odey1979

I have a 68 cutlas s with a 3 speed manual and I want to put a manual overdrive in it for highway use. Anyone done this and if so what will fit? Thanks in advance.

joe_padavano

The easiest way to get a manual trans with O.D. that fits is to find one of the A833 four speeds with O.D. These were used in Chevy pickups in the 1980s and the Chevy version should bolt to your bellhousing (there are also Chrysler versions). I don't know about overall length or yoke spline count, however. Note that Ford had a similar Toploader four speed with O.D., and while the trans will bolt to your bellhousing, the Ford input shaft will be wrong.

Options beyond that are expensive and require more work. The T5 is commonly available but weak. Even the World-Class versions are limited to about 300 ft lbs. You would need a V8 version from an F-body, and these have the angled shifter so you'll need an aftermarket shifter to work in your application. Fabrication will be required to get the shift lever correct, especially if you have a console. Again, I don't know about crossmember location or driveshaft length. The good news is that the GM T5s use the same yoke as your trans.

Beyond that are the aftermarket five and six speed transmissions, such as Richmond, TKO, etc. Some of these bolt to your bellhousing, some do not. You can also get an aftermarket bellhousing that allows a T56 from a later F-body to bolt to a BOP block. All of these will require floorpan mods, crossmember mods, and driveshaft mods. All will run about $2500 installed, or more.

66400

Chevrolet offered a Saginaw 3spd OD trans 65-69 in passenger cars and light trucks.

Also 55-64 Chevrolets had a muncie 3spd OD trans but it was a non syncromesh first gear.

Henry

odey1979

Thanks guys. I'm just hoping to stop the engine from crying for mercy at highway speeds. I'll look into those options

oldcutlass

What gear ratio are you running? You can also add a gear vendors overdrive if your just looking at dropping your rpms and not going to a 4 speed.

odey1979

Not sure yet of the gear ratio. What is a gear vendors overdrive. I don't want to change the rear end ratio since first is already pretty high. A 4 speed and new gears. Ok. That could work but just tossing a 3 speed with over drive in would be ideal for me. And yes. Main concern is to lower rpms at higher speeds but not loose the low end I so have. Thanks again

joe_padavano

The GearVendors O.D. is an external unit that mounts behind your current trans and has a set of overdrive gears in it. Expect to pay ~$2500 plus the cost of a new driveshaft.

A used A833 can be had for a fraction of that. I've seen them for $700 on CL.

joe_padavano

OK, sorry for the mis information. The Chevy version A833 used a unique bellhousing. This trans does not bolt to a normal BOP bellhousing, though it does have the usual GM ten spline input shaft. It also uses the larger truck bearing retainer, not the smaller automotive one.



It is possible to machine an automotive bellhousing to fit the truck bearing retainer, and it's also possible to change the bearing retainer on the trans (Jeep guys do this for SM465 swaps), but you'd need to modify the BOP bellhousing for the correct bolt pattern. The good news is that the bearing retainer is what locates the trans, so the bolt locations need not be super precise.

joe_padavano

Here's a little more info on this swap into a Chevy.

odey1979

I actually have that A833 trans in my storage trailer but it's set up for 4 wheel drive. I'd have to change the tail shaft to use it. Im looking around and thinking maybe ill just go with a 4 speed Saginaw or Muncie and change the rear end to a different gear. Maybe do a 442 setup.

Oldsguy

Welcome to CO, smooth sailing at lower RPMs soon eh?

Octania

I was told some time ago in looking into getting a Muncie redone that they can now make these overdrive 4-speeds. Basically, straight thru is 3rd gear and then alternate gears where 3rd used to be are now overdrive 4th. Flip the 3-4 actuating lever over and it's all set.

I have no experience with this voodoo so cannot say if it's feasible or a good idea.

joe_padavano

This is exactly how the factories made the OD versions of the A833 and Ford Toploader four speeds. These transmissions retain first, second, and fourth (which becomes third) gears and swap out the former third gears for an OD set that then becomes fourth when you flip the shift lever. Unfortunately, nothing for a Muncie is cheap anymore, and you end up with a wide ratio four speed.

The reality is that the ratios in the trans and the rear end by themselves don't matter. What matters is the effective final drive ratio. For example, 3.91 gears with an 0.78 OD are the same as 3.08 gears with a 1:1 fourth. Of course, the difference is the effective ratio in first, which depends on the trans. For example, if you did Chris' Muncie gear swap in a close ratio trans, the 2.2 first yields an effective 8.6:1 final drive ratio. If you started with a stock wide ratio Muncie, the 2.52 first and 3.08 gears gives you an effective 7.76 final drive ratio.

OLD SKL 69

Welcome to CO! Hope you get your trans situation straightened out. I've installed aftermarket overdrives: Borg Warner, Tremec etc. with great results. Much better for cruising and their built to handle the power output.