Serious Tranny Help

FamilyGuy

New Recruit
Owner/Operator
Hello, so here I find myself trying to figure out what's wrong with my 2009 M2 Freightliner's Allison Transmission.
It drives good most of the time, but suddenly the tranny light turns on and it jumps to 3rd or 4th gear, if I restart the engine it'll reset and run fine.

Occasionally I'll have to wait a while for it "cool" off and reset, for the truck to run again.

It has 420k miles, recent tranny flush and replaced all sensors.

Please, any ideas?

Thinks in advance for any advice offered.
 

Techmaster

Rookie Expediter
Mechanic
Sounds like it needs to be plugged in to Allison doc, if you get a code I could help alot more. Certain codes will activate range inhibitor and lock the Gear the fault was set in. What sensors were changed and why? I'm assuming nothing internal
 

RETIDEPXE

Veteran Expediter
Late to the party but if you have fixed it, great, be interested to know what was found.

Otherwise, maybe the following will help. I've been running the same 07 M2 for 11 yrs now and am at 1.53 million miles. The Allison 3000HS has never been opened up, just regular service and filters, and is still performing well. The only problem, besides one output shaft seal, and large amount of brass shavings in the fluid early on, is water getting into the main harness and slight corrosion.

The 1st time after doing an under chassis wash where you drive over a torrent of water spray, trans wouldn't shift past 3rd, cost me $250 at an Allison dlr, hooked up his computer and did some minor wire splices up near the driver side lower firewall. This was at 450,000 mi.s.

A couple yrs later and about 750,000 miles I noticed some sporadic 5th to 4th downshift/upshifts at a steady cruise, but only during rained soaked roads. I crawled underneath, unscrewed the threaded ring holding the harness together closest to the transmission (not the one by the drivers firewall), pulled it apart, looked dry inside, plugged and unplugged a few times to clean any minor corrosion dust on the pins, screwed it back tight and haven't had a problem since. Been an amazing transmission and is holding up on my second motor so far, but I know it's days are numbered. I've have not been able to find an Allison 3000 or smaller go this far and the RV forums are happy to get 150,000 miles out of theres.

If you are only having issues during wet weather, might check the connections.

That's all I got.
 
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