I am starting to re-assemble my M-21. These things really seem to be bullet proof, at least for the low torque 302 in my Z. With 289K miles, the unit looked brand new inside except for some shift fork and synchro wear. I want to go back with synthetic gear lube. I would like to get everyone’s opinions on manufacturer preferences and weight considerations. I Live in Charleston, SC where ambient air temperatures range from low-20'sF to well over 100 F. The car will be driven hard at times, but not raced or abused. Thanks for your input.

With the miles you got out of regular gear lube I would think you could put anything in and not have to worry. Heck, try Beer.:)

I've tried beer, then I got thirsty and the transmission broke. I would like to go back to gear oil. SEK Z28, what were you using before for gear oil?

<BLOCKQUOTE>quote:</font><HR>Originally posted by 68SS396:
I've tried beer, then I got thirsty and the transmission broke. I would like to go back to gear oil. SEK Z28, what were you using before for gear oil?<HR></BLOCKQUOTE>

68SS396, It's been about 10 years since I serviced the tranny. The car was stored waiting for the restoration funds/garage to become available, but I recall using Valvoline gear oil as specified in the chassis manual. I believe it was 75-80-90W.

I have either read it in a magazine or from a previous post here, not recommended synthetic oil in muncies. If I can remember some if it, the synthetic oil lubed the gears to good and caused trans to jump out of gear. Sorry can't remember all of post or article. May try searching here though.

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Jay 69 SS-350

Gentlemen, After a lot of discussions with some other folks too, the consensus is to stay with the original crude based gear lube as per Chevrolet’s specifications. I am told people have used the synthetic and it works fine, but all have talked about how the Muncies leaked it out like a sieve. Evidently, their sealing qualities are not too good. With the service I got out of the standard gear lube, I’d probably be crazy to change! Thanks for all your comments and help.

I have 2 vehicles with Muncie transmissions. In one ('68 SS396 Chevelle) I have Redline MT Gear Oil (Synthetic) and the other ('69 Nova SS) I have Mobil1 80W90 (Synthetic).

The Chevelle's Muncie has been together for almost 4 years and NO leaks. The Nova has been on the street all year and no leaks.

No gear jump outs, no gear noise, no leaks, no other strange problems others may report. The biggest bonus to me for Synthetic is that the transmission shifts with no problems/low efforts when it's below 40 degrees F.

I must add that both transmissions were rebuilt by professionals (Liberty Gear in Taylor, MI).

Glenn in Detroit

I have been using Amsoil synthetic oils in everything I own from my pro street '69 427 4 speed Camaro to my air compressor, with great results. If you are going to use a synthetic, Amsoil is the best. If you want more info give me a e-mail address and I'll send it to you.

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'69 RS SS396 pro street
427/4spd/9"

The plot thickens again. I thought the synthetic would provide additional protection during extreme temperatures as Glenn has indicated. Now I'm back to wanting the synthetic! Thanks for your comments, there is nothing like real life testimonials.