C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Black tag?

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Old Jun 25, 2014 | 10:44 PM
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Default Black tag?

So I pulled the trans today. Its been rebuilt obviously. Is this what everyone considers a "Black Tag"?


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Old Jun 25, 2014 | 11:51 PM
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Originally Posted by smooth1990
So I pulled the trans today. Its been rebuilt obviously. Is this what everyone considers a "Black Tag"?


Yes, that's a black tag.
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Old Jun 26, 2014 | 02:12 AM
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The 044 build is '92 & '93 and is the last of the 610Nm. There are later "black tag" transmissions BUT they're NOT 610 Nm units. There's considerable misunderstandings regarding ZF identification.
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Old Jun 26, 2014 | 08:30 AM
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Originally Posted by WVZR-1
The 044 build is '92 & '93 and is the last of the 610Nm. There are later "black tag" transmissions BUT they're NOT 610 Nm units. There's considerable misunderstandings regarding ZF identification.
As I understand it...The ZF6 came pre-assembled, pre-filled from ZF in Germany. It was a non-serviceable part. So when a customer brought the car in with a trans issue, they send the old one back to ZF and install a new one. ZF in turn would reman the trans and those became replacements. If this was done after '93, the reman'd trans was built with the 'blue tag' gears, which were quieter. Those trans would have the original black tag, as well as a blue tag added to it. (manufacturer tag, not the one in the pic)

Transmission noise was a relatively common complaint with the black tags, depite the use of the DMF, and people would bring them in, and they got replaced. Being a non-serviceable part, they couldn't take apart to see if it was actually faulty. So they just pulled it and replaced it.

At least, this is how I understand the story about the ZF in the C4.
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Old Jun 26, 2014 | 11:34 AM
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Originally Posted by WVZR-1
The 044 build is '92 & '93 and is the last of the 610Nm. There are later "black tag" transmissions BUT they're NOT 610 Nm units. There's considerable misunderstandings regarding ZF identification.
Isn't the input and output shafts bigger on the black tag transmission?
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Old Jun 26, 2014 | 12:19 PM
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Originally Posted by smooth1990
Isn't the input and output shafts bigger on the black tag transmission?
No - neither.
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Old Jun 26, 2014 | 12:31 PM
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Originally Posted by WVZR-1
No - neither.
Hmm that's what I thought was the difference. What exactly is different between the two then?
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Old Jun 26, 2014 | 01:59 PM
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Originally Posted by smooth1990
Hmm that's what I thought was the difference. What exactly is different between the two then?
There are only two input shafts for the ZF. An LT1/4 - L98 length and an LT5 length. All 610 Nm and 540 Nm are the same.


Originally Posted by smooth1990
Isn't the input and output shafts bigger on the black tag transmission?
You asked bigger and they're not and that's what I answered. The pitch of the internals are different on both the counter shaft gears and the main-shaft gears which resulted in the "less noise" and also the diminished power handling capabilities. The main-shaft is "different" but NOT bigger.
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Old Jun 26, 2014 | 05:28 PM
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Originally Posted by WVZR-1
There are only two input shafts for the ZF. An LT1/4 - L98 length and an LT5 length. All 610 Nm and 540 Nm are the same.




You asked bigger and they're not and that's what I answered. The pitch of the internals are different on both the counter shaft gears and the main-shaft gears which resulted in the "less noise" and also the diminished power handling capabilities. The main-shaft is "different" but NOT bigger.
Thanks for clearing that up! I wasnt sure!

Any idea how much power the black tag 610 Nm can handle?
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Old Jun 26, 2014 | 05:47 PM
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Originally Posted by smooth1990
Thanks for clearing that up! I wasnt sure!

Any idea how much power the black tag 610 Nm can handle?
I don't recall ever seeing a # posted that actually "broke" a ZF. Have ZF's failed? Certainly but then one needs to know the why. Could be poor maintenance or any number of reasons. I'd think most were maybe abuse (being beat on), not used hard but "abused".

One needs to understand 6th wasn't intentioned to be an everyday "high speed" gear. One goes crazy with rear axle ratio and starts asking for more from 6th and it just wasn't intentioned for that use.
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Old Jun 27, 2014 | 12:28 AM
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Originally Posted by smooth1990
Isn't the input and output shafts bigger on the black tag transmission?
Not sure if it was wider (diameter) or just cut differently, but the black tag and blue tag require different throw out bearings.
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Old Jun 27, 2014 | 01:18 AM
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Originally Posted by lt4obsesses
Not sure if it was wider (diameter) or just cut differently, but the black tag and blue tag require different throw out bearings.
That's not a difference dictated by the input shaft but the guide tube that is used in the build, guide tubes are different diameters. There's two lengths, LT1/4-L98 with both diameters and LT5 in both diameters. Swapping the guide tube and retainer ring can change the release bearing required for the install.
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