I recently installed a rebuilt M21 muncie 4 speed trans in the 35 and i was recomended to use 30 weight motor oil, break it in by running it on neutral for some minutes and that i should be good to go. Well the gears go in ok at start up but tend to get harder at the driving point (warmed up) The linkage is new and well adjusted. Im thinking maybe the type of oil i used is couseing this? I used royal purple synthetic oil sae 10w-30, or is something wrong internally? Thanks in advance with any help...
I have never heard of running MOTOR oil in a Muncie transmission.... You should be running 90w in that.
I ran 80W-90 in mine...You might want to have a pro look at it...you may have prematerly worn out the synchros!
First, I've never heard of running motor oil in a Muncie tranny. They're supposed to have gear oil! About any and all Muncie problem - you might want to try sending a PM to Brian Lawrence. He's an Alliance member and a wizard when it come to manual trannys in general and Muncies in particular.I've known him for about 30-odd years and if he can't solve your tranny issues, nobody can. ( http://www.jalopyjournal.com/forum/member.php?u=98053) Mart3406 =======================================
The first hour of operation of your trans is very critical. Similar to breaking in a new cam shaft. There is a moly based assembly lube which needs to mix with the gear lube to make sure your lubricant flows easily thoughtout the trans. We recommend natual crude rather than synthetics, natural crude with it's imperfect molecules doesn't tend to leak like synthetic with perfect molecules. The natural crude also cushions the gears during operation. We recommend Pennzoil, Valvoline or similar products in a 80-90 weight. Fill trans with it in a level postion, about 3 pints (give or take) and let the excess or overflow leak out before installing the fill plug. Rotate the input shaft 3-4 times. During the first 1/2 hour of breaking inthe trans do not operate the engine without the rear wheels turning. If you are tuning the engine during the first 1/2 , please have the rear wheels off the gound so that the gears and shaft are rotating in the trans. If you take the car out for a test run during the fist 1/2, do not return and park the car with the engine running and the trans in neutral. Let the enginr and trans cool down and then go back to tuning the engine or adjustment After the first 1/2 hour you can drive it like you intend to without any concerns. Thats the info I was given by Jeff from midwest muncie when I bought mine not to long ago hope this helps you
Well, at this point im gonna drain what's in there and pour in some 80-90 and hope for the best, or save up some funds and have a pro look it over?? This all sucks couse these trannys aint cheap. Talk about a expensive lesson...
I'm wondering if the Royal Purple synthetic oil, which probably works well in an engine, is maybe just a bit too "slick" to use in a manual trans. I could imagine that the blocker rings in the synchros might be having a hard time dispersing this oil when they attempt to engage the tapered contact surface of the gears. The synchro needs to momentarily stop the gear from spinning to allow it to engage smoothly so there has to be some amount of friction between the surfaces. The Royal Purple may be "over lubricating" things in this area and not allowing it to work as designed. I'd think it could make it feel as though the synchros were worn out, even though they're brand new. I doubt that you've damaged anything in the trans, but I'd be curious if simply changing to conventional gear lube cured the problem. I don't think it's uncommon to run 30w in some manual transmissions. Chrysler used to recommend using ATF in their older 4 speeds and they were sure easier to shift in cold weather.
Since we're talking about munices here I have a question. There's a guy in my area that is selling a rebuilt m21. I don't know much about these and I was wanting to know how can I tell if its a muncie? Also how can I tell the difference from a M20, M21, and a M22? Is there a casting number or bolt pattern that can identify one from another? Thanks for any info!
The first gear does not have a bushing, (metal to metal) on the main shaft. It will lock to the main shaft without the proper lube (80-90 wt). Years ago,,early 70's, I was running a 68 Camaro small block 302 w/ muncie. B&M came out with a fluid called Trick Shift,, it was Blue in color and looked like automatic trans fluid. They recomended it in 4 speeds,, Long story made short, the trans locked in first gear at the traps at 120 mph. I was lucky to get it out of 4th gear, pushed in the clutch and the disc expanded into the pressure plate, the motor wound so tight it whipped the engine oil like butter. When it all settled down and I came to a stop,, the tally was a pair of slicks ruined, rear end gear broken, driveshaft twisted, transmission wasted, clutch wasted, and the engine in need of a set of rods. Not to mention the button holes in the drivers seat. I did not get any help from B&M for the damage. So,, look into that trans I'm sure it will need some attention.
B&M came out with a fluid called Trick Shift,, it was Blue in color and looked like automatic trans fluid. ] it looked like ATF 'cause it was ATF,i've still got a few cans kickin around that a customer left.[after 20+ years i think it's mine]
>>>>>,I always ran 90W gear lube in my M-21 & M-22 Muncies to break em in ,,BUT ,,in the Alaska winters ,,i ran Auto Trans Fluid in em ,,Gear lube gets pretty stiff in cold temps ,,,werked so good ,,i ran ATF all summer up there ,,
>>>>>,In '71 ,when i was with the Fred Gibb/Dick Harrell Super Stock Team ,,GM told us to run ATF in our M-22 Muncies in the '69 Camaro ZL-1 and the DZ-302 Z-28's ,,those were basicly crash boxes ,,,never used the clutch to shift ,,werked great too ,,
along time ago a guy who built my muncies told me to run gear oil but to put some automatic trans fluid in with it, he had been building them forever and told me in the mornings when the gear oil is so thick the atf helped it shift easy, ive been doing it for 20 years and ive never had any problems with any of my muncies he built, they all shift like butter. dont know if its right but it works.
get the casting numbers off the side of it and theres a couple web sites that you can look it up, thats how i found out mine was a m21
Back in the '80's ,when i had a Triumph TR-7 and a Jag XKE ,,British Leyland sent out a newsleter too all owners ,,to switch to ATF in our manual transmissions ,,NOT to use gear lube no more ,,SO,,I Did,,werked Mucho Better ,,
I have just been through this problem with mine (also a M21). Couldn't work out why it would shift good cold but hot it got real notchy and selecting reverse was impossible. I ran through all these scenarios with HAMBers and in the end it was about getting proper disengagement of the clutch. I don't know but I think maybe the clutch plate expands a little when hot and if it grabs just a little, shifting gets hard. I reconfigured my pivot and linkage and it's shifted beautifully since. I would definitely start there. Pete
Anybody ever heard of the practice of adding a small bottle of the GM Limited Slip additive to their manual transmissions? I've heard from a couple of different people that the instructions for the original Doug Nash 5 Speeds recommended this additive but since Richmond took over production of the Street 5-Speed, they don't mention it anymore in the installation manual. Anybody familar with this?
Claymart nailed it. Synthetic motor oil is too slippery. The syncros need some friction to work. Switch to AFT if you hammer the gears hard and aren't too worried about gear and bearing life over many thousands of miles. Use 90w gear lube if you want maximum life from the trans, but can put up with slightly slower shifts, especialy in cold weather.
M20 has 2 grooves on the input shaft. M21 has 1 groove, M22 had none, and come with a drain plug. Also the old 1963 -1965 M20 had no grooves, but can be identifed by the smaller 7/8 cluster shaft. case # 3831704 and 3851325 1st was 2.56
All the discussions on fluids is interesting, but. The OP's solution is right here, in my opinion. Frank
I don't see it as rocket science, I suppose someone can always put a spin on any subject and elevate them to mystical levels. I've been using 85-90 name brand gear oil in all my manual boxes since day 1. I've had some hard-shifting Muncies when it got around zero degrees, but only for a few blocks at most. Bob
I've bought Muncie parts from a company in Syracuse, New York named Auto Gear Equipment. Knowledge guys who have always been helpful. They recommended specifically Valvoline 80W-90 as best for my Muncie M22, which I understand is not synthetic. As I recall the discussion, the synthetic oils are too slick for the syncros -- which is consistent with several inputs here.
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