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Discussion Starter · #1 · (Edited)
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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Out of curiosity, when was the last time you flushed it and what kind of fluid did you use?

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with a bit over 340k
More likely a drive shaft/bearing issue.
Not something to slack on, get it checked. You could wind up cracking the case, which requires a trans pull to repair properly on an Allison.

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.

You could drop and service yourself, but that bearing needs to be pressed on/off (to the correct spot), and they'll spin and balance the shaft assembly with all of the new parts on it.

If you're able to, $$ can be saved by dropping the shaft yourself and taking it to 'em for service.
 

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Discussion Starter · #4 ·
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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Discussion Starter · #5 ·
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.
I will look into this. I can definitely drop it and take it to a qualified shop.
 

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I'd do a drive by 1st, let 'em have a visual inspect.
Parts most likely have to be ordered, time scheduled, etc.

While the fluid is a much discussed topic, the biggest benefit is service life.
100k TES-295(delvac or transynd) vs 25-50 (severe duty/not) Dex.

Something to consider at the next service interval.
 

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Doesn't a Tech 2 give visibility to trans slip? And some display devices, like Edge CS2, also? I think all transmissions have some amount of slip, but there's a point at which the slip becomes a real problem. The problem described by the OP doesn't sound like trans slip to me.
 

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I had the same issue and when I crawled under it the center hanger bearing rubber was all beat out. 3 new U Joints and a hanger bearing with a balance thrown in cost me around $250 + parts.

The parts are less expensive if you buy the and take them to the shop rather than buy the parts at the driveline shop. Got all mine at Rock Auto for under $100

PS, I bought a Timken Hanger Bearing and it did not have the studs on the hanger, so I had to purchase two bolts and with nylon lock nuts to mount the hanger Bearing
 

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Discussion Starter · #9 ·
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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It may be the trans but I'd be willing to bet its the carrier bearing, u-joints, transmission mount, or a combination of the three.

Is the truck 4WD? I have the same truck in 4WD dually and its always had that shudder from a stop. Its the crappy driveline angles when the truck is unloaded. Loaded down its really not an issue.

I ended up doing the carrier bearing, u-joints, transmission mount, and I think I even shimmed the crossmember or trans mount to improve driveline angles (its been a long time! I think I posted about it though with pictures) and now its really not an issue anymore but it may be very slight if you're "looking for it"

If you google/forum search that issue, you will find many many people have had the shudder on stock unloaded trucks like ours...

Keep us posted
 

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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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Discussion Starter · #12 · (Edited)
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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Discussion Starter · #13 ·
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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Discussion Starter · #14 · (Edited)
Put everything back together today. I could tell in the first 10ft that the shudder and clunk are GONE.


 
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Put everything back together today. I could tell in the first 10ft that the shudder and clunk are GONE.


Maybe the u joints are my issue after all... 134k miles isn't high for them from what I've read but I suppose not terrible. It looks like you got the acDelco ones with the zero fittings. That's the route I plan on going too so i can grease them when indo my front end.

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Discussion Starter · #16 ·
Yes AC Delco U-joints.

They fit perfect and were @$21 shipped for both with Amazon prime.
 
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Put everything back together today. I could tell in the first 10ft that the shudder and clunk are GONE.


Woman in the back ground standing there thinking " there he is taking pictures for his dumbass friends online":grin2:
 

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leg cross attitude. :teehee
 

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Put everything back together today. I could tell in the first 10ft that the shudder and clunk are GONE.
The front shaft is stationary when driving in 2WD ... Unless.... the front axle actuator is locked up in the 4WD position.

You need to check this out more.....
 

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I may be wrong but I think he was talking about the front of the drive shaft u joint

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