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Old 05-04-2008, 09:39 AM   #1
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4th Generation Zexel Tornsen Rear End

Hello All,

I recently purchased a rear end that was supposedly a 3.23 Zexel Torsen rear end from a 1999 Z28 to put into my 1991 GTA. The rear end was already pulled so I cannot verify it came fromt the Z28 they had in the junk yard. The numbers on the differential are 9020 98701309. I have a few questions that I am hoping you guys can help me with before I put the rear end in the car.

1) How can I make sure that this is an actual Limited Slip rear end? I will spin 1 wheel and the other wheel spins in the opposite direction. According to some websites this means it is an open differential. However, I have also read that the Zexel Torsen does not operate like a typical LSD and cannot be identified by the "wheel spin test." I pulled the back cover off. Can someone post a picture of what the Zexel Torsen internals look like?

2) Will my GTA wheels mount directly to the new rear end or do I need some kind of wheel spacer?

Any help would be greatly appreciated! I do not want to put this on my car and have the dreaded 1 wheel peel.
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Old 05-04-2008, 09:52 AM   #2
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Re: 4th Generation Zexel Tornsen Rear End

The easiest thing to spot is the torsen does NOT have a 5/8in shaft that the spiders go on. And that it uses helical cut side gears instead of bevel side gears and spiders.
Click the image to open in full size.
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Old 05-04-2008, 10:08 AM   #3
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Re: 4th Generation Zexel Tornsen Rear End

also, your wheels will mount directly to the rear but they will stick out about 2" more on each side.
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Old 05-04-2008, 11:20 AM   #4
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Re: 4th Generation Zexel Tornsen Rear End

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Originally Posted by 87zjeff View Post
also, your wheels will mount directly to the rear but they will stick out about 2" more on each side.
2" more on each side?

Oh man, that's too much for me. I was considering a swap for better brakes, but if it's 4" wider overall, then I'll pass.
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Old 05-04-2008, 11:25 AM   #5
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Re: 4th Generation Zexel Tornsen Rear End

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also, your wheels will mount directly to the rear but they will stick out about 2" more on each side.
2" more on each side?
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Old 05-04-2008, 11:32 AM   #6
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Re: 4th Generation Zexel Tornsen Rear End

Put the rear in. I have my wheels spaced out 3/4" from factory and they could still go more. The factory rear wheels are tucked too far inward IMHO.
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Old 05-04-2008, 02:44 PM   #7
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Re: 4th Generation Zexel Tornsen Rear End

I installed a rear from a 4th gen in my 92,I measured the old rear and also the 94 before I took the old one off,just to see where my wheels would be afterwards,the difference is 1'1/2 on each side,don't know if all 4th gen rears are the same,mine is from a 94 z28 with disc brakes,best thing to do is measure both rears and that will tell you where your wheels will be when your done.
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Old 05-04-2008, 03:46 PM   #8
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Re: 4th Generation Zexel Tornsen Rear End

Quote:
Originally Posted by wildjyoung View Post
Hello All,

I recently purchased a rear end that was supposedly a 3.23 Zexel Torsen rear end from a 1999 Z28 to put into my 1991 GTA. The rear end was already pulled so I cannot verify it came fromt the Z28 they had in the junk yard. The numbers on the differential are 9020 98701309. I have a few questions that I am hoping you guys can help me with before I put the rear end in the car.

1) How can I make sure that this is an actual Limited Slip rear end? I will spin 1 wheel and the other wheel spins in the opposite direction. According to some websites this means it is an open differential. However, I have also read that the Zexel Torsen does not operate like a typical LSD and cannot be identified by the "wheel spin test." I pulled the back cover off. Can someone post a picture of what the Zexel Torsen internals look like?

2) Will my GTA wheels mount directly to the new rear end or do I need some kind of wheel spacer?

Any help would be greatly appreciated! I do not want to put this on my car and have the dreaded 1 wheel peel.

Your 91 GTA should already have the 28-spline axles needed to install the Zexel Torsen differential so there should be no need to install the entire 4-th gen axle assembly/rear end unless you want to. Just remove the differential from the 4th gen and install it into yours. I would recommend getting a solid bearing spacer to replace the crush sleeve and upgrade to a new diff cover/girdle.

The Zexel torsen is inherently a "limited slip" differential, and with it's gears instead of a clutch pack, never needs to be rebuilt like a standard limited slip does. **HOWEVER** the main flaw with a Zexel torsen is that when BOTH wheels lose 100% of their traction, it will act exactly like an open rear rend. So, if you ever get on ice (or put it on jacks like you did) where the wheel that is slipping completely loses all it's traction, the whole thing will just spin like an open differential. If you put some sort of tention on the other wheel, then both should spin forward when you spin the one. Have someone hold the other wheel in place so it can't move while you spin yours and see what happens. They should then both spin forward.

The only way to get away from this is to buy a High Biased model that has a clutch and spring set in it that will overcome the tendency for it to operate as an open when there is no traction on one of the tires. These were made specifically for Motocross purposes and weren't ever available in our cars. Still, you can buy them new from Reider Racing for $600.00. I just bought one for my 84 T/A which finishes upgrading my my rear to *Hopefully* handle the new motor I am installing.
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Old 05-04-2008, 04:21 PM   #9
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Re: 4th Generation Zexel Tornsen Rear End

Might as well buy an Eaton Detriot Truetrack with positive pre-load for $450.
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Old 05-04-2008, 04:25 PM   #10
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Re: 4th Generation Zexel Tornsen Rear End

Aye, what twilightoptics said. The Truetracks are a a bit cheaper than the Zexel Torsen models.
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Old 05-04-2008, 04:43 PM   #11
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Re: 4th Generation Zexel Tornsen Rear End

Quote:
Originally Posted by afremont View Post
2" more on each side?

Oh man, that's too much for me. I was considering a swap for better brakes, but if it's 4" wider overall, then I'll pass.
2" out is JUST right...Here's a 4th gen rear, stock wheels & 245s...

Click the image to open in full size.
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Old 05-04-2008, 04:47 PM   #12
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Re: 4th Generation Zexel Tornsen Rear End

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Originally Posted by afremont View Post
I was considering a swap for better brakes, but if it's 4" wider overall, then I'll pass.
Then put the brakes on your 3rd gen rear, along with swapping the zexel in. There is a tech article for the brake swap here. I already did the zexel swap, and doing the LS1 rear brakes now.
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Old 05-05-2008, 09:40 AM   #13
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Re: 4th Generation Zexel Tornsen Rear End

Thank you very much, I appreciate your help! It looks like I do have the 3.23 Zexel Torsen rear end. However, mine is different from the pictures because I have what looks like a vertical gear pattern directly next the the large gear in the rear end (I will post pics).

I thought all rear ends after 1998 were cut down a bit shorter, so the rear end should only cause my wheels to stick out about 1" on each side. I think it looks fine and actually gives a more aggressive stance. My old rear had drum brakes, so I do not think I can switch things over.

Everyone, I greatly appreciate your help! I have working on my restoration for 3 years and am hoping to get the car on the road this year!
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Old 05-05-2008, 11:51 AM   #14
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Re: 4th Generation Zexel Tornsen Rear End

Quote:
Originally Posted by wildjyoung View Post
My old rear had drum brakes, so I do not think I can switch things over.
Did you even look at the tech article I mentioned about swapping brakes???


http://www.thirdgen.org/ls1reardisc
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Old 05-06-2008, 12:37 PM   #15
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Re: 4th Generation Zexel Tornsen Rear End

Quote:
Originally Posted by wildjyoung View Post
Thank you very much, I appreciate your help! It looks like I do have the 3.23 Zexel Torsen rear end. However, mine is different from the pictures because I have what looks like a vertical gear pattern directly next the the large gear in the rear end (I will post pics).

I thought all rear ends after 1998 were cut down a bit shorter, so the rear end should only cause my wheels to stick out about 1" on each side. I think it looks fine and actually gives a more aggressive stance. My old rear had drum brakes, so I do not think I can switch things over.

Everyone, I greatly appreciate your help! I have working on my restoration for 3 years and am hoping to get the car on the road this year!
What wheels do you have now? If they are stock, or stock size, they won't stick out, but rather, line up almost perfect. Look at the pic I posted above.

Last edited by Stephen; 05-06-2008 at 12:43 PM.
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Old 05-07-2008, 07:47 AM   #16
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Re: 4th Generation Zexel Tornsen Rear End

I currently have the gold spoke GTA rims. I saw your picture above and really like the tire placement with the 4th Generation axle, so I am going to install the entire thing. It gives the car a much more aggressive stance.
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Old 05-08-2008, 01:14 AM   #17
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Re: 4th Generation Zexel Tornsen Rear End

I dont mean to thread jack, but since I'm running C5 Vette wheels on 2in spacers, when I install a 4th gen disk rear I can toss the rear spacers? That would definitly be nice.

Max,
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Old 05-08-2008, 01:17 AM   #18
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Re: 4th Generation Zexel Tornsen Rear End

Yes. Sell them to the next C5 wheel on a 3rd gen rear owner.
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Old 05-08-2008, 02:00 AM   #19
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Re: 4th Generation Zexel Tornsen Rear End

Haha, yeah I've noticed I'm faaaaaarrrr from the first guy to use these wheels.

Thanks,
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Old 05-08-2008, 06:04 AM   #20
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Re: 4th Generation Zexel Tornsen Rear End

98-02 rear end,
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.


And below is Z06 wheel with 315/35/17 tires,
Click the image to open in full size.

Click the image to open in full size.
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Last edited by Zepher; 05-08-2008 at 06:08 AM.
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Old 05-08-2008, 11:10 AM   #21
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Re: 4th Generation Zexel Tornsen Rear End

Zepher, KILLER stance from the rear. I have 275/40/18 on the rear, so I'm close. You wouldent happen to know the backspacing on those ZO6 wheels would you? I wonder if I could squeeze a 315 on my C5's after the axle swap.


Thanks,
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Old 05-08-2008, 08:01 PM   #22
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Re: 4th Generation Zexel Tornsen Rear End

Thanks.
I have no idea what the backspacing/offset are. I think they are AFS replica Z06 wheels, 17x9.5". the 315 I am running is a Sumitomo, which are much skinnier than other brands/models.
The Z06's used to have 315 BFG G-Force KD's on the wheels and I couldn't put the wheels on my car with those, it would rub the inner fenderwell and the wheel wouldn't turn..
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Hooker Headers, Borla Catback, Lakewood LCA's, BMR Adj. Panhard, 2" Skulte Adaptors, 17" ZR1's w/ Nitto 555RII's,
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Old 05-09-2008, 09:26 AM   #23
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Re: 4th Generation Zexel Tornsen Rear End

Zepher I agree, the stance on your car looks great! I actually think the factory should have put the wider rear on the car in the first place. It gives the car a much more aggressive stance.
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Old 05-09-2008, 09:26 AM
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