Great story GF. For anyone that wants to hear the noise go to YouTube and in the search box type strange engine noise 05 Colorado. It's not my truck but sounds exactly like it.

I had a bad deceleration vibration and clanking on my 2001 Chevy 2500HD. It would even do it if I shut the truck engine off and coasted. Took it to several places and none had any ideas or had seen it before. It ended up being bad U joints, but you couldn't tell until they were removed.

I'm about to install the "rub kit" from Merchant Automotive on my 07 Dmax.. If you catch it in time, you can save yourself big $$$$. Usually happens somewhere around 130k miles from what I've gathered. GM fixed the issue on 2007.5 and on models. It's not really a transmission issue, just the transfer case. In a nutshell, the thin alum outer ring of the pump rocks and digs into the magnesium case. Eventually it rubs a hole thru the case and the oil leaks out. The kit includes a re-designed pump outer ring that spreads the contact points between ring and case over a much larger area. If you have a pre 2007.5 4x4 Dmax, you need this for sure. I believe 4x4 Suburbans (and maybe a couple other models) also have the issue. Lot of threats of legal action but haven't seen anything yet.

Well here is the verdict for mine. T- case shot, can't even get core cost back. To many holes and interior chewed up. Never noticed any signs on the driveway of leaks. Was told holes very small, any leakage soaked up by dirt on top of skid plate. Unfortunately as you all know Chevy will not back there product on this. But wait, doesn't end there. Since I was having same issue in reverse they did a tranny inspection. Found part of the reverse gear and bunches of metal flakes and chunks. Guess I won the daily double. Final bill is yet to come, but I'm sure it will be over 4500$. Sure would be nice if Chevy would man up and help people with the T-case issue, including those that have already fixed the issue at their own cost.

Ouch! I haven't heard of many Allison failures. How many miles?

On the transfer case, sometimes the holes are above the oil level so they only leak when moving. Most owners report not seeing evidence of oil leak before it burns up.

Ya, I didn't notice any leaking. How do you check the fluid in the TC?

There's a fill plug on the back above the drain plug.
I use the Sonnax pump and snap ring kits in all that will accept them.
https://www.sonnax.com/parts/1694-tr...pump-plate-kit
https://www.sonnax.com/parts/1697-tr...-ring-retainer
I've seen the other style plate kit wear through
https://www.etsy.com/listing/7419458...dba6e590d2189b

Installed the Merchant Automotive kit today. It's a nice well made piece. Looks like I caught it just in time (130K miles)
The little steel insert had broken but was still in place somehow. Even with the steel insert in place, the magnesium was heavily worn behind the insert. Almost all the wear was on one tab cut-out which is above the oil level.


https://cimg1.ibsrv.net/gimg/www.off...7bd6afbe7a.jpg
Broken steel insert
.

https://cimg1.ibsrv.net/gimg/www.off...b93020dbd1.jpg
New pump housing installed. Old pump housing above for comparison.



https://cimg4.ibsrv.net/gimg/www.off...440adee646.jpg
Found old steel insert hanging off pump housing tab.



https://cimg8.ibsrv.net/gimg/www.off...74250aae8e.jpg
Wear from steel insert rubbing on case. Needed to Dremel off the ridge created by the wear.

Hi zz, mine wasn't an Allison. Glad you caught yours in time. Theory on why I didn't notice leak in drive way. I drive a lot of gravel and dirt roads so the skid plate that protects the T-case was full of dirt. As the case leaked, which all on this thread know is very small, the dirt would soak up the fluid. Yes the price is an ouch, but could have been way worse. Was able to get most parts at mechanic cost