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Discussion Starter · #1 ·
Hey y'all,

I tried to ask this question before, but I failed to illustrate exactly where I was leaking from.

This time 'round I got some "better" pictures, and also a illustration straight from the manual.

What I need is to identify where the leak is coming from (probably transfer case), and what I can do to remediate the leak.

So to introduce the truck - '99 K2500 ext. cab, '97 engine vin S (probably not that relevant)

Continuing I've got a NP243C transfer case (anybody else have this with similar issues?), and a rusty, sandy U-joint right in between where the prop-shaft connects.

637958


I've recently placed the truck in a garage so that I can follow the leak more closely.

I've lost about a third of a gallon (1 litre) of brownish ATF. I haven't overfilled the transfer case because I haven't filled it since I got it in April - and I don't think the previous owner had touched it for at least to years.

I haven't opened the fill/drain plug for the transfer case yet - because I'm not entirely sure what fluid I'm gonna put in there (I'm thinking I'll put Dextron VI same as the tranny, any ideas about this?).

So I'm thinking the leak is coming from the transfer case side of the U-joint, because the prop shaft doesn't contain any ATF, or other fluid, as far as I'm aware.

I wan't to change the U-joint on both ends of the prop-shaft, but I'm not 100% what U-joint to get. I've posted some rough measurements in the pictures below. I'm worried that this won't fix the leak, so I'm thinking of buying a new oil seal for that part of the transfer case (anyone know what part I should get?).

The pictures are below - let me know if there's something I didn't cover, I'll answer to the best of my ability.


637959

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Looks like your rear differential pinion seal is leaking. Pull the U joint and Yoke and replace that seal.
Look on Youtube for some DIY videos
 

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Discussion Starter · #3 ·
Looks like your rear differential pinion seal is leaking. Pull the U joint and Yoke and replace that seal.
Look on Youtube for some DIY videos
Thank you for good and fast answers as always OkDually!

When it comes to the seal, would "Transfer Case Input Shaft Seal" be the correct one? I see TIMKEN and SKF has seals for the NV243C.

Regarding the U-joints, I'm looking at the MOOG ones - can anyone recommend this or other ones?
 

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Both brand of seal are good.
 

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Thank you for good and fast answers as always OkDually!

When it comes to the seal, would "Transfer Case Input Shaft Seal" be the correct one? I see TIMKEN and SKF has seals for the NV243C.

Regarding the U-joints, I'm looking at the MOOG ones - can anyone recommend this or other ones?
The transfer case is towards the front ( shown in your diagram) Your rear diff is leaking so you would need a rear pinion seal: 1999 CHEVROLET K2500 PICKUP 6.5L V8 DIESEL Turbocharged Differential Pinion Seal | RockAuto

As far as U joints go, you can use Moog, Ac/Delco, or GM Genuine, Dana (spicer)
 

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I think we may need a wider shot so we know for sure what you are taking about. You diagram is for the rear and points to the differential end of the shaft, not the transfer case. If its the differential end its likely engine oil from oil filter changes or a leak around the oil filter or cooler lines or even higher up like a valve cover. The joke is that is how GM designed the front U joint to be lubricated. I have had trucks where I had to replace the rear joint twice and at 300k miles the front was still fine perhaps due to the oil?

Replacing the U joint won't have anything to do with the leak. Also other than figuring out the correct joint replacing them can be a little tricky and require somewhat special tools and techniques. May be a job better left for a drive line shop. In the past I have fought with trying to hammer or press them in for hours only to find out that a shop could do it in 5 mins and only charge like $20 not to mention they won't bend and otherwise damage things in the process like I did.

You also really need to check all the possible fluids and know for sure where this is coming from. A liter of fluid is a lot to be down even in the transmission. A liter of engine oil would also not be the best thing and if its a liter of diff oil or transfer case fluid you could be running nearly dry since those things don't have a heck of a lot more to start with.

Front diff has 2 plugs you can see by looking at it from in front of the front left tire. The smaller lower one is the drain and the bigger one up higher is the fill / level check. With the truck sitting level the fluid should be up to the fill hole. I would have to check but I think this just takes 80w-90 gear oil. These don't commonly leak from the input shaft so if you are loosing a liter of the lube from there I would be looking for a replacement differential. This thing doesn't hold much more than 2 quarts so if its lost 1 its got to be really low.

The 243 transfer case isn't the 'auto' one or the one that has the 'pump rub', its actually a pretty reliable case. Similar to the diff its got 2 plugs facing the back of the truck. Bottom is drain. Higher one is the fill level one. This case uses ATF and with the truck level should be up to the fill hole. Also similar to the diff this doesn't hold much more than 2 quarts so if its lost one its running really low. I would say the same thing about the output shaft seal leaking, not a common place for a leak just due to a tired seal, if its leaking there is likely deeper issues.

As I noted in your last thread is its possible that you have failed seals between the transmission and transfer case so transmission fluid is actually leaking into the transfer case and causing it to be over filled (and your transmission to be low).
 
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This is very confusing...... The pics you posted appear to show the front drive (propeller) shaft output side of the transfer case. Just where is this leak? In the front drive shaft or the rear?
 

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Timken is a great deal brand you want the transfer case rear output seal easy to replace. I used Moog brand U-Joints on my sub and I always ask for the ones with a greese fitting in the end cap. I feel the ones that are built like that are stronger that with the fitting in the cross section plus it is easy to get to when you have to greese the joint.
 

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Discussion Starter · #10 ·
Thanks for the very detailed post 57diesel!

My diagram is wrong - catched it after you mention it. Wasn't the best idea to write this up after a night shift heheh!

OK, so I'm 99.9% sure this is ATF, it doesn't smell like engine oil and it has a red color to it.

When I go to check the level in the fill hole of the transfer case, if this is full/close to max, that would indicate a leak from the tranny to the transfer case right? Is it possible to change that seal without disassembling the whole tranny?

I will take a wider shot in the daylight tomorrow, up here in Norway we don't have many hours of it hehe.

Thanks again 57, OkDually and JMJ. I would not be able to be at it and wrenching if it weren't for you fellas.

Tommy, its dripping down in the front... sorry for the confusion.

Shane, I was thinking about getting those with the greaseable end caps too, thanks for confirming!
 

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Yes if the transfer case is full our over filled but the transmission seems low then its got to be the seals between them. Transfer case for sure would have to come out to access those seals but I don't know enough about the 4L80E to know where the seal is in those. If its like some of the older ones the seal may be in the adapter piece that is between the trans and transfer case.

Another thing that could be leaking in that area and have transmission like fluid in it but again not more than quart or two total would be the power steering. The pump is kinda above the front diff and there are plenty of hoses and things the fluid could run along before it drips. You also have the brake booster above the same general area and again plenty of hoses to run along before you get a drip.
 

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Ok Its the front. Things are clearer now. Most likely Its the seal. It as a common problem with older transfer cases. Not hard to replace.
Un bolt the drive line.
Pull the yoke
You will see the seal
Pull it out with a seal puller or a trusty big screw driver.
Gently tap in the new seal using a hammer tapping on a socket that is slightly smaller diameter than the outer diameter of the seal. Or you can buy a seal installer tool.
When you have the yoke out inspect it closely. If it has a groove or worn spots from the old seal. Replace it or it will leak.
If the output shaft has a lot of play Up, down, side to side then the bearing may be bad. That will require pulling the x fer case to fix.

To check if the rear transmission seal is leaking ...
Start truck let it warm up, Check Xfer-case fluid level,
Check trans fluid. Truck Idleing and in neutral.
Then go out and drive around truck for a while, 20 minuets or so.
Park truck and check the x- fer case fluid and trans fluid. If Fluid pours out of the fill hole in the X-fer case when you pull plug, and transmission fluid is low. The rear trans seal is most likely bad. If fluid levels are the same as before you drove it , the seal should be good.
Usually when the rear seal on the transmission goes out it blows fluid out of the rear drive shaft seal on the Xfer case Not the front.
So i am hoping you just have a bad front output seal in the Xfer case.
Hope this helps.

.
 
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Looks like your rear differential pinion seal is leaking. Pull the U joint and Yoke and replace that seal.
Look on Youtube for some DIY videos
OK - I don't think hes talking about the joint at the rear differential. It's the one at the transfer case I believe.
 

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OK - I don't think hes talking about the joint at the rear differential. It's the one at the transfer case I believe.
My mistake..
 

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If this is sealed like the 4L80 output shaft, it uses an O ring on the output shaft that seals against the inside of the front of the yolk. If that O ring is missing or damaged, oil will leak from the breather hole in the yolk just ahead of the U joint. That sounds like what you're seeing.
 
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