As topic states whats the difference between a M20 & M21?
M20 & M21 Difference
Started by
DanWA
, Oct 07 2007 10:19 PM
13 replies to this topic
#1
DanWA
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Posted 07 October 2007 - 10:19 PM
#2
_Rob 5000_
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#3
DanWA
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Posted 08 October 2007 - 09:59 PM
Cheers mate... me and the search tool don't get along too well
#4
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Posted 29 October 2007 - 09:07 PM
I was talking to the gearbox and diff shop who specialize in aussie stuff not long ago and they said the only difference is the M21 has a longer input shaft and that is all.
#5
TerrA LX
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Posted 29 October 2007 - 09:11 PM
^ you have been mislead
#6
rodomo
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Posted 29 October 2007 - 11:34 PM
Yep, thats the difference between 6 & 8.
#7
_1ARC_
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Posted 04 January 2008 - 01:07 PM
Can anyone please tell the differance in length of the input shaft bewteen the 6 and 8 M20. Thanks
#8
FastEHHolden
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Posted 04 January 2008 - 02:20 PM
V8 is the long one.
#9
_1ARC_
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Posted 04 January 2008 - 03:08 PM
I realise the the V8 is the long one, but if I do not have one to compare with how will I know. Cheers
#10
VitcLJ
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Posted 04 January 2008 - 03:30 PM
38mm in modern measure 1 1/2 inches in old imperial 
#12
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Posted 04 January 2008 - 07:10 PM
M20 for 6 and 8 cylinder have the same ratios but different length input shafts and bearing retainers.
V8 M20 and 21s have a different ratio for 3rd gear, so the input shaft and counter gear are also different.
V8 M20 and 21s have a different ratio for 3rd gear, so the input shaft and counter gear are also different.
#13
Dr Terry
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Posted 04 January 2008 - 08:07 PM
Hi Guys.
The original question "what is the difference between an M20 & an M21 ?" hasn't actually been answered fully yet.
When referring to Aussie 4-speeds, the M21 is the 'close ratio' gearbox, while the M20 has the 'standard' ratios.
The ratios for the M21 are 2.54/1.80/1.44/1.00, while the M20 ratios are 3.05/2.19/1.51/1.00.
There is also an Aussie M22 which is the 'wide ratio' gearbox. Its ratios are 3.74/2.68/1.68/1.00. It was seen in 6-cyl HQ-WB commercials.
There are 2 more ratios sets seen in Aussie 4-speeds, they are the std XU-1 'M20' with 2.54/1.80/1.25/1.00 ratios. Last, but not least is the rare optional XU-1 & L34 gearbox with 2.32/1.68/1.25 /1.00 ratios. The M20 XU-1 ratio set was also homologated for the L34.
All 5 ratio sets were available in both 6-cyl & V8 length gearboxes, except the M22. The M22 was 6-cyl length only, but a V8 length M22 can be made by using the front shaft from a V8 M15 (3-speed column shift) box.
In HK/HT/HG Holdens the M20 was an Opel 4-speed gearbox, the M21 was a 'close ratio' Saginaw 4-speed (2.54 1st gear), while the M22 was a 'wide ratio' Saginaw 4-speed (2.85 1st gear) usually seen in 6-cyl commercials. The Opel M20 was also seen in LC Toranas prior to mid-1971.
Dr Terry
The original question "what is the difference between an M20 & an M21 ?" hasn't actually been answered fully yet.
When referring to Aussie 4-speeds, the M21 is the 'close ratio' gearbox, while the M20 has the 'standard' ratios.
The ratios for the M21 are 2.54/1.80/1.44/1.00, while the M20 ratios are 3.05/2.19/1.51/1.00.
There is also an Aussie M22 which is the 'wide ratio' gearbox. Its ratios are 3.74/2.68/1.68/1.00. It was seen in 6-cyl HQ-WB commercials.
There are 2 more ratios sets seen in Aussie 4-speeds, they are the std XU-1 'M20' with 2.54/1.80/1.25/1.00 ratios. Last, but not least is the rare optional XU-1 & L34 gearbox with 2.32/1.68/1.25 /1.00 ratios. The M20 XU-1 ratio set was also homologated for the L34.
All 5 ratio sets were available in both 6-cyl & V8 length gearboxes, except the M22. The M22 was 6-cyl length only, but a V8 length M22 can be made by using the front shaft from a V8 M15 (3-speed column shift) box.
In HK/HT/HG Holdens the M20 was an Opel 4-speed gearbox, the M21 was a 'close ratio' Saginaw 4-speed (2.54 1st gear), while the M22 was a 'wide ratio' Saginaw 4-speed (2.85 1st gear) usually seen in 6-cyl commercials. The Opel M20 was also seen in LC Toranas prior to mid-1971.
Dr Terry
#14
FastEHHolden
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Posted 04 January 2008 - 08:42 PM
theres a cut and paste for a sticky!!
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