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Discussion Starter · #1 ·
I was home over the weekend (we have a house 100 miles away, job required a move) and stayed with a friend. I have been bugging him for a year now about how he takes care of his vehicles. Specifically, he has a 1990 Chevy 3/4 ton with SM465 and NP241C, with 125,000 miles on it. He bought the truck new. He said the tranny was making a noise when it was very cold, so I asked him when the last time he changed the fluid was. He had never changed the fluid in anything but the engine. Wow, I was expecting sludge to flow when we pulled the plugs. So we took it to the shop (see pic) and put it on the lift. We also had to weld up the exhaust a little and he's 6'6" tall, so getting under it is a hassle when it's on the ground.

Before we pulled the plug, I got an 8 oz drinking water cup to catch the first fluid to see what condition it was in, never having seen 10 year old fluid with high mileage. Oh, BTW, he tows a trailer (3 axle) with the truck (usually with my jeep, or parts jeeps, on it), and had towed out an 18 wheeler three days prior. So we pulled the plug and I caught the fluid, ALL OF IT! There was literally 6 oz (1/4 quart) of fluid in the tranny. Impossible I said, so I grabbed a punch to stick into the hole to make sure there wasn't a blockage. Nope, that was it. I told him this wasn't good, so we pulled one of the side PTO covers and looked inside. The gears were fine and there was no buildup of metal flakes on the magnet in the bottom of the tranny. We put the right amount of fluid back in (135 oz, 4.2 quarts) and checked the other levels. The transfer took 2 quarts (it only holds 2.2 quarts) and the axles were low 1 quart each. We refilled everything with synthetic and finished the tasks. If I had not seen this first hand I would have told you it was impossible. I'd have called you a liar and said it would have burned up long ago.

He said the truck shifts much smoother now. /wwwthreads_images/icons/smile.gif One question: Why was there ATF (it was DEFINITELY ATF) in the tranny? I am also running a SM465, but it has gear oil in it, I thought they all took gear oil. The transfer I can see (chain driven), but the tranny? I'm glad I swapped the same tranny into my jeep, that way if I run out of fluid I'll still have 50,000 miles I can travel before I worry about it (that was a joke!).

JEEPN
'81 CJ-8 Scrambled!
GM151/SM465/NP205 twinstick/7" Lift/33" Swampers/ Scout II D44's F&R 4.10's & Lockrights
 

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Newer transmission gears are hardened and polished to perfection. Late model bearings are the same.
Computer controlled manufacture means tighter tolerances and less 'banging' slop in the gear sets and bearings.
Most transmission linkages are designed with, 'Save the stupid driver' in mind, much more precise, and much more forgiving of missed shifts...
(Anyone remember what happened to Muncie synchronizer rings when you missed a full power shift?)
Engagement dogs that pull into each other when someone doesn't get it all the way into gear, and buffered shift linkages to stop 'bounce' when some gorilla decided to slam it into gear...

New transmissions use a lighter oil to penetrate and coat better. It also climbs as well as the old thick oil did, but it's capable of much higher temperatures and pressures.
The lighter oil climbs and protects even in extreme cold, and when it's been contaminated by moisture...
New transmission ratios produce contact pressures that need oil more like hydraulic than lubricating. The old 90 wt. just can't cut it anymore.
Lighter oil also cuts down on the horsepower parasitic drag of the chassis and drive line.

Your friend is stupid (for not checking the transmission, or not taking it into have it serviced in ten years), but lucky...
If I would have tried that, my gear sets would have been able to come out through the drain plug hole...

Did you check the seals and gaskets on the trans to find out where the oil went?
It's always worth your time to change as may seals and gaskets as you can reach anytime you do a 100,000 mile service...

Better call him and make sure he checks the drain plug in a couple of days....

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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Discussion Starter · #3 ·
Definitely not disputing the "stupid" part, but he's a really great guy with a heart of gold. So this leads me to ask, can I run ATF in my SM465? Or rather should I? Are they the same tranny? Mine is a '71 and his is a '90, but they're both cast iron. The answer to where the oil went is the seals, all of them were wet, which means they need to be replaced, no doubt about it. Will they get replaced? Probably not anytime soon (hell, it took him 10 years just to CHANGE it, now you're asking about SEALS? One decade at a time please.

JEEPN
'81 CJ-8 Scrambled!
GM151/SM465/NP205/7" Lift/33" Swampers/D44's F&R 4.10's & Lockrights
 

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Aaron

Your re: is right on track. My Transmission & T-case rebuilder/expert has been telling me this for a few years now. Only trouble is no one would believe me when I told them to add 1/4 ATF to their 90wt gear oil. And they wonder why I don't cook a tranny or t-case (running in sand, dirt and deep water, just drain and replentish after every time you abuse it.)

May I use your quote?

DaveAZ

 
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