Hey guys, Just a thought. Does anyone know of a 6-speed manual tranny that will bolt up to the I6? I love the low end power I get out of my truck, but I'd like to get a little better gas mileage on the freeway. Thinkin' maybe another overdrive, maybe at ~.50:1 might do it. I've heard somewhere that the 6-speed out of the Dodge Viper might work, but not sure about the source. Just an idea for now, but any thoughts ya'll might have would be interesting.

Thanks.

 

The Ford 4OD has a .71 final gear. I don't know for sure, but I suspect most ODs have a final gear like that. So the six speeder would just break it down into closer segments. Too much clutchin' for my old knees!
Tip: Pump up the tires and slip it out of gear going downhill.

 

A t56 built for a ford 5.0 would prolly be your best bet, I think its got multiple starter holes, as well as the same bolt pattern as the 300 for mounting, so it will accept the 300s flywheel. Ive been told the t56 is only good for about 500 ft lbs though. Im considering using this in my monster 280Z car, but thats because the tires will be so much smaller, and a .6 6th gear can be used, and a high rear end gear as well, just looking for watever I can get for acceleration. But my motor might put out too much torque.

 

Do you mean a 'ZF' that's a 5-spd with overdrive in 5th?

 

The t56 is available with a ton of different ratios, but a .5:1 6th gear is the most common.

As far as getting the trans in the truck, there are so many different variations of the t56 you've really got some homework to do. It looks like your truck is an 89, so it has a hydaulic clutch. The Mustang version of the t56 uses a cable clutch. The GM t56 used in the f-body from 98-02 uses an internal clutch salve cylinder that looks almost identical to the one in your M5OD. If they were right next to each other I could tell them apart, but probably not otherwise. They are close enough that they might actually be the same part with a different hose on them. If that's the case you could probably use the Mustang bellhousing (if the trans mates to it) and clutch with a GM disc and get it to work. Another option is the t56 from the 93-97 f-body. It also uses a hydraulic clutch, but uses an external slave cylinder and a ******* pull type pressure plate and will require some innovation. The shifter also appears to be significantly farther to the rear of the t56 than the m5od, but bending up a custom shifter to clear the seat shouldn't be too big of a deal.

For the ammount of work I doubt you would get enough benefit to justify it. There probably wouldn't be any mileage increase at all. My old truck got 12 mpg with a 2.73 gear and that jumped to 18 mpg with a 3.08 because it didn't take as much throttle to pull the shorter gear. Something to think about.

 

I was not aware that the F-body had a 6-spd. learn something every day

 

.5 OD wouldn't do a thing for the 300 if you have the usually lousy rear axle gears to go with it. Heck, you might not get out past 4th gear in some cases using a T56.

Usually, lower rpms is nice, but since the 300 dislikes revs, a set of 3.73's and the stock tranny will do just fine. Better mileage and better oomph off the line. Keeping the I6 in the powerband and not running lower rpms just because you want to is key here.

 

I would love to have one of those in my pick-up … but the complete swap must be pretty expensive … I found a link, but I didn’t have the courage to make the call !
http://www.ttcautomotive.com/English/products/T-56.asp
There’s just too many thing to take in consideration (from my point of view anyway) ;
The shifter is on the end of the trany, (not in the centre like my T18)
Must change the ratio of both differentials (in my case) to be useful,
Not sure that the Hydraulic clutch will work,
Etc, etc …
Like Sylver Steak said ... a lot of work for the benefits !

I would sure want to hear and see one installed, if there is one out there that did have the courage to built it !

Cris

 

Alfred, I know what you're saying, but in general I just have to disagree.
I bought my 83 new with the 3.08 and 4 OD. At 60 mph it only spins 1600 rpm....that gave me 22 mpg. I can use 4th gear from 45 mph on up, below that I just stay in 3rd...it's a 1:0 ratio of course.

 

Thanks for the input guys, all very interesting. It definitely gives me something to think about. One more question tho, Alfred you say that with 3.73's I'd get "Better mileage and better oomph off the line". Currently I'm running a 3.55 rear, 3.54 front combination, I agree that putting in a taller gear would increase my power, but wouldn't a shorter gear like a 3.08 get better mileage? Not withstanding, that for the cost of putting in new gears, with such a minimal power increase from the 3.55 to the 3.73, Wouldn't I be better off jumping to a 4.10 and increasing my tire size from 31's to 33's? Thanks again everybody.

 

Try Richmond truck transmissions they are expensive but I love mine. You have a vareity of ratios to choose from, most use the original bell housing for a T18/19 so the starter and old style external slave cylinders will work without too much trouble.

 

I really think that without a killer engine the 6 speed is a waste. You would have to install at least a 4.10 gear to make 6th usable, and then you'd have a useless gear on the other end.