Re: Hi all...new guy here with some transmission questions

Posted by Anthony Pallett On 2013/4/25 6:46:12

I'm going to apologize in advance for the lengthy post.

The modern OD automatics are are computer controlled so a switch to 12v would be required (or possibly just a 12v battery and related wiring to just run the trans but I have never seen this).

The common for GM are the 700R4 which has a hard time dealing with the torque of a slightly warmed over 350 so I don't know how it would do behind a torquey Packard the final (4th gear) is .70 so about a 30% reduction in RPM its essentially a TH350 with an overdrive. You have the 4L60E which is stronger (kinda like a TH400 with an OD) It has a.696 OD which is just a hair over a 30% reduction in rpm they came in a lot of trucks and later Comaro/ Firebird stuff and I really don't see one breaking ever unless you abuse it a lot.

Then ford has the AOD these would have been in Mustangs LTD's ect. Pretty much any automatic ford cars from the 80's on. The OD is .667 so you would get about a 33% reduction in RPM I'm not super familiar with these, I know that it like its GM counterparts are electronically controlled and I have known a lot of Mustang racers who loved them and had a lot of luck but a Fox Mustang is around 2600 lbs and they don't really produce much HP and torque in stock or slightly warmed over form (most range from 210-260HP stock and go up from there).

I don't know about Chrysler OD transmissions. For a long time they didn't really have a rear wheel drive car so if you went that route you would be looking at probably a truck transmission or a very new one out of like a Charger or 300C

As for manual OD transmissions the only real viable options are the T-5 and T-56. there is a T-45 (early 4.6 mustangs) but i have heard its pretty weak but I haven't owned one first hand.

The T-5 is plentiful (cheap) and came in pretty much everything S10, Ranger, Mustang, Comaro. There are two versions a world class (WC) and a non world class (NWC) the the WC ones are stronger have better build materials. The NWC are early 80's production up till about 1985 the WC is 1986 and later till they were replaced by the T-45 in around 1996. I haven't confirmed this but word on the street is the V6 and 4cyl variants are NWC you have several gear sets with these some are quite steep (such as with a 302 Ford you are in first gear long enough to shift to second) so do your research before you buy one. The OD's range from .80 (20% reduction in RPM) to around .63 (29% RPM reduction) I have a WC T-5 in my fox body mustang and they do not like speed shifting but despite all my abuse its still holding in. With mine I can do 80 at 2000 RPM with a 3.25 rear axle ratio it will shift at 1800ish RPM but prefers to be shifted around 3500 RPM with my setup.

As way as modern manual transmissions the T-56 is king they are used in Dodge Vipers (with a .50 OD or 50% reduction in RPM) to Corvettes and all Mustangs (including the world beating Shelby GT500) the non Viper T-56's have around a .75 OD or a 25% reduction in RPM and they are quite strong the Viper is a torque monster V10 and the GT500 makes 650hp and over 600 ftlbs of torque. The down side is cost, they generally cost around 3000 dollars but I don't think you would ever brake it behind any Packard engine.

The final option is a gear vendors OD if they don't have one for your specific trans they have a universal one I believe they have several OD ratios to choose from and their staff are very good about figuring out what one is right for you. But this is a 12V only option working with a solenoid to activate the OD.

I'm sure there are dozens of other options using adapter plates and creativity but these seem like the most logical choices to me hopefully someone will find the info useful.