Author Topic: 643 flex plate?  (Read 2598 times)

Offline glang

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  • 1998 Prevost XLT
643 flex plate?
« on: May 31, 2006, 04:12:00 PM »
Anyone know if a 643 allision takes the same flex plate as a 740? I need a flex plate to fit an 8V71. Hoping to put the 643 in a MCI5 for a friend if we can get the right parts.

Gary

Offline TomC

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Re: 643 flex plate?
« Reply #1 on: June 01, 2006, 07:24:12 AM »
I don't believe so-different sized torque converters.  Although, the five speed version MT655 did have a larger torque converter for higher horsepower.  I would call Allison since the MT643 is still a widely used trans.  The HT740 is by far the superior trans (if you can fit it).  The MT643 gets torque converter lockup in the upper end of 3rd and all of 4th.  Whereas the HT740 locks up in the upper end of 2nd (can get lockup in 1st if you pull the gear shift lever to first) and in 3rd and 4th.  Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline glang

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  • 1998 Prevost XLT
Re: 643 flex plate?
« Reply #2 on: June 01, 2006, 08:21:58 AM »
I have a 740 in my Prevost but the 740 is to long for an easy hookup in the MCI5. The 643 is 31.5" verses the 740 at 37.5.
Thanks for input

Gary

Offline Tom Y

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Re: 643 flex plate?
« Reply #3 on: June 01, 2006, 06:55:40 PM »
Glang, I bought some used Allison parts from a place that is all they do. USA Parts 800-USA-7899, They are in Missouri.  They were helpful with me and had good prices.  Goodluck Tom Y
Tom Yaegle