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Discussion Starter · #1 ·
I have a 2007.5 GMC Serria 2500HD LMM with the 6-speed Allison Transmission 4 wheel drive, the other day I went and picked up a mini excavator and was towing it home when I noticed something iv never noticed before. I stopped at a red light in town and when the light turned green I let off the breaks and pressed the accelerator. As the engine began to rev up to start moving from the stop, a loud clunk and then a jerk happened as I started moving. It only happens when I'm completely stoped and then start to move (1st gear only) when I have a heavy load. It doesn't do it if I dont completely stop, as in if I let it roll a little at like 1 or 2 mph and then go. It also doesn't happen when I'm unloaded or towing a light weight utility trailer and lawnmower. Would this be caused by a slip yoke needing lube or maybe the trans. Mount bolts being loose?
 

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Do you have any vibrations at high at highway speeds?mite check carrier bearing if you have one.the rubber has a tendency to break apart .worth a look see.
 

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Dam got interrupted by my grandson I didn't read that before i posted that LOL
 

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Discussion Starter · #5 ·
Lol it's a straight aluminum drive shaft. I plan on crawling under these to check the trans mounts to see if there loose. I check the trans fluid and it's still bright red ( no dark color) and smells like new fluid. I've had the truck for 6 years and I do all my own maintenance. 262,000 miles and iv never experienced that. 🤔
 

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Sounds like a problem with the trailer. I agree, if there’s a problem in the trans, the Allison controller plays no games. Almost always get a default and MIL.
 

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Does it only do it when the one trailer is hooked up. Is the tongue loose on it or fluid level low
 

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I have a 2007.5 GMC Serria 2500HD LMM with the 6-speed Allison Transmission 4 wheel drive, the other day I went and picked up a mini excavator and was towing it home when I noticed something iv never noticed before. I stopped at a red light in town and when the light turned green I let off the breaks and pressed the accelerator. As the engine began to rev up to start moving from the stop, a loud clunk and then a jerk happened as I started moving. It only happens when I'm completely stoped and then start to move (1st gear only) when I have a heavy load. It doesn't do it if I dont completely stop, as in if I let it roll a little at like 1 or 2 mph and then go. It also doesn't happen when I'm unloaded or towing a light weight utility trailer and lawnmower. Would this be caused by a slip yoke needing lube or maybe the trans. Mount bolts being loose?
I feel your pain I know exactly what u are talking. About. If you haven't had the experience of the clunk and jerk nobody has a clue . I've experienced exactly what you talking about. I haven't figured it out either. But it's nothing to do with your trailer or ujoint. It's to drastic of a clunk and jerk. Mine feels like the things going to fall in the ground what ever it is. Or busy a housing.. good luck I never found mine
 
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