TH-400 Head Scratcher...

Caver Dave

Caver Dave

Just holdin' it down here in BFV
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Mar 10, 2005
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Hooterville (24171)
2 years ago when rebuilding the Moss ('72 Commando), I departed from the BOP patterned TH-400 for an AMC-belled TH-400, which removed the cast-iron block-to-BOP bell adapter AND came with a 32-spline output to mate with the D-300 (versus the BOPs "Texas-pattern"). It was a total freebie from the guy I bought the D-300 from, as it was in front of that TC in his UA J-truck.

Install was fine, re-used the 25K# tube-fin Hayden cooler, EDIT: with lines feeding horizontally (nipples at side)... new Derale electric sender in test port...

Until this weekend, the main symptom was *random* puking ATF out the dipstick... like would happen once every 20th startup, typically on cold start-up and once topped back off, would be fine. Had 5 rides on it... 2 in stoopid heat (Waldens Ridge & GER) and 3 cooler (2x URE & local)

Checked some the usual suspects, like:
- Clogged case vent... confirmed open 3psi compressed air
- Missing/doubled o-rings on extension... replaced filter, no cracks/chunks with extension/o-rings in place, but replaced them
- Over filled... confirmed dipstick marks aligned with top of pan

Fast forward to Thursday when loading it up... would hesitate moving on throttle = low fluid, so added a pint, put it on the trailer and proceeded to puke most of that pint out.
Came off the trailer Friday just fine...
Fired it up Sat AM to ride COLD and was back to same "low fluid", so added a pint, level good on stick and was good until we hit the HQ leaving... dumped at least a quart šŸ¤¬ THANK YOU to all that suggested a manual transmissions... Not today Satan! :flipoff2:
Added a quart back, drove to Cane Creek(?) parking, added another pint, @skyhighZJ checked the cooler and was definitely not hot... was fine thru Dutch John, but added another pint back at double parking lot due to more "spewage"
Hit Daniel from the top side, but realized it didn't have 1st... temps went 220*-250* and wouldn't get going, so baled on the uphill, with RQ tugging me back over the crest... added another (LAST) pint and rolled back to camp where I did have 1st again
Sunday, needed another pint COLD to even register on the stick, put it back on trailer and puked again
Yesterday, felt a little low, but made it off trailer...


At this point, thinking there's a pump issue (one of many causes for puking) and reckon it'll come out over the winter for rebuild(?), but hoping someone here may have some "WTF" insight?
 
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Random thought but is the tcase sealed separately or could the fluid be moving there then coming back causing the ā€œover fullā€ puking situation and also the random ā€œlowā€ reading?
Air trapped in the line/cooler messing with levels?

It was weird cause the flow to the cooler in front of the Rad was definitely working. The lower (inlet) was warm and the upper (return) was significantly cooler. Your e fan was also pulling air a crossed it for sure.
 
Let someone with more A/T knowledge chime in, but I don't think that type of oil cooler can run vertical like that. I think it traps air in the top of the tubes.
 
skyhighZJ said:
Random thought but is the tcase sealed separately or could the fluid be moving there then coming back causing the ā€œover fullā€ puking situation and also the random ā€œlowā€ reading?
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Will pull the upper plug on the D-300 to see if there's been any mixing... only had the recommended amount (3 pints?) of gear oil in it due to flat clocking...
skyhighZJ said:
Air trapped in the line/cooler messing with levels?
Click to expand...
Kamel said:
Let someone with more A/T knowledge chime in, but I don't think that type of oil cooler can run vertical like that. I think it traps air in the top of the tubes.
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Bebop said:
Agreed
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So @Kamel & @Bebop, you think the new orientation is problematic?
My assumption was the pressure in the cooler circuit (interweb sources say "the cooler circuit is only fed by pump flow that's been relieved by the pump's pressure relief valve") would push any air in that line/cooler back to the pan and wouldn't matter how it's mounted... just like turning the water back on in your house burps/pushes the air in the lines out after draining. I mean it's not like an air bubble in a waterpump not allowing it to flow, right?
skyhighZJ said:
It was weird cause the flow to the cooler in front of the Rad was definitely working. The lower (inlet) was warm and the upper (return) was significantly cooler. Your e fan was also pulling air a crossed it for sure.
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Agreed... has done fine "cooling" over a few 100 miles since (very thorough cleaning prior to) re-install and 20 years prior to that...
 
images


Air gets trapped at the top.
 
There's something about an oiling issue towards the tailshaft that causes issue and heat. I haven't had a chance to look for it yet. I remember seeing it a while back.
 
R Q said:
There's something about an oiling issue towards the tailshaft that causes issue and heat. I haven't had a chance to look for it yet. I remember seeing it a while back.
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Itā€™ll definitely heat the rear up if your shaft isnā€™t oiled. Hee hee.
 
Already determined that wasn't your problem, but stock GMT800 coolers and the aftermarket ones everyone installs have the inlet and out pointed down.

20210906_160603.jpg
 
LBarr2002 said:
Already determined that wasn't your problem, but stock GMT800 coolers and the aftermarket ones everyone installs have the inlet and out pointed down.

View attachment 407044
Click to expand...
Agreed. Mine is the same way.
It is considered bad practice though.


From Pete @ Hughes on another forum :
Overfull, overheating, loose/cracked/damaged filter extension up near case entry, loose valve body bolts/leaks at valve body, or warped/mismatched pump halves are all potential causes for fluid venting.
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Just heard from the rebuilder... multi issues were found (suspect pump, TC, and forward clutches GONE w/all others being close to gone)

He's done a full rebuild... clutches/steels/sprags/pump, shift kit, rebuilt TC, deep steel pan, steel lines (while I've not had any issues from rubber, I get the danger), larger cooler, and made the missing "pilot bushing" (AMC TC stubs were 1 13/16" dia. and all that are currently available are "GM" TC's that have a smaller stub OD, so a very thin bushing is needed).

Said it'd be ready on Friday and "plan to drive it home"! Forecast is 55* and partly cloudy, so of course that's what I'll do šŸ˜Ž
 
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