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Warning! The Kid rebuilding a Muncie

Kid_Again

Well-known member
Joined
Jul 6, 2004
Messages
1,171
Location
NJ - Which exit you from?
Corvette
65 SB Roadster, 66 BB Coupe
This ought to be interesting.

I'm replacing my #match M20 Muncie in the '66 with a '69 M21 that I bought for $200 a few years ago. I thought it would be a good time for me to learn how to rebuild a Muncie and I got some tips from Gary (GTR1999) to get me started. Since I couldn't wait for the instructional video to arrive in the mail (and I seem to be incapable of following the shop manual), I just HAD to crack the case and see what was inside. Actually, all the gears looked pretty good with the exception of the reverse pinion gear which has some ground up teeth. No chips in the case and it looks like the previous owner used Redline oil so it seems to have been well cared for. The obvious problem is that all the bearings sound like potato chips. I THINK they are the original bearings. The speedo gears need replacement.

If you see the cracked case picture, you'll see the first problem. The idler shaft has a flat ground into it and that flat should be on the bottom...you can see that it is not aligned correctly so that, I think, means it was rebuilt by a hambone.

The casting and applied numbers say it is a September '69 M21 and it has a single ring on the input shaft.

Of course, I messed up because I should have unscrewed the nut on the input shaft and it'll be a booger to get it off now. A "Muncie Nut Wrench" costs $50 and to hell with that. All I need is to cut some 3/8" flat stock in the shape of a wrench and cut a "U" slot to grab the nut. It's left hand thread, I believe.

I'll post pictures as I move along at a snail's pace. It was either Mac or Tom Bryant who put money down that I'd wind up with 4 reverse speeds and one forward. Cute, real cute. Hey, at least I don't have an annoying split window to block my view.

BTW, see that heart stamped into the boss on the top of the case? WTF is that? Maybe the mark of the previous hambone?

ttfn
 
One of the magazines out there, either Corvette Enthusiast or Corvette Magazine, just had a two or three part series on re-building a Muncie. Looked like a pretty detailed article with lots of pictures. You might want ot check it out.

Benrie O.
 
Joe,
You may have already considered this but you're switching from a WR to CR Muncie. The first gear is lower at 2.20 compared to 2.54 I think. You probably have a 336 gear so you may find the acceleration may be not what you expect.
The WR work very good with 308 336 355 and 373 373's. The CR was usually paired to the 370 411 gears. Not impossible but you may want to check the ratio and comparisons.
Good luck
Gary
 
...you're a mind reader, 3.55 gears in the bb


....i'll give some thought to your advice


thanks for all the responses........:w
 
You might get away with the 355's. The 370 or 373 would work better but that would require a diff build and the best 373 gears are out of stock now till 09. I would build it and try it. If it's not what you like you can do the M-20 over and put it back. That way you'll have the original tranny back in the car fresh and you'll have tested out the M-21.:upthumbs
 
OK, that's a decent plan, appreciate the advice!



a guy like you can do a muncie rebuild in a few hours...me, i'm looking at the shop manual and wondering how they could fit THAT many parts in such a small case....set this detent, pull this shaft, align that pin, tote that bale lift that barge;LOL


....i've got the whole summer to figure out how to get four reverse gears out of a muncie...the legendary M21.5
 
I feel slighted. My M22 doesn't have a heart stamped into the case. I would guess that it might be an inspection stamp or, like you said, it was put on by the last rebuilder. I think that mine is a 1969 too. It is in very good condition except it was used as a drag racing crash box and the synchro keys were removed. I think that the blocker rings are ground smooth too. It's been a while since I was inside of it.

My '59 is a 2.20 low with a 3.36 and with the 283/270 Duntov cam and dual carbs it doesn't like to move away from a dead stop. I had a 3.70 posi in it for awhile and it was perfect (except that the guy set it up wrong and it howled it's way to becoming a razor blade factory. I swear that you could have shaved with those gears).

Tom
 
VNV tells me he's already set aside a spot on his driveway in anticipation of my first drive with the rebuilt Muncie.

Cute

Real cute.
 
VNV tells me he's already set aside a spot on his driveway in anticipation of my first drive with the rebuilt Muncie.

Cute

Real cute.

Yes in fact I've also have two 55 Gallon drums of "Oil Dry" Standing by and a powered riding fetilizer sprader ready to go to coat my drive way.:D





"Kid_Again.."Hey, at least I don't have an annoying split window to block my view."
 
"A "Muncie Nut Wrench" costs $50 and to hell with that."
Amen! I made one from a square of 1/8", bolted piece of 1" flat stock to it for the handle.
 
6T7L71CPE, i like your approach...that's what i was going to do until i reviewed the entire videotape from 5speeds.com

the objective of this tape is to get the one-timer to rebuild a box using common hand tools....his rebuild kit comes with a new input shaft nut and he just uses a cold chisel to split and remove the old nut and to install the new one, he uses a BF pipe wrench....causes very little damage and he just cleans up the face with a mill bastard

...the only "special" tool that he used is a press to pop off the gears from the main shaft

...a hammer and chiesel? yeah, we got that:cool


btw, VNV, i carry two bags of cat litter in each car, just to make sure that i don't ruin either your driveway or the roads that we new jersey taxpayers have purchased....you're welcome



...and yes, my idler shaft is installed incorrectly because the cutout sits in a recess in the intermediate plate and is locked in...what probably happended is that the shaft was put in incorrectly and pulling the case together with the tailcase bolts pushed against the plate, pushing the idler shaft farther out into the hole in the front of the case, causing that to widen...may have to bush it

idiot
 
Well this project sounds very interesting. Sounds like I can learn a lot watching you rebuild this tranny. Of course.. I'll be drinking and watching while you'll be pressing and banging and chiselling and bastard milling.:D
 
Sure, you can use the hammer and chisel, but the difference between Corvette owners and Mustang owners is, we can make tools...I saw that on National Geographic once.
 
You have to watch out that the PW doesn't marr the chamfer of the nut. If you look at the cover it forms a oil slinger with that chamfer so it should be burr free.
If I can get my wrench back I'll let you borrow it just cover the postage.
Gary
 
OK, OK, i'm embarrassed into making my own front nut tool:eyerole......gary, don't bust a gut getting the wrench back, if it works out, i really appreciate your offer....i understand that the chamfer on that nut must remain intact in order to prevent an oil leak!!!!

...so, with JL66REDCPE's post, i now have two places to break down..if i break down near the Richland General Store, i can roll into john's driveway BUT if i'm going REALLY fast, i may be able to roll all the way to mark's house...it's good to have options:w

...i just broke the tranny down to it's components and the synchro's look new, there are no chipped teeth beyond that one missing tooth on the reverse gear...i'll post pictures tomorrow but what you'll see is nothing remarkable..the case gaskets peeled right off so my guess is that it had a fairly recent rebuild (by Bubba)

..what concerns me is the idler shaft is not as tight a fit as i would have expected since it basically dropped out of the back of the case....my rebuild kit will come with a new shaft and if i don't like the fit, off the case goes to get bushed...the other observation was that the rollers on the back end of the input shaft were totally dry (which was probably the potato chip feel when i turned the input shaft (the bearings are fine)), so i'm glad that i cracked the case.....the final point is that the oil seems to be automatic transmission fluid, it's red and of low viscosity...i've never seen red line MT oil but this seems odd

no, one more point, the bottom of the case had a HUGE deposit of fine metal shavings, in the shape of a 2" ring or donut...what is that?????
 
I can get you the wrench no problem. The donut ring is a magnet, doing it's job.
 
gary...replied to your PM...OK, never heard of a magnet inside a muncie, it clearly did it's job...whereas the previous rebuilder did not do his job of cleaning out the case...the case, tail and plate will be steam cleaned and trued on each end before monday
 
Sounds like someone was thinking to use a magnet in the trans. It's amazing how much fine metal gets in the oil if you don't do something to draw it out. I'm using both a magnetic drain plug and a Filtermag on my new engine. I was told to put a few small earth magnets inside the oil pan but I already had it on by that time. I have a problem with that idea in that there is no way to drain out the metal that those would attract. The drain plug can be cleaned off and the Filtermag traps the metal inside the oil filter. I guess that it's still better to have it stuck to a magnet inside than to be circulating with the oil.

Tom
 

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