Since the onset of very cold weather again over the past few days I have noticed that if I start the engine (block heater used) and put the truck into forward gear without a proper warm-up (to pull it out of the garage for warm-up) I get a loud "clunk" sound from the rearend. It only does it when it's cold and only does it once until another very cold start-up again. I think it's related to putting it into gear w/o a proper warm-up. Does this sound right? I know I should be waiting before putting it into gear but just trying to get it out of the garage so as not to wake the whole house up :).

I recently changed the rear-end fluid out to Mobil 1 synthetic from the stock fluid.

Thanks! Rob

On edit: Ooops - probably should have been in the Allison Trans. forum :(

I have experienced the same thing and the dealer cannot replicate it. I have even left it over night and met them early but I can not duplicate the clunk. It happens most every time my D/A is backed out of my long driveway..... after approx 15 feet, there is a "clunk" that seems/sounds/feels to be in the rear end followed by a "squeaking" sounding like a brake pad or drum rubbing in the rear.

The dealer first replaced the front yoke w/ a nickle one because of a tSB concerning a "clunk" and that fixed it for a while but it's back. At wits end. Replaced rear diff w/ Mobil1 75-90 thinking it would help. Did not at all. Any ideas?

Try greasing your slip-yoke. Anti-sieze works great.

Will try the grease - thanks!

Ramaporunner, Sounds like mine is a different issue than yours. Mine only does it once when first put into gear when cold (upon first pressure applied to drive train). I pulled my truck head-in to the garage tonight to see if it does it putting it into reverse tomorrow AM instead of forward gear.

That happened one time so far this season to me. It sat outside during my work period in about 10 degree weather. It may just be from a little bit of condensation it the rear end causing it to freeze up a bit. But don't know what to do to keep it from doing that though.

Try greasing your slip-yoke. Anti-sieze works great.
Anti-sieze is NOT a lubricant!!

It has some abrasive qualities & I would not use it to "grease" anything

That happened one time so far this season to me. It sat outside during my work period in about 10 degree weather. It may just be from a little bit of condensation it the rear end causing it to freeze up a bit. But don't know what to do to keep it from doing that though.

Yea, that's what I'm thinking. FWIW it was 1*F this AM and it didn't do it this AM (put it in reverse rather than forward) :confused:

Anti-sieze is NOT a lubricant!!

It has some abrasive qualities & I would not use it to "grease" anything
The label says "Anti-sieze lubricant"

Prevents seizing,galling and corrosion of metal parts in temperatures of -65 to +1600 degrees.
It does say not to use in bearings crankcases or gearboxes.

I have used it on the splines of the slip-yoke on my last truck and it had over 100k when I sold it. never had any problems. It did solve the driveline clunk for me.

mine does this to! I believe its the rear brakes releasing! When you park these at night the brakes are red hot,set the ebrake let it sit overnight in 10-20f or even colder, and you get some moisture frezeing on the pads caliper and rotor! Its normal, never does it when its warm!

mine does this to! I believe its the rear brakes releasing! When you park these at night the brakes are red hot,set the ebrake let it sit overnight in 10-20f or even colder, and you get some moisture frezeing on the pads caliper and rotor! Its normal, never does it when its warm!

I think you are right! I've really paid attention to it the last few days. It is worse the first couple days after a wash or during times when the roads are wet in very cold temps. After a few days of dryness, it stops doing it. It does sound like it comes from the rear brakes.

The label says "Anti-sieze lubricant"

Prevents seizing,galling and corrosion of metal parts in temperatures of -65 to +1600 degrees.
It does say not to use in bearings crankcases or gearboxes.

I have used it on the splines of the slip-yoke on my last truck and it had over 100k when I sold it. never had any problems. It did solve the driveline clunk for me.There is a reason they don't recommend their own product for such use.
It is not a lubricant in the typically thought of manner.
It "lubricates" against "seizing, galling and corrosion of metal parts" by setting up a barrier between dissimilar metals (most bolts/nuts are not made of the identical material that they are securing). In order to do this it incorporates a base that inhibits corrosion & is not easily dissolved (unlike most true lubricants) along with very fine gritty particules that serve to minimize any actual physical contact dissimilar metals may have. Put some between your fingers & rub it together for a short time, it will feel rough & anything but slick.

Does this really sound like a product you want to place between 2 surfaces in motion, that must also maintain contact?
Certainly there are products available more suited/recommended for this type of lubricating application (ie-bearing grease,etc...)
Although you stated you had no trouble, applying products for use in applications other than their intended purposes can lead to warranty issues, & accountability problems on the professional level.

My brothers truck had a similar sound. He took it in and they replaced the entire rear gear set. Dealer told him they have done more than a few. His is an 03'