[RocktimusPryme]

Im having a little trouble here. My longtail th375 (the one that is in a 400 case) in my wagon is dripping fluid right onto my H pipe from the seal that the driveshaft slip yoke goes into. Pretty common and something I have changed before, but Im struggling to find the correct one for the oddball th375. I dont want to get under there and pull the seal only to find I ordered the wrong one.

First, Im not sure Im using the correct terminology.

Is the one I am looking for the Output Shaft Seal, or the Extension Housing Seal?

And then if anyone happens to know the correct part number for the one I need I would appreciate it.

[Half-Inch Stud]

I also need the same seal for a build. Customer said he'd buy it. So i'm listening....

[Schurkey]

Originally Posted by RocktimusPryme

My longtail th375

Curious about this. I thought there was only one tailshaft/housing for a 375. No "long" vs. "short", just one length.

Am I wrong?


What vehicles came with TH375s? I'm thinking certain early-mid '70s station wagons.

Look up one of those, compare part numbers to known TH400 part numbers. The oddball is probably for a 375.

If the seal is that wiped-out, be sure to inspect the yoke and the bushing.

[RocktimusPryme]

I actually almost said “I think they might all be long” but I don’t know for sure so that was just an educated guess.

I actually tried that before I posted here. On Rockauto. I posted 1973 Olds Vista Cruisers and 1973 Safari and didn’t see anything listed for a 375.

That is where I got the notion to ask about the terminology of what the seal I’m looking for is called though.

[b-man]

They have a TH350 output yoke if I’m not mistaken, I’d be looking for a common TH350 tailshaft seal.

[scott70]

Output shaft seal/ driveshaft seal. I remember back in the day pulling 375s and drag racing them. They were cheap and I went through a few of them before finally switching to 400s. I'd install thm400 shift kits but they had thm350 sized driveshaft splined end. I wouldn't be surprised if they used thm350 driveshaft seals. Everyone I ever used was a long shaft from a early ish 70s big pontiac. I didn't find them to handle abuse well.

[Formulas]

My TH375 experience is limited and dated but yes TH350 output and every friction point has less clutch / friction area

[chrisp]

https://www.ebay.com/itm/17509674053...-53481-19255-0

[RocktimusPryme]

Originally Posted by chrisp

https://www.ebay.com/itm/17509674053...-53481-19255-0

I saw that one, but the terminology throws me. Also I don't remember ever needing to change a bushing when Ive changed an output seal before.

[RocktimusPryme]

I watched a video on the bushing part of the equation and I have a better idea of what I’m looking at now. Squirrel over on the HAMB came through with a PN for me.

But the eBay one linked is probably correct too, it’s just for both. You need a special tool for the bushing removal/install. They are pretty pricey though.

SKF 15041 is the seal. Shows on Rock Auto for a 1971 vista cruiser.

[Ben M.]

Originally Posted by RocktimusPryme

Also I don't remember ever needing to change a bushing when Ive changed an output seal before.

You really really should though. It is a bushing with a seal on the end. You remove the tailshaft, pull off the seal and use the special tool to yank the bushing out. Most shops neglect to do this but on a car that sits for long periods of time, you can get some interesting failure modes from a scored bushing. It helps hold the driveshaft in place in addition to giving it a smooth lubricated surface to ride on.

Failed bushing:


Result:


It will destroy your governor gear and then your car will sit in 1st gear and you'll scratch your head (as will numerous ghetto tranny shops) as you can't figure out why it continues to do so a few thousand miles after you replace the bad gear.

[Schurkey]

Originally Posted by Formulas

My TH375 experience is limited and dated but yes TH350 output and every friction point has less clutch / friction area

The bands are the same, but at least two of the clutches--maybe all three--have fewer discs inside.

The tailshaft housing has "375" cast right into it, on the ones I've seen. Mind you, I thought the TH375 was over-and-done-with by the later '70s. My understanding was that the factories making TH350s couldn't keep up with demand, so they punted and started shoving light-duty 400s into the vehicles, with the tailshaft and overall length the same as the TH350s they were replacing. I'm hearing they were still using the TH375 in the '90s. Which was news to me at the time--I heard this less than a month ago. I don't know how GM may have changed it by then.

For the record, the TH375 was a light-duty 400-family transmission. The TH375B was a heavy-duty 350-family transmission.

['ol Pinion head]

Last few years ive scrapped a bunch of the "375" tailshaft housings & mainshafts. Busted case short tail T400's & a fresh pulled Chevy T375 cores were something I never turned up my nose at.

[RocktimusPryme]

Originally Posted by Schurkey

For the record, the TH375 was a light-duty 400-family transmission. The TH375B was a heavy-duty 350-family transmission.

Im curious how the math works out there. Would that make them both about the same strength?

FWIW this is a cruiser car. Right now it has a smogger olds 455 that probably makes 119 HP and wont even spin the tires.

In a perfect would I would like to go back to Pontiac power with a mild 350ish HP build. So I would think the TH375 is probably fine in my case. I may consider an OD at some point, but it has 2.73 gears so it is passable for now.

[stevep]

The 375 does use the 350 rear seal. If you replace the tail bushing, they usually have to be finished in place.