[TommJr]

For about the last month I have been listening to a clunk in my tranny, or rear end for that matter. It only does it when I go into reverse. When I go into reverse, It will sometime clunk when I'm moving, or sometimes it will happen when I'm sitting there idiling. I'm not a mechanic, but I think it sounds like some sort of pump, or converter or something. Like I said, sometimes It does it when I'm moving, and sometimes it just does it sitting there. So I don't think it is gears in the rear end, or some kind of moving part.


I have already flushed my tranny twice and replaced factory fluid with Transynd. I also have changed my front and rear differential fluid twice, and have replaced with Amsoil synthetic. The truck has 37,000 miles on it. So needless to say, the maintenence is getting done.


Maybe someone has an idea on what is going on.


P.S.- there is no visible leaks anywhere. And fluid is full. Maybe there is a tsb on something like this.

 

[dslbrnr]

Mine did that to. I changed the rear axle oil to Mobil 1 and that fixed it. It took a little time for the oil to circulate before it stopped though.


04 LBY

 

[Elvis in Texas]

Tomm;


Does it only "thump" when you are:


Parked (say for the evening), Fire her up, plece it in Reverse and back up, place in forward gear, give a little throttle and "thump"?


Elvis

 

[problemchild]

Mine does it too. But I think its the rear springs your hearing. Mine make noise all the time.

 

[big0chevy]

I don't think that it is the rear springs that are making the noise, because it will do it when I am not moving. I don't think that it is in the rear end. Anymore comments would be nice.

 

[TommJr]

It is almost like it is a hesitation in a pump. Sometimes it delays when it clunks, sometimes it does it right away. Sometimes it doesn't do it at all. All fluids full. Changed fluid twice. No broken teeth in differential. Everything checks out.


Sometimes I think it is just my imagination.

 

[big0chevy]

I know what you mean. It used to only do when I was hooked up me trailer, but it does it know even with out it

 

[SmokeyMax]

I have had other autos that disable ABS while going in reverse. It makes a funny popping sound. My Truck was doing it for a while and then quit.

Hope this helps.





SmokeyMax

 

[RonJT]

I read this thread yesterday and my transmission did it for the first time that night!


My symptoms are a delayed clunk without the truck moving. I placed it in reverse--foot on the brake--and then the clunk occurred.


I was not sure I heard it right so I recycled from reverse to park back to reverse--without moving--another delayed clunk.


Truck is a 04 LB7 with 7500 miles on it.


I had just came back from a two hour freeway drive with about 4 miles to the house from the freeway.


It did not do it this morning.


Truck has new Mobil1 in the rear differential at 1500miles and two gallons of transynd oil at about 2000miles with a new spin on filter.


Ron

 

[Dura_Mike]

I'm not sure if this info will help, but I received a video tape with my owners manual. The tape was a 15 minute owner orientation for the Allison 1000 transmission. The video mentions a number of sounds that the Allison trans will make that are considered normal. One of the normal "clunk" sounds is the park ratchet pawl disengaging. Sometimes the pawl will not disengage until you just start to move. Is there a chance that could be the noise you hear?


My Allison has a definite gear whine in first gear and a barely audible pump whine when in park.

 

[big0chevy]

Dura-mike I know what sounds you are talking about, but this is something that I have not seen on all of the trucks. Just a select few. Acutally the only ones that I have seen this happen on is the cal. trucks not any of the other trucks. Maybe it has something to do with that. I don't know and I cannot find anyone else who can give me a explination on it.

 

[TommJr]

Hopefully the noise is just my imagination. Or it is a common noise made by the Allison. Like I said, all fluids are good, so Hopefully all is well.

 

[FISHHOG]

Hopefully the noise is just my imagination. Or it is a common noise made by the Allison. Like I said, all fluids are good, so Hopefully all is well.

TRY LUBING THE DRIVELINE SPLINES


<H1>Info - Driveline Clunk #99-04-20-002B - (08/21/2003)</H1>Driveline Clunk


2004 and Prior Light Duty Truck Models


2003-2004 HUMMER H2


This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 99-04-20-002A (Section 04 -- Driveline/Axle).



<H4>Important</H4>


The condition described in this bulletin should not be confused with Driveline Stop Clunk, described in Corporate Bulletin Number 964101R (Chevrolet 92-265-7A, GMC Truck 91-4A-77, Oldsmobile 47-71-20A, GM of Canada 93-4A-100) or Bump/Clunk Upon Acceleration, described in Corporate Bulletin Number 99-04-21-004A.





Some owners of light duty trucks equipped with automatic transmissions may comment that the vehicle exhibits a clunk noise when shifting between Park and Drive, Park and Reverse, or Drive and Reverse. Similarly, owners of vehicles equipped with automatic or manual transmissions may comment that the vehicle exhibits a clunk noise while driving when the accelerator is quickly depressed and then released.


Whenever there are two or more gears interacting with one another, there must be a certain amount of clearance between those gears in order for the gears to operate properly. This clearance or freeplay (also known as lash) can translate into a clunk noise whenever the gear is loaded and unloaded quickly, or whenever the direction of rotation is reversed. The more gears you have in a system, the more freeplay the total system will have.


The clunk noise that owners sometimes hear may be the result of a buildup of freeplay (lash) between the components in the driveline.


For example, the potential for a driveline clunk would be greater in a 4-wheel drive or all-wheel drive vehicle than a 2-wheel drive vehicle. This is because in addition to the freeplay from the rear axle gears, the universal joints, and the transmission (common to both vehicles), the 4-wheel drive transfer case gears (and their associated clearances) add additional freeplay to the driveline.


In service, dealers are discouraged from attempting to repair driveline clunk conditions for the following reasons:
<UL ="BULLET">
<LI>Comments of driveline clunk are almost never the result of one individual component with excessive lash, but rather the result of the added affect of freeplay (or lash) present in all of the driveline components. Because all of the components in the driveline have a certain amount of lash by design, changing driveline components may not result in a satisfactory lash reduction.
<LI>While some owners may find the clunk noise objectionable, this will not adversely affect durability or performance</LI>[/list]

 

[Bowhunter]

Thanks FISH.


Good stuff. Answered a major concern I have had from day one.

 

[big0chevy]

I will try to grease the splines and let you know what happens.

 

[Dustin]

I had this same problem in my half ton pickup. I have the crew cab duramax now and it too was doing this when I bought it. It is not in the transmission at all, it is in the transfer case. I switched to a blue fluid gm makes called Auto Trak II transfer case fluid. The slip properties are different in this fluid and it should take care of the problem. You need to drain the fluid which is probably red, and it shouldn't be, there was a bulletin several years back to switch to the Auto Trak II transfer case fluids, but a lot of the dealers haven't done this. Fill with the new fluid and drive about 10-15 miles and drain again. Fill with two quarts of the Auto Trak II fluid and drive. This problem can take up to 100 miles to completely stop. It has worked both times on both of my trucks.