Mystery Transmission Fluid Leak?

[BradL84D30M1008]

So two months ago I was under my '84 M1028 to remove my starter and have it rebuilt......underside of transmission pan, transfer case, and adapter were all dry, had probably put ~1000 miles on the truck through last deer season with no leaks of transmission fluid whatsoever from anywhere.

This past weekend I'm back under the truck to re-install my rebuilt starter, and I notice four or five drops of transmission fluid have accumulated on the underside of the transmission pan. The truck had been sitting stationary for 2 months in one place. I could not see if any transmission fluid had actually dropped to the ground under the truck,just looked like 4 or 5 drops had "condensed" on the underside of the transmission pan.

I'm guessing that the origination of the transmission fluid could perhaps be where the fill tube drops in from above - maybe an o-ring for the fill tube finally dried out after 34+ years and sitting idle for 2 months?

Funny thing is, I dried off the bottom of the pan, and then drove the truck for ~100 miles around the deer lease this weekend, and had no further drips off the transmission pan at all....can't tell that I've lost any transmission fluid from the transmission.

Any ideas what could cause such a phenomenon?

On a positive note, rebuild of the starter and re-connection/cleaning of both electrical connects seemed to have cured my issue of intermittent clicks/non-starts......truck now starts instantly with no issues.

 

[Loco_Hosa]

Likely coming from the dipstick tube. When your driving every day the trans cooler stays full, but if you park it for a few days that fluid slowly drains back into the trans. The higher the level, the more pressure on that seal.

 

[BradL84D30M1008]

Great insight, thanks

 

[Barrman]

Your truck was mad at you for not driving it. Now it is happy. Or, what he said above.

 

[BradL84D30M1008]

How does the transmission dipstick tube seal below? With an O-ring? Been a long, long time since I've ever dealt with that issue......

 

[BradL84D30M1008]

If I've looked up correct part in the TM, it's 1259475, for the fill tube seal and it's only $3.24 online......amazing....

How does the transmission dipstick tube seal below? With an O-ring? Been a long, long time since I've ever dealt with that issue......

 

[Loco_Hosa]

It's not even a part you have to special order, you can get it at the local O'Reilly's. I believe there's a nut that holds the dipstick tube in place, you'll have to loosen that nut in order to be able to lift the dipstick tube out of the way, replace the seal, maybe put some RTV around it if you wanted to, and you're done.

 

[BradL84D30M1008]

Any tricks of the trade for removing the old seal? It actually looks like it might be more of a grommet?

Thinking I don't want it to break apart or disintegrate while removing it and leave debris in the pan?

Guessing you probably insert seal/grommet first, then insert fill tube?

 

[ken]

They don't stick to the case for the most part. They swell up and get soft. Then leak. You should be able to pull it out with you fingers pretty easy. When you pull the tube fluid will come out and make a mess. The level in the pan rises when the fluid drains back from the gear box and cooler. You may want to drain the pan some first. When installing the new one, grease the inside so the tube slides in with out pushing it into the pan. Yes it looks like a T shaped grommet.

 

[BradL84D30M1008]

Thanks for the tips, very much appreciated

 

[rustystud]

The dipstick seal is a silly little thing that leaks a lot. Just get a new one.

 

[Dave Kay]

Ditto on the dipstick tube-seal, did mine when I last drained the trans and she stayed clean as a whistle... for a while. Back then I wasn't driving truck much and began to notice a small drip from the left driver's side, trans pan. Wiped it and re-torqued the trans-pan bolts but a few days later there was that drip again. Fiddled with the speedo-input cable a bit and thought I fixed the leak again. Days later I STILL noticed drips only now they were worse. Finally pulled the whole speedo-cable assembly out and replaced ALL seals inside and out. Be aware that if parked on an incline you'll get some fluid coming out. This is a common problem on these TH400's so I say look there first for the obvious. Hope that helps somebody.

 

[BradL84D30M1008]

Where is the bolt that attaches the transmission fill tube to the back of the engine? Or whatever it attaches to keep it stationary?

I couldn't see an attachment point from under the truck, nor could I see it from above?

I removed the air filter housing, but still couldn't see how the fill tube attaches.

There is a big wire loom running across in that vicinity, between the fill tube and the intake manifold, which may have been obscuring the bolt I need to remove?

They don't stick to the case for the most part. They swell up and get soft. Then leak. You should be able to pull it out with you fingers pretty easy. When you pull the tube fluid will come out and make a mess. The level in the pan rises when the fluid drains back from the gear box and cooler. You may want to drain the pan some first. When installing the new one, grease the inside so the tube slides in with out pushing it into the pan. Yes it looks like a T shaped grommet.

 

[cucvrus]

As you are laying up looking forward on the starter side(right) it will be on the 2 o'clock bell bolt to block. It breaks off a lot and may need welded back on. Good Luck.

 

[BradL84D30M1008]

Based on the schematic in the TM, I was looking/expecting the fill tube mounting tab to be on driver side, not passenger side of the tube......thanks for the tip on the 2 o'clock position, that should be reachable if I can just see it!

As you are laying up looking forward on the starter side(right) it will be on the 2 o'clock bell bolt to block. It breaks off a lot and may need welded back on. Good Luck.

 

[cucvrus]

Wrong answer. It is on the passengers side. 10 o'clock would be drivers side and I know it is not there. It is on the same side as the starter. Trust me. But if you mean the tab comes off the tube and goes towards the engine you got me. But it is still on the passengers side of the bell housing.

 

[BradL84D30M1008]

I had the fill tube grommet replaced this week while I also had the trans fluid and filter changed......also had any other exterior gaskets/o-rings replaced like for modulator, etc. while it was in transmission shop.

Tech showed me I had some grit in the bottom of the pan when he had it down.....my question is, after 2,000 miles of dusty off-road use in south Texas over the past 2 years, shouldn't I expect some grit in the pan from all the dust and sand I've been driving through? Or is something more serious afoot?

 

[cucvrus]

No dirt from the road conditions should get inside your transmission. If that were the case I would be screwed every week. It is normal to have some dirt and grit in the bottom of a pan. There are a lot of things moving and working wearing in a TH400 transmission. Any transmission for that part. I think you are good. If you find clutch material and metal. I would be concerned. Good Luck. I have lots of ICE to plow this AM.

 

[ehuppert]

No dirt from the road conditions should get inside your transmission. If that were the case I would be screwed every week. It is normal to have some dirt and grit in the bottom of a pan. There are a lot of things moving and working wearing in a TH400 transmission. Any transmission for that part. I think you are good. If you find clutch material and metal. I would be concerned. Good Luck. I have lots of ICE to plow this AM.

J

Just an FYI for those going to replace filter and gasket. I've switched over to the duraprene pan gaskets for any transmission work at the shop(when they're available). The readily available cork or rubber gaskets are a pita, always seem to seep, leak, whatever.

The duraprene is more expensive, but better product!!

Eric

 

[cucvrus]

I have been using the gasket and The Right Stuff with great success. No leaks after that. I use The Right Stuff as my primary sealer adhesive on all mechanical applications. Tractors, vehicles, lawn mowers, log splitters. What ever I need to seal and have no leaks. I do like the new trans pan gaskets that you can reuse. They have the steel crush washers built right in.