trans upgrade
it looks like we are going to have to wait to upgrade to a newer MH so I would like to upgrade the Turbo Hydramatic 400 to the 700R trans. Has anyone done this here? Seems at 65 mph its topped out, so...
Forum Discussion
Two things, First, I would not consider a 700R4 in a motorhome. Even though you can build it, it is a light duty trans and just not designed to take the load. Guys that build them for race, build them to last for a limited number of runs, not a constant heavy load. The one big thing everyone forgets about racers - they break stuff. The see breaking things as the normal cost of doing business.
The 4L80E is the same load rating, and uses many of the same parts as the TH400 did, which has been proven to have long term reliability. The only disadvantage of the 4L80E is weight - but it has to be heavy to be tough.
As far as Gear Vendors vs 4 speed, my big concern with Gear Vendors is torque converter stall speed. If you get the engine spinning too slow, the TC slips, and you loose efficiency. Before I installed the 4L85E, I was running 3.53 gears and a step up 1:1.1 chain case. Unless I was traveling 70 mph, the TC would slip, so it was impossible to save fuel by driving slower. You have to look at your gearing and figure out what your typical operating RPM will be. You need it to be above 2500 RPM, and really should be above 2700 RPM at moderate cruising speeds. Otherwise you won't gain anything.
One other idea to consider would be to change your rear end ratio, and then put different gears in 1st and 2nd for your TH400. You can buy different ratios, which will allow you to still get off the line with a taller diff ratio.
Many ways to skin a cat.
The 4L80E is the same load rating, and uses many of the same parts as the TH400 did, which has been proven to have long term reliability. The only disadvantage of the 4L80E is weight - but it has to be heavy to be tough.
As far as Gear Vendors vs 4 speed, my big concern with Gear Vendors is torque converter stall speed. If you get the engine spinning too slow, the TC slips, and you loose efficiency. Before I installed the 4L85E, I was running 3.53 gears and a step up 1:1.1 chain case. Unless I was traveling 70 mph, the TC would slip, so it was impossible to save fuel by driving slower. You have to look at your gearing and figure out what your typical operating RPM will be. You need it to be above 2500 RPM, and really should be above 2700 RPM at moderate cruising speeds. Otherwise you won't gain anything.
One other idea to consider would be to change your rear end ratio, and then put different gears in 1st and 2nd for your TH400. You can buy different ratios, which will allow you to still get off the line with a taller diff ratio.
Many ways to skin a cat.
