I've got a 66 with a 352 mated to a 3 speed. I'm trying to decide which tranny to use. I have a cruiseomatic that was said to be recently rebuilt when I bought it. Thought about adding a performance stall converter with a shift kit but there is a part of me that wants to swap in a 4 speed to lower the rpms on the highway. Any ideas?

 

Both the automatic and the 4 speed have a 1 to 1 high gear (final drive) ratio, so the hiway rpm would be pretty close for both. The auto WILL have some converter slippage, so it's not as efficient as the stick, (or a lock up converter auto for that matter). But you won't find that on a 3 speed auto anyway. You'd have to go with an AOD or simular. (not an easy task since you've got an FE. $$$$

The higher stall speed converter won't help a bit either if your looking for mileage.

Good luck,

 

I forgot to ask if I decide to go with the automatic, will the crossmember from my 3 speed work?
Rob

 

mrwillie66,

I would not go with a Cruis-O-Matic for several reasons, the biggest being they have ancient technology and don't get rid of internal heat very well either. They have similar problems as FMX and it is all related to cast iron main case. They just aren't very durable in comparison to later models you can select.

If I were going to swap to an A/T and wanted it to be a "bolt up conversion" I'd probably use a C6 out of a mid 70's F Series that had a FE Engine. There are Aftermarket add on O/D units available for the C6, if you are not working the truck hard, often.

I more likely would retro fit an AOD however. I understand there are adapters available for that now.

Also I concur with Custom Cab all final transmission output ratios are 1:1 unless the trans is specifically an overdriven unit. On the other side of the coin, without benefit of a lock up converter, as he popints out, T/C Slip will actually underdrive the transmission, especially with a Cruis-0 or FMX, & that's one of the things that leads to "premature demise" . . . .

DO your homework on this and get infromed before you lay out time money & effort.

AND, yes since you have a 66, the rear trans X member will accept whatever mount you need IF you stay with FoMoCo A/T that's 66 or later. . .

FBp

 

Pete, thanks for the info. Where can I find those adapters for the AOD?
Rob

 

im kinda new to transmissions : whats a locked torque converter? would that give you the same drive ratio as a standard?

 

A lock up converter uses a fluid applied clutch inside it to stop any slippage, usually only in hi-gear(drive or overdrive).

 

I know this has been hashed to death, but I believe the fuel (and thus money) you save by swapping in an OD automatic behind an FE would be far outweighed by the tremendous cost involved. It would be very easy to spend $1500 - 2000 and probably even more. Just somethin to think about ??
Later, Phil

 

How about the heavy duty 3 speed with overdrive (R11) or the Clark 5 speed.

 

Those might work nicely too. I have NO experience with either though.
I like the way a *built* automatic shifts, so it's never been a priority, with me anyway.

Later,

 

Well I just scored a 3 speed overdrive from ebay. I think that it will be more fun grinding gears!! Will also be towing a trailor on the highway so I wont have to get a loan to pay for gas! Just need to locate a shifter and I'll be in business.