6BT swap in a '76 Winnebago RV?

Ok here's my thoughts. The B series engine have a lower operateing rpm than the 440, therefore your going to need a overdrive somewhere in the drivetrain to be able to get down the road at a decent speed. Also just because a trans does good behind a monster gas moter dosent mean it can take the low speed torque of a diesel. But there are good Dodge trans that are fitted behind the 6B and changing the trans out is a good idea. What you need to find out is the gear ratio on the axle and find out how this works with what you have and make adjustment if necessary.

thanks for the input. Hadn't really thought about the gearing. The same friend suggested getting everything out of a school bus with what I want in it already and said that he'd found a mid 90's one on ebay for about 1500. Sounded kinda low to me but the idea sounds good since it would have almost everything I'd need and it's way cheaper than a salvaged dodge truck. Anyone else?

Figured out I have a Dana 70 rearend with something lik 4.56 gearing. A friend suggested 3.73 gearing for the swap. My question is with a newer 24valve 6bt and overdrive auto tranny out of a Dodge 3500, Would I end up with the best mileage for the power in this 12,000 GVW Winnebago? I guess I need to find out what a Dodge M400 with a 6bt and auto tranny had in the rear end, eh? Or would whatever rearend gearing is in the 3500 be what I would want?

motormech1 said:

Figured out I have a Dana 70 rearend with something lik 4.56 gearing. A friend suggested 3.73 gearing for the swap. My question is with a newer 24valve 6bt and overdrive auto tranny out of a Dodge 3500, Would I end up with the best mileage for the power in this 12,000 GVW Winnebago? I guess I need to find out what a Dodge M400 with a 6bt and auto tranny had in the rear end, eh? Or would whatever rearend gearing is in the 3500 be what I would want?

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1st and 2nd gen Dodge CTD's get best fuel mileage below 2K rpm, 3rd gen moves this up a few hundred rpm, I'm not sure where the "power band" starts for a 3 gen, but you need to know that for setting up the optimum gearing. I would ask anyone that tows with a 24valve what they have.
I've towed 12K GCWR up and down the west coast with my 92 Dodge with just the stock 160 hp and it's not bad. I'm geared lower, I turn just over 2000 rpm at 65mph. My mileage sucks but I have the power to pull.

Allison auto?

Why not put an allison auto behind the 6bt? sae 2 or 3 would be much stronger than a dodge auto and you would have the room and ability to carry the extra weight, just a thought.

Gaza

If you decide to go with the Dodge trans you'll need to uprgrade the torque converter at some point. They are a source of a lot of complaints on the Dodge CTD forums and most suggest a better aftermarket unit even on a stock Dodge, if used for towing or hard running. I'd definitely budget in the biggest, baddest tranny cooler you can lay your hands on too. If the Winnie was a 440 the stock radiator should be enough.

look for a bus with a cummins and an allison. still need higher gears.

Most of the buses with the 6BT/Allison 4 speeds were 1:1 final drive ratio, unless you get lucky and find a really recent one that has OD. I wouldn't buy into the Allison is tougher than ??? whatever brand you insert either, they do burn up too. There is a reason Chrysler used their own transmission in the Dodge trucks, same thing with the Getrag that often gets a bad rap, fact is NV4500 is not as tough but is definately more popular of a swap when rebuilds are considered. Your best bet is to buy a donor vehicle that has an OD trans. and your going to want to keep the rpm around 2k when considering axle gearing. I know a fellow who has done a bunch of conversions like this one. Very good conversion for you, nearly a direct bolt in with the right donor.

I would look for a 94-95' Dodge Cummins, 4 speed auto w/lockup converter, 3.54 axle. Wrecked etc. You can run that trans, with or without the PCM. Lockup converter is huge for economy on the road. And the lower numerical(higher) gear ratio is also, this is a torque monster remember, gassers needed that 3.73+ to get that lumbering beast moving.

heres a 1975 travco swap. http://community.webshots.com/album/232660691ZBdqUT?start=0

'76 Dodge M400 chassis powered by a 440 should have a D70 HD with 4:10 gears. A dodge auto 518 or 47RE/RH will give you a .69:1 overdrive ratio which is the highest you can get...anywhere! My wife and I repowered a '73 Travco with a 6BT and 518 out of a '93 Dodge pickup. Retained the original 4:56 gears (this coach orignally had a 413 in it) and can cruise @ about 60-65 MPH and get around 11-13MPG towing a boat or a car. Would be nice to have "one more gear" sometimes, and I'm also sure that a lockup converter would gain us at least another 2-3MPG.