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Discussion Starter #1
I am considering changing my rear gears from 3.42 to 3.73. I have a Tremec 3650 5 speed with .62 overdrive 5th gear and a 3.38 1st gear. I have 27" rear tires.

The 3.38 1st gear is fine with the 3.42 rear but I'm wondering if the low 1st gear will be too much of a creeper gear with the 3.73's.

My transmission came out of a 2004 Mustang GT which came with 3.73 rear gears and 25 3/4" rear tires so I'm thinking I should be okay. I just cruise in the car and don't race it.

Anyone have any thoughts on this?
 

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I'm jealous of your extra gear on the 5 speed! Wish I could go for longer drives on highway. I have 3:73's with 25 or 26" tall tires and it revs pretty high on the highway. But that's because I plan to do some bracket racing and I want that gearing.

If you don't plan on racing, I am pretty sure that if I was you I'd keep the gears you already have.

Just my 0.02
 

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Discussion Starter #3
I'm jealous of your extra gear on the 5 speed! Wish I could go for longer drives on highway. I have 3:73's with 25 or 26" tall tires and it revs pretty high on the highway. But that's because I plan to do some bracket racing and I want that gearing.

If you don't plan on racing, I am pretty sure that if I was you I'd keep the gears you already have.

Just my 0.02
The reason I'm considering the 3.73's is because at 65mph its turning about 1800 rpm which isn't lugging it but not far from it. The 3.73's would gain a little over 100 rpm at 60-65 mph and let me use the overdrive more than just at lets say 70 mph and above.
 

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I’d do 3.73s all day with an extra gear. I Run 4.10s in my car with a th350. Zings the motor pretty good. But my engine makes peak power just a touch above 7k rpms. I have a 3.55, 3.73, and 4.10 gear set. I’ll probably throw the 3.73s back in. Save on my valve train a little...
 

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Discussion Starter #7 (Edited)
383 with TKO600 and I love my 4.10s with 26 in. tire!
Deryl--According to my calculations, with your 26" tires and 4.10 rear with a 2.87 TKO 600 1st gear ratio, your final drive ratio in 1st gear is 11.77:1.

With my 27" tires and 3.42 rear with a 3.38 1st gear ratio, my current final drive ratio in 1st gear is 11.56--almost the same as yours. It's fine in first the way it is now. If I go to 3.73s it would be 12.61:1 in 1st gear. I'm wondering if that would be too low for 1st gear.

I'm convinced the 3.73s would be great with my overdrive and enable me to use it a a little lower speed (& more within the speed limit :) ). But I just wonder what 3.73s would be like in 1st gear with a 12.61:1 overall ratio.
 

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72, 2 Dr, 383, 700r4
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I just installed a 700r4 and 3.73 gears. I'm not road ready yet but my Chevelle friend is running that combo and loves it for the street. No way with a TH350.
 

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What’s the 2nd gear ratio in your trans and what’s the final drive ratio of that work our to? Maybe your 1st gear will be irrelevant unless pulling a trailer up a hill or a tree stump out of the ground..
 

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Discussion Starter #10
What’s the 2nd gear ratio in your trans and what’s the final drive ratio of that work our to? Maybe your 1st gear will be irrelevant unless pulling a trailer up a hill or a tree stump out of the ground..
Second gear is 2.00 so final drive would be 7.46.
 

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Discussion Starter #11
I just installed a 700r4 and 3.73 gears. I'm not road ready yet but my Chevelle friend is running that combo and loves it for the street. No way with a TH350.
Do you know what 1st gear ratio is in your 700r4?
 

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first gear in a 700r4 is 3.06, second is 1.63, third is 1.0 an the OD is .70. an i'm running 3.55 rear. very nice on the highway at 70-75 mph
 

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Deryl--According to my calculations, with your 26" tires and 4.10 rear with a 2.87 TKO 600 1st gear ratio, your final drive ratio in 1st gear is 11.77:1.

With my 27" tires and 3.42 rear with a 3.38 1st gear ratio, my current final drive ratio in 1st gear is 11.56--almost the same as yours. It's fine in first the way it is now. If I go to 3.73s it would be 12.61:1 in 1st gear. I'm wondering if that would be too low for 1st gear.
I don't think you're going to notice a difference between 11.56:1 and 12.61:1, other than the sound.
 

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Discussion Starter #16
I don't think you're going to notice a difference between 11.56:1 and 12.61:1, other than the sound.

When you boil it all down I guess that is my real question--how much difference would it make for normal driving--especially in 1st gear. It's not bad now so I guess the tires would make about 1 revolution more at a given RPM. I guess it would wind up a little quicker in each gear. I welcome that in 2nd, 3rd and 4th plus I would have OD that is more useable from 55 mph on up.

I have observed 00-04 5 spd Mustang GTs & Mach 1s which came with 3.73s and my same transmission fairly often and they seem to wind up pretty quick but also seem street friendly. Since my tires are 1 1/4" bigger diameter it would probably be okay.
 

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What’s the 2nd gear ratio in your trans and what’s the final drive ratio of that work our to? Maybe your 1st gear will be irrelevant unless pulling a trailer up a hill or a tree stump out of the ground..
Hah, I was thinking the same thing! Use second gear for most stop light starts and then use first to smoke the punk in the lane next to you.

Most of those overdrives in MHO are too steep for our cars so the added gear is really a good thing. Put the gear in it and have a blast....
 

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Discussion Starter #18
Hah, I was thinking the same thing! Use second gear for most stop light starts and then use first to smoke the punk in the lane next to you.

Most of those overdrives in MHO are too steep for our cars so the added gear is really a good thing. Put the gear in it and have a blast....
Yeah--When I had the transmission built it was supposed to be .68 OD but turned out to be .62. Overall it's good now but the 3.73s may be coming in the near future. We'll see. :cool:
 

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Discussion Starter #20
Thanks everybody for your input. It's been very helpful. Not sure what I'm going to do yet but leaning toward going 3.73. If I do should be in the next 6 weeks or so. Will report back!
 
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