Transmission fluid mystery

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Hi guys! I have a problem on my K1500 92 Suburban. The transmission fluid goes to the transfer case ! So I have a leak on the output transfer case seal. I've replaced it, but
nothing changes. When I open the filler plug of the transfer case, 3 or 4 liters of transmission fluid goes out ! And then, when I drive about 200 miles, I loose the same quantity from the 4L60.... And I can find the lost fluid again in the transfer case....What could be the problem as I can't imagine the transmission fluid going from a gearbox to another one! What could be the way used by the fluid? What should I replace to keep the transmission fluid at its right place? Moreover, the transmission is a new one from TCI (less than 20 k miles)
Any help will be great!
Thanks in advance for your help!!!! Phil
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you have a bad seal at the FRONT of the transfer case

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My 89 did a similar thing. Except it would pump the fluid out of the transfer case and into the transmission. I found this out after I started searching for a high pitched squeal coming from the drive train and found the transfer case about 1 qt low. Never had a leak under the truck so I checked the transmission and, you guessed it, over full.
In any case, I had the replace the seal between the transmission and the transfer case. It was kind of a big job, but the shop manual gave fair instructions. The seal is a double seal (dual cup seal) to hold pressure from both directions. The problem was the engineers did not provide a drain hole between the seal to indicate a leak.
This changed sometime before 97. There now is a drain hole in the adaptor that connects the transmission to the transfer case.
Good luck.

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Roller wrote:

There is? I've never seen one on the GM products. Jeep had that drain hole, which was a much better system...but I'm still fixing GM products that put the trans fluid into the t/case without showing any signs of leakage.
Ian
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you either ?
never seen a 'drain hole' on a GM............the way the adapter is constructed, it's not possible
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Man, this really ticks me off, but you are right. I must have been working on a neighbors truck because I did see a drain hole ... somewhere!
In any case, after reading this, I was forced to crawl under my truck to look and, you guessed it, no drain hole. Then I pulled my shop manual, and there is only the single double seal shown.
My truck is a 97 K1500, 350, Auto, with a NV243(electric shift).
So, as I mentioned in my other note, my 89 had this seal leak at about 35K miles. My 97 has 107K on it and I have not had a problem. When the seal let go on my 89, it almost took out the transfer case because the fluid transferred out of the transfer case and into the transmission. If the opposite happens, and you overfill the transfer case, what fails? Do you loose fluid out the vent?

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Roller wrote:

Yeah...other makes do this. Jeep used a seal at the rear of the transmission, and one at the front of the t/case. When fluid leaked from one or the other, it didn't transfer to the other part, it just leaked into the adapter section, and there was a drain hole in the adapter section. GM uses a gasket to seal the t/case to the rear of the transmission, and the one seal on the input shaft of the t/case to keep fluid in/out on the t/case. Rarely does the t/case fluid go into the trans, usually always the other way around in my experience.

Most of the time....I just notice that trans fluid comes pouring out of the t/case fill plug when doing regular maintenance inspections. This automatically tells you what has happened. Usually, the t/case doesn't seem to spit the oil out anywhere. There is probably only a certain amount of fluid that will transfer into the t/case due to the level of fluid in the trans.
Ian
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So, what bad stuff would happen if you just left the extra fluid in the transfer case?

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Roller wrote:

It's probably the transmission that will suffer more from being low on fluid, then the t/case being high on fluid.
Ian
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But it can come out somewhere... When that seal let go on my 700R4 the tranny fluid would spit out from <somewhere> while decelerating off of the expressway, spray over the exhaust, and cause one HELL of a smokeshow. Funny, several mechanics didn't believe me that the tranny fluid kept dropping and insisted it was coolant going through the engine... Idiots...
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case vent
the vent is supposed to be hooked to a long tube going up behind the engine, but lots of times it isn't..........

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That makes sense, I never bothered to check where the ATF had been blowing out. I did feel bad for that lady in the minivan behind me on that offramp though. It really was a LOT of smoke. ;)
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SBlackfoot wrote:

As Gary mentions, you probably had oil coming out the vent. There is no seal on the GM transmissions at the rear if it's a 4x4. It's the front seal on the t/case that fails. In that case, the fluid goes nowhere, but into the t/case. Your situation is totally different then what is being discussed in this thread.
Ian
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How do you figure? The seal on the front of my t-case went out allowing ATF to fill the t-case. My ATF just found a way out when put under pressure (in a spectacular fashion I might add) which is rather unusual. I don't see how that is terribly different than Phil's situation...
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SBlackfoot wrote:

Sorry, just going by what your post said. You said "when that seal let go on my 700R4". There is no seal on the transmission that allows the fluid to go into the t/case, but as your subsequent post mentions, you really meant the front seal on the t/case. I haven't seen a transfer case blow oil out of its vent...but I've seen lots of transmissions blow oil out their vents. So my assumption was that you were talking about your transmission blowing oil out.
Ian
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No need for apologies Ian, it's obvious that slackjaw is either full of it or just making up stories. How could a transfer case build up enough pressure to blow enough fluid out to create the kind of smoke he's talking about? I've never seen it and don't believe it for a second. Bob
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Oh you can't be serious...
Hell do a quick Google search, I'm sure I posted about the problem when it reared it's ugly head in late 2000 or so.
Pfft... Rookie.
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Sorry, but I don't care what you posted or when you posted it. If that much ATF got on your exhaust, it leaked out of your transmission and not your transfer case. Bob
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oh, really
post your proof for this amazing theory
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SBlackfoot wrote:

You tell me Gary, how does a transfer case get enough pressure in it to "spray over the exhaust, and cause one HELL of a smokeshow"? I'm not saying they can't leak but I've never seen one leak that bad unless it had a hole in the case. As you well know however transmissions are notorious for blowing ATF on the exhaust and smoking like hell. Bob
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