 5SFE car, the F/R bias is the equal up to a force of 30 kg/m^2. Above that they are not equal, and at 80kg/m^2 of MC pressure, the rear only sees 60kg/m^2?

So we can say that the brake bias is equal up to 30kg/m^2. Above this point the brakes become more front biased. When you hit 80kg/m^2 of pressure, it transmits only 60 (75%) to the rear.

Noting that differences in caliper piston size, pad size, etc also effects stopping power, so an even dist f/r off the prop valve does not mean that both ends are producing the same stopping force to the wheels.

Am I on the right track?
 
#15 ·
kirkosaurus said:
Jim King is incorporating ABS into his MKI using the MKII stuff. I would not want to do this as it adds alot of weight.
From the short time I've spent in this forum, it sounds like the MK1 has some serious braking issues. Though maybe not the best solution, ABS definitely helps both ends of the car stay at/near their full braking potential. I wonder where Jim is getting his knuckles from. Is he swapping those from an MK2 as well or are there some ABS corolla ones that might be a direct fit?
 
#16 ·
rnoll98 said:
From the short time I've spent in this forum, it sounds like the MK1 has some serious braking issues. Though maybe not the best solution, ABS definitely helps both ends of the car stay at/near their full braking potential. I wonder where Jim is getting his knuckles from. Is he swapping those from an MK2 as well or are there some ABS corolla ones that might be a direct fit?
The MKI actually brakes rather well, it was engineered biased more toward the front for a safety standpoint.

Jim is using the MKII knuckles and hub assemblies as he is also swapping in the 3SGTE and axles. You can read more about his swap inthe MK1.5 forum.
 
#17 ·
I wouldnt mind doing a prop valve setup , the stock lock and plow symptom isnt really a problem for me but sometimes I lock up the inside front tire for a sec going into corners hard and on our last run I watched a guy in an Mk1 in front of me lock up his fronts and plow off the side of the road (almost falling 20ft down into a creek bed) so it would be nice to be able to adjust it a bit as I see fit. I was also thinking about that Jetta rear brake upgrade... Hmmmmmmmmmmmm
 
#20 ·
It sounds to me like both mk2 valves might be better than the mk1. Any1 consider trying a swap yet? Would they even work on an mk1? I wonder... I haven't ever looked at 1 before but theoretically it might be possible to open up the front side a lil with a drill (not messing up the threading) & decreasing the front bias.
 
#23 · (Edited)
Good info on the Mk2 prop valves, Mike. BTW, aren't all those pressures in Kg/cm^2 (square CENTIMETER)?

Along with the MK2 ABS, I'll be installing the 93+ turbo MC and proportioning valve when I get around to that project. The added weight (perhaps 15lbs) will be worth it, I think. Being that all MK2s came with wider rubber in rear than front, it makes sense that the braking pressure would be more rear biased than in the MK1 (assuming similiar caliper pistion size ratios). So hopefully I'll have the rears nearer 100% braking capacity when the fronts EXCEED 100% and the ABS finally kicks in.

And while ABS sometimes hinders stopping (snow, rippled pavement), 9.5 times out of 10 it may save your a$$. Or at least keep you from flat spotting your tires on the race track. Turn 1 at Streets Of Willow is a perfect example. It's up hill, leveling somewhat at the turn in point with the braking zone somewhat off-camber/slight right-hand bend, leading to a 2nd gear right-hand 180. I approach it around 90-95mph in a MK1 SC. Faster in higher HP cars, of course.
In the MK1 you really have to brake early and <small cat>-foot the braking here or you end up locking and dragging the inside (RH) front wheel a 100 feet or more. At best you leave a little cloud of blue smoke, at worst you end up in the dirt run-off area looking pretty silly. Either way the tire suffers. Most tracks have braking zones with similiar problems.
 
#24 ·
the theory behind the valve in the rear, is that the stock valve limits the rear brakes by design, and removing it and replacing it with an adjustable will allow you to tune the fronts to do more work because you could limit the rear less than what stock was set at. The problem is for that to work, the rears need to lock before the front without a valve. (It doesnt, on a mk1) Then you use the valve in the rear to limit rear pressure, balancing out the braking bias. The problem with having a valve in the front lines, is how the valve works. It works by allowing an even pressure split between front and rear, and then tapering off while the unvalved line continues to build pressure. If the valve is in the front, you would get a linear increase in rear braking power, while the front tapers off. This would be more unstable than not running a valve at all, and having a completely even brake pressure all around.

It seems like putting the valve in the front is the only way to get the best pressure bias without resorting to changing calipers/discs or dual masters. Its not recommend to put a valve in the front on a street car, but it has been done before and dirt/circle track racers sometimes do this for better turn in (at least according to tilton)

I'm considering switching my valve from rear to front. I havnt done it yet because i'm still researching whether or not I should. I'd theorize since the mk1 is fairly light and doesn't take much pressure to lock up all 4 wheels, you could get away with a valve in the front. You'd think that pushing on the pedal hard enough to cause the valve to start cutting the slope off the front pressure would already be past the point of all 4 wheels locking up. I'm curious on anyones opinion on this, or if anyone has heard of or run a front valve only.
 
#26 ·
JFY... the needed parts to remove the valve are avalible stright from your parts car out back ;-)...

there is a T fitting (sits right by the front engine touqre mount in the engine bay) that has the same threading as the stuff going into/from the stock valve adn there is a stright inline peice in the frunk (i belive thats the right one... been a while sence i pulled one)


just use the T on the top and then the inline one on the bottom...

now if you find that your bias is still to much either front or rear... you can simply add a valve... but this gives you a great baseline feel for what the brakse are doing... the T is for the fronts and the inline one is to the rears... my guess is you will more then likely find the rears a bit more powerful then you want so a valve would be as simple as adding fitting adapters and installing a valve... not much different if you find the fronts to powerful but that will reqiure some bending of the stock lines

mark
 
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