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Author Topic: Do you have an MC5 with 8V71 and automatic?  (Read 1817 times)

Offline Fredward

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Do you have an MC5 with 8V71 and automatic?
« on: June 16, 2014, 11:10:13 AM »
As some of you know I am converting from the four speed spicer to an Allison MT647. I know there are quite a few MC5s here on this forum. If you have an MC5 with an automatic, is there a modification to your bedroom floor to accomodate the change? If so, could you post a picture? I'm looking for ideas.

I am almost ready to re-install the engine and so I can measure my driveline angles. If necessary, I may need to raise the engine which would require cutting a hole in the bedroom floor. I know some have gotten by without this modification, but I'm interested in seeing examples of those who did.

Fred
Fred Thomson

Offline lvmci

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #1 on: June 16, 2014, 12:27:14 PM »
Hi Fred, I have a 5A 1966, it was the original manual trans, the previous owner had trans swapped out at hb industries in El Cajon (San Diego) with a MT643, the engine is on a slight angle, but no modifications to interior, which had already been converted, lvmci...
MCI 102C3 8V92, Allison HT740
Formally MCI5A 8V71 Allison MT643

Offline Dave5Cs

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #2 on: June 16, 2014, 04:51:59 PM »
Yep my 5C only has the 6v71 and 740 but is still slightly skewed to the left no problems with the bedroom other than the bump i forget are there in the middle of the night. ???
Dave
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Offline mcilee

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #3 on: June 16, 2014, 07:29:39 PM »
Ours has the auto and several years ago we put in a rebuilt Allison. We have an 8V71 and there is no indication of engine mount or slide modification. 
We bought this MCI 5 in 1994, have enjoyed over 100,000 miles in the last 15 years. Lookin' forward to many more miles and smiles with a great machine.

Offline Lin

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #4 on: June 16, 2014, 09:47:02 PM »
Fred, you have already seen how we modified ours, but that works because the area involved is under the bed.  From your question, I am guessing that your bed is not in the same place.  Without knowing exactly what you have, it is difficult to offer any meaningful suggestions.  Maybe you could post pictures of what you have.

As mentioned in my email, a big issue aside from merely fitting the engine in is how you would get to the compressor if you ever needed to do it.  Without some sort of up top access it could require removing the engine.
You don't have to believe everything you think.

Offline Ed Hackenbruch

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #5 on: June 17, 2014, 07:30:42 AM »
Nope, PO didn't modify our floor either.
1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA

Offline Fredward

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #6 on: June 19, 2014, 09:57:05 PM »
Thanks Guys. Just wondering. I'm about ready to reinstall the engine transmssion.. Then I'll do a driveline angle measurement and see where I end up.
Fred
Fred Thomson

Offline Fredward

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #7 on: June 27, 2014, 11:24:35 AM »
Well I stuffed the 8V71/MT647 combo back in last night and measured all the driveline angles. Gave the numbers to Allison and they ran it through their driveline calculator. It predicted an unacceptable driveline vibration because of the different angle between the transmission and rear axle. They put it 90 degrees out of phase and the vibration is eliminated so I'll be installing the driveshaft 90 degrees out of phase and leaving the motor mounts alone. Thanks for the input everybody.
Fred
Fred Thomson

Offline bevans6

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Re: Do you have an MC5 with 8V71 and automatic?
« Reply #8 on: June 27, 2014, 12:29:04 PM »
Can you easily change the phase of the driveshaft?  I am going from memory here, and I didn't really pay attention to this when I was installing my engine, but I had the idea in my head that the driveshaft was keyed so that it could only be put together one way, and it was out of phase by around 45 degrees stock.  I am probably totally off base, but that's what I thought I saw.

Brian
1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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