2003 duramax 2500 HD 4 wheel drive Strange noise

Jaysbay

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I recently had the entire top end on my motor rebuilt, You name it I replaced it, As you all know it gets expensive and I could not afford a new truck. I just got my truck back from the shop after the rebuild and put about 400 miles on it and it runs perfect and sounds great. I decided to haul my 5th wheel trailer home from the desert, about a 4 hour drive. I noticed a strange noise when I had it in tow mode when the truck was downshifting only. It does not make the noise on the up shift, Only when it's downshifting. Now when I take it out of tow mode the noise goes away. It is only making the noise when I let off the pedal. Any ideas on what could be going on ??. I did check the level of the transmission . The noise it makes, sounds like a steering box that is running out of fluid. I started thinking this morning perhaps the noise could me coming from the mid transfer case, I looked at the transfer case and I do see a leak at the seal. I am not sure how that mid transfer case gets fluid, Does it get fluid from the transmission ?? or is it a sealed unit like a differential case??.
Thanks guys for reading my post
Johnny
 

2004LB7

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The transfer case has its own fluid. Plugs on the case allow you to drain and fill it. Definitely don't let it run dry

Also, check for play in the u joints and shaft coming out of the transfer case
 

Jaysbay

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ok cool, What fluid is recommended ? I can google that as well. Have you ever heard one that is low on fluid ??, This thing sounded like a steering fluid pump running out of fluid , But only when i let off the throttle .
Thanks for the reply
 

2004LB7

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ok cool, What fluid is recommended ? I can google that as well. Have you ever heard one that is low on fluid ??, This thing sounded like a steering fluid pump running out of fluid , But only when i let off the throttle .
Thanks for the reply
It's possible the whine or noise is the differential gear whine. Might want to check the fluid on those too.

ATF like the transmission is suitable for the transfer case. But I like 0w-20 for better lubrication. Also better to fill from the sensor on the top and do two quarts.
 

Jaysbay

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How many miles on the truck? Have you done the pump rub fix?
Thanks for asking, I believe you are talking about how the pump rubs a hole in the case??. I did have to do that a couple years back, I installed a safe guard metal sleeve inside to keep it from rubbing a hole in the case.
 

Jaysbay

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It's possible the whine or noise is the differential gear whine. Might want to check the fluid on those too.

ATF like the transmission is suitable for the transfer case. But I like 0w-20 for better lubrication. Also better to fill from the sensor on the top and do two quarts.
I am going to pull the plug tomorrow and see how much oil is in there, I can see that the seal is leaking, could be real dry. I know that that there is what i believe is a cable or it could be a wire that runs from the transmission into the differential, Does that wire/cable activate the tow haul switch ??.
If so that would make since .
 

2004LB7

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I am going to pull the plug tomorrow and see how much oil is in there, I can see that the seal is leaking, could be real dry. I know that that there is what i believe is a cable or it could be a wire that runs from the transmission into the differential, Does that wire/cable activate the tow haul switch ??.
If so that would make since .
Tow haul is just al algorithm in the programming to adjust the shifting pattern. Normally with higher MPH/RPMs and torque converter locking up sooner. No special gear ratios or mechanical activation. 4wd on the other hand does. The front differential has on the axle a motor that will engage the locking of the shafts together for the 4wd. Then the transfer case has to lock in the front drive shaft. On the transfer case there is also a speed sensor so the transmission computer along with the engine computer knows how fast the shaft is spinning for vehicle speed and shifting
 

Jaysbay

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Tow haul is just al algorithm in the programming to adjust the shifting pattern. Normally with higher MPH/RPMs and torque converter locking up sooner. No special gear ratios or mechanical activation. 4wd on the other hand does. The front differential has on the axle a motor that will engage the locking of the shafts together for the 4wd. Then the transfer case has to lock in the front drive shaft. On the transfer case there is also a speed sensor so the transmission computer along with the engine computer knows how fast the shaft is spinning for vehicle speed and shifting
Wow great explanation . Let me ask you this, So when the truck is in 2 wheel drive is the the shaft that is running from the transfer case to the differential turning??
 

2004LB7

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Wow great explanation . Let me ask you this, So when the truck is in 2 wheel drive is the the shaft that is running from the transfer case to the differential turning??
You might want to specify which drive shaft and which differential. As there are two of each
 

Jaysbay

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You might want to specify which drive shaft and which differential. As there are two of each
Well i guess you can tell I don't know my truck much lol. I know a have the rear end drive shaft the big aluminum one that goes from the rear diff to the mid transfer case then another one that goes from the transfer case to the front diff. I don't know to much about how this truck really works . The transfer case that is between the front drive shaft and the rear drive shaft is the one that is leaking I probably have this ass backwards, I'm not much of a mechanic . I noticed what i thought was called a mid transfer case is leaking, and if it was spinning in 2 wheel drive, would that cause a whining noise
 

2004LB7

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First things first. Check the fluid level in the transfer case. There is only one and it sits, as you describe, between the front and rear drive shafts. Once you check/correct the fluid then we can go from there
 

Jaysbay

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Thanks 2004LB7
It is pouring rain today in So Cal , I am hoping the rain stops tomorrow so I can check the oil level in the transfer case, Regardless I am going to have to replace the seal, I understand there is also a bushing that should be replaced at the same time. I understand the bushing takes a special tool to remove it. I called a local shop here in town and they have the tool and offered it to me to borrow for a couple days.
 

PureHybrid

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Is the tool made to change the bushing while the case is installed? As far as I know the case has to be split to change the bushing
 

Jaysbay

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Is the tool made to change the bushing while the case is installed? As far as I know the case has to be split to change the bushing
PureHybrid I am not sure ? I read somewhere that you should also change the bushing as well, Heck I am not even going to pull the transfer case to replace the seal, Perhaps I misunderstood what they were talking about. They probably talking about the tool to install the new seal. I was going to 3d print the tool to set the seal in place but after seeing that it was going to take 25 hours to print the tool , I am just going to barrow it from a local shop.
Thanks for the reply
Johnny
 

jlawles2

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I made a seal driver tool by taking the seal to the hardware store and buying a plastic bushing fro PVC pipe that fit over the seal. this gave me the internal clearance to not damage the rubber hump sticking out the back.

If there is no vertical play in the front driveshaft yolk where it sticks into the transfer case, then the bushing does not need to be replaced.

The front propeller shaft (driveshaft) is on the driver side running between the transfer case and the front differential. This shaft when in 2wd is not powered and may or may not turn. To help minimize or eliminate the turning of the shaft GM put a disconnector between the differential carrier and the passenger side on the axle shaft (internal to the housing). With the truck on the ground and in 2wd you can grab the front propeller shaft and turn it (it's probably the rusty tube almost directly below the oil filter). If you cannot turn the shaft, then jack up the front and try again, if you can turn it then, the disconnector or the disconnector actuator is not working. If with the front raised you can not turn the shaft, then there is an internal issue with the transfer case.
 

Jaysbay

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Mar 28, 2024
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I made a seal driver tool by taking the seal to the hardware store and buying a plastic bushing or PVC pipe that fit over the seal. this gave me the internal clearance to not damage the rubber hump sticking out the back.

If there is no vertical play in the front driveshaft yolk where it sticks into the transfer case, then the bushing does not need to be replaced.

The front propeller shaft (driveshaft) is on the driver side running between the transfer case and the front differential. This shaft when in 2wd is not powered and may or may not turn. To help minimize or eliminate the turning of the shaft GM put a disconnector between the differential carrier and the passenger side on the axle shaft (internal to the housing). With the truck on the ground and in 2wd you can grab the front propeller shaft and turn it (it's probably the rusty tube almost directly below the oil filter). If you cannot turn the shaft, then jack up the front and try again, if you can turn it then, the disconnector or the disconnector actuator is not working. If with the front raised you can not turn the shaft, then there is an internal issue with the transfer case.
Wow what a great explanation , I did not know that about this truck. I had the transfer case rebuilt about 8 years ago and was surprised that the seal is already leaking. I was going to start with replacing this seal because it is leaking but I will check out your idea prior.

What concerns me most is the whining noise when I have it in tow haul mode and the truck starts downshifting , Could be that the transfer case is empty or there are some internal issues. My first attempt is going to be to drain the fluid. If I don't use the tow haul mode I don't hear the noise .And when I do use the toy haul mode and I am at normal driving speeds the noise goes away and returns when the transmission starts downshifting.

It could be in the transmission I am not sure. I will get a chance to work on the truck over the weekend. I was going to 3d print a seal punch installer
but it was going to take like 20 hours to print , So I think I will use the PVC technique instead.

Thank you for letting me know how this front driveshaft works. I figured it spun the same speed as the rear shaft but just wasn't locked in.

Johnny