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Ratio of Overdrive w/T-86

Anybody know if all the Studebaker overdrive units the same? V8-6 ? I have a 3speed in my Avanti (factory) with dealer added overdrive. I know the gear ratios in the T-86 as they are in the Avanti shop manual, but am trying to find the ratios in the OD..Want to change the rear end gears to make it more highway friendly. Has a 5.50 in it now and even in OD raps up too high for good highway cruise and gas milage. About 3400 to 3600 and 55 mph. Any easy way to figure the OD into the equation without trial and errror switching ring and pinion until it works. I've been told that the factory std. 3.31 would work but that is what the book says for just the 3sp. Any help would be appreciated. I've got a chance to buy a set of NOS 3.73 gears. Thanks Dave B

Reply to
mcavanti
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Most Studebaker V-8s w/overdrive use a 3.73 which will give you about 2200 rpm at 65mph. I can't even imagine a 5.50. If your speedometer reads reasonably accurately with that ratio, you will have to change the speedometer gear and pinion both to make the speedometer work. Paul Johnson

Reply to
Paul Johnson

Jack up one rear wheel, leaving the other on the ground. Turn the drive shaft until the wheel turns exactly two turns, counting the number of D-S turns it takes. Unless I have figured it wrong, this gives you the ratio you have now.

I assume that you have already noted what RPM you're turning at 60 MPH.

What RPM do you want to be turning at 60 with the new RE? Do the math and figure out what ratio you want. (If you want lower RPM at 60, it will be a lower number - lower than 3.73, if that'ss what you have now, as Paul suggests.)

I'm going on vacation ("from what?" you say), so don't bother me if I'm wrong.

Reply to
Karl Haas

The Studebaker overdrive unit gave a 30% overdrive. I'd go either

3.73 or 4.09 rear ratio for something that is still zippy but will give a more friendly cruising RPM.

The 3.73 gears will not fit in your existing rear end. 4.09 should fit. The housing is the same but the thickess of the flange on the center carrier is different and the ring and pinion gears will not be in the correct position if you try to put 3.73's in there.

Lee DeLaBarre Daytona62

Reply to
Lee

My PowerHawk has 2.92 gears w/ OD. It cruises at an even 2000 rpm at 60 mph and will yield 24-25 mpg.

JT

Lee wrote:

Reply to
Grumpy AuContraire

Reply to
WayneC

My 59 Lark had the 259 with 3 speed and overdrive with a 3.54 rear gear. I would cruise at 65 to 70 for hours and get around 18 to 20 mpg. That included a 500 cfm Edelbrock 4 barrel carb. It was a real pressure to drive out on the road. I never had a tachnometer so I don't know what rpm it was turning.

Reply to
blacklarkviii

Thanks for all the imput. I did forget to mention it has TT. The only way I could actually measure the MPH was with a stop watch and milemarkers as your right, the speedometer was not accurate. I had the car on a hoist and used the chaulk measure and that's why I think it has a 5.5. Again thanks. Dave B.

Reply to
mcavanti

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