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Old 4 Weeks Ago
Greg5OH Greg5OH is offline
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Join Date: Mar 2020
Location: Ortonville
Posts: 1
Default MT643 lag in 2-3 upshift

Hey guys, I dont own a wanderlodge but this seems like the most tech savvy RV forum.

89 monaco crown royale, bendix accelerator system, MT643 trans, cummins 8.3 250HP.

Issue I am having is a very delayed 2-3 upshift. Upshifts in all gears occur around 2200-2300rpm.

It hangs in 2nd gear peak RPM for a good 4-6 seconds, longer if going up even a 1 or 2% grade, soometimes up to 12 seconds. Then goes into 3rd, then converter locks and now we have some good proper acceleration, all the way to my desired cruise speed of 65mph.

I also see the bendix system is starting to pull fuel at the top of 2nd gear, I see boost dropping from 25 psi down to about 7psi then finally it shifts. I know this trans needs torque input to shift up. Perhaps thats the main issue?

Any ideas welcome.

Greg Balandyk
Ortonville, Michigan
1989 Monaco Crown Royale
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Old 4 Weeks Ago
Randy Dupree's Avatar
Randy Dupree Randy Dupree is online now
Forum owner
Join Date: Dec 2007
Location: Port St Joe,Fl
Posts: 37,013

Welcome Greg!
I think the 643 can sometimes need to be "forced" to shift.
Has your trans always been like this?
In your ownership?
How long have you owned it?
Will it shift if you lift your right foot briefly? to force the shift?
email me at randy@randydupree.com only.

Randy Dupree
2000 LXI 43
Port St Joe Fl.

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Old 4 Weeks Ago
Good Ole Bird's Avatar
Good Ole Bird Good Ole Bird is offline
Senior Member
Join Date: Dec 2019
Location: Larose
Posts: 336

Maybe what you're experiencing is the 2nd gear lock up...

Mine seems to operate very similar to your description...
Flee from the wrath to come!!!

Good Ole Bird - 1980 FC35 250T


Larose, LA
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