I'm looking into buying a TKX 5-speed to replace the Super T10 that is currently in my GS 455 Convertible. My question is about gear ratio's. My car has 3.42 gears and a 27 inch tall tire. They offer a 3.27 first gear or a 2.87 first gear. My T10 has a 2.88 first gear. The 3.27 seems pretty low to me but that is what Modern Driveline is recommending. I don't race the car but there is some "spirited driving" from time to time. The engine makes so much low-end torque I think the 2.87 gearing would be better. If you've done this swap what is your opinion? Ken
I have NOT done this swap but have researched it before I installed the M23Z with the 2.98 first gear. I have 3.08s so it makes them act like 4.15s in 1st gear compared to when I had the M21 with a 2.20 first gear. If you select the 2.87 first gear, it will change your effective rear gear ratio to 3.41. You will not notice a difference. If you are happy with how the car performs and how you take off in first gear, I would say that 2.87 1st gear would suit you. If you select the 3.27 first gear option, you would have an effective first gear equivalent to swapping in 3.88 rear gears. It would make for a snappy car. I'd be more concerned with the top overdrive ratio. There are 3 available options for 5th. With the 2.87 first you can have .82 that would behave like 2.80 rear gears at cruise. The .68 would behave like 2.33. The only overdrive option for 3.27 first gear is .72, which performs like 2.46 rear gears in overdrive. To further show the strengths and weaknesses of each overdrive, you currently have a 60MPH cruise at about 2500 RPM 3.42 rear gears, 27" tires and 1:1 4th gear. The .82 overdrive at 2500 RPM sets you at 71.5MPH. The .68 overdrive at 2500 RPM sets you at 86MPH. The .72 overdrive, again at 2500 RPM, shows 81.5 MPH.
Thank you both for your input. I do like the way the car feels with the 2.88 first gear I have now and think I'll go with the 2.87 /.68 overdrive. The guy at Modern Driveline was pushing the 3.27/.72 set up so I figured I'd ask here. Thanks, Ken
I have 3.42 rear, and the TKX with 327.1 first and .72 OD in my '68 with BBB. My '64 Skylark has the TKO with a 3.55 rear, the 327.1 first and .68 OD with the Nailhead. I live in Paris Arkansas, and have driven the '68 to Wichita and back several times as well as to Bowling Green and back. Have driven the '64 to Ocean Springs and back as well as to Ft. Walton Beach Florida several times. Both cars are happy at 85MPH only stopping for gas, and they pretty much both run within a few MPH/RPM of each other. Almost unnoticeable. Both cars run about 2500-2800 at highways speeds (varying 75-90) And both are very easy on 1st gear, whereas the '64 with the T-10 was always breaking loose if I was not careful to slip the clutch more than I liked, especially on incline, and almost like driving on ice when the roads were wet. But the shorter gears make it very easy to ease out on the clutch which is great for the clutch. And coming out of the hole they just jump and are gone. The gear spread is perfect for both cars at any speed. I got both from Modern Driveline as well. Decent folks to work with.
It almost sounds like I can't go wrong with either one. With all the stop and go traffic around here anymore maybe the 3.27 gear is the way to go. I want to start using the car a lot more this year instead of it sitting in the garage most of the time. I rebuilt the T10 myself about 12 years ago and it surprised me that it has held up to the BBB torque with no issues. When I get the TKX we are putting the T10 and a warmed up Buick 350 that is sitting on the engine stand ready to go into my son's '70 Skylark Convertible with a 3.42 rear. He plans on installing a TKX in his later down the road. I agree, Modern Driveline has been very good to work with so far. Thanks for the real world review. That helps a lot. Thanks, Ken
First gear ratio X rearend ratio around 10 is good. If you're not racing it doesn't matter too much. 3.27 x 3.42 = 11.2 2.87 x 3.42 = 9.8 I have a 2.56 first with a 3.73 rear = 9.54. This is very agreeable on the street with a mild 455, but at the track with slicks I wish I had a steeper first gear (or slightly more rear gear). I've found in general that a lower first gear ratio is more "fun" and with overdrive there is no penalty at highway speeds.
