SM465 Trans Rebuild Problem

[ChevyK20BBC]

Hello everyone, I'm having some transmission problems. Well to start off, last week I pulled my sm465 cast iron top transmission because it was popping out of third gear, So I ordered a complete rebuild kit with synchros, and small parts. I also replaced 3rd gear and its slider with the updated torque lock style. I also installed the 3rd. gear spacer on the countershaft that replaces the snap rings between the gears. I also rebuilt the whole top cover with new springs and balls, and I replaced both 1-2 3-4 shifting forks because the coating was worn, and I just wanted to be absolutely sure everything was done. So anyway I put it all back together,everything seemed to go together smoothly and I double checked everything. I drove it and everything was great, shifting smooth, no popping out of gear, no grinding or whining, all good. Then the next day I drove it and now it grinds when I shift from 3rd. to 4th. on the up-shift. It goes into gear but doesn't sound very good. If I wait a second between shifting it doesn't do it? Shifting normally it grinds and I need some Ideas on this, Please and Thank you.

[VileZambonie]

Did you replace the clutch? Is the free play correct? Did you use the correct fluid? Does the rebuild kit want you to use synchromesh?

[1967KaiserM715]

I would look at the clutch first as well.

I haven't seen any 465 rebuild require anything but the factory requirement of fluid, only the NV4500 and similar transfer require the funny fluid. I have been wrong before though.

If I recall, factory was 80/90 weight gear oil.

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[ChevyK20BBC]

I didn't replace the clutch it was done about six months ago, but I did adjust it tonight and it was loose a bit and I got all excited and went out for a ride and got the same thing, I thinking I need to change the fluid after the rebuild to get the assembly lube and stuff out. so I'm gonna try that. I use Lucas gear lube 80w-90. I usually use the stabilizer in it also and I didn't have any this time so I'm going to add some of that when I change it. Its so weird if I wait between shifting it doesn't do it. When I shift normally it almost feels like there is no synchro there.

[1967KaiserM715]

Did you visually inspect the 3-4 slide? If that was bad from previous grinding, that could explain it, and it could have destroyed the new syncro.

Another thing could be a bad fork, but doesn't seem like it as it would likely be popping  out of gear.



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[ChevyK20BBC]

I replaced the 3-4 slider, it came with the updated 3rd. gear. And the synchro was new. Also I did changes the shifting forks, both 1-2 and 3-4 shifting forks. I spent over 500.00 dollars worth of parts. anything that was slightly even worn I replaced it. I still haven't tried changing the fluid again, having some bad weather here today. Does anyone think it could be a possibility that the new fluid needs to be changed after the rebuild? with all the assembly lube and grease that's mixed in it. Or am I wasting more money changing the oil again? Thank you for everyones help I'm really in need of it, I'm ready to drive the truck into a lake.

[ChevyK20BBC]

Do you think it could be possible that my sychro could be stuck on the cone it rides on, and causing it to grind when shifting?

[ChevyK20BBC]

I ordered some STA-Lube 80w-90 gear lube GL-4. I'm gonna try that, I was thinking of maybe taking one of the PTO covers off and checking things out when I drain it. Does anyone have any other advice?

[1967KaiserM715]

It is possible the synchro siezed, too tight tolerance, too much heat. An oil change and removing a PTO cover could allow enough room to inspect the syncro.

Rereading, it sounds like it is only happening in 4th, about the only thing that could cause grinding is the syncro. A bearing issue may be possible, but typically would cause issues elsewhere.

The wait between shift probably allows speed matching of gears, and also why pulling in and out of 4th is ok.

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[AZ4X4SQBDY]

What did you use as an assembly lube? If something was too slippery it could cause an issue with the synchro. Off the top of my head, I am thinking moly or teflon.

[ChevyK20BBC]

Well I drained the fluid today and I got big problems, I took the PTO cover off and both 3rd. and 4th. sychros are more worn than the old ones that were in it. The 3rd. gear sychro seems tight, and tha 4th gear synchro is really loose. and both of them are worn bad, and its only been 5 days since the rebuild. I don't know what to do, I guess I gotta pull it again and maybe just put the old synchros back on. I don't have any more money to put into this thin, I'm already at 550$.

Also another thing I noticed is the spacer I put in on the countershaft for the so called upgrade is now LOOSE and I can spin it and move it around. Has anyone ever seen a spacer loose, Is that how it supposed to be? It was tight when I put it together.

Please Help..

1) what could cause the synchros to be junk in a week?
2) Should I just take the spacer out and put the snap ring back in?


Thanks Everyone

[ChevyK20BBC]

One other problem I just remembered when I was rebuilding it, when I pressed on 3-4 slider hub I went to put the snap ring on and it wouldn't fit, so I took some 100 grit sand paper to the snap ring until it fit in the groove. It wasn't much but just wondering if that could have anything to do with these other problems.

[1967KaiserM715]

Well, something was missed during the rebuild is my guess (we're only human) it could be that spacer was the issue, and the gears walked, causing the slider to eat the syncros. Or there wasn't enough lubrication(assembly lube) and it caused accelerated wear.

It hurts when we do a rebuild and it fails- I rebuilt a 350 once for a friend, still not sure what exactly went wrong, just the end product was no compression on 3, destroyed rod bearing on 8, number 3 main bearing spun, most of intake valve on 1 missing (spring in head, keepers were still sitting in the retainer around the top quarter of the stem.) And wiped several lobes off the cam.

Ran great for the three days it worked. Rebuilt another, still going. Figure it was just 1 bad part that took everything else with it.

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[ChevyK20BBC]

well I ended up getting some sta-lube 85w-90 GL-4 gear lube and putting that in and it is shifting pretty good now. Some day ill take it back apart again if I run into any more problems