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Allison trans question

3414 Views 21 Replies 9 Participants Last post by  BoiseRob, 
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I have a 2007 Classic CCLB SRW LBZ 3500 with a bit over 340k on the stock trans. I have been noticing a shudder/shaking and what seems to be very minor slipping when I pull off from a stop even when empty. This shaking stops when up to around 20 mph but it happens every time I accelerate from a stop. I checked the fluid and it is bright red, at the proper fill mark and doesn't smelled burnt. I am wondering if I should start considering a rebuild or replacement transmission. My truck doesn't have any mods other than a CAI and aftermarket wheels - never been tuned. It doesn't see any heavy towing, but I do pull a 7x16 enclosed toy hauler with my Harley or zero turn mower in it on short trips.

Any suggestions from the more experienced Duramax / Allison folks on easy fixes or should I start shopping for a trans?

I would like to be proactive on a fix and not have any unexpected down time / get stranded with the truck.
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bam5128 said:
Out of curiosity, when was the last time you flushed it and what kind of fluid did you use?

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@21k miles ago with Dextron VI - what the original owner's manual says.

I know that is a hotly debated topic too...
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Hook'em_Horns! said:
I would seek out a local driveline shop to service the shaft assembly. At those miles, you're past the life of the center bearing/U-joints.

If you're able to, $$ can be saved by dropping the shaft yourself and taking it to 'em for service.
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I will look into this. I can definitely drop it and take it to a qualified shop.
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Crawled under and took a look. I can see that the front driveshaft U-joints from the transfer case are worn out and have play. This is probably also the minor clunk noise I hear.

I'm going to tackle those first myself and check the results.

It appears that the previous owner has already replaced the carrier housing / bearing and rear U-joints.
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Got the front shaft out and melted the U-joints out with a torch. Wasn't that bad. I'm going clean up the driveshaft and yoke ends while I am waiting for the UPS man to drop off the new U-joints.

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bam5128 said:
I've had this clunk going on in mine when stopping and pulling out. Ive recently replaced the trans mount when doing transgo jr and pump rub kit. I've pulled and greased the rear drive shaft splines with red mobil1 grease. Could this be related?
2500HD ECSB 4X4.

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Not sure, but I will post up my results after I get it back together.
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Put everything back together today. I could tell in the first 10ft that the shudder and clunk are GONE.


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Yes AC Delco U-joints.

They fit perfect and were @$21 shipped for both with Amazon prime.
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SilverGorillaLML said:
Woman in the back ground standing there thinking " there he is taking pictures for his dumbass friends online":grin2:
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Yes she was along with watching the grill.

:laugh:
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