How is final drive ratio determined in the 4t65e HD? Is it by the differential, the internals or a combination of the two? Is there a way to tell if the differential is an HD? Is there any way to tell what the differential ratio is?? For example, 3.03 or 3.76?

I will be doing a lot of work on my car this summer and I'd like to change the differential to a 3.03 if I can find one in a boneyard.

It's determined by the differential, and the chain gear ratio. What I mean by that is, at least on the 4T60e's, you can have a chain with 35/35 gears, 37/33 gears, or 33/37 gears. The number is teeth per gear. Less teeth means smaller gear.

There info on wikipedia on which GM cars that had that transmission have what final drive ratio. Normally in the 2.93 range if you get one from a Buick, geared for economy.

Thanks. I'll check out wikipedia. Did not think to check there.

3 differential ratios were available for the 4T65-E's: 2.86, 3.05, and 3.29.

3 chain ratios were available as well: 37/33, 33/37, and 35/35.

The combination of the two determines what the overall final drive ratio will be. If your goal is to get an overall final drive ratio of about "3.03", then I would suggest finding (or building a 4T65-E) with a 35/35 chain ratio and use a 3.05 ratio differential in it. That would give you a trans with an overall final drive ratio of 3.05:1.

I have ID tag code deciphering charts for these transmissions on my website here: http://www.gmtuners.com/transmission/index.htm so if you go to the junkyard, you can determine what gearing the transmission you are looking at has -- that is IF the ID code tag is still on that transmission and is legible.

-ryan

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quote Originally posted by Darth Fiero: 3 differential ratios were available for the 4T65-E's: 2.86, 3.05, and 3.29. 3 chain ratios were available as well: 37/33, 33/37, and 35/35. The combination of the two determines what the overall final drive ratio will be. If your goal is to get an overall final drive ratio of about "3.03", then I would suggest finding (or building a 4T65-E) with a 35/35 chain ratio and use a 3.05 ratio differential in it. That would give you a trans with an overall final drive ratio of 3.05:1. I have ID tag code deciphering charts for these transmissions on my website here: http://www.gmtuners.com/transmission/index.htm so if you go to the junkyard, you can determine what gearing the transmission you are looking at has -- that is IF the ID code tag is still on that transmission and is legible. -ryan

Thanks, Ryan. That is exactly what I am looking for. You're a real asset to the Fiero community. Thanks, again.