Advice on Transmission Fluid Change for 1980 C10

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Grit dog

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If it’s operating fine then absolutely change it. Sounds like a good truck if it’s never been apart and still is truckin.

If you don’t pump it out the cooler lines to get the majority of old out, I’d get a pan with a drain plug and change it about 4x depending how much comes out. That’ll effectively replace about 90% of it.
 
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Grit dog said:
If it’s operating fine then absolutely change it. Sounds like a good truck if it’s never been apart and still is truckin.

If you don’t pump it out the cooler lines to get the majority of old out, I’d get a pan with a drain plug and change it about 4x depending how much comes out. That’ll effectively replace about 90% of it.
Click to expand...
Unless you’re lucky and there’s a drain plug in the tq converter but it’s not likely.
 
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Grit dog said:
Unless you’re lucky and there’s a drain plug in the tq converter but it’s not likely.
Click to expand...
The only factory torque converter that had a drain plug in them were old Fords. (I've only ever seviced trucks, don't know about cars.) Aftermarket converters may have a plug, but the OP stated he believed the trans was not apart.
 
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Dex III is the same as Dex/Merc from what I've read.
 
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Added more fluid and it drives great! Shifts smooth and all is well. Now, could someone please help me ID this trans from the pan? It's a leaking mess under there btw.
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Look at post 2 of this thread
 
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TH350, aka turbo 350
 
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Stock TH350 is a very durable, reliable transmission. Many sources of aftermarket parts if you want to build it to be even stronger.
 
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DoubleDingo said:
Look at post 2 of this thread
Click to expand...
Well, there were a couple and I wasn't sure
Dmack said:
TH350, aka turbo 350
Click to expand...
That was one of my guesses
75gmck25 said:
Stock TH350 is a very durable, reliable transmission. Many sources of aftermarket parts if you want to build it to be even stronger.
Click to expand...
Good to know. After filling it back up with fluid, it ran and shifts fine. I probably won't rebuild unless I have to. That said, it appears to be leaking quite a bit, that's why it was low I guess. Now to find out where that leak is coming from. Also, it looks like there's a drain on that pan doesn't it! Seeing as how it was 2 1/2 quarts low, looks like if I just let it leak for a while it will change itself. lol

Also, judging by the RTV around the pan, at least the pan has been been dropped sometime in the last 45 years. My guess is that's at least one source of a leak. I might change the filter and pan gasket once I get some other things fixed.
 
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Yes, your pan has a drain plug. HydraMatic stopped installing drain plugs in the early 70s as a cost cutting move, so more than likely the pan or transmission has been swapped.

Possible leak spots: the transmission pan, dipstick tube or o-ring, kickdown cable seal, speedo cable seal, the oring around the vaccum modulator, rear seal, or the accumulator cover oring. Those call all be changed with the trans still installed. The o ring around the pump, or the seal around the torque converter neck could be leaking, but those require transmission removal and disassembly to repair.
 
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dex/merc,
take your pick at wallyworld. I just picked up several gallons of valvoline on sale
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Matt69olds said:
Yes, your pan has a drain plug. HydraMatic stopped installing drain plugs in the early 70s as a cost cutting move, so more than likely the pan or transmission has been swapped.

Possible leak spots: the transmission pan, dipstick tube or o-ring, kickdown cable seal, speedo cable seal, the oring around the vaccum modulator, rear seal, or the accumulator cover oring. Those call all be changed with the trans still installed. The o ring around the pump, or the seal around the torque converter neck could be leaking, but those require transmission removal and disassembly to repair.
Click to expand...

Wouldn't surprise me to find out that my granddad or uncle at least changed the pan. I can hear them grumbling now about why would some engineer remove the drain plug ##$%$#...

Thanks for the places to look. Hopefully it isn't too bad.
 
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AlabamaDan said:
Wouldn't surprise me to find out that my granddad or uncle at least changed the pan. I can hear them grumbling now about why would some engineer remove the drain plug ##$%$#...

Thanks for the places to look. Hopefully it isn't too bad.
Click to expand...

Any GOOD engineer would design a product with routine maintenance in mind. A good engineer knows the importance of maintenance.

Without a doubt, the bean counters vetoed the drain plug!!

Bean counters play an important part in manufacturing, but I think they have way too much power.
 
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