Transmission Turboglide Swap - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 09-17-2012, 03:11 AM Thread Starter
 
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Transmission Turboglide Swap

I have a 1967 LeMans with a Turboglide transmission.
I would like to change this transmission to something else because it gear ratio is rather short therefore when cruising on the freeway at 70 Mph, the engine is going between 3500 and 4000 Rpm and at this rate my gas milage is around 8Mpg.

Does anybody has advice on what I should do?

Any recommendations will be greatly appreciated

Thank you
Ricardo
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post #2 of 6 (permalink) Old 09-17-2012, 12:11 PM
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It might be cheaper and easier to swap out the rear gear for a taller one.
What gear ratio does does the rear end have now?
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post #3 of 6 (permalink) Old 09-18-2012, 01:43 AM Thread Starter
 
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I will find out and let you know. My mechanic mentioned it to me but I can't remember right now. Thank you for your post.
Ricarod
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post #4 of 6 (permalink) Old 09-18-2012, 01:51 AM Thread Starter
 
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Rear End Ratio

I just found out that my rear end ratio is 3.70

Thanks
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post #5 of 6 (permalink) Old 09-18-2012, 03:53 PM
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There's the problem: the 3.70 rear ratio. All non-overdrive automatic trannies have a 1:1final rear ratio, so the swap of your probable Super Turbine 300 2 speed to a TH350 or TH400 would leave you with the same issue: high rpm on the open road. (Turboglide is a 3 speed tranny designed for the '58 Chevy, and had a "GR" on the shift quadrant for grade retard. A complex and problematic tranny.) You are left with installing an overdrive trans like a 200r4, 700r4, 4l60e, etc, ($$$) or swapping in a longer legged rear gear, like a 3.23 or 3.08. I installed a 2.56 rear end in my '67 (replacing the 3.36 unit) and my fuel economy went to over 20mpg at 75mph (2450rpm). The car is slower off the line, but after 30mph is attained, there is no noticable difference....except for low rpms, great fuel mileage, and high cruising speeds.
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post #6 of 6 (permalink) Old 09-20-2012, 07:18 PM Thread Starter
 
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Thank you all for your help.
Very valuable information so THANK YOU
I don't know which way I will be going.

RS
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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