Leaking SM -465

[K20-Bowtie]

Hi Folks,

My first post for assistance. I have a newly acquired 72 C20 4x4 with a SM 465 transmission which is appears to be leaking from the front input shaft. The fluid on the ground smells/feels like gear oil and is not motor oil, so I can possibly rule out the rear main seal. I plan on putting dye in the transmission just to verify the location of the leak.

What are the chances the seal will fix the issue or perhaps the front bearings are worn as well?

Is there a diy way to check the play in the shaft?

This thing is a beast, so I plan on borrowing a transmission jack. Thinking I’ll take the transfer case out as well & check the same. Heck, might as well put a clutch & throughout bearing in while I’m at it.

Thanks everyone.

[gmc684x4]

Nice k20 any pics ?

When apart you will have to check shaft seals as well for signs of wear grooves etc they may need replacement as well

You may luck out find a missing bolt

[K20-Bowtie]

In terms of checking for wear on the transmission shaft, would it be obvious by visual inspection or is there some other method to check for wear?

Here are a few more pics. I've started a gallery on this site, but not sure how to share the link.

The engine has a slight miss, so I changed the plugs/wires and will be installing a pressure regulator - have 15 psi on an Edelbrock. Understand thats way too much.

[gmc684x4]

Very nice looking truck
I have not had one of my Sm465 apart

from experience though with looking at seals on something that spins look for wear marks and grooves that will cause leakage axles main seal area on a crank etc

[K20-Bowtie]

Thanks gmc684x4. Hope to yank it out in a couple of weeks.

[gmc684x4]

Here is what anouther fellow found his leak
And yes a worn front bearing will also allow it to leak as well by letting the shaft have more free play

https://forum.ih8mud.com/threads/cal...ective.461937/

[gmc684x4]

anaheim gear 1-800-477-1103

This place came up a few thread reads across google

[57taskforce]

https://m.youtube.com/watch?v=0wMUZ-m4f6w

https://m.youtube.com/watch?v=IPy62F4-nD0

https://m.youtube.com/watch?v=04gMWHJL88M

Nice looking K20. Those aren’t very easy to find in your part of the country. I grew up not to far away from Winchester.
I used these three videos as a guide when I went thru my 465. If your going to tear it down far enough to work on the input shaft, buy the whole bearing/seal/synchro kit and freshen the whole thing up. Odds are your gears and shafts are fine so all you’ll need is bearings, seals, synchros, maybe the gear bushings, and possibly a third gear pop out repair if your having that issue. (I wasn’t) Remember in order to get the top cover off the transmission it has to be partially engaged in reverse. If it’s not partially in reverse you’ll never get it out without breaking the top cover or the reverse shift fork. It’s not hard to rebuild the 465 at all. You’ll need a good set of lock ring pliers(not the same as C-clip pliers) and a press though. This is my suggestion. If you’ve got one shaft or bearing that’s worn enough to leak the others probably aren’t far behind. Same goes with the 205 you’ve probably got for a transfer case. You’ll have it out any way so it’s a good time to go thru it as well. They are both very strong and very very easy to rebuild. The parts for my 465/205 combo weren’t even $250 total, including new nos gm gear bushings and paint.

[K20-Bowtie]

Thanks 57taskforce. Great videos.

[57taskforce]

Anytime, glad I could help. It’s really a simple design one you jump into it.

[akart]

Just for fun put some 205 sealer in that 465. I had a leak and it fixed it. 205 is supposed to swell existing old seals. Worth s try.

[K20-Bowtie]

Thanks akart. It's worth a try.

I see lots of threads of people attempting to fix SM465 leaks without success and sometimes making things worse. Seems like there are lots of problems where the SM465 couples with the NP205.

For what it's worth, I've never been a big RTV fan. I've always used gaskets and been careful to torque the bolts in a rotating fashion. I'll problally eat my words one day .

[akart]

Originally Posted by K20-Bowtie

In terms of checking for wear on the transmission shaft, would it be obvious by visual inspection or is there some other method to check for wear?

Here are a few more pics. I've started a gallery on this site, but not sure how to share the link.

The engine has a slight miss, so I changed the plugs/wires and will be installing a pressure regulator - have 15 psi on an Edelbrock. Understand thats way too much.

Your right about the fuel pressure to the Edelbrock. It is supposed to be 6lb. You mentioned a regulator,which would be good. But as an option There is the Edelbrock fuel pump ELD 1721 which delivers 6lb. Kind of pricey. Also that carb likes a 1" fiber spacer to keep it cool. I have done this to my truck and am happy w/the results. Might want to lean it out a bit too w/rods and jets. There is info at this sight for that. I am getting 12-14 MPG.

[gmc684x4]

Sealer in a can is a short term temporary fix at best

Sm465 to np205 leaks are primarily due to not replacing the oring on the np205 input shaft and checking the surfaces for wear

Any shaft seal surface that has worn surfaces needs replacement or be ready sleeved to restore the sealing surfaces

The failure of restoring shaft seal surfaces and not replacing orings will make up a large smount of failing to reseal there transmission