Transmission question

[sbc383rulz]

i am currently in Iraq and have some time to research/ plan. i have a 69 c2500 with a vortec 383 and a 4 speed NP trans 4.11 gears. i need either overdrive or ALOT taller gears in the rear, truck is a freeway beater most of the time with a few loads every now and then. my question is what overdrive manual trans would be the best, or would a D70 swap from a cummins dodge with 3.07 gears be best? i was thinking about a T56 but i dont know how it would hold up with almost 400 HP and a 4600 pound truck!! anyways thanks for the input (in advance) Gill

[Longhorn Man]

If you don't mind the crude, yet bullit proof 4 speed, I would go with a Dana or GM 14 bolt rear myself. If you intend on keeping the taller 3/4 ton style tires, I would not look for a 3.07-ish gear, but more in the 3.50-ish to 3.73-ish area.

[sbc383rulz]

14 bolt doesnt have any taller than 3.73's. i already tried a set of 3.54 in a dana 60 and they were "OK" but i would need a overdrvie with that aswell to get real freeway cruiser, thats why i was figuring a trans with a taller overdrive would be good with 4.11's. the overdrive trans i have seen usually dont have a very deep first so the 4.11s would work out to still be able to tow decently. i would also like to be able to shift a little quicker, the old NP dosent like anything near "speed" shift as im sure you know. Gill

[kwmech]

Originally Posted by sbc383rulz

14 bolt doesnt have any taller than 3.73s Gill

3.42 and 3.21 are ratios avail for the 14 bolt from the factory and now the after market

[sbc383rulz]

the gear vendors is really nice, i wouldent have to change my trans crossmember i have the bellhousing crossmember and no trans support at all!.
i have never heard or seen anything for a 14 bolt taller than 3.73, thanks for the info i will do some more research today! its looking like this truck might take a backseat to another project when i get home, kinda hard to take a family around in a reg cab truck!! thanks for the input guys!! Gill

[Fitz]

My 67 stepside is running a 4.10 rear gearset with a Gear Vendors two speed overdrive. With 31 in tall rear tires this gives the equivalent of 3.07 rear gears so the truck cruises at 75 mph with the engine showing about 1800 rpm. Same effect as using a trans with an overdrive built in but there is probably a cost difference. The Gear vendors unit is priced around 1500.00 but it's also rated for 1000hp. Don't know if a T56 will stand up in your application or not.
If you look into a stand alone overdrive you'll need to figure in the cost of shortening and reballancing the driveshaft (mine lost 31 inches!) and having the Spicer 50 uJoint the GV unit requires welded on the end. You'll also have to move the trans crossmember.

[WyoGMC]

If you are thinking of going with the T-56, get one from a Ram SRT-10. The 04's had 4.10 gears. But it is a tall OD gear. That is one of the reasons Dodge put 4.56 in other years. A lot of guys would not even use 6th gear unless they were going over 80 mph.