So I may have a line on a lowish mileage 2002 4t65e-HD. I'm trying to see how much of a disaster this will be to fit in my M15 4t65e equipped '99 Bonne L36.

Its my understanding that there are three issues here...

1. That I would need a shorter HD axle for the pass side.

2. The 4t65e-HD has a 2.93 ratio... my stock tranny is 2.92. How bad is that going **** off the PCM?

3. That the gear selector switched from external to internal at some point. How hard is it to adapt that?

Any thoughts, I 'd appreciate it. Thanks in advance.

BKNJ

The 4T65-E and the 4T65E-HD are pretty much identical beasts on the outside. You might have trouble with electrical connectors and mounts, but it all depends on what car it came from.

Going from a 2.84 gearing to/from 3.06 changes the 4T60-E shift points by about 100 RPM, IIRC. Doing the math, a 0.01 difference should throw your shifts off by about 5 RPM.

Your stock non-hd trans should be either a 2.84 or 3.06 gear ratio (or it'* 2.86/3.05, I honestly forget). All 4T65HD'* are 2.93.

You would need different programming to make it work properly (pretty easy).

The external to internal PNP'* are easy. You would just need to add it on externally since your car has the external.

The pressure manifold inside the trans would need to be swapped over as well. The 02 will have a single pressure type manifold and your 99 will have a manifold with many pressures. I'm unsure if the valve body would have all the holes for the pressures you would need. I believe it does though. So you could pull the side cover, switch the electrical harness, pressure manifold and be all set.

It'* 2.84 and 3.06 on the Bonneville 4T60-E'*.

I don't have a 4T60E. I have a 4T65E... an M15... which according to Wikipedia (granted, not the best source) is a 2.92 ratio.

Thats why I'm curious if the 0.01 difference in ratios between the M15 4t65E and the 4T65E-HD (2.93) would cause serious problems for the computer.

The thing about final drive ratios is that PCMs are programmed to shift at certain speeds, and the speeds show up incorrectly when you go to a new ratio. If you were to switch from a 2.92 to a 2.93, the speed difference would be negligible and wouldn't call for a retune. If you were to go from a 2.86 to a 2.93, the speed difference wouldn't be negligible, and you may end up shifting at over 6000 RPM if you were not to do a fresh tune on your Bonneville.

There is no such ratio as 2.92 for the 4T65E transmission, so it'* time to change that Wikipedia article! I just searched Wikipedia, but I can only find M15 for the Bonneville under the 4T60-E. The 4T60-E did have a 2.92 FDR, and it also had 2.84 and 3.06. The 4T65-E can be found with 2.93, 2.86, and 3.05 ratios. All the ratios are close like that, so if you find a drive ratio that'* not spot-on to the 4T65-E as these guys list it but is very, very close, you're probably looking at the ratios of "the other" transmission.

Best of luck, and let us know how it goes!

Gear ratio on a 4T65 in an NA car is either 3.05 or 2.86, it'* not 2.92. I've looked that up in the ATSG manual and factory service manuals.