SM465 gear oil

[sethv]

I plan on putting new oil in my SM465 tomorrow as it is getting loud, and hard to shift.

Is Royal Purple 75w90 gear lube any good? Or should I go non synthetic?

If not Royal Purple, what are other gear oils I could put on there? Actually, I would prefer not to use Royal Purple as it would get expensive.

Thanks.

[oldblue1968chevy]

I would guess any 80 90 wt gear oil....

[James McClure]

Seth, when is it loud and in what gear? Usually if a gear train becomes noisy it needs more than a change of lubes. The SM465 is a very stout unit not prone to many failures unless it's run low on fluid. I have one in my truck and it's got almost half a million miles on it. The most common problem you'll have with most manual transmissions isn't the trans but the clutch, pressure plate, throw out bearing or linkage. jim

[GmtGmt]

75W90 Mobil is good stuff for these trannys

[tucsonjwt]

I just topped off my SM465 with 80-90 gear oil from Autozone (did not take much) 8 years ago and it has been fine since then. Check the adjustment on your clutch first - your adjustment screw should show about 1 inch of thread past the adjustment nut. I have found that the nut works loose on my truck, and the transmission is then hard to shift and gears don't shift well. I would not use synthetics since you have old seals and gaskets, unless you just want to do a complete rebuild for some reason, then fill it with synthetic.

[sethv]

My tranny is noisy in the low gear. (1st or L, whichever way you look at it), and sometimes it pops out of 1st or L gear when I'm going down a steep hill.

It also leaks, forgot to mention that in the OP.

Don't really know too much about clutches, I have a habit of breaking things that I don't know what I'm doing...

[75ChevyGuy]

$35.08 for GM# 89021677 75-90 synthetic or $16.84 for GM# 89021671 80-90. Not too bad of prices. That's what I use in my truck, I don't trust all the other crap that's out there.

[lilpoindexter]

If it leaks, just keep it topped off with your favorite regular oil from Walmart or Autozone.

[tucsonjwt]

If you mean true 1st gear, that is a gear that I would never use, unless I was stuck in mud or pulling a tree stump out of the ground. SM465 has a L for 1st gear, then 1,2,3. The 1st gear(L) is "square cut", and I don't believe it has a synchro, according to my drivetrain mechanic. If that is the only gear giving you a problem I would forget about it and don't use it. I would stick with the recommended 80-90 gear oil - get the cheap stuff from the auto store if you are leaking oil. But first I would have someone check your clutch adjustment if you are not up to doing it yourself. It is really simple to do, it you want to read up on it. As is often said on this forum, the SM465 is just about bullet proof, and the clutch is usually the culprit with shifting problems. You can get a whole rebuilt SM465 for $500-$600 with exchange, but my guess is you just need a little clutch adjustment and keep the fluid topped off if you are really leaking a lot. Good Luck.

[sethv]

Thanks for the help guys. I'm going to run to the parts store when I get paid and get cheap 80 90 gear oil.

[HybridK]

I've been reading about this in other forums and thought I'd throw my two cents in. GL-4 80w-90 is what's supposed to be used in these transmissions. The GL-5 and later fluids (especially synthetics) make shifts more difficult because they make it "too slippery" for the synchros to do thier job effectively. It's not a huge difference on a light duty transmission like a t-10 or an M-22, but the gear clusters on these are so heavy, not to mention the big clutches they run, that they are very sensitive to over lubrication because they have so much inertia. If you're having a lot of trouble downshifting like a lot of people do, just blip the throttle between downshifts (double-clutching, if you will) to make less work for the synchros. As far as noise goes, 1st/low and reverse will always be noisy because they're spur gears. If it's noisy in the other gears you might have issues beyond fluid.