Re: Can you share more info Kaegi?

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Posted by Ken Dunnington [] on Saturday, June 05, 2021 at 15:38:46 :

In Reply to: Can you share more info Kaegi? posted by jase [] on Saturday, June 05, 2021 at 13:11:01 :

OD vs Direct being better or not is dependent on the rest of the drive train and intended use. If you have limited ratio options for the ring/pinion(as with the Chrysler 9-5/8), then the OD is often times desired. But if you can gear the ring/pinion for it, the direct drive transmission is superior in the ratio gaps between the gears.

The following is not NP540 specific but might be informative.

I have IH T34 and T35(and later T495) transmissions squirreled away for a future project. These are 5-speeds that are based on a Fuller 5 speed, similar in size to NP540. The T34 is OD. This is achieved via replacing the 4th gear in the direct trans with a gear that results in OD and is thus 5th gear. The former 5th gear remains direct and is now 4th. So the pattern is like this:

1 2 OD
R 3 4

T34 ratios: 6.21, 3.43, 1.81, 1.00, .082

You can see there is fairly large gap in the ratios between 2nd and 3rd, it's like skipping 3rd gear entirely in the direct T35:

1 2 4
R 3 5

T35 ratios: 7.17, 3.43(3.96), 2.41, 1.81, 1.00

The result is that of the two, I consider the direct T35 as superior to the OD T34 as long as one does not desire the OD due to a high ratio ring/pinion.


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