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Author Topic: M20 Vs M21 Gearbox  (Read 16788 times)
normd
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« on: August 30, 2003, 02:23:18 PM »
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Hi Guys
          Please correct me if I'm wrong  :-/
 I always thought the difference between the two was the M20 was an "Even" ratio box normally for sedans , utes & vans and the M21 was a "Long" (60mph) 1st gear and 3 close ratio's at the top, for Hi Performance cars & V8's . The difference is in the V8's, they had a "fine spine" front shaft .
        Both boxes could be fitted to 6 cyl's . The M20 I've got in my FC was fitted for a V8 and my mechanic said he just "swapped" the shaft. (wasn't ripped off , didn't cost anything).
        I have just checked a site called "cheersandgears.com" and these are the spec's they quoted for an LJ XU1

"1972-74 Holden Torana GTR XU-1
Inline 6: 3310cc/202ci, 190bhp/5600rpm BHP, 200ftlbs/4000rpm
Length 172", Width 63", Height 53"
Wheelbase 100", Track 52", Weight 2350 pounds
They were fast, small, light, hard-riding, and great fun to drive. With the standard 3.36:1 differential ratio, the M21 gearbox gave them maximum speeds in each gear of 50, 75, 100, and 125 mph. The taller 3.08:1 ratio differential raised the speeds in each gear by about 10% and increased the top speed to 135 mph."
  This is why most guys were after M21's when I was racing.
       So if you guy's want to get your FE/FC to really "rip" along , looks like an M21 is the way to go..
    Anybody else had experience with these ......
   Cheers
   Norm d
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« Reply #1 on: August 30, 2003, 03:24:43 PM »
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NormD your a legend mate , Good on ya - 17 bourbon and coke cans into a good night and you make sense to me mate
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Jockster
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« Reply #2 on: August 31, 2003, 01:46:26 AM »
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G'day Norm
You are correct about the different gear ratios between an M20 and M21 gearbox, the M20 gearing allowed for fast acceleration from a standing start, where the M21 was more of a high speed cruising box. The V8 box didn't actually use a fine spline until the later V8's (VH and VK Commodores, but all of the V8 front shafts were longer than the six cylinder shaft by about two inches to accommodate the bigger clutch and longer bell-housing of the V8. The later M20 and M21 gearboxes as fitted to Commodores and the last of the Torana's also had a modification done to them to overcome the weakness of the second gear synchro retaining circlip of the earlier boxes.
Cheers
Jock
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« Reply #3 on: August 31, 2003, 07:25:24 AM »
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JOCKSTER
THE T5G BOX (VKGPA & WALKINSHAW) ARE THE ONLY V8
BOX THAT RAN A FINE SPLINE FRONT SHAFT AND ALL GETRAG (VS S2 AND VT).ALL AUSSIES ARE COURSE SPLINE,THERES EVEN AN M19 BOX (1 TONNER).M20 AND M21 ARE DIFFERENT RATIOS SO U CAN'T PUT A M21 FRONT SHAFT IN A M2O BOX WITHOUT SWAPPING THE CLUSTER.
EASY WAY TO TELL ALL M21 BOXES HAVE TWO LINES ON FRONT SHAFT,M20 HAVE 1 AND M19 HAVE NO LINES ON FRONT SHAFT.V8 AND SIX ARE THE SAME BOX EXCEPT FOR LENGTH OF FRONT SHAFT.EXTREMLY RARE TO FIND A M21 SIX BOX,USUALLY SLR TORANA,XU1 M19 BOX IS USLESS RATIO WISE
BRAD
« Last Edit: August 31, 2003, 07:26:47 AM by FCV8UTE » Logged
ACE
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« Reply #4 on: August 31, 2003, 08:42:25 AM »
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Hey normd
Heres the Ratios  M20         M21
                1st      3.05         2.54
                 2nd     2.19         1.83
                3rd       1.15         1.38
                4th       1.00          1.00
L34 Toranas used a closer ratio M21 with a 2.32 1st gear. (Cluster gear part number 9939484 ).
BRAD i've never heard of a M19 gearbox (1 Tonner)
They are M22!
NOTE! M22 was the code for the "AUSSIE" 4 speed as used in some Holden commercial vehicles(HQ-WB). The Muncie 4 speed gearbox (HQ350.) code is MC7.
ACE Cool    
« Last Edit: September 01, 2003, 05:00:18 AM by ACE » Logged
customFC
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« Reply #5 on: August 31, 2003, 09:32:55 AM »
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I have an Aussie 4spd in my FC, and I suspect it is a 1 tonner box. Is there any way to tell without dropping the box out?
Regards
Alex
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« Reply #6 on: August 31, 2003, 09:59:06 AM »
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G'Day Ace
M22 is the muncie gearbox as fitted to corvettes, early (read true) Monaros (350)
John M
« Last Edit: August 31, 2003, 09:59:32 AM by fcmayberry » Logged

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normd
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« Reply #7 on: August 31, 2003, 12:21:54 PM »
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Thanks Guy's for all the replys  
   "What other site on the net would you get this type of feed-back"
    Alex , I bet you are like me , PLENTY of "wheel spin" in 1st & 2nd....... even with 10" wide "slicks" Shocked
The old motor was 186 = 190 HP, This motor is a 192 = 245 HP (Dyno'd)
    Next Question.......
   What do you Guys suggest , change the ratios in the box , or put in a "taller" diff centre , I am running a 3.36 "CIG"  (welded) at the moment  .  Would a 3.08 be better or do you think it would handle a 2.78 and really stretch the gears out , keeping in mind the power band in the motor is supposed to be 3,500 - 8,500 heaps of grunt ? ? ?  
     I've been out of this since the early 80's , so ALL suggestions are welcome as I want to plan early before deciding what to do , looks like I've got a company who are willing to plant a few $$$ in the "old beast".
    Cheers Guys
     Norm

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« Reply #8 on: August 31, 2003, 08:08:36 PM »
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the M22 can be an aussie 4 sp or a Muncie, same number, totally different box, the only way to tell without looking at internals is by how useless 1st gear is with one tonner gearbox,the only problem with changing diff ratio is when you are in 4th gear all boxes are 1to1 ratio the jump would kill off a bit of the power ,but on the other hand been strong HP that would overcome it a bit,the torana used a 3.08 ratio in most applications as it was a good all round diff ratio ,
The M21 are not all the same ratio,the XU1 had taller gearing and are very hard to find now where as the M21 v8 box is still common
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« Reply #9 on: September 01, 2003, 03:01:57 AM »
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Aussie 4 speed as per the HQ manual Volume 3, page 3 four speed transmission M20 and M21 (both of which could be fitted to six or eight depending on input shaft).

M22 Muncie gearbox, as used in Corvette etc.

One tonner box was an M20 (On the six) as the diff ratio was 3.55:1 therefore when matched to M20 had stump pulling first & second gear and then on the normal.

I still have the orinigal w/shop and spare parts manuals purchased when my dad bought a one tonner new in 1973 or there abouts.

Ace has listed the correct gear ratios for the M20 & M21.

M22
First       2.52:1
Second  1.88:1
Third      1.46:1
Fourth   1.00:1
Reverse 2.59:1

John M
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« Reply #10 on: September 01, 2003, 04:00:49 AM »
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 the LC-XU1 had an opal 4 speed ,the LJ-XU1,GMH had developed its own all Australian four speed gear box, known as the M-22. The additional power and torque of the 202 permitted taller gearing for the indirect ratios. First was 2.59 for a maximum of 46 mph at 6200 (down from the 186's 6400 red- line). Second was 1.83 for 61. Third was a nice long l.25 for an exhilarating 98mph, with the ton easily possible. Like the standard GTR, the XU-I came with a slippery diff' running 3.36 gears. Or you could order 3.08 gears. Outright acceleration was only fractionally better than the 186 engined car, but the work was easier.
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« Reply #11 on: September 01, 2003, 04:54:15 AM »
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Hey Effie C,
You're right. There are M22 Muncies but i think thats Chevs code. The code for a Muncie in a HQ350 is MC7.
It sounds like from your reply that you don't believe that some Holden 1 Tonners were fitted with M22 "AUSSIE" 4 speed gearboxes. The M22 gearboxes fitted to some Holden 1 Tonners  had a 3.74 1st gear ratio.
There was a number of diff ratios used with the M22 gearbox. These ratios were  3.36-1, 3.55-1, 3.90-1 and a 4.44-1 STUMP PULLER!
My reference: Holden Parts Book M37058.
HX Holden parts book M37865.
45 years of Holden Page 56.
50 years of Holden Page 44.
Regards ACE Cool
« Last Edit: September 01, 2003, 05:19:47 AM by ACE » Logged
Dr_Terry
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« Reply #12 on: September 01, 2003, 07:16:28 AM »
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Hi Guys.

This M20 & M21 thing crops up all the time.

The option numbers M20/M21/M22/ MC7/MC6 etc mean different things on different model series.

If you look at HK/HT/HG model series, M20 means Opel 4-sp, M21 means Saginaw 4-sp (close ratio) & M22 is the wide ratio Saginaw 4-sp used only on 6 cylinder commercials.

For HQ/HJ/HX/HZ/WB, the numbers M20, M21 & M22 are all Australian 4-speeds of various ratios. Just to confuse the issue M22 is a Chev option number for a Muncie 4-sp. For the HQ350 4-sp Muncie in Australia, GM-H used the option code MC7 (I made this error in my first book).

In GM-H language, M20 only means 'standard 4-sp', on a Gemini their M20 is the Isuzu 4-sp that came from Japan with the 1600 motor. (Confusing eh?) & the 4 cyl LJ/TA Torana 1300 also has an M20 box (English Vauxhall origin)

Getting back to the HQ type M20 (6cyl & 253 V8 only) its 1st gear ratio is 3.07, the M21 (308 & 253 only) has a 1st gear ratio of 2.54. The M22 (6cyl One Tonners only) has a 1st gear ratio of 3.74.
These boxes carry thru to the VK Commodre (M22 finished with the WB One Tonner).

For Toranas all 6cyl LC 4-sp to June '71 were Opels (M20). From July onwards GTR & lesser models get the standard M20 from the HQ whereas the XU-1 gets a special M21 (same ratios as the M21 308 box except 3rd gear is 1.25 (instead of the normal 1.38). The '73 Bathurst XU-1 had an alternate set of ratios available with a 2.32 1st gear (this box is as rare as). The LH L34 had the 2 XU-1 type M21s available as well.

The option number MC7 was used again for the optional A9X box, the Borg-Warner Super T-10 which is a close cousin of the Muncie anyway.

All the Australian 4-speeds use a 10-spline input shaft (except for the special build 6cyl box used in the 1979 Repco Round Australian  Rally - these were custom made for increased durability).

All the V8 Aust 4-speeds have a longer front shaft & throwout bearing support (the shaft is 1.25 inches longer than the 6 cylinder boxes). You can swap the longer V8 shaft & support for the shorter types (watch the tooth count !!). Dellow used to make a spacer plate that enabled a V8 box to bolt into a 6 cyl bellhousing while keeping the longer shaft. If this is still available it may be a cheaper alternative.

Regards.

Dr Terry.

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« Reply #13 on: September 01, 2003, 07:47:07 AM »
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Bloody hell, Terry. No wonder they call you Doctor!! Shocked Shocked Shocked
Man, you have a definitive answer for every question there is. Either you have a very big computer, a LOT of paperwork, or a very large cranium Wink. Either way, you are definitely an asset to this forum.
Thanks.
Rob J
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« Reply #14 on: September 02, 2003, 09:41:28 AM »
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ratios & more ratios.

what are the gear ratios and speeds for an Aussie 4 speed coupled to a 2.78 diff  driven by a 202 ?
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Phil
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« Reply #15 on: September 02, 2003, 09:52:23 AM »
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It would appear it depends on what the general fitted the Aussie four speed too in the first place.
As far as I know the 2.78 : 1 ratio diff was only ever fitted behind the auto, but more than likely wrong.
John M
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« Reply #16 on: September 02, 2003, 11:24:37 AM »
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I used to run a 2.78 diff behind a 308 Monaro and it worked fine, but I think there would not be enough torque in a 202 to make adequate use of the high gearing. In one of my current FC's I am using an Aussie 4 speed with a 3.08 diff and it works quite well economy and power wise.
Brad referring to my earlier post when I mentioned fine splined Aussie 4 speeds, I partly agree with you and partly disagree. I used to work on a lot of VH and VK V8's when I was in my original workshop and as an automotive lecturer with TAFE. I had at least ten 309 powered VH's and Vk's that we worked on come in with fine splined Aussie  4 speeds. Where it gets murky is that they were never listed by Holden so you couldn't buy a Holden clutch plate for them, but a Ford fine spline clutch fitted. One of these boxes damaged a front shaft and we couldn't buy that either it wasn't listed anywhere by holdens, the numbers on the other gears were M21 and the Aussie M21 front shaft fitted straight in so they weren't imported boxes. It is possible that they may have been a run of specials that escaped or  some special boxes that were built up, but it is interesting anyway. If anyone has any info about these I would like to know more
Cheers
Jock
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normd
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« Reply #17 on: September 02, 2003, 01:08:05 PM »
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WOW ........   Info Plus   Thanks Guys , Making note of EVERYTHING .

Jockster , I'm not worried about running out up top speed , but did the 3.08 give a good range in each gear? as I have WAY too much power down low .. ? ?(motor is 192 ,full race cam , triple carbs) The flywheel is still original , lightened ones give you more rev's but you lose torque.  I'm still running 13" wheels , and very low profile tyres.

John m   Yes  mate , think the 2.78 comes out of HG/HT auto's    , V8 maybe...
 Cheers
 Norm
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« Reply #18 on: September 02, 2003, 07:22:13 PM »
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the 3.08diff works fine with a  good range in all gears with a strong motor,even a mild 186 goes well with this ratio, i have found the 3.55 ratio is ok around town but not much chop on freeway,the 3.36 is good around town and ok on hi way , by the way i have had several cars with standard engines using 3.08 diff and found the car was fine around town and great on hi way,
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« Reply #19 on: September 03, 2003, 05:17:31 AM »
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the 161 red motor is a bit underpowered in stock form with the 3.08 diff
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