I run my Evo is A stock for autocross. I run on Kumho V710s. Lately I've noticed that when my inside rear would lift and I would get on the throttle the lifted tire would completely break loose, acting like an open diff. I know this really effected my times. It has been getting worse with every autocross. I replaced all of the diff fluids this past fall with Diaqueen and they all looked good. I have been running the V710s on my car for the last 2 and a half seasons.

Has anyone else experienced this?

Is there a part in the diff that neads to be replaced, or is the diff just not strong enough for the V710s?

TIA for your help.

 

What do you mean by break loose? Also if you are driving the car you can't really see you inside rear tire. So are you getting feedback from people watching you? Or from pictures taken at an event?

We have a clutch type LSD in the rear. When you get on the gas, provided your wheel hasn't touched the ground, the tire/wheel in the air should rotate at about the same speed (slight slower) than the one on the ground. If you had an open diff it would rotate at a higher speed.

 

I'm able to increase the lock-up of the rear diff by about 40%. It's a noticable difference to the way the car responds to throttle, the car has less push and will rotate much better....kinda like the General Lee.


PM me if you would like to know more.

Jon@TRE

 

Jon@TRE: What method do you use to lock the diff? Is it still open on off-throttle?

On the USTCC car, we shimmed up a stock diff until it was fully locked. Over time, the shims ground some **** up in there and the diff gradually unlocked. The sweet setting came as the diff was coming unlocked, and the understeer on entry lessened but the car was still slideways coming off the corner. Still works, but now back to stock? lock levels and the push is back.

I think the ideal solution is a 'locker', completely open until there is slip, then fully locked. Don't have the $ to test my theory...I'll stick to shimming. Drive a chevy/gmc full size pickup and get it sideways...very satisfying.

 

By break loose, I mean the lifted inside wheel is spinning faster than the planted outside rear. I can feel and hear it happening. The engine revs but the car doesn't go anywhere on the beginning of corner exit when the inside wheel is up in the air. It seems like all the power is going to that lifted wheel. Kind of like a rear wheel drive car with an open diff. Once the inside rear is on the ground again, the car bucks a little bit(seems to be transfering power from front to rear over and over again) and then fully hooks up and takes off.

 

Someone needs to visually verify it happening from the outside because feeling it doesn't really count. It is also very unlikely to happen with a clutch type diff. If your rear diff isn't working you would experience certain symptoms. It could be your ACD controller that you are feeling that is adjusting torque distribution between front and rear based on available traction?

 

Yeah the stock clutch packs suck *** but I have a way around them. I can grind a different profile onto the new side plates to get you whatever you prefer. I like the unit to go loose when I lift and lock-up solid when I'm back into it.

Jon@TRE
www.teamrip.com

 

I can hear the tire spinning on the ground when it touches down. I drive with my windows down and my exhaust isn't very loud.

I think your right about the ACD, but that happens after the tire touches down.

My theory is that when the rear inside tire is still up in the air and the LSD won't lock up, the ACD keeps sending torque to the rear, expecting it to lock up, but the inside tire just spins.

 

Jon,

Do you have an idea of what needs to be replaced in my diff? I'd like to do your mod but its not legal in A Stock.

 

This almost sounds like what I experience from time to time. See my old thread:

https://www.evolutionm.net/forums/sh...d.php?t=228096

In my situations, I don't recall the engine revving, but with a helmet on and all it's hard to say as my car isn't the loudest at the track! To me there is a noticeable gap in forward momemtum/accleration for a brief moment.
I think I'm lifting a tire, but I think that's hard to do in 4th gear! I experienced this again 2 weeks ago on the same track/turn as noted in situation 3 in the thread link above. I've never experienced this with a passenger and it's always while turning to the right, so weight distribution might has something to do with it - or I like to turn tighter right!?! I'm running lowered springs now too...

Same thing or?

 

First, who would know unless you're bragging to everyone about it.

Secondly, I doubt that anyone who be able to tell the difference unless they knew what to look for and how to measure for it.

Lastly, if the car is fast they'll probably be looking for engine type mods and not the rear diff.

Jon@TRE

 

I have a friend with an 05 that has had this same problem since he did a clutch. Its the ACD. I'm not sure why the rear diff would let the wheel in the air spin freely but the very same thing is happening on his EVO. The car sends nearly all power to the wheel in the air. He didn't have this problem until doing the clutch.

 

BTW its good to see Gears posting in here!

 

Why don't you swap out the front sway bar? I thought that was legal in A Stock? That will decrease the corner dive and might limit the outside rear tire from getting completely off the ground.

 

You're right. There are probably tons of things I could get away with, but it's not my style. I'd rather lose than cheat.