Allison MT643 Not Upshifting

[colson04]

I bought a Ford L9000 with a 7.8L Ford engine and Allison MT643 automatic.

I've known this truck for the last 12 years, driven it many times and helped wrench on it. This May, it lost the ability to upshift. It left, ran 55mph down the road as normal. Got to field, loaded, and never upshited correctly again. Transmission fluid level was a gallon low when it got back to the farm. Topped fluid level up, no change in shifting. This truck sat since May while it was decided what to do. I purchased it a week ago as the owner doesn't want to put anymore money into it.

I test drove truck last Thursday after sitting for 3 months. Trans temps low, it shifted all the way just fine and ran 55mph easily. About 5 miles in, temp came up and trans immediately dropped two gears. I contacted Wellers regarding the issue. They immediately said governor. I pulled the governor and found the outer shell is scored badly.



I'm stopping at Wellers this afternoon. Their Allison rep said they could replace the outer shell while I wait, but if that doesn't resolve the shifting issue, then the bore may be too worn and then the case is scrap. Either way, I bought the truck for about scrap value and I think it's worth swapping a transmission if thats what it takes. Engine starts well in all temps, brakes are fair and both rear ends were replaced in 2010.

 

[Truck Shop]

They immediately said governor.

Agree, and that shell is very rough, and the case is probably a reflection of that governor.

 

[cfherrman]

If you try to run it che k the shift modulator linkage

 

[Birken Vogt]

Those transmissions are getting scrapped by the dozens/hundreds I am sure, lots of fire trucks with them aged out. They are probably getting more scarce now because they aged out a long time ago and have been sitting around in someone's yard for years until wife said take it to the scrapper. But probably one to be found somewhere. I know where there are 3 or 4 that were parked up good.

 

[colson04]

Well, it was well worth my while stopping at Wellers. They took care of my governor for a freckle of what I was expecting, gave me some solid information and wished me luck. Said to give him a call if it doesn't work and they'll get a reman built for me.

Went back to truck, inspected governor suction screen (very clean actually) and dropped the pan. Fluid was red, but not as tranparent as new. No chunks in pan, just some fine dark residue. Nothing but a tiny bit of fuzz on the magnet. Installed pan, 4.5 gallons of fresh synthetic ATF and off for a test drive. Truck shifted as intended for our 5 mile test drive through the hills. Had my brother drive my pickup and followed me to the jobsite where I'm clearing trees. This truck will be used to haul chips and stumps mostly. Maybe some logs. If it lasts until the job is done, I'll call it a win.

 

[colson04]

Loaded and dumped, no issues.

 

[56wrench]

Nice silage endgate

 

[colson04]

All of our silage trucks have them. They work excellent for clearing the load, and they have a self locking system that keeps the load from pushing the gate open when they're down.

Also works great for hauling chips, stumps and logs as the gate easily clears the load and nothing gets hung up.

 

[56wrench]

We used to use the semi-floating, mechanical automatic latch type that worked well unless the driver turned while unloading or wasn’t trained in the proper hoisting/unloading procedure, causing the gate to twist and/or buckle