# New Rear end gears



## sknight751 (Feb 20, 2009)

I have a 1968 lemans that originally came with a 350 2v, 4 spd, AC, and Safe T Track rear end. I believe it has 3.09 gears. 

The car now has a nice 455 4V in it and I would like to change the gears. I would like some recommendations. I see that the GTO usually came with either 3.23 or 3.36. Sometimes 3.55. 

I frequently run on the expressway so I want to make sure it does not rev too high at 70 mph.

How much of a difference in performance will there be between the 3.09 and 3.23? Will 3.55 be too much-too many revs and highway speeds?

Thanks


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## Petey D (Feb 14, 2009)

3.55s will be okay at highway speeds, and you'll notice a big difference in "seat of the pants" acceleration fron the 3.09s. The purists will say go with the 3.23s.


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## 68greengoat (Sep 15, 2005)

And us non purists with 455's say, put in 3.55 if you don't mind going thru a little extra gas. That's what I'm going to put in mine when I have the xtra $. My buddy has a '68 400 with 3.55s and a Muncie tranny, I don't think it revs too high(I don't know the exact rpms). I suppose with a 455 it will rev a little higher. O'well, it's not like I'm running it year round.


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## geeteeohguy (Feb 2, 2008)

Pontiac didn't offer a 3.09 gear...it was a 3.08. That said, I would verify the gear ratio before changing it out. If it IS a 3.08, that's a GREAT ratio for a torque-mionster 455. Good power, excellent cruising, and the 455 won't know the difference. I wish I were able to find a 3.08 posi.....I'd like to change out the 3.36 in my '67 with something more hiway friendly.If you want to get rid of your 3.08 posi, let me know!!!


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## ppurfield001 (Jan 21, 2008)

sknight751 said:


> I have a 1968 lemans that originally came with a 350 2v, 4 spd, AC, and Safe T Track rear end. I believe it has 3.09 gears.
> 
> The car now has a nice 455 4V in it and I would like to change the gears. I would like some recommendations. I see that the GTO usually came with either 3.23 or 3.36. Sometimes 3.55.
> 
> ...



I recently installed 3:55s in my posi rear, replacing 3:90s, and my 1967 GTO cruises around 2,100 RPMS at 70 mph with a Muncie 4-speed. I like the 3:55s -- the car rocks off the line. Good luck.


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## geeteeohguy (Feb 2, 2008)

Ppurfield: how tall are your tires? All my '65 and '66 GTO's with 3:55 and 4 speed ran down the road at 3400 at 70. My 3:36 '65 4 speed with stock height (26.4") tires runs about 3000 rpm at 70. 2100 rpm's at 70mph is about a 2.73 rear gear with a stock height tire.


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## geeteeohguy (Feb 2, 2008)

My mistake...2100 RPM at 70 with 26.4" stock tires is actually a 2.51 gear ratio!!!


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