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LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 5:10 pm
by Mako Koiwai
On our '99 Anniversary Edition CS Miata, we're suppose to have a LSD. Mechanical, not Viscous. Either works or it doesn't ... doesn't wear our like the weak viscous LSD in the rear of the WRX.
If we jack up one side, and the rear wheel turns freely, doesn't that mean we DON'T have a LSD?
It shouldn't matter which side we jack up, correct?
Apparently the rear dif was changed out at some point, and it seems like it was replaced with an open differential.
Gee ... maybe that's why we're having so much trouble getting power down coming out of corners?
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 5:16 pm
by Jason Isley BS RX8
Mako Koiwai wrote:On our '99 Anniversary Edition CS Miata, we're suppose to have a LSD. Mechanical, not Viscous. Either works or it doesn't ... doesn't wear our like the weak viscous LSD in the rear of the WRX.
If we jack up one side, and the rear wheel turns freely, doesn't that mean we DON'T have a LSD?
It shouldn't matter which side we jack up, correct?
Apparently the rear dif was changed out at some point, and it seems like it was replaced with an open differential.
Gee ... maybe that's why we're having so much trouble getting power down coming out of corners?
The jack up and spin one tire trick does not work with a Torsen, which is what the 94'+ Miatas have.
http://www.miata.net/garage/vlsd.html" onclick="window.open(this.href);return false;
The times I have driven that car I never had any reason to think it had an open diff.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 5:19 pm
by Steve Ekstrand
That's a torsen diff in the 99 Miata's with LSD. Jacking both tires off the ground won't tell you anything because you have to have some load for it to lock at all.
err, yeah... What Isley said.....
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 6:24 pm
by Mako Koiwai
So how does one check for the presence of a Torsen LSD?
Since we raised the car up to legal ride heights we've been having a lot of problems getting power down. One has to be very judicious with the throttle or else one gets a lot of inside rear tire spin on corner exit. We're actually lifting the inside rear tire completely off of the ground. That's unusual for a Miata isn't it?
Next need to check to see that we still have pressure in our front Penske reservoirs. Last time we checked a couple of months ago, they were fine. Replacing the front A arm tomorrow which suffered a sheared off sway bar attachment point at the last practice. 1.125" front sway bar; HD sway bar mounts.
The Side by Side shot with Tim's car, Ryan driving shows that are car were remarkable similar in cornering attitude. But Ryan did note that it was hard to get the power down on our Miata. He said that last year there was a time when Tim's car felt like that, but then Tim had the rear end "overhauled," and then it was "1,000 times better." We've replaced the bushings and had the Penske's rebuilt earlier in the year ... but the problem persists ... not sure what else we can do? We've softened the rebound in the rear quite a bit ... that helped ... and we're running the front as stiff as possible ... quarter off full stiff on rebound.
We're running 150 psi in front; 125 in the rear. Any other suggestions?
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 6:27 pm
by Mako Koiwai
Checking out Jason's link now ...
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 6:32 pm
by Bob Beamesderfer
Mako Koiwai wrote:Checking out Jason's link now ...
The 10AE came with a Torsen. There are no external indications on any Miata differential that will tell you whether it's open or limited.
Isn't Tim's car the Sport model? Might have stiffer rear sway bar.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 6:33 pm
by Mako Koiwai
The Torsen action helps prevent a push in super tight corners. The one downside of the Torsen is that if one wheel is completely off the ground (zero traction) then the charactoristics of the Torsen will make it basically an open diff, both wheels have to have at least some traction for the unit to function properly.
... we've got to get that inside rear tire touching the ground!
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 6:33 pm
by Mako Koiwai
(Q)How do you identify Torsen's without dissasembly?
(A)The Torsen won't always turn both wheels when you turn the driveshaft, sometime if they are cold they will. One way is to take out the fill plug to see the Torsen gears which is hard to do because of the angle. Another way is to attempt to turn both half shafts in the same direction at the same time (tranny in neutral), can't be done with a Torsen. The foolproof way is to pull the stub axle on the type 1 or the drive axle on the type two. If you don't see a bar and can see directly thru the diff. it is a Torsen. If there is a bar, (spider gears) it's an open.
No bar=Torsen Torsen-Shaft.jpg (57 KB) Bar = open or RX-7 clutch type opendiffbar.jpg (39 KB)
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 6:47 pm
by Aaron Goldsmith
Mako Koiwai wrote:The Torsen action helps prevent a push in super tight corners. The one downside of the Torsen is that if one wheel is completely off the ground (zero traction) then the charactoristics of the Torsen will make it basically an open diff, both wheels have to have at least some traction for the unit to function properly.
... we've got to get that inside rear tire touching the ground!
Yes, soften the rear swaybar. Ended up disconnecting the rear bar in the supra and with a big front bar to solve that exact problem, got tired of v710 smoke at the exit of every corner. Got the Turbos spooled real good though.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 7:32 pm
by Jason Isley BS RX8
Mako Koiwai wrote:Next need to check to see that we still have pressure in our front Penske reservoirs. Last time we checked a couple of months ago, they were fine. Replacing the front A arm tomorrow which suffered a sheared off sway bar attachment point at the last practice. 1.125" front sway bar; HD sway bar mounts.
The Side by Side shot with Tim's car, Ryan driving shows that are car were remarkable similar in cornering attitude. But Ryan did note that it was hard to get the power down on our Miata. He said that last year there was a time when Tim's car felt like that, but then Tim had the rear end "overhauled," and then it was "1,000 times better." We've replaced the bushings and had the Penske's rebuilt earlier in the year ... but the problem persists ... not sure what else we can do? We've softened the rebound in the rear quite a bit ... that helped ... and we're running the front as stiff as possible ... quarter off full stiff on rebound.
All your problems sound like what you would get when you have a front bar issue. I have never heard of a Miata Torsen letting go on a stock car, and there is nothing to rebuild in there, no clutch pack.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 7:33 pm
by Jason Isley BS RX8
Bob Beamesderfer wrote:
Isn't Tim's car the Sport model? Might have stiffer rear sway bar.
A bigger rear bar would make it worse for Tim/Ryan.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 8:05 pm
by Bob Beamesderfer
Jason Isley BS RX8 wrote:Bob Beamesderfer wrote:
Isn't Tim's car the Sport model? Might have stiffer rear sway bar.
A bigger rear bar would make it worse for Tim/Ryan.
Yeah, that makes more sense now that I think about it again.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 8:13 pm
by Mike Simanyi
A bigger rear bar wouldn't be legal in Stock.
Mako, you have to keep that rear wheel on the ground for the Torsen to work. Your options include stiffening the front bar and softening rear rebound damping. I'd start with the latter since you probably already replaced the stock front bar.
Mike
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 8:15 pm
by KJ Christopher
Jason Isley BS RX8 wrote:
All your problems sound like what you would get when you have a front bar issue. I have never heard of a Miata Torsen letting go on a stock car, and there is nothing to rebuild in there, no clutch pack.
I agree. The RX8 had the exact same problem when my front bar came loose in San Diego.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 9:09 pm
by Mako Koiwai
Should we try increasing the pressure/damping beyond the 150 psi that we have in the front Penske reservoirs?
Increase the rear pressure also ... to help drive that inside wheel down?
So I guess it's OK in Stock to disconnect the rear bar ... you just can't change it out ... right?
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 9:57 pm
by Eric Clements
[quote="Mako Koiwai"
So I guess it's OK in Stock to disconnect the rear bar ... you just can't change it out ... right?[/quote]
Only if the factory service manual says that disconnecting the rear bar is OK for normal street duty.
Re: LSD? To Have Or Not To Have
Posted: Sun Nov 16, 2008 10:04 pm
by Jayson Woodruff
Mako Koiwai wrote:The Torsen action helps prevent a push in super tight corners. The one downside of the Torsen is that if one wheel is completely off the ground (zero traction) then the charactoristics of the Torsen will make it basically an open diff, both wheels have to have at least some traction for the unit to function properly.
... we've got to get that inside rear tire touching the ground!
Yes, I think this is what's happening to us in the MX5 at El Toro on some of the harder turns.
Jay W
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 6:47 am
by Bob Beamesderfer
Mike Simanyi wrote:A bigger rear bar wouldn't be legal in Stock.
Mako, you have to keep that rear wheel on the ground for the Torsen to work. Your options include stiffening the front bar and softening rear rebound damping. I'd start with the latter since you probably already replaced the stock front bar.
Mike
Wasn't saying he should bet one. Just noting possible difference in 99 Sport vs. 10AE
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 6:50 am
by Bob Beamesderfer
Mako Koiwai wrote:Should we try increasing the pressure/damping beyond the 150 psi that we have in the front Penske reservoirs?
Increase the rear pressure also ... to help drive that inside wheel down?
So I guess it's OK in Stock to disconnect the rear bar ... you just can't change it out ... right?
One adjustment at a time. Soften the rear rebound damping.
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 7:15 am
by Mako Koiwai
We had the rear rebound set to 5 turns off of full stiff on our Penske's at the last event ... after the front bar attachment point broke. Can't go much softer.
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 7:17 am
by Mako Koiwai
In the last few years there has twice been a LSD check for a class at Nationals ... where they had the competitors jack up one side of the car ... I believe, as opposed to front or rear. How we're they testing for an LSD doing that?
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 7:55 am
by John Coffey
So how does one check for the presence of a Torsen LSD?
Take off the rear cover and look inside. Spinning wheels to check for an LSD is foolish.
In the last few years there has twice been a LSD check for a class at Nationals ... where they had the competitors jack up one side of the car ... I believe, as opposed to front or rear. How we're they testing for an LSD doing that?
That's got to be the dumbest thing I've ever heard Solo2 tech do.
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 8:02 am
by Christine Grice
They have had us jack our cars up on one side and remove two tires but it had nothing to do with checking for an LSD. It was just so that the competitors/impound could get a better look at the suspensions. For example, missing bumpstops on a stock mini.
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 8:03 am
by Steve Ekstrand
When they checked diffs in STS2 this year they were removing halfshafts and looking inside. Not turning wheels.
Re: LSD? To Have Or Not To Have
Posted: Mon Nov 17, 2008 8:29 am
by Jason Isley BS RX8
John Coffey wrote:In the last few years there has twice been a LSD check for a class at Nationals ... where they had the competitors jack up one side of the car ... I believe, as opposed to front or rear. How we're they testing for an LSD doing that?
That's got to be the dumbest thing I've ever heard Solo2 tech do.
Not when it is done in a class with only open diffs. And this year they pulled an axle.