Transmission Gearing
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From: Minnesota
Transmission Gearing
This topic started in a discussion about differential gearing, but I thought I should start a new topic to continue the thread.
mtflat gave the gollowing info for the 4 spd gearing:
So what is the ratio for the first gear for the HD and LD 3 spd? I don't know for sure what I have -- it may be a HD 3 spd -- but the guy I bought the truck from said it was a 4 spd.
I have a couple of sources and I think I can get a used 3 spd with the open drive (LD). Assuming I should rebuild the tranny, can I use my 4 spd gears on the 3 spd output shaft? Does it make sense to try to get a little lower (assuming that 2nd on the 4 spd is lower than 1st on the LD 3 spd) starting ratio?
Thanks again.
Charles
mtflat gave the gollowing info for the 4 spd gearing:
Originally Posted by mtflat
I think Ford used the same tranny in 47 and in 48 (which is what mine happens to be)
Ratios in 48 for 4 spd spur or synchro gear transmission:
1st = 6.4, 2nd = 3.09, 3rd = 1.69 and 4th = 1.0
This is all in the shop manual. Practical - if you start out in 2nd gear you're about half way between the HD and LD 3 spd ratios. 3.50 rear will work fine, but 3.0 ? Don't think I would go that low.
Ratios in 48 for 4 spd spur or synchro gear transmission:
1st = 6.4, 2nd = 3.09, 3rd = 1.69 and 4th = 1.0
This is all in the shop manual. Practical - if you start out in 2nd gear you're about half way between the HD and LD 3 spd ratios. 3.50 rear will work fine, but 3.0 ? Don't think I would go that low.
I have a couple of sources and I think I can get a used 3 spd with the open drive (LD). Assuming I should rebuild the tranny, can I use my 4 spd gears on the 3 spd output shaft? Does it make sense to try to get a little lower (assuming that 2nd on the 4 spd is lower than 1st on the LD 3 spd) starting ratio?
Thanks again.
Charles
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Joined: Oct 1999
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From: Kalispell, MT
The 3 spd HD should be marked T87D on the passenger side of the case. I believe it is the same size as the 4 spd case, but I don't know what might swaps might work. All trucks since 42 used open drive tranny, unlike cars.
The 3 spd LD is much more slender - just like the car tranny.
Ratios:
3 spd LD - 2.819, 1.604, 1.0 R=3.625 (floor shift 49,50)
3 spd LD - 2.78, 1.62, 1.0 R=3.63 (column shift 51,52)
3 spd HD - 3.714, 1.871, 1.0 R=4.588 (floor shift or column are the same ratios)
4 spd - 6.4, 3.090, 1.690, 1.0 R=7.820 (spur gear and synchro versions use the same ratios)
All these figures are from the shop manual. I can't verify accuracy. Hope this helps.
The 3 spd LD is much more slender - just like the car tranny.
Ratios:
3 spd LD - 2.819, 1.604, 1.0 R=3.625 (floor shift 49,50)
3 spd LD - 2.78, 1.62, 1.0 R=3.63 (column shift 51,52)
3 spd HD - 3.714, 1.871, 1.0 R=4.588 (floor shift or column are the same ratios)
4 spd - 6.4, 3.090, 1.690, 1.0 R=7.820 (spur gear and synchro versions use the same ratios)
All these figures are from the shop manual. I can't verify accuracy. Hope this helps.
Last edited by mtflat; Sep 27, 2006 at 12:29 PM.
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