45 replies to this topic

[hanra]

Is it possible to determine box type without dismantling?

Also, how do I read the date code??? Fitted to 10/75 SL/R 5000.

Box details are:

7433771

Ser #: T423745

Date: K52

Edited by hanra, 23 July 2011 - 10:34 AM.

[S pack]

Is it possible to determine box type without dismantling?

Also, how do I read the date code??? Fitted to 10/75 SL/R 5000.

Box details are:

7433771

Ser #: T423745

Date: K52

With the box out of the car select 1st gear and count how many turns of the input shaft for one turn of the output shaft.
M21 will be 2.54 turns input for 1 turn output.
M20 will be 3.05 turns input for 1 turn output.

[dattoman]

And also post a pic up of the imput shaft

[hanra]

Once its out of the car Ill check those things.

Looking at the date code thought would K stand for October? 5 stand for 75? And 2 stand for 2nd day?

My car has the original motor in it, Ive confirmed that. And being 10/75 build this box sounds like its about right to??

[S pack]

Once its out of the car Ill check those things.

Looking at the date code thought would K stand for October? 5 stand for 75? And 2 stand for 2nd day?

My car has the original motor in it, Ive confirmed that. And being 10/75 build this box sounds like its about right to??

Little bit unsure on that one.

K52 could be October 5th, 1972 or October 1975 2nd day.

Others with more knowledge of date codes on boxes cast in 1975 will probably be able to confirm.

[Collo]

There was a bloke collecting gearbox numbers on here a while ago. HQSS maybe? He'd probably know, if no one else chimes in.

Edited by slr_v8, 23 July 2011 - 09:48 PM.

[rodomo]

HQSS maybe?

http://www.gmh-torana.com.au/forums/topic/39701-aussie-3spd4spd-date-codes-and-serial-numbers/

[S pack]

Thanks for that link Rob.
Looks like cast date code K52 is October 5th, 1972; going by the research HQSS has done. Also Serial No. T423745 appears to be consistent with a 1972 cast date.

[hanra]

Yeah seems a bit of a shame that its not the original gear box.... 72 I guess would be HQ? Ill have to crack it open and see what gears its got inside... spewin...

[Collo]

HQ or LJ, depending if it's an M21 or M20. I don't think the LJ's had the M21.

[hanra]

Is there a means to identify it as M21 or M20 whilst still in the car?

[Shtstr]

With the car raised & 1st gear selected, mark the position of the tail shaft and turn the engine over by hand whilst counting the engine turns until the tail shaft has completed 1 turn.

Turn the engine over by the harmonic balance bolt.

You will need to be accurate!
M20 = 3.05:1
M21 = 2.54:1
M22 = 3.74:1 (stump pulling 1 Tonner)
L34 = 2.32:1

Have fun!

the last on your list first gear 2.32-1 is also listed as 73 box for xu1 aswell
He is a link to the gear ratio's
http://www.monaropar.../aussie4spd.htm

Edited by lcxu105, 26 July 2011 - 02:07 PM.

[hanra]

Doesnt M21 have 2 grooves on the front shaft ?

Are these the two grooves everyone speaks about??????

[warrenm]

That is the 2 grooves.

[yel327]

With the car raised & 1st gear selected, mark the position of the tail shaft and turn the engine over by hand whilst counting the engine turns until the tail shaft has completed 1 turn.

Turn the engine over by the harmonic balance bolt.

You will need to be accurate!
M20 = 3.05:1
M21 = 2.54:1
M22 = 3.74:1 (stump pulling 1 Tonner)
L34 = 2.32:1

Have fun!

That won't work all times. XU-1 M20 has 2.54:1 1st gear, and plenty of people now convert V8 M21 boxes into V8 versions of XU-1 M20.. Note also that M22 isn't just a 1-tonner box, it is the HQ commerical 4spd, also used on HJ-WB 1-tonner and optional on most 6cyl HQ.

[hanra]

This box I have has 2 grooves on input shaft, 1st is approx 2.5 turns to 1, 2nd is approx 1.8 turns to 1, 3rd is approx 1.4 turns to 1, 4th is 1 to 1.

However it's the date code on the case that makes things confusing..... It's dated October 5th 1972 via the cast code.... My car is October 1975. Could it be just a GMH stuff up???

72 would make it a 6cyl M21 with V8 input shaft??? Is that possible to do?

[yel327]

It won't be a 6cyl M21, the only cars that I know of that ever had one of these was the 6cyl VB Commodore rally cars. It will simply be a HQ M21 box out of a late 1972 HQ most likely a 308 but they were also optional on 253. The M21 has a 1.38:1 3rd gear which yours has.

Note that you can convert both the 6cyl M21 or an XU-1 M20 box to a V8 box by using a normal V8 M21 input shaft. 6cyl M21 was available for homologation purposes on XU-1 but I don't think anyone has come forward with proof of one ever being made. It was probably a special purpose only option like the HK-HT 12-bolt diff, which were not factory fitted but dealer (or race team) fitted after delivery.

[fuzzypumper]

So what do the 2 digit codes painted in yellow on the casings mean?

The 4 speed from my SLR has #7433771 T692006 11C5 TH ( yellow painted code on side and top of gearbox casing)
Th other spare gearbox I have is #7433771 T?????? 19F4 HC (yellow painted code on side and top of gearbox casing)

[S pack]

So what do the 2 digit codes painted in yellow on the casings mean?

The 4 speed from my SLR has #7433771 T692006 11C5 TH ( yellow painted code on side and top of gearbox casing)
Th other spare gearbox I have is #7433771 T?????? 19F4 HC (yellow painted code on side and top of gearbox casing)

The TH and HC codes stamped in yellow on the gearbox casings are production codes for the assembly line.
I have no idea which gearbox each of those codes specifically relate to but as an example: the HT code might have been used on all V8 M21 gearboxes and the HC code might have been used on all V8 M20 gearboxes.
So if the Production Broadcast Sheet for a car had HC in the square under G/Box then a HC coded gearbox would be installed.

Also, 7433771 is the part number for the bare gearbox side cover only, it does not identify the complete gearbox in any way, shape or form.

[yel327]

"72 would make it a 6cyl M21 with V8 input shaft??? Is that possible to do?"
Yes, that would make it a v8 m21, not sure if it has been clarified in this thread (it is in many others) but M20/M21 only relates to the gear ratios. You can interchange the input shafts from 6cyl to 8 cyl.

Open up the inspection cover and read the part # on the cluster, that will sort the M20/M21 issue.

This will help you

http://www.monaropar.../aussie4spd.htm

M20 and M21 don't even relate to the gear ratios. M20 means basically "the standard 4spd for the model" (at least up until mid 70's). That is why you see M20 on Geminis, and why the Opel 4sp in HK-HG is referred to as M20. The wide ratio Aussie 4spd was also M20 as it was the standard gearbox for the HQ commercials, GMH later changed this to M22 preumably when it became optional on other HQ's. M20 also refers to the XU-1 box, same reason as wide ratio box.
M21 is the high performance 4spd. In Aussie 4spd's, as well as the 308 4spd box M21 also refers to the close ratio box used on the L34 and optional on XU-1 with 2.32:1 1st gear. It also refers to the Saginaw 4spd introduced in HK around Monaro and GTS release which from memory was available on all engines except 161, standard behind 307 when 4spd standard or optioned and also standard when 4spd optioned on a ute or van. A wider ratio Saginaw (coded M22) was used with 6cyl in HT.