/6 with 4 Speed OD, rear gear recommendations?

TheDemonator said

I have to second what Orv says.

I have an 833OD from a 75 Dart Sport, my OD ratio is .73

Running a 4.10 rear gear makes my car very quick off the line... and when you go into OD it is just a shade under a 3.00 gear ratio... decent for freeway cruising.

Besides that... turning a ratio like this saves the 833OD from being "torn up" because it no longer "lugs" in OD.

It seems as though the factory gear ratios originally used in the cars equipped with the 833OD were installed for strictly mileage purposes... and the "lugging" experienced while in OD was the cause for these transmissions getting a bad rap, because the stress was too great for the aluminum housing construction. Using a 4.10 (or a 3.23, 3.55, 3.73 or 3.91) vs a 2.45 gear makes a world of difference in these transmissions reliability.

You can also have the aluminum case bushed so it will not wear.

Click to expand...

Anytime you transfer torque through the countergear and not straight through the transmission by coupling the main drive gear (GM terms Chrysler terms eludes me at the moment) to the mainshaft (output in this case), the countergear shaft will load against the transmission case. Unbushed aluminum cases generally cannot stand up this over time and the countershaft hole(s) in the case wallows out or elongates (Muncie four speeds with an aluminum case are renowned for this). Because the OD transmission gear set exchanges third for fourth, anytime you are in high gear the countergear is loaded, causing the OD gearset transmission to wear the unbushed aluminum case seemingly faster than a straight four speed non OD transmission. Switching to an iron case, having the case bushed, or switching to a bushed aluminum case (Passon Performance, perhaps others) should minimize or eliminate the problem.