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Trannies for a Diesel Engine Last Updated Dec 25, 2002 Other relevant link:
--------- If you are an 80 Series guy I just learned after a few phone calls that Specter Off Road is now offering the parts to convert your 80 series to a standard transmission. This would allow you to run the NV4500 or NV4500HD (heavy duty version for high output engines) or other standard transmissions including USA spec and non-USA spec Toyota transmissions such as the H55F 5 speed. Regarding Cummins engines and other diesels, because they seemingly put out so much torque, you'll pretty much need a pretty beefy transmission. In my book there is really only one tranny for daily driving, the NV4500, great low 1st gear with a 5th gear too. Because B series Cummins motors are governed in most situations to top out at 2500 rpms, you have to pay close attention to gearing. Use this online gear calculator to determine what tire, axle, and transmission ratios you will need. Therefore, if you have any plans to off-road the truck you are going to need a low 1st gear to counteract the mildly "high" axle gearing you are going to need (3.73, maybe even 3.30), unless you encorporate some sort of doubler/crawlbox. However, larger tires can also help with counteracting axle gearing. But you will also need the 5th gear so unless you use a 5 speed I would avoid a Cummins conversion or other diesel engine conversion that cannot produce medium-higher RPMs by all means. Because the 6BT has a pretty standard bellhousing pattern, a number of transmissions will work. Because 4BTs have the same bellhousing pattern as a 6BT, the same is true for these engines. 6AT engines have a bellhousing pattern that allows a stock SM465 with bellhousing to bolt to them. SM420/SM465 are 4 speed GM transmissions with a low first and relative medium to large engine output ability. The SM 465 is typically very durable and will hold up fine to even a powerful Cummins 6BT. One pretty common problem with big American diesels found in Suburbans and full size trucks is they frequently blow up their transmissions. A friend who owns a turbo diesel 6.5L Chevy V8 in his Suburban has had the transmission replaced 3 times in 80,000 miles. Iit's also had it's computer replaced three times and is an electrical nightmare / total lemon at 96,000 miles. Anyways, for a 6AT Cummins repower you should be able to use any tranny you want as long as it's at least as strong as a factory Land Cruiser transmission. The only problem, as I've heard from Royal Rose, is that even with the 6AT's higher rev band (versus the B series Cummins engines) is that it still needs a 5 speed transmission or some way of getting acceptably lower highway rpms if you plan on using your truck on the highway. Royal can do 65 mph all day with 4.11 axle gearing, a SM420 transmission, and 33" Pro Comp tires. Other ways to get around this are to run tall tires (like 35" or above), a transmission with a granny first (like a SM 420 or 465), fast axles (like 4.11 or 3.73), and a 1:1 4th gear. Because I'm a NV4500 fan there are actually two models available which I'll discuss. The NV4500 and the NV4500HD. Both will bolt to B series Cummins engines. NV4500s also came available behind Chevys but in order to utilize the Toyota's offset transfer case, you will need a special adapter from Advance Adapers which will relocate the clutch release and activation mechanism to the driver's side of the transmission. The difference between the NV4500 and NV4500HD is that the HD version (heavy duty) is built specifcally for high torque (diesel) applications and I've been told is the only tranny that will hold up to the Cummins 6BT versus the automatics that I have heard of having some trouble. There is also a NV5600 which is a 6 speed transmission that I know relatively nothing about about other than a 6.0:1 first gear and closer gearing betwween the axles. I'm told from the late 90s and on the NV5600 is now what is available being Dodge pickups equipped with Cummins 6BT engines. You might also be interested in the Cummins T-Case section. |
