[JoelDaniel]

I am gonna be doing a clutch job in the near future and I am thinking about getting a rebuild kit from www.gearzone.net for my transmission while i'm at it. Anybody ever done this before? Is it something that someone with no transmission experience could figure out?

Joel

73 Firebird, 400 c.i., M-21, 4.10 Posi

[JoelDaniel]

I am gonna be doing a clutch job in the near future and I am thinking about getting a rebuild kit from www.gearzone.net for my transmission while i'm at it. Anybody ever done this before? Is it something that someone with no transmission experience could figure out?

Joel

73 Firebird, 400 c.i., M-21, 4.10 Posi

[Virginian]

Now, I too have a gearzone kit that is patiently waiting for me to get a burst of energy. Fortunately, when I do, I have a parts washer and a press at work. I need to get some assembly grease first, too. Love those needle bearings.

"What could have happened, did."

[Half-Inch Stud]

Yes.
Yes.

"Syncronizers" are called Blocking Rings. You want the Brass Blocking Rings with fine grooves on the Inside Diameter.

You want to be rebuilding a Muncie with a 1" diameter Counteshaft support. If you gots a 3/4 or 7/8 countershaft support, then you at best got a 6cyl or 350CID engine up front.

HIS.

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Jon Wood]

go to: http://www.autogear.net/. They have all the parts. They are also the ones who make the parts that gearzone sells, so chances are that they will be cheaper. I would talk to both of them. There is a "how to" rebuilding video for sale at: http://www.5speeds.com/muncie.htm. They also sell a gland nut wrench for pretty cheap, which is very helpfull for final assembly.

[JoelDaniel]

Thanks for the input guys. I was wondering though, what if when i tear it apart my gears are bad or something. Then would the rebuild kit be useless? My transmission works fine now, it just leaks pretty bad, and grinds a bit going into 4th. So my gears are probably ok right?

73 Firebird, 400 c.i., M-21, 4.10 Posi

[goatseeker]

Joel,
You'll know as soon as you open it up if your gears are bad - so you'll be able to use the kit wether you need new gears or not.
AutoGear makes a really nice supercase ($265)that is a tremendous improvement over the original Muncie case - I just put one on my M20 with the rebuild. If you plan on banging the tranny much I highly recommend the Supercase with the iron midplate.

http://kurtspontiac.homestead.com/TimSimpson66GTO.html

[Will]

I did some asking around about the supercase and steel midplate for the tranny in my '73. At first I thought I had an M-20, but now I'm fairly sure it's either an M-21 or close ratio T-10 as there is very little RPM drop from 1st to 2nd gear and ever since installing the 3.73 rear gears I find myself driving it like a 3-speed, skipping 2nd gear altogether.

In any case, I was told that the gears in the M20 are what usually break and that a supercase or steel midplate won't preven this. The gears are just plain weak, and upgrading them is really expensive.

Can anyone confirm this or add input? I really have no idea one way or the other and I'm trying to decide whether it's worth it to invest in the supercase and a mid plate for this tranny, or just take care of the bearings and seals and save the money for a TKO-II.

Also, is an M-21 significantly stronger than an M-20, or is it pretty much the same tranny with different gear ratios? Maybe the different 1st gear ratio makes the gears themselves stronger?

As far as rebuilding it, I've heard it's pretty straightforward. After looking inside a manual tranny and an automatic, the auto looks a lot more complex to me yet I know they're not that terribly difficult to rebuild. I definitely plan to tackle a rebuild on this tranny over the winter as the seals leak pretty bad and the 1st gear synchros are worn out.


----------------------------
'72 Formula 400 Lucerne Blue, Blue Deluxe interior - My first car!
'73 Firebird 400/4-speed Black on Black, mix & match.

[Hibrass]

Will,

The M21 and M20 are the same tranny with different ratios.... As long as you are comparing tranny's with the same size counter shaft.. The M22 used a different gear cut and was somewhat stronger than the M21 and M20..

Later,

Hibrass

"If you don't know the dog, Don't yank his chain."

[Virginian]

I'm going to get an M-22 and a Supercase and put one of those wide ratio conversion gearsets in it. That ought to be pretty good.

"What could have happened, did."

[youngleadfoot]

im only 19 yrs old and had little experience outside of motors and i was albe to figure it out; so go for it. it is not too big a job but i would suggest getting a book for it.

[goatseeker]

Actually the case is probably the weak point of the Muncie. It is what retains the mainshaft and countershaft (and therefore the gears) in proper alignment to transmit the engine torque to the driveshaft. As such, it is exposed to considerable twisting forces itself and the stock aluminum case will often crack at the front or near the mounting ears. Comparing the Supercase to the original case side-by-side, you can see that the newer design is much beefier at the front opening where the drive bearing sits. The mounting ears also project from thick bosses on the newer case instead of the thinner cast webbing on the original. The inside of the case is thicker and machined much better too which elminates stress risers produced by the rough casting of the original.
The gears are probably the strongest part and unless the tranny was driven hard while in need of a rebuild will probably be in good condition. The M22 had a higher spline count and the gears on the M22 were cut at less of an angle than the M20/M21 and that is what produced the characteristic "rock crusher" sound of the M22 but otherwise the steel used to make the gears was the same. M20's and M21's differed only in gear ratio unless I am mistaken.
I don't think any Muncie can be made "bulletproof", but for about $500 for a Supercase, steel midplate and rebuild kit, you can build yourself a pretty stout unit that will probably last a long time and be much cheaper than a TKO.
Just my 2 cents
Tim

http://kurtspontiac.homestead.com/TimSimpson66GTO.html

[unclescratch]

The GM dealers used to have a special wrench for removing that left-hand threaded nut beneath the front bearing retainer. It's no longer available, BUT, they have a wrench in with their special tools under another part number that works perfectly!!! If you need, I can try to look it up for you. You will need that press and probably a bearing splitter (can autozone lend you one??) and an assembly/teardown manual. I used a piece of conduit and vaseline petroleum jelly to reload those needle bearings (cheap and effective) I also found what I needed in the dealers parts room to R&R the rear bushing in the tailhousing. You can do it. Take your time. Found this special tool at my local GM dealer, Kent Moore J-36727. It may be helpful in dealing with that left-hand threaded nut at the front bearing. Perhaps you can beg/borrow/rent it to help with your efforts.

[Virginian]

at least on needle bearings. :-) Maybe if I do it in the winter... And then, I don't feel comfortable until I drain the tranny if I know it's in there too. I am gonna find some of that green assembly grease.

"What could have happened, did."