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REAR DIFF QUESTIONS

vr4play

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Feb 7, 2008
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397
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Cincinnati, Ohio
Is anyone else out there running an evo rear diff? I thought it felt better on the street but after my first auto-x in the dry I may be changing my mind. With my new suspension set up and new race tires I am lifting the rear inside tire 6-8 inches off the ground. I can't accelerate out of a turn because that tire is just spinning like mad. I think I am almost getting the front tire off the ground too. I am going to make some spring rate changes this weekend and try it out again next weekend, but I used to lift the rear tire before with the viscous diff and the car would still pull some. If my suspension changes don't work I may be giving TRE a call to get this thing upgraded. I may also try a new center viscous.
 

kartorium

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Jan 14, 2002
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ellensburg,wa
What diff are you using up front?

How the crap are you lifting the inside rear 6-8 inches...seems like a lot.

Busted something in the rear? Sounds like it went open.

Depending on what center diff you're running, it could be part of the problem. I had a website bookmarked that explained why, but I can't seem to find it.
 

jepherz

Staff member
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Aug 8, 2004
Messages
7,877
Location
KC, Missouri
Pics or ban. 8 inches is like the ground clearance of a Ford f150.

I don't see how an evo diff would have LESS forward momentum with one tire off the ground that a viscous unit, unless it isn't working properly.
 

Rausch

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Dec 21, 2004
Messages
12,049
Location
Cleveland, OH
Quote:
I had a website bookmarked that explained why, but I can't seem to find it.

Discussed the different types of diffs, and applied then to roadracing? Discussed from a DSM standpoint? I'm trying to find that one, if that is the one you're thinking of.
 

kartorium

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ellensburg,wa
yeah, it was specific to dsm and the awd platform. The application of different types of diffs and what happens if you combine the wrong ones. IIRC it talked about how for most dsm's a front LSD is extremely beneficial, then went into detail about using a mechanical rear lsd, the pro's and cons. The whole site was dedicated to autocrossing and road racing a dsm. I think my bookmark is taking me to a craigslist ad for some reason though /ubbthreads/images/graemlins/confused.gif

I thought it was this one.... click

...but I can't seem to find it on that site.
 

Rausch

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Dec 21, 2004
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Cleveland, OH
That is the one I was thinking of. I had printed it out at home, but can't find it online either....
 

Armitage

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Oct 16, 2003
Messages
715
Location
Herndon, VA
What Evo diffs are (bolt on) compatable with our cars?!
 

vr4play

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Joined
Feb 7, 2008
Messages
397
Location
Cincinnati, Ohio
There are no pics of the car going through the sweeper area where the back was way up, but here are a few pix I did find. One with the front tire up a bit and one with the rear up about an inch.
click
click
 

Quoting Armitage:
What Evo diffs are (bolt on) compatable with our cars?!



CLICK

It's not exactly a bolt on deal. The diff innards bolt in, but you have to do some halfshaft modifying.
 

skivittlerjimb

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Joined
Jun 20, 2003
Messages
1,440
Location
Danville, CA
What tires are you running? With sticky enough tires and a stiff enough rear sway bar I would guess that 6"-8" of inside rear tire lift is possible. Not quite VW A1 GTI tripod territory, hopefully?

img.php


Going from and open rear diff in my old GVR4 to a viscous LSD rear definitely helps the rear end do more work getting around tighter corners. There are a few situations where I wish in would kick in sooner, as well as a few situations where I wish the viscous center would transfer power rearward faster (typically tight uphill hillclimb corners).

Any chance you'll share what spring rates your running, too? Pretty please? /ubbthreads/images/graemlins/smile.gif

-Jim B.
280/1000
 

JB

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MA
^The man from Maine speaks the truf. /ubbthreads/images/graemlins/applause.gif
 

vr4play

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Joined
Feb 7, 2008
Messages
397
Location
Cincinnati, Ohio
[quote

Any chance you'll share what spring rates your running, too? Pretty please? /ubbthreads/images/graemlins/smile.gif





I am currently running 400lbs front and 550lbs rear. I have a 22mm front bar and a 24mm rear. This week I am switch the front to 500lbs to see how that works. I also have a call into Jon @ TRE to send him my stock Evo 9 diff for a upgrade.
 

CP

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Aug 30, 2004
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8,938
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West Simsbury, CT
Your issue doesn't seem to have anything to do with your rear differential, but rather the suspension you're running. Too much body roll results in your unloaded rear tire parting company with terra firme.
 

gtluke

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Joined
Sep 16, 2001
Messages
4,210
Location
dirty jersey
My car lifts the rear tires really easy too, I think I made a post how I got stuck in a parking lot because of it too. haha
I think my evo rear shocks just don't have enough travel, as soon as the body starts to roll the wheel comes up.
On uphill tight turns I just blast the inside tires loose in 2nd gear. I don't think the car has much body roll, doesn't feel like it at all.
But I really love my evo mr shocks. It's like I need to lower it another 3 inches in the strut travel and lower the shock towers. Seems really dumb, guess the rear shocks just aren't perfect or maybe I have no idea what I'm talking about. I'm going with the latter /ubbthreads/images/graemlins/laugh.gif

I have an evo 1 rear diff in my car, but it's the exact same VCU that's in 4 bolts normally. I'd like to try and evo3 mechanical diff though, might be fun.
 

vr4play

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Joined
Feb 7, 2008
Messages
397
Location
Cincinnati, Ohio
My 92 Galant always lifted the rear inside tire. I was using a 4 bolt vsc rear diff and the rpms would rev up and as the viscous fluid heated up the revs would drop and off the car went. The only suspension changes that have been made from my 92 to my 91 are the addition of a 22mm front bar and swapping 2g Koni rear shock for the KYB Agx's that were on the car. The Agx's were not up to the task of the 550lb springs that I am running on the rear. I already had Koni's on the front and when I was swapping everything over I had the front shocks dyno tested at koni and he said they were still like new so I only bought rears. I also removed 500lbs of weight from the 91. Before with the vsc rear diff when the diff would start to lock the car would start to rotate and it was fast out of the corner with both inside wheels spinning a little. These cars handle the best with the rear tire off the ground I just need to make it go when I stomp on the throttle. I think that the stock evo diff only locks up about 30% - 35% and the viscous can reach close to 100% it just has a delay. From what I have read all of the fast evo guys are sending there diffs to be upgraded. The rear suspension on those cars it much better than what we have so it doesn't effect them as much. I am going to try the stiffer springs on the front to keep the rear tire closer to the ground but the side effects may be that the car will push on corner entry. It would be worth it if I can accelerate out of the corner though. I will let you know how it works out this weekend.
 

vr4play

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Joined
Feb 7, 2008
Messages
397
Location
Cincinnati, Ohio
New springs installed and the car felt loads better. It pulled out of the corners almost like my other car used to. I could even get the back to slide a little. It pushes a little bit more than before but not uncontrollably. Now I just need to learn to drive again. I am still going to send the diff to TRE for an upgrade but I think the suspension is much better now.
 
Last edited:

Olson

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Joined
Oct 7, 2006
Messages
1,237
Location
Moreno Valley CA
Have you tried to disconnect the rear swaybar?
 
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