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Austin-Healey 100 BN1 Gears

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G'day all,
Is there a 100 specialist among us who can help with my rather obscure enquiry?
I have two used 100 BN1 type cluster gears, one bears part number 1B-3693 & the other is 1B-3694-JBE. Both these items have the same helical angle on the third speed gear (‘third’ of course being ‘second’ in the BN1 application). Among my collection of odds & ends I found another cluster (with several teeth broken off the ‘third’ gear) which has a different helical angle. The latter item bears the part number 1B3474.
According to Clausager's “Original Austin-Healey” a note on page 45 lists ‘Other mechanical changes’ (at the end of the list of 'production changes - by engine number') and states that: "From gearbox number 5146 (in Mar 1954?) a modified third speed mainshaft with larger and stronger gear teeth was fitted."
Anderson & Moment’s 'Restoration Guide' doesn't make a reference to this change.
Does anybody know which part number came first? Can we assume that 1B3474, being the lower number came from a pre 5146 gearbox? I am trying to figure out if my 100 has the strengthened gears.
My 100 BN1 was built in mid July, 1954 and I have tried unsuccessfully to find a gearbox number. I acquired the cluster with part number 1B3474 when I bought another BN1 that had been dismantled since 1971. The odd thing is that the chassis number is 20 or so cars later than my first BN1 and I believe that cluster gear number 1B3474 was originally fitted to this car, whereas 1B-3693 came out of my first car's gearbox.
It would seem to indicate that the change of specification came in July ’54, not March as suggested by Clausager.
Sorry if I have rambled a bit but I did say it was an obscure enquiry!
Cheers,
Alwyn
 
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That's pretty obscure, for sure. Michael Salter is restoring--I think--a very early BN1 and has been doing a lot of research: https://www.netbug.net/blogmichael/?page_id=54

He lives in Canada now, but is a Kiwi. He just came up with a BN2 second gear for another forum member.

OK, just found out the other member found a gear at a lower price from: https://www.britishcarpartsbyleo.com/ No personal interest--and this site is new to me--but the other member said he is very knowledgeable.
 
Whether March or July of 1954 is the change date the "third" gear cluster in my car--BN1L222333 built in December 1954--broke when I guess I made one too many upshifts. At the time I was in Lompoc, CA on my way to visit my children in LA after having attended Conclave in Tahoe. I didn't feel that nursing the car home to MD with only 1st and 3rd was a wonderful option and I had no time to spend searching for a replacement part or transmission so I contacted Smith Brodie and wound up with a Toyota 5-speed.

I have never looked back.
 
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Michael Oritt said:
Whether Mary or July of 1954 is the change date the "third" gear cluster in my car--BN1L222333 built in December 1954--broke when I guess I made one too many upshifts. At the time I was in Lompoc, CA on my way to visit my children in LA after having attended Conclave in Tahoe. I didn't feel that nursing the car home to MD with only 1st and 3rd was a wonderful option and I had no time to spend searching for a replacement part or transmission so I contacted Smith Brodie and wound up with a Toyota 5-speed.

I have never looked back.
Click to expand...
. Michael, just out of curiosity, has your fuel mileage noticeably improved since making the change to the Toyota conversation with the different gear box ratios? Thank you.
 
I don't know but doubt there would be any significant difference. 5th gear on the Toyota is an overdrive and probably not very different in ratio than that of the 3rd OD on the original transmission.

I also have a 3.5 Lempert diff installed and at 3000 rpms in 5th with 180 tires I am turning right at 70 mph. My usual highway mileage is 24-25, perhaps 1 mpg better on an interstate with sustained speeds.
 
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Thank you for sharing the information Michael, I will keep it in my memory bank if I decide to do a conversation someday. Always nice to compare notes and apply improvements to my next build.
 
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