Transmissions and Drivetrain Need help with your trans? Problems with your axle?

M39 vs MK6

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Old Nov 17, 2015 | 06:25 AM
  #1  
PurelyPMD's Avatar
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From: Newtown, CT
Car: 1987 IROC Original Owner
Engine: LB9
Transmission: M39 MM5
Axle/Gears: G80 G92 J65
M39 vs MK6

Other than the 5th gear ratio being different, what are the differences between these two transmissions? Stiffer case, different input/output shafts, beefier internals, gear angles?

Is this similar to the M21 vs M22 comparison or is there more to it?

Anyone out there with intimate knowledge I would appreciate your input here.

Thanks
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Old Nov 17, 2015 | 07:11 AM
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Re: M39 vs MK6

The TBI and LG4 (grocery cart) cars got a .63:1 5th.

The L69 & LB9 (performance) cars got a .73:1 5th.

There is no other difference whatsoever between them. Same intermediate gear ratios, same weeeeek case, same tiny gears, same same same.

As far as the various 6-cyls, I haven't the vaguest clue what they got.
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Old Nov 17, 2015 | 05:45 PM
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From: Newtown, CT
Car: 1987 IROC Original Owner
Engine: LB9
Transmission: M39 MM5
Axle/Gears: G80 G92 J65
Re: M39 vs MK6

Did one have electronics for the speedometer or speed sensor and the other not?

Thanks
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Old Nov 17, 2015 | 05:52 PM
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Re: M39 vs MK6

No.

The setups for a cable speedo and for a VSS are COMPLETELY interchangeable. The transmission is the same. In fact in some years Camaro still used a cable with the VSS in the instrument cluster but the Birds used a trans-mounted VSS, in otherwise identical transmissions differentiated by application as described above.

Can't comment on 6-cyls. Those transmissions don't fit anything I would ever have and I would never use one for anything so I couldn't care less.
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Old Nov 17, 2015 | 06:39 PM
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jmd
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Car: `86 SS / `87 SS
Engine: L69 w/ TPI on top / 305 4bbl
Transmission: `95 T56 \ `88 200-4R
Re: M39 vs MK6

Originally Posted by sofakingdom
The TBI and LG4 (grocery cart) cars got a .63:1 5th.

The L69 & LB9 (performance) cars got a .73:1 5th.

There is no other difference whatsoever between them. Same intermediate gear ratios, same weeeeek case, same tiny gears, same same same.

As far as the various 6-cyls, I haven't the vaguest clue what they got.
Now that we no longer spout the 2.74 first gear tale anymore . . .

The 0.63 was not limited to LB9 / LG4; my first NWC T5 was 0.63 and from an '84 L69 Trans Am. The 0.63 makes perfect sense with 3.73 rear gears, which were offered with the L69 and LG4, but never the LB9, nor TBI.

And yes, 5th is the only difference between the two.
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Old Nov 17, 2015 | 07:03 PM
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Re: M39 vs MK6

Every L69 one I ever got, had a .73:1 in it. (my original and 2 others)

The only one I ever got that I knew for sure came from LB9 (actually came out of a 91 1LE car) had .73:1.

Every other one I ever got (quite a few, therefore likely to be from the more common cars) had .63:1.

I screwed up and put a .63 in my car once. (just the stock gears, 3.73) It SUCKED. It made the car feel like it needed another gear in between 4th and 5th; kinda like the 700-R4 feels almost like it needs a 1½th gear.

I threw a handful of .63 gears away once. Got tired of em sitting around. I think I've pared my T-5 junk down to the point that I don't have any more of em.

AFAIK all the V8 T-5s in these cars came with about a 2.95:1 1st gear.
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Old Nov 17, 2015 | 07:10 PM
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From: North Salt Lake
Car: '86 Camaro, '94 Camaro, 3 others
Engine: LG4 ->L29, L32->LR4, L36, LG4, L31
Transmission: 700R-4, T5WC, 4L80E, SM465, 4L60E
Axle/Gears: 3.42, 3.23, WTB/WTT 2.93
Re: M39 vs MK6

According to the GM heritage center, there were L69 / 0.63 combos, but in '85, not '84.
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