Manual Spicer to Used Allison Auto swap questions

[oldmansax]

We have a'73 MCI with the standard 8V71 and 4 speed manual transmission. The local fire company is going to sell a 1976 Dodge tanker that has a Cummins 903 and a Allison 4 speed auto trans. I don't know the number of the trans yet.  I know the tanker was originally a government fuel tanker for an air base. It is low milage, around 35,000.  I am thinking about bidding on the truck & putting the auto trans in my bus. I am looking for comments for or against. Will it bolt up? Adverse effects on fuel milage? Top speed?  I thought about swapping out for the whole Cummins/Allison package but the 903 doesn't have a real good reputation.

[Jerry32]

Iwould think that a 903 in a truck hauling 80,000 70 100,000 lbs is a good test of an engine. I have an old semi tractor with a 903 in it and itr still runs but smokes a lot.   Jerry

[NJT 5573]

The 903 is heavy, but it would make a great bus engine.

[Dallas]

Tom,

The military pumps out up to 800HP@2900rpm with the V903.

George Lowry use to have a PD4106 he put a VT903 in that pumped out well over 400HP. He also had a bullydog propane injection system.

With the engine/trans setup matched as it is for the firetruck, it's possible that it is putting out well over 350HP at 2800rpm.

I've had good luck and bad luck with 903's. I think it all depends on how you treat them, just like any other piece of equipment.

One didn't last 80K miles with an experienced driver, another I had was well into the 500K range before we even thought about doing an in frame major on it. I think the difference was that the experienced driver didn't want to run it over 2150, where the one that lasted forever was in a yard truck and got beaten up dailey, moving trailers from warehouse to warehouse and dock to dock.

If it were me, I'd use the transmission that comes with the truck, providing you want an auto.

Good Luck,

Dallas

GO BUSSING!

[frank-id]

Allison trans are the best, if set up correctly.  If you use all the power package from the truck, everything should be a doable change.  Some time ago, I searched for nearly a year to find the parts to connect a Cummins small cam to an Allison MT643.  New parts were about $4K.  Most all Allisons can be manipulated for abount any vehicle application.  My advise is to check what ya have and what is available.  You may need to fabricate new mounts for the engine.  Measure several times and change once.    Frank   in Idaho

[TomC]

On a weight to weight basis, the 903 weighs about the same as the 8V-71N.  It is wider since it is a 90 degree V-8 compared to the 63 degree of the 8V-71.  I would use the Allison on the 8V-71 and sell the 903 to a yacht owner for a boat anchor.  You can keep within about 1 mpg of the manual if you drive it properly. Problem is that the Allison is so much fun to drive, most are flooring it all the time, hence 2-3 mpg less. Good Luck, TomC

[Lee Bradley]

I think I would save my money for a new/rebuilt Allison designed for your Detroit.

[oldmansax]

Thanks for all the replies!

Dallas, I am familiar with what the 903s are capable of but this one is not turboed AND was set up to haul fuel around an air base.  I have driven the truck it is in & it is pretty sluggish. Also, my Detroit only has 50,000 on it and, what can I say, I just LIKE that screaming!      I ran one in a Diamond Reo with straight pipes. Boy did it sound good........while I could still hear! 

TomC, Thanks for the input on fuel mileage. I was wondering how close I could get to manual tran mileage.

I guess what I really am looking for is will the Allison bolt up to my 8V71 and is there anything else major I would have to change? How about rotation? My bus is usable like it is and we use and need it regularly. I don't want to put it out of commission for months while I retrofit a new trans nor do I want to put a bunch of money in something that is doing the job now. An auto would be nice from the standpoint of driveablilty and I think Phyllis would like it better.

I guess everything is a trade off......

I will try to get the model number off the tranny this weekend.

I wonder if there are any bus mechanics who need a 903 for their yacht.......

[RJ]

Tom -

To answer your basic question, yes, the Allison will bolt right up to your 8V71, but you'll need the different bell housing used by the automatic, along with some additional small parts (modulater, etc.)

FWIW & HTH. . .