It sound as though our hands are tied with the ratios on the O.D. trannys.
I imagine that we would be looking at changing out the gear cluster for just about any ratio change. As I understand it, third on the O.D. tranny is straight through as forth would be on a regular four speed, and forth on a overdrive is achieved by inverting the shift lever and running forth or over
drive in this case, back through the gear cluster in what would be third gear on a regular four speed. That said, I'm wondering how much we could play with the rear end gear ratio, to perhaps lessen the distance between the gears, or at least make the stretch less appearent. I've got a line on a 8.25 limited slip that will need a ring and pinion anyway so now is the time to discuss any options.

That's the only downfall to the whole 4 speed wide ratio ordeal that no matter what you do there's a pretty big drop between 1-2, and a fair drop between 2-3...

I'm running 3.55's as that gives good on street performance, but retains a fair final ratio for long highway trips in mileage...you can get away with up to 4.11's on the street (with a 2.99 final ratio on the highway)...

The 8.25" has a fair spread of ratios to play with, I think if I did my build up again learning from what I know now, I'd have taken the 3.73 ratio instead. The next build I do will be 3.91's for sure.

There are some rpm calculators you can check to see the drop in rpm with your tranny and rear ratio...also your tire size will also determine a slight change in how things go too...

Most guys here are on the T-5 5-speed conversion plan so they can have a closer ratio tranny and still have the OD gear.


Good luck on the 'engineering' plan!


-D.Idiot

Was at a car show today and a guy said that you could use a drum from a 84 or 85 van. I think he said a caravan, and replace the 904's 3rd drum with it and get 3rd gear to be overdriven. Sounds a little strange. Is there any truth to this?

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

1. What does this have to do with the A833OD?

2. What advantage does doing the impossible with an A904 get you that changing the rear axle ratio does not?

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Joshua

It sounds like it is impossiable from your responce, but using a low rear gear and still being able to drive it around town with a high third gear sounds nice. Kind of like the Gear Vendors overdrive unit but without it.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

The way 3 speed autos are built high gear is direct. The bands and clutches don't allow for anything other than two stages of reduction, direct and reverse. You might be able to get two reverse ratios, but do you really want to go that fast in reverse? To get an overdrive with a planetary gearset you have to drive the sun gear, hold the planets stationary and take the output from the annulus. There is no way to do this the way the trans is built. If it were possible to have an overdrive without adding another planetary or giving up say 2nd gear the factory would have done so. Manufacturers try very hard to reduce cost and complexity.

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Joshua

Passon has their Hemi overdrive that would help with the rpm drops. Ratios are 2.66, 1.59, 1.00, .80.

With 4.10 gears, the overdrive gives you 3.28's on the highway.

Or, for less money, you could run a standard /6 4 speed with the 3.09 first gear and 3.23 rear and have virtually the same thing.

Ratio percentages for the Hemi OD are 59.77%, 62.89% and 80%. For the 3.09 gear standard 4 speed are 62.14%, 72.92% and 71.43%. Gear to gear, the standard 4 speed is closer than the Hemi OD, except for 3-4.

IMO, if you want a closer ratio setup and reasonable rpms on the highway (without going 5 speed), the best way to fly is the 3.09 4 speed with a 3.23 or 2.94 rear gear.

The rpm drops between the gears in the 3.09 trans are better even than a T5, but you don't get an OD gear.

With that said, my R154 arrived last Friday.

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car