Thread: Changing internal gearing? (not final drive)

Do you mean change the gearing of 1st-4th? Like a whole internal gear swap from a different tranny.

Originally Posted by my97gtp

Are the gear ratio's in a 4t60 different? Im not sure if you would be able to change the parts and make everyting still fit and work the way it should. Its been a long time since i was in autotrans class so hard to remember everything.

That is part of the reason I was going to go to school one extra year. I planned on taking a year of auto classes (transmissions being one of the classes). But after thinking about it, it just wouldn't have been worth the extra money.


Ron why don't you just put some bigger tires on your car

And you think YOU have it bad lol. The 4L60E transmission has a 3.06 first gear then jumps waaaayyy down to 1.6ish for 2nd! Thats ok, the M90 cars make so much torque everywhere it doesnt bother me, especially since RWD cars hook up My cutlass cuts low 1.6 60' times on drag radials in full street trim, with a 2200 rpm torque converter. After the car comes off the line its a very small powerband, between 4950 and 6800 all the way down the track. 1st gear is basically a lever to move the car. The above with was 3.73 gears. I was going to stick 4.10s back in but since I am putting a turbo on the car I will never go through the traps in 3rd with that or the 3.73s as i crossed the line at 6K rpm in 3rd with the 3.73s. The car has 3.23 gears in it now so I should be safe for a while. Ron back to your wanting to change gear ratios, I dont know of anyone that has done this with any fwd GM trans but for other rwd old transmissions there are kits but VERY expensive. Remember in changing ANY of the gearing you altering every gear ratio 1st - Reverse. If its a strip only car then I would go with a higher stall converter and run 3.29 or 3.69 gears to let the engine sit higher in the powerband. Traction is always the problem with these cars so it makes it hard to have a car that does everything everywhere.

Originally Posted by Trannyman95

Traction is always the problem with these cars so it makes it hard to have a car that does everything everywhere.

Dont you love having a car that you can say that about? I do. I mean, its not like a Geo Metro or something, LOL.

Well Scotty thats why I put the engine in a rwd car lol.

4L80E ratios are
1st-2.48
2nd-1.48
3rd-1.00
4th-.75

4T80E ratios are
1st-2.96
2nd-1.63
3rd-1.00
4th-.68

4T60/65E ratios are
1st-2.92
2nd-1.57
3rd-1.00
4th-.71

There are a few different final drives for the 4T60/65E that will work in these transmissions BUT becaues the gears are of different tooth count and none of the other ratios are HD diffs I dont think the gearing changes between the two as the diff case is different sized for the gearing. IIRC the choices are 3.29 as the HD diff is, 3.05, and 2.86 for NON HD

Nope the internals are much larger and heavier in the 4L80E. The old THM400 uses the same gear ratio also, minus OD. Most guys want to go with a 2.75 1st gear conversion in those transmissions, Ive never heard of anyone wanting to go backwards! GM used the lower ratio in 1st for better in town acceleration. The 700R4 was originally designed for trucks and that is how the 3.06 ratio in 1st came into play and they never changed it. With NA engines its crap with the HUGE drop from 1st to second gear, but with the L67 in the car it doesnt car since there is so much torque across the powerband.

Well if its a race car get a 4500 stall converter then it will always be in the sweet spot lol. After the car launches its never going to be at a low rpm again, so that really doesnt matter. A Lingerfelter book that I bought a long time ago talks alot about the engines' powerband matching the trans, and having a manual trans or 6 speed per say keeps in in a really tight rpm range through the ran where an auto works better with an engine with a broad powerband. He plotted on a graph the rpms through each gear in the quarter mile and from that graph you average out what rpms you are at the longest period of time and that is where you focus everything on, not the peak numbers or the low rpms just going into each gear. Again if my cutlass with an ugle 3.06 first gear and a 2200 rpm stall converter is really never under 5K the whole way down the track and watching that on a HPT graph doesnt have much to it, its a very flat line the whole run and the engine sits within an 1800 rpm powerband almost the whole lenght of the track. It isnt in first gear long and it hooks up very hard, there is no wasted time feather or easing into the throttle, its WFO when the tree drops and hang on!

Originally Posted by Trannyman95

With NA engines its crap with the HUGE drop from 1st to second gear, but with the L67 in the car it doesnt car since there is so much torque across the powerband.

That explains why the GTs' pull till about 35-37mph then bog out, the gear change (if it were possible) would really help out the NA crowd, but then again none of us stay NA for that long