Good Day Everyone!

I've got a fluid leak under that truck that has me scratching my head. I searched this forum & found some ideas that I looked into, but I'm still stumped. Here's the synopsis:

Last winter, I had a rear output shaft seal leak. I took it to a local transmission/drive line shop. At the same time, I had the 100,000 maintenance done which included changing the fluids in the transmission, both differentials, transfer case, etc. The transmission shop used the specified fluids.

I noticed drops of fluid on the driveway under the skid plate beneath the transfer case each day. I took it back to the guy & he said there was too much oil all over the place to find a leak, suggesting it was left from the old seal leak. I washed it off, but it stayed iced up for most of the winter, so I couldn't see much of anything.

I did not use the truck too often in the winter. Really, not too much until the last couple of weeks. Leaks weren't noticeable, but to be honest, I didn't pay too much attention. I assumed the drive train/transmission dude was right- old fluid from the leaking output shaft seal still dripping off.

For the last couple of weeks I have a lot more evidence of leaking. Up until today, I'd drive 5 or so miles, park it and find a 2-3" diameter 'oil spot' under the skid plate. I had no really long drives.

Now that the weather is better (Finally!), I looked hard under the truck. The skid plate under the rear transfer case had fluid on it, dripping from a drain hole in the plate. But, fluid was in many other places nearby.

I scrubbed the bottom of the truck clean. I parked it for several days and there was no leak at all. I drove it about 15 miles and the leak was back, but just on the skid plate. The transfer case above it was still clean. I washed it again, idled it & no leak showed. I even tried moving the shift level up & down, pausing at each range. I engaged 4WD in & out a few times. I drove back & forth many times. No Leaking.

Today, I drove the truck (freshly cleaned bottom) about 120 miles & everything from that skid plate to the rear of the truck is coated with the fluid. I could smell it cooking on the exhaust after about 25 miles. It is very, very wet with fluid under the truck.

If I look at the transfer case, the rear half has oil. The front half is dry. The bottom of the truck above it is very, very wet. The drive shaft is coated all the way back, as are the exhaust pipes & the bottom of the truck. The rear differential caught so much oil it was dripping off of it. So, the fluid flew pretty far if the leak originates near the transfer case. The fill & drain plugs don't seem to be the culprit, as when parked, no leaks show up. Also, when parked, no oil is around the new output shaft seal.

Oddly, the rear torsion bar I Beam (just rearward of the skid plate) has fluid on both sides of it (Is the fluid going forward and backward?) and my tail gate has a nice coating of fluid on it up about a foot. the top of the bumper has fluid, too. (Wind current magic?)

I can't tell what what color the fluid is. When I wipe it on a paper, it is brownish black, but I may be picking up dirt, too. On the ground it soaks into the pavement too quickly, leaving a brown stain. I tried leaving paper under the truck to find a color, but it has rained for many days, messing up that idea. I tired smelling it to se if I could identify it by comparison. I could not smell anyting at all.

Are there, perhaps, breather tubes that might be dumping only when the truck is moving? Is it likely the transmission guy overfilled something & fluid is expanding when hot & coming out of a relief hole? If I could wash it & ride under the truck while it's moving I'd be able to see it (until I got coated!).

I sure appreciate any experiences you have with similar leaks. I really don't have much faith in taking it to the original shop (or a different one) because it will be either too clean or too oily for the mechanic to find it. Also, I'd rather keep the money in my pocket & fix it if I can.

Thanks Again. I appreciate any knowledge you wish to share.
Paul

 

Are you losing enough to see a drop in a level (it sounds like it). I had a leak in the transmission rear seal of a newly rebuilt transmission that coated the whole truck undercarriage and even the rear window (K5 Blazer). To be coating everything like that it should be very apparant on a dip stick or fill plug. Check the easy one's first - motor oil and transmission. If they are at proper level then pull some fill plugs and see what the deal is.

Also I see you have a 2500 - hydroboost brake units can leak real bad when they are going out. I know my 96 Suburban 2500 that I just sold my dad had power steering fluid all over, but not all the way back to the tailgate. Maybe just give the power steering fluid a peek just to rule it out though.

 

Mr. Shamrock-
Thanks for the ideas of where to look. (Especially since I sure haven't found anything so far.)
The coolant, brake, transmission, power steering levels are ok. The engine oil is OK, too.

I dove back under, concentrating on brake lines & fluid as well as things forward of the first oily spot. Still not figuring it out (yet).

I did see gunk around a rubber hose on top of the transfer case. It heads forward, toward the transmission. I lost it half way. Maybe it is a breather & dumped on the transfer case housing.

Today (assuming the rain ever slows down this month), I'll pull some fill plugs, like you suggested & look for low fluids. I did wash under there again, so I'll have a more or less clean look. If it's too clean, I'll tow a heavy generator around until it gets warm & starts leaking.

My Latest Guess: The guy who did the fluids may have accidentally over filled something because it was about zero outside and now it is getting hot and dumping out a breather hole. (Still- Just a guess) But, my trans temp gauge never got over the usual spot- Just over the first line.

Second Guess: Somewhere I saw a diagram of the transmission. There is a shaft seal between it and the transfer case. Looks like (I might be wrong) if the seal leaks, trans fluid and transfer case lube will mix & go into one or the other, eventually over filling one of them- maybe causing a breather to dump stuff.

Does that sound legit? (Hope not- That one sounds like a project beyond my skills, tools & time limitations or an expensive repair)

Thanks!
Paul

 

You are correct - I just had one done on a 1998 Z-71. There is a seal and a gasket between the transfer case and transmission. The transmission will fill the transfer case, but you should see the transmission level getting low although if it is a slow leak it might not be noticeable yet. You will definitely know when you pull the transfer case plug - have a drain pan ready. If it's bad your looking at about $300 at a trans. shop.

 

Thanks!
I bit the bullet & took it to a local trans shop that has a reputation for extreme honesty. His guesses, before looking, were:
Overfilled transmission & now getting warm enough to vent out
Overfilled transfer case
That expensive seal
Cracked transfer case housing, but doubtful

I'll post what he finds out!

 

Cool let us know.

 

Thanks For Your Interest! The saga continues ...
It isn't pretty-

It appears that there is an oil pump inside the transfer case. Apparently, it is held by two ears on the case. It developed play, walked back and forth, eventually wearing a hole in the case.

The mechanic wasn't comfortable welding (or even JB) because of the tolerances. He wasn't confident that it would not be very thin & wear a new hole quickly, or cause a mis-alignment of components inside. (I guess the hole is in exactly the wrong place.)

This big problem, however, is that this transfer case, unlike most of the other parts on this truck, is quite specific to the set up. (Year 2000, Sierra 2500, 6.0 liter, 4L80E Transmission). It is proving elusive. He had a used 80,000 mile one lined up at LKQ for $800.00, with a one year P&L warranty; but when they prepped it for shipping, LKQ found it wasn't the correct case. I learned that the output spline is different on my truck than it is on most of the others. Something else is different as well, but I can't remember what he said it was.

The best(??) find so far was a 200,000 mile used one, but the guy wanted $1800.00 for it.
Also, the transmission mechanic said at 200,000 miles the housing may be just as worn. Apparently this is common on this case (hence the design change in later years). A case half alone was found, but that person wanted $1200.00 + shipping. I guess folks know this is like gold.

Even remanufactured ones are scarce. The closest one was via a dealership and was 5 days away. Oh yeah- And $2500.00 for the part.

So, for now, the mechanic is still looking for a good one or a good case half to rebuild my existing one.

He's really going to bat for me on this one. But, he has a reputation around here of doing that for his customers. (Along with super honesty.) A person I know had 3 estimates on his car trans repair- Lowest = $2800.00. Someone told him to try this shop. He showed the owner the estimates he already had, asking if he could do it for the same as the lowest estimate. He beat the lowest one alright- The repair bill was $58.00!

I'll keep you posted. (Assuming I don't go broke courtesy of the truck & get the computer repossessed. Just kidding. I Hope.)

Paul

 

Damn - All I can say is YUCK!!! Post the exact part number that you are looking for here and we can try and locate one for you. Have you tried eBay?

 

Thank You!
I'll stop at the Trans Shop today & ask the mechanic the exact part number(s) he needs.
Paul

 

My truck's back in action.

First, I want to thank Mr Shamrock for all the ideas & helpful suggestions he gave. I sure learned a lot!

I've listed the repairs, hoping it will help someone else diagnose a leak from the transfer case- and maybe save a costly repair.

History: Last winter I did the first ever 100,000 mile fluid change (actually, the transmission shop did it for me). The mechanic found copious amounts of water in the transfer case & both differentials.

I wonder if the previous owner used the truck to explore the bottom of a lake? An ice fishing oops, perhaps? There are other tell-tale signs of a prior submarine experience I've discovered since purchasing the truck. I don't think the factory installs seaweed under the dashboard. (If they did, they'd charge extra for it, to be sure!)

The transfer case, as mentioned earlier, suffered from GM's "Walking Pump" or "Pump Rub" where the oil pump retaining clip rubs itself sharp & pokes a hole in the transfer case rear half. The lubricant gets pumped out of the case, but only while the wheels are moving. Eventually, the case pumps itself dry. I got lucky & beat the clock.

The transmission doctor disassembled the transfer case to inspect & clean every component. The pump retaining clip was laying the bottom of the transfer case.

He cleaned & de-greased the area, etched it for grab & JB Welded the hole shut. (With my OK to try this, as opposed to a new case half. All the used ones were mostly rubbed through already. "New" ones were scary expensive. He wasn't confident about welding it- Because of the magnesium & the location, I think.)

He installed an upgrade kit from Merchant Automotive to try and spread the pump's load over a greater surface area. It seems like a creative solution to this problem. Time will tell. Here is a link to their web page. There's a link to a very good video on the page. pump_rub_fix_transfer-case-pump-upgrade-kit

The rear output bearing was scored & burned. I could turn it by hand and hear it grinding away. Of course, the rear output shaft seal, new in December, was messed right up and my new Trak II fluid ($$$) was very kindly rustproofing the bottom of the truck & possibly the windshield of anyone driving behind me when the hole popped open. (Hope Not)

All the seals, gaskets & small parts also got replaced. The chain & gearing turned out to be fine. The case was re-assembled after an overnight cure of the JB.

The mechanic inquired about a vibration while driving & looked at the rear drive shaft for me. There was a problem with how it was balanced, but I don't remember what the specific problem was. However, he took care of it. I remember seeing weights glued on the shaft when I first went under the truck when I bought it. (I guess that beats what we did as kids- Drill & tap a hole, inject antifreeze or oil & bolt the hole shut.)

The truck works great. It sure is quieter in 4WD than it was the day I got it, too & shifts in and out of 4 WD much more smoothly. Who'd a thunk it?

I'm confident the JB Weld will hold, especially since the pump upgrade kit spreads the load around to several points.

I've had good luck with JB. Once, as a young & broke 16 year old, I JB Welded a cracked block on my 64 Chevy Nova Wagon. It lasted as long as I had the car & my brother after me & the guy who stole it after that. I wasn't 'ridin-in-style' but I wasn't walking to work.

The bottom line cost was much less than what I thought it would be- $875.00 total. It's a blessing to have an honest business person helping me out. Very nice gentleman, too.

Again, Thank You Very Much Mr. Shamrock!

Paul