Traction Lok Gear Ratio - Vintage Mustang Forums

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post #1 of 16 (permalink) Old 12-02-2012, 12:37 PM Thread Starter
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Traction Lok Gear Ratio

I am thinking about changing my 9" rear end gear ratio for more low end performance. Currently traction lok, 3.50 gears, 28 spline, TKO500, 3.27 first, 1.98 second, 1.34 third. 1.0 forth, .68 fifth gear. I am thinking of upgrading to 31 spline at the same time. Not concerned about gas mileage. My Mach 1 isn't a daily driver. I am thinking at least 3.73 gears. I just don't have a good feel for gear ratios. Experts, please provide your thoughts. Alan
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post #2 of 16 (permalink) Old 12-02-2012, 01:00 PM
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With that 3.27 first gear IMHO anything lower than what you have now is going to make it useless. Sure, you could go 3.70, 3.80 or 3.89 because you have the .68 OD. If you WERE going to go this route I'd talk to somebody like Standard Transmissions about changing your 1st gear ratio from 3.27 to 2.87. IMHO, I'd stick with the 3.50 rear gear and swap the tranny out for a TKO 600 with the 2.87 first and .82 OD.
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post #3 of 16 (permalink) Old 12-02-2012, 01:14 PM
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Why 31 spline axles? Unless you're planning to make some serious horsepower and run slicks, those 28 spline axles are plenty strong. I used to drag race a mild 351C on nitrous with drag slicks on factory 28 spline axles and never had an issue.

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post #4 of 16 (permalink) Old 12-02-2012, 01:40 PM Thread Starter
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I am just doing a what if, maybe I already am setup well. My tko500 is an awesome tranny after liberties gear had at it. Not changing the tranny. Keislers speed analyzer says the following when compared to a close ratio toploader. 295-40-17
TKO 500; 3.50 rear, acts like 4.93, 3.70 rear acts like 5.21
TKO 600; 3.50 rear acts like 4.32, 3.70 acts like 4.57, 3.90 acts like 4.81

It comes back to me, this is the data I was looking at when selecting the tranny.

Maxim can you go the the Keisler speed analyzer and report what your ratio acts like when compared to a close ratio toploader? Also how does your car run in first and second?

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post #5 of 16 (permalink) Old 12-02-2012, 02:01 PM
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Quote:
Originally Posted by Alan _MacDougall View Post
I am just doing a what if, maybe I already am setup well. My tko500 is an awesome tranny after liberties gear had at it. Not changing the tranny. Keislers speed analyzer says the following when compared to a close ratio toploader. 295-40-17
TKO 500; 3.50 rear, acts like 4.93, 3.70 rear acts like 5.21
TKO 600; 3.50 rear acts like 4.32, 3.70 acts like 4.57, 3.90 acts like 4.81

It comes back to me, this is the data I was looking at when selecting the tranny.
That's fine for the OD, but it's the steep first gear that is going to hurt with a lower rear gear.
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post #6 of 16 (permalink) Old 12-02-2012, 02:18 PM Thread Starter
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bartl, thanks for your input.
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post #7 of 16 (permalink) Old 12-02-2012, 03:08 PM
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Quote:
Originally Posted by Alan _MacDougall View Post
Maxim can you go the the Keisler speed analyzer and report what your ratio acts like when compared to a close ratio toploader? Also how does your car run in first and second?
Not quite sure what you're after. But I have a 3.27 first with a .68 fifth gear. With my horsepower level (est. 550hp-600hp) if I stick my foot in it, my car just obliterates the tires (275/60/15) in first and second gears at any speed.

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post #8 of 16 (permalink) Old 12-02-2012, 03:25 PM
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My rule of thumb is 12:1 max starting line ratio (SLR), determined by 1st gear X rear gear. You can sneak a little higher if you run a really tall tire, like a 275/60-15 but generally its a pretty decent rule for the lowest rear gear

So for you 12/3.27=3.669 gear, or a 3.70. I wouldnt go much lower than that.

On the other end that gives you 3.70*.68=2.51, decent for the highway

With that being said, LOTs of 5.0s ran 3.73s happily with T-5s and ended up slighty above 12.0:1 SLR

I wouldn't go much more than that though, or 1st gear will be a pain and you'll find yourself starting in 2nd everywhere

FWIW, I run a TKO-600 with an SLR of 11.77 with 275/60s and 1st seems short


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post #9 of 16 (permalink) Old 12-02-2012, 03:30 PM Thread Starter
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Maxum what is your rear end gear ratio?
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post #10 of 16 (permalink) Old 12-02-2012, 04:24 PM
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Quote:
Originally Posted by Alan _MacDougall View Post
Maxum what is your rear end gear ratio?
Maxum runs 4.11s.

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post #11 of 16 (permalink) Old 12-02-2012, 04:35 PM
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Quote:
Originally Posted by My427stang View Post
My rule of thumb is 12:1 max starting line ratio (SLR), determined by 1st gear X rear gear. You can sneak a little higher if you run a really tall tire, like a 275/60-15 but generally its a pretty decent rule for the lowest rear gear

So for you 12/3.27=3.669 gear, or a 3.70. I wouldnt go much lower than that.

On the other end that gives you 3.70*.68=2.51, decent for the highway

With that being said, LOTs of 5.0s ran 3.73s happily with T-5s and ended up slighty above 12.0:1 SLR

I wouldn't go much more than that though, or 1st gear will be a pain and you'll find yourself starting in 2nd everywhere

FWIW, I run a TKO-600 with an SLR of 11.79 with 275/60s and 1st seems short
I'm fascinated by SLRs. What I have a hard time is applying that to tire sizes. Is 11-12 based on what tire? I'm at same spot Alan is too. I have 3.50 rear with 2.87 and .7 OD and 27.7 rear tire. I'm debating 4.11 or 4.30. Which gives SLR of 11.8 or 12.3.

'71 Fastback
9in 31 spline 4.30 Winters Performance True Trac, 4r70w manual valve body and hardened gear set, 408w with 225 High Ports, FTI Solid Roller cam, Super Vic; Aluminum MMC driveshaft, 3" Exhaust.
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post #12 of 16 (permalink) Old 12-02-2012, 04:39 PM
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Alan, do you run yours in 1/4? Lots of guys select their rear by what rpm they are running through the traps. Like if they need more RPM or are running out, they gear accordingly.

'71 Fastback
9in 31 spline 4.30 Winters Performance True Trac, 4r70w manual valve body and hardened gear set, 408w with 225 High Ports, FTI Solid Roller cam, Super Vic; Aluminum MMC driveshaft, 3" Exhaust.
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post #13 of 16 (permalink) Old 12-02-2012, 05:09 PM Thread Starter
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Thanks guys, good info. I also am interested in understanding the SLR further. I haven't run the 1/4 yet. But it would be a good idea to do it this summer to really understand where I at. Alan

Last edited by Alan _MacDougall; 12-02-2012 at 05:17 PM.
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post #14 of 16 (permalink) Old 12-02-2012, 05:12 PM
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When considering SLR, bear in mind that if you have decent torque you don't need to be on the high end of SLR. That and the span from a 3.27 first gear to a 1.98 second gear is waaaaaaay wide. If you've got a motor that makes good power up high that you've got to wind the p!ss out of it in first to be able to catch second with enough rpm to keep it in the power band.
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post #15 of 16 (permalink) Old 12-02-2012, 07:50 PM
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Quote:
Originally Posted by CrackrStang71 View Post
Maxum runs 4.11s.

That is correct. And if I ran any shorter of a tire (275/60/15) in the back, I would probably drop my gears down to 3.91. My first gear is fairly short with 4.11's.

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393 Windsor AFR 205 heads with 11.5:1 compression, Victor Jr. intake, solid roller cam with shaft mount roller rockers
Tremec TKO 5 Speed






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