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GMH built vehicle with factory fitted 6cyl M21
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Mike81973 Offline
#21 Posted : Sunday, 30 May 2010 7:17:45 AM(UTC)
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Hi Johno,
Yes my 30 F 3 M21 box has the two piece reverse shaft and the 899 cluster.

As far as I know this is the original box for my pre release Bathurst 73 XU-1, this will be one of, if not the earliest date boxes for these models as mine looks to be the first WA sold 73 Bathurst XU- 1.

Mike

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HK1837 Offline
#22 Posted : Sunday, 30 May 2010 8:19:44 AM(UTC)
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Mike, an M21 doesn't have an 899 cluster. That is an XU-1 box. M21 has a 497 cluster or on the rare occasion a 484 cluster (L34 and XU-1 optional box). Interesting to get a bit closer to the changeover date to 1-piece reverse idler. Looks like mid 1973 still had the 2-piece shaft by your XU-1 box.

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Mike81973 Offline
#23 Posted : Wednesday, 2 June 2010 8:32:06 AM(UTC)
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Mike here again,
I know of several ratio and types of M21, firstly there was the Saginaw box designated M21 then there is the V8 all Aussie M21 box modeled on the Saginaw ratios, next is the 1972 and 73 XU-1 M21 with a different ratio third gear and 899 cluster, and lastly there is the optional 1973 2.32 ratio third gear, so when you say that a XU-1 box is not a M21 I am confused, can you please explain?

Mike

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HK1837 Offline
#24 Posted : Wednesday, 2 June 2010 8:49:15 AM(UTC)
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We were always talking about Aussie 4spds, so Saginaw and Muncie M21 references are irrelevant.
XU-1 box isn't an M21. If it was a 1973 LJ XU-1 would have M21 on the BODY ID plate. FOr HQ and LJ (and some HJ) with the later style BODY plate, GMH only stamped the BODY plate if an optional component was fitted. So for example a 1973 HQ Kingswood XV4 (GTS 4 door) will have M20 or M21 stamped as the standard box in a V8 Kingswood (which is the base vehicle for a HQ GTS 4 door) was an M15. An original M15 Kingswood will be blank. Same for HQ Sandman, base gearbox for any of these is M15, so Sandman will have M20, M21 or M22. For an LJ GTR with standard rear axle it will be blank in all 3 spots (ENG TRANS RRAXLE). An XU-1 is also blank on TRANS therefore the box isn't an M21. If it was it'd say M21. Much closer to correct is M20, but that isn't right either as the cluster and input shaft are different, however the best way to categorise a box is by the 3rd gear it uses, and the XU-1 uses an M20 3rd gear. To be absolutely correct, an XU-1 aussie 4spd is just an XU-1 4spd. In 1973 the M21 ratio set and another set with an even taller 1st or 2.32:1 (also used on L34) were homologated for race use (along with normal M20 set also), however none have yet come to light as far as I know, ie an XU-1 with M21 on the BODY plate. The M21 ratio set 6cyl M21 is really the only 6cyl M21. The 2.32:1 1st gear box like the XU-1 4spd is probably best known as just the L34 4spd, but i'm not sure what you'd call it to be correct - it does use an M21 3rd gear so maybe it is an M21 L34 box! The VB rally Commodore is the ONLY factory fitted M21 6cyl that I have yet found. As stated before no XU-1 with one of the optional ratios has come to light as far as I know, would love to find one though and view the BODY plate.

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Mike81973 Offline
#25 Posted : Wednesday, 2 June 2010 10:31:13 AM(UTC)
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Hi again,
its all news to me, and I have been working on and driving these for many years.

How do you explain that most GTR Toranas, mine included have M20 stamped on their tag, and my XU-1 authanticity letter from Holden states M21 for my XU-1?

My XU-1 and my GTR were both made in the same week in August 1973.


Mike




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HK1837 Offline
#26 Posted : Wednesday, 2 June 2010 5:34:16 PM(UTC)
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No idea about M20 on the GTR tag. It should be blank as the standard gearbox on an LJ GTR is an aussie 4spd M20. Must be mistakes. I know Acacia Ridge were very careful with this stuff but the Elizabeth plant made plenty of mistakes on HQ's so LJ would be no different. Probably the best correlation is a standard 1973 HQ GTS350 coupe. This is a model in its own right, and hence is blank for ENG TRANS and RRAXLE. However any other HQ fitted with a 350 has L30 on the plate as it is an optional engine for them. Gearbox wise the MC7 Muncie is standard on the GTS350 coupe, and it is hence blank, an auto version shows M41 (TH400). However you will see MC7 on a HQ GTS 4 door as it is an option package (XW8) on a V8 Kingswood sedan. This is exactly the same principle as a GTR (=Kingswood V8), XU1 (=XW8). Dr Terry might be able to elaborate more on the reason why you have M20 on your GTR's ID plate.
Holden authenticity letter is easily exaplained, it is wrong. They always stuff these up. I think about every 5th or 6th one I see is correct.
If the 899 cluster aussie 4spd was an M21 it would state so on the BODY tag.
I think the answer is it's true name is simply "XU-1 4spd". It was only available on XU-1 as part of the XU-1 package. GMH didn't even give the engine a code as far as I know, like L20 for the standard 202HC. Hence why the LJ XU-1's i've seen have XU1 on the BODY plate for the engine code.

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Dr Terry Offline
#27 Posted : Wednesday, 2 June 2010 6:18:51 PM(UTC)
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Yes, Byron has made some good points there.

Firstly, the GM-H letter is simply incorrect, there were no M21 boxes fitted to Torana XU-1s.

Secondly, GM-H has caused a lot of confusion by allowing 3 option numbers to describe so many different gearboxes. M20 for example can describe a Gemini 4-sp, a Torana TA 4-sp, an HK/T/G Opel 4-sp or just the standard (3.05) Aussie 4-speed.

M20 it seems just means 'standard' 4-speed for that model. M21 seems to mean the 'close ratio' option & M22 the 'wide ratio' option.

I've never seen M20 stamped on a GTR body plate. Likewise I've not seen M21 stamped on an XU-1 body plate. I'm not saying they didn't do it, I'm just saying I've never seen one. To confuse the issue totally what should be stamped on an L34 body plate if it has the 2.32 1st gear 4-speed fitted in place of the 2.54 box. M21 is already stamped there.

I think it would be easier to call them:-

M20 Opel
M20 Aussie 4-sp (3.05 1st)
M21 Aussie 4-sp (2.54 1st)
M22 Aussie 4-sp (3.74 1st)
XU1 Aussie 4-sp (1.25 3rd)
L34 Aussie 4-sp (2.32 1st)
M21 Saginaw (2.54 1st)
M22 Saginaw (2.85 1st)
MC7 Muncie (HQ 350)
MC7 BW Super T10 (A9X)
MC7 BW Super T10 (A9X - Optional X ratio box)

See what I mean.

Food for thought.

Dr Terry

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Mike81973 Offline
#28 Posted : Thursday, 3 June 2010 3:22:54 AM(UTC)
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Thanks guys for your very informative comments.
You are right about the GMH letters being wrong, I had to get three for the XU-1 before I got the information required.
First they got the diff ratio wrong and unknown to me the build date, when I asked them to correct the diff information they still had the build date, so then I had to ask for that to be corrected with the next request.
Now I can correct my information on what is a M 21 also.

I have possibly the eariest Bathurst 73 broadcast sheet ( pre release model ) and it has the trans section blank and further on the code XU, as painted on the box, so you will be right about XU-1 boxes not being M21 this is just the closest matched box as regards gear size and strength and first gear ratio.

Thanks Mike

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HK1837 Offline
#29 Posted : Thursday, 3 June 2010 4:09:11 AM(UTC)
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GMH did use the same code for the same series of box with different ratios in other places other than M20. So the possibility of the XU-1 box being coded M20 isn't out of the question. M15 was used as the code for the all synchro aussie 3spd introduced in HK. This box existed in 2 x different ratio sets: HK-WB 6cyl and HG-WB V8 with a 3.07:1 1st gear, and the HT V8 version with a 2.48:1 1st gear. So the possibilty of the M20 coded aussie 4spd having 2 x ratio sets (3.05 1st and 2.54 1st) is not impossible, however a code was not necessary as the 2.54:1 version was unique to the XU-1 vehicle package.
So while I agree with Dr Terry's methodolgy of calling the box as he has to avoid confusion, again if you were to try to pigeon hole each aussie 4spd box into a code I reckon if you use the physical 3rd gear fitted to the box, that will give you the best fit. There are only 3 x 3rd gears used:

2813491 (M20), 2813492 (M21) and 2820696 (M22).

As the XU-1 box uses the 2813491 gear it would best fit as an M20.

The other 2 x homologation close ratio boxes on XU-1 use 2813492 so they are both M21, and the L34 box which is the same as one of the XU-1 homologation boxes (bar the input shaft length) is also M21.

Lastly, Mike there is no real strength difference between M20, M21 and M22. All the same. The XU-1 box is no closer to M21 than it is to M20 in actual different parts used. It differs from an M20 in cluster gear and input shaft only. It differs from an M21 in cluster gear and 3rd gear only. Maybe we should call it an M20.5 or M20 1/2!!!!


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silverJ Offline
#30 Posted : Thursday, 3 June 2010 5:25:51 AM(UTC)
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Sorry if I confused anything asking Mike about his reverse idler
as I've met & spoke to mike a few times & know he has an 899 & the
box he's discussing here.

Know what you mean about tags mistakes Byron, my XU1 build tag has
one & I've seen the same mistake on another XU1 built on the same
Adelaide around the same day. Musta been the work experience kid or
someone had a big night on the turps.

Think my GMH letter is "worded" correctly:
4 Speed Manual Transmission (With XU1)

You blokes are more able than me to research this type of thing but
theres a paragraph in the factory LJ workshop manual supplement thats
had me thinking on this M20/M21 issue. It reads as:
"The 4 speed transmission fitted to the GTR XU1 model is the same as
fitted to Holden 308 V8 models, except for a 1.25:1 3rd gear & a
shorter clutch shaft to adapt to the 6 cylinder engine".
Its the only factory literature I've seen relating to what an XU1
box is.

J
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HK1837 Offline
#31 Posted : Thursday, 3 June 2010 5:45:46 AM(UTC)
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J

That wording is a good despription of an XU1 box if you are talking ratios. If you were talking physical differences you could just as easy state: "The 4 speed transmission fitted to the GTR XU1 model is the same as fitted to a normal GTR except the cluster gear and input shaft are changed to adjust the ratios". At the end of the day an XU-1 box ratios might appear to make it closer to an M21, but the physical differences have it closer to a 6cyl M20. Doesn't matter anyway, i'm just glad someone has made repro input shafts and clusters for them so they can be rebuilt an used as intended!

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Mike81973 Offline
#32 Posted : Thursday, 3 June 2010 6:17:47 AM(UTC)
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Hi Mike again,
Paul is right I not only have the late XU-1 box, but I have also have in rebuilt condition various other boxes as spares for my cars, these include M 20 6cyl, M20 V8, M21 V8, XU-1, 6cyl V8 ratio third & M22 6cyl.
I have also built up a M22 V8 at one time also, so I have seen most of the combinations.

As to a XU-1 box being closer to a M 20, sorry we must agree to disagree as I will never agree with your supposition.

One the main areas that blow under severe conditions are the teeth between the front input shaft and the cluster gear.
The M22 is the weakest here having a greater helix angle and smaller tooth root diameter and attachment and this will be the reason that Holden never built a M22 all Aussie for a V8, they just do not last.
M22 use the same input shaft as the three speed box of the same years.

The next strongest box is the M20 as the end thrust created by the reduced Helix angle of the input shaft is less and this combined with a greater diameter input shaft gear helps spread the load better, consequently lasting longer.

The strongest box is the M21 this is why Holden put them and derivatives behind the highest performing vechicles.
while the input shaft still has 19 teeth they are thicker with thicker attatchments and probably a lesser helix angle again, but most importantly the input shaft gear diameter is the largest and this gives the greatest strength in this area.

While I completely agree with you about the XU-1 third gear being different to the V8, the XU-1 box is structually a variation of the V8 box, as indicated by Paul, in fact you can take a XU-1 front shaft and fit it straight into V8 box, this is what I did in one of the boxes previously mentioned above, and this is also the same combination I started to talk of in the 6cyl M21 in the 1 tonner.

I don't mean to critisize, but I am a first class machinist by trade having a knowlege of gear cutting and their weaknesses, so have a different perspective than most people.

Mike


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HK1837 Offline
#33 Posted : Thursday, 3 June 2010 8:21:58 AM(UTC)
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Mike

Fair enough on the M21 strength, although i've been building them for years too and see as many blown up M21's as I have M20's! M22 V8 wasn't needed as V8 had enough torque to drive M20. At the end of the day they are exactly the same boxes, and if the M21 gets a bit more strength due to it's slightly different teeth well it certainly needed it behind cars like the L34!

I think you'll find though that the XU-1 6cyl is an M20 structure ie it uses the same main shaft assembly as the M20 complete with all gears, synchros etc. It is just the cluster and input that differ to adjust the ratios. An M21 main shaft assembly uses a different 3rd gear (actual part not ratio), hence it has a different cluster gear to an XU-1, and can only be used with an XU-1 input shaft if you use an M21 cluster - which is what you describe you had done previously. Also if you look closely at early parts catalogues, the M21 boxes also used a different reverse gear, and this gear isn't listed in the LJ catalogue. Not sure exactly what is different, but it is different for some reason. I've been meaning to look closer at this difference is, so this will prompt me to do it. I still have 20 or so 4spds in the shed, and many are in bits!

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silverJ Offline
#34 Posted : Thursday, 3 June 2010 9:33:10 PM(UTC)
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What I posted earlier is about all I got, like I said, you blokes
combined have more examples to look at or books or trade skills &
knowledge than I got access to.

Yeah I'm glad the repro clusters are about too, my 899 had to be
replaced.
I'm also converting a M20 like Mike with M21 cluster, 3rd & a 544
input I have spare.

Have heard the reverse gear thing before, dont know if it helps but
I've ended up with 3 types of reverse gears. My XU1s box had a gear
with no anti lash groove, the M20 has a very deep slot for the
plastic bit & metal spring & have just turned up a NOS gear that has
a slot but not as deep as the M20.
Cant seem to get pics to work here but can Email it to you.

J
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#35 Posted : Friday, 4 June 2010 8:27:16 AM(UTC)
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Hi Guys.
I have not had a chance to really have a good solid read of the thread so far but on the subject of the
reverse gear change over.
I have wondered if it happened at the same time as the implement of the oil seal front input shafts.
From information given to me by S pack from GMH Torana.
The change to oil seal inputs happened at box serial number T536514
This was according to Bulletin No.171 Dated 17th April 1974.
The strange part of this is that from my collection of aussie box date and serial numbers
12 J 3 so 12 9 73 cast has a serial number of T535569.
So just prior to T536514 serial number but many months prior to the the date of the bulletin.

Just for interest the T535569 box is a 6cyl 3spd and it runs the slinger type input shaft.
Being a 3spd box I would be more likely to believe it is original still compared to most 4 spd boxs from the same era.

Jono .I have emailed you about the bits and pieces but your question about the difference in the actual case for the one piece reverse gear, which is pictured here


has got me thinking that if we can find a rough date as to when this case was introduced (More accurately when the last example of the early case was used) it will tell us that a split reverse could have been used on these but a one piece could not have been used before this date.
I hope that all makes sense.
Basically it would give a rough date as to when the earliest a one piece reverse would have been fitted.

HK1837 if you do go through your box's I would be greatly interested in any serial number and date codes you come across in your search and now thinking on this what is the latest of the early design cases you come across and the earliest of the later design cases.
Also if it is not too hard if you do get any date and serial numbers around the mid 1971 era if they are the early smooth case type or the ribbed case type.
Cheers Paul.


Edited by user Friday, 4 June 2010 8:33:32 AM(UTC)  | Reason: Not specified
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#36 Posted : Monday, 16 December 2019 8:10:56 PM(UTC)
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Originally Posted by: Mike81973 Go to Quoted Post
Hi Mike again,
Paul is right I not only have the late XU-1 box, but I have also have in rebuilt condition various other boxes as spares for my cars, these include M 20 6cyl, M20 V8, M21 V8, XU-1, 6cyl V8 ratio third & M22 6cyl.
I have also built up a M22 V8 at one time also, so I have seen most of the combinations.

As to a XU-1 box being closer to a M 20, sorry we must agree to disagree as I will never agree with your supposition.

One the main areas that blow under severe conditions are the teeth between the front input shaft and the cluster gear.
The M22 is the weakest here having a greater helix angle and smaller tooth root diameter and attachment and this will be the reason that Holden never built a M22 all Aussie for a V8, they just do not last.
M22 use the same input shaft as the three speed box of the same years.

The next strongest box is the M20 as the end thrust created by the reduced Helix angle of the input shaft is less and this combined with a greater diameter input shaft gear helps spread the load better, consequently lasting longer.

The strongest box is the M21 this is why Holden put them and derivatives behind the highest performing vechicles.
while the input shaft still has 19 teeth they are thicker with thicker attatchments and probably a lesser helix angle again, but most importantly the input shaft gear diameter is the largest and this gives the greatest strength in this area.

While I completely agree with you about the XU-1 third gear being different to the V8, the XU-1 box is structually a variation of the V8 box, as indicated by Paul, in fact you can take a XU-1 front shaft and fit it straight into V8 box, this is what I did in one of the boxes previously mentioned above, and this is also the same combination I started to talk of in the 6cyl M21 in the 1 tonner.

I don't mean to critisize, but I am a first class machinist by trade having a knowlege of gear cutting and their weaknesses, so have a different perspective than most people.

Mike


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thread dig... sorry
but one that needs one last piece of info to add to all the above
(which is basically correct on all counts)

the issue that is part of the cause of broken boxes ....
usually teeth off the front of the cluster and/or the input gear
is the design of the gearbox itself.

drop the clutch on any of the Holden M series boxes (even the 3 speed)
and the force is transmitted thru the input shaft to the cluster .. which
moves rearwards. Gear teeth go fractionally out of mesh due to the
clearance inherent in the design allowing the counter shaft to move
rearwards and you lose a tooth (off it or the input gear)

This issue is worse on boxes with high mileage due to wear on the
counter shaft 'dimpled' washer... allowing the cluster gear to move
backwards (in some cases i have seen) by up to 2mm

Goodbye gearbox.... :(

Edited by user Monday, 16 December 2019 8:11:46 PM(UTC)  | Reason: Not specified

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