TH350/TeraLow 4:1 NP231 ?'s - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-07-2006, 02:36 PM Thread Starter
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TH350/TeraLow 4:1 NP231 ?\'s

Hey gang...
Interesting problem - no one knows how to solve (at least the guys at Teraflex or the guy I talked too).

I have an 88 YJ w/a 98 4.3 V6 bolted to a TH350 bolted to a teralow NP231. After lots of highway driving or any flat towing with the transfer case in neutral (the tera kit does provide a true neutral), the transfer case has pumped most of the fluid from the TH350 into the transfer case. The tranny has good seals but the tailshaft and adaptor are designed to allow a little fluid flow to lubricate the adaptor bearing. Somewhow that fluid is being sucked into the transfer case. Is that possible?

I know from other swaps that the input shaft on the transfer case is hollow and may or may not have a plug in it (from inside the case) depending on the tranny - auto or manual. I do not remember if my shaft has a plug or not. It is a 21 spline that was behind a 5 sp manual and then the auto was placed in front later. I might assume that the transfer case input shaft has no plug since it was behind a manual.

The vent on the tx case is open - that's easy to check. The vent on the auto is on top and I can't check that I know how too. Could it be casuing this problem?

You guys have any wisdom here? The jeep runs great, I just have to add tranny fluid to the auto and drain some from the tx case.
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post #2 of (permalink) Old 01-08-2006, 07:29 AM
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Re: TH350/TeraLow 4:1 NP231 ?\'s

Maybe the friction of the bearings is turning things in the transfer case enough to turn the output shaft of the transmission. Where do you leave the transmission when you tow?
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post #3 of (permalink) Old 01-08-2006, 12:12 PM Thread Starter
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Re: TH350/TeraLow 4:1 NP231 ?\'s

I have been leaving it in park. But it also does it when I drive the jeep for long distances!?
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post #4 of (permalink) Old 01-08-2006, 06:45 PM
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Re: TH350/TeraLow 4:1 NP231 ?\'s

You've got me stumped, but I don't know much about automatical transmissions.
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post #5 of (permalink) Old 01-08-2006, 07:46 PM
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Re: TH350/TeraLow 4:1 NP231 ?\'s

Betcha it doesn't happen while driving or towing, but immediatly after as it cools.

T-case gets hot - gasses expand, when it cools down the gasses contracts, sucking the ATF from the tranny into it.

Check the vent on the t-case - it may have a check valve that's supposed to prevent it from letting water in it, but it's closing on cooling. Some have a little plastic float valve that closes.

If the tranny had an open vent, or the t-case vent didn't close, it wouldn't happen.
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post #6 of (permalink) Old 01-19-2006, 08:21 PM Thread Starter
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Re: TH350/TeraLow 4:1 NP231 ?\'s

Sorry for the late reply. Work has been crazy!!!

I checked the vent tube for the t-case - it still has the factory check valve - it runs up to the firewall. I think it's a check valve, it has a mushroom type cape on it. The TH350 - I have no idea.

I can reach up on top of the tranny and feel what I think is the vent - it feels like a mushroom headed cap also, but it is irregular like it's is broken or missing a piece.

I did talk with a tech at Advance Adaptors. He said it shouldn't happen. The only openings in the tcase are a vent hole on the face of the mating surface on the input side of the tcase (it's at about 1 o'clock if your facing the case), the hollow input shaft, and the actual case vent that is plumbed to the engine compartment. The case was designed to sit behind an auto and fluid swap was common through the input shaft - but not much since the input shaft has a splined shaft from the tranny stuck in it.

Does any of that help with the diagnosis?
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post #7 of (permalink) Old 01-19-2006, 10:51 PM
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Re: TH350/TeraLow 4:1 NP231 ?\'s

I have to cautiously say "Bingo."

"""""I checked the vent tube for the t-case - it still has the factory check valve - it runs up to the firewall. I think it's a check valve, it has a mushroom type cape on it. The TH350 - I have no idea."""""

That check valve - opens when the gasses expand when it gets hot or warm. After you stop driving or pulling it, that check valve closes (it's supposed to close to keep water out when fording a stream.) As the T-case cools it creates a small vacuum inside, air can't get in through the vent, so it pulls whatever is handy from the tranny - fluid.

Try taking that check valve off and putting a little cheapie fuel filter on instead -- $1.00? The filter can breathe both ways and still keeps dirt out.

Most of those check valves don't seal as well as yours apparently does, that's why it's not a common problem.

ATF is thinner than 90wt too. Next time it's apart seal the shaft's splines with something like Hi-Tack, but not silicone. Silicone can get in the auto tranny and really destroy it. Hi-Tack should stay put fine.

Try the filter - let us know.
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post #8 of (permalink) Old 01-21-2006, 06:43 PM Thread Starter
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Re: TH350/TeraLow 4:1 NP231 ?\'s

I'll drain the t case back to normal level and fill the tranny a bit and give it a go....I've already pulled the check valve on the vent.

I think I'll flat tow it across town and back - it happens the quickest that way.
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post #9 of (permalink) Old 01-22-2006, 08:16 PM Thread Starter
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Re: TH350/TeraLow 4:1 NP231 ?\'s

Well...more weirdness!!! I flat towed it across town - actually more like two counties over - to wheel just a bit ;-) on some lame trails left in NW Georgia after the latest round of closures (that's another post!).

Anyway, here's the sitrep. The t-case was at normal level. I put approximately the same amount of fluid (minus a bit) back in the tranny that I had drained from the tcase. Vent cap on the tcase removed and replaced with a paper cartridge fuel filter (that was tested for flow by gently blowing and sucking air through it). After 40 miles of flat towing (tcase in neutral, tranny in park), there was ATF blown all under the inside of my hood and down the firewall from the tcase vent hose. I checked the tcase level and it was 3 cups over full.

Well....I drained/refilled (and added) and wheeled for a bit. Checked the tranny level after it was good and hot and it was just right. I drove it home while my wife drove the burb back. The jeep is cooling off right now in the garage. I'm going to check the tcase level in an hour or so and see what I have.

I am completely bumfuzzled now!!!
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post #10 of (permalink) Old 01-23-2006, 06:24 AM
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Re: TH350/TeraLow 4:1 NP231 ?\'s

It's that darn automatical transmission. Get a shift-it-yourself box and you won't have those problems. [img]/ubbthreads/images/graemlins/grin.gif[/img]
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