Clunking on deceleration?

[Jason_Staggs]

Just a thought... does your model truck have torsion bar front suspension? I had a 2004 Suburban 2500 that used to clunk like this when you put it in reverse. Turned out that the bushings on the torsion bar mount, where it connects with the frame, were bad on the left side.

Yeah it’s torsion bar. I believe all 4wd 400s are but I’m not 100% on that. I’ll give that a look before I yank the transmission tonight.

 

[movietvet]

Does seem like there’s definitely more showing than mine.

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My GMT800 has the seal extension boot on my seal. It is there for protection of the slip yoke seal surface and has the hole in it to show a leak if there is one. The sealing surface is of course at the end of the case, like in the first picture here.

 

[Jason_Staggs]

I started removing the transfer case last night and I just want to get confirmation on something before I go through the entire process for naught. If it turns out it is my transmission output shaft clunking against my transfer case input shaft that if I replace my transmission main shaft it should make the noise go away until the new one gets worn out as well correct? All this is riding on if it actually is my transmission making the noise, but I can’t think of a single other thing that would be making the noise come from the mating area.

 

[movietvet]

Hopefully @NickTransmissions can chime in with the answer.

 

[NickTransmissions]

I started removing the transfer case last night and I just want to get confirmation on something before I go through the entire process for naught. If it turns out it is my transmission output shaft clunking against my transfer case input shaft that if I replace my transmission main shaft it should make the noise go away until the new one gets worn out as well correct? All this is riding on if it actually is my transmission making the noise, but I can’t think of a single other thing that would be making the noise come from the mating area.

Something would have had to grenade in either the trans or t case for this to be happening. The output shaft splines into a coupler that "joins" it with the t case. Clunking is usually driveline moving against the t case or transmission (if 2WD) due to slightly changing pinion angles. One possibility is the snap ring securing the output shaft at the front planet broke, allowing the shaft to move longitudionally in the case and forcefully thrust against the t case coupler. This isn't common but heard of it happening.

To replace your output shaft (assuming that's the problem), you're disassembling and rebuilding the trans (replacing the output shaft in the process.

 

[Jason_Staggs]

Something would have had to grenade in either the trans or t case for this to be happening. The output shaft splines into a coupler that "joins" it with the t case. Clunking is usually driveline moving against the t case or transmission (if 2WD) due to slightly changing pinion angles. One possibility is the snap ring securing the output shaft at the front planet broke, allowing the shaft to move longitudionally in the case and forcefully thrust against the t case coupler. This isn't common but heard of it happening.

To replace your output shaft (assuming that's the problem), you're disassembling and rebuilding the trans (replacing the output shaft in the process.

So you’re not convinced that the splines could have some play in them due to being worn down and is what causing the sound? I’m all for anything that prevents me from rebuilding my trans.

 

[NickTransmissions]

So you’re not convinced that the splines could have some play in them due to being worn down and is what causing the sound? I’m all for anything that prevents me from rebuilding my trans.

No. If they are worn to that extent, you'd have stripped them by now.

What is convincing you the "clunk" is wven coming from the tcase or trans? Clunks are typicall driveine or suspension, etc.

 

[Jason_Staggs]

No. If they are worn to that extent, you'd have stripped them by now.

What is convincing you the "clunk" is wven coming from the tcase or trans? Clunks are typicall driveine or suspension, etc.

My friend was under my truck while I was getting it to make the noise and he said it sounds likes coming from where the transmission and transfer case mate together and when it makes the noise I can hear it almost directly beneath me. I don’t believe it’s suspension because all my bushings, leafs, and u bolts appear to be in good condition and I’m not convinced it’s my driveshaft because my front ujoint appears to be solid and my rear is less than 2 years old. I’m not dismissing your ideas I’m sure you have WAY more experience with these trucks than I do, I’m just going off what I can see hear and feel. I also know it’s extremely difficult to diagnose without being there to also see hear and feel the vehicle

 

[NickTransmissions]

My friend was under my truck while I was getting it to make the noise and he said it sounds likes coming from where the transmission and transfer case mate together and when it makes the noise I can hear it almost directly beneath me. I don’t believe it’s suspension because all my bushings, leafs, and u bolts appear to be in good condition and I’m not convinced it’s my driveshaft because my front ujoint appears to be solid and my rear is less than 2 years old. I’m not dismissing your ideas I’m sure you have WAY more experience with these trucks than I do, I’m just going off what I can see hear and feel. I also know it’s extremely difficult to diagnose without being there to also see hear and feel the vehicle

Im not say it isn't; you're there with the vehicle so would be in a better position to tell than someone on the net. Just was curious as to how you determined the source area. Other than an occasional clunk, did you have any drivability symptoms?

 

[Jason_Staggs]

Im not say it isn't; you're there with the vehicle so would be in a better position to tell than someone on the net. Just was curious as to how you determined the source area. Other than an occasional clunk, did you have any drivability symptoms?

None at all just the clunking when releasing the throttle like I’m going to coast or when I go to reverse. I had a slight vibration around 50 but that was because I put my driveshaft in the wrong way I flipped it and it went away.