T120 Speedo Gearbox Drive

[andyw1260]

Hello all and a very happy biking new year to all & one.
 
Can someone enlighting me as the correct speedo drive ratio for a 68 T120 British MPH.
 TMS told me in the summer 1.25 to 1 yet they now say 15/12 sounds the same but is it they sell both ratio's I feel independant advise would be best.
 I would also like to know if a BSA speedo drive of the same era would do  Ref  BG5330/168 which is also a 15/12 Ratio.
My Speedo is a SSM 5001/06 1000  correct for the year.

        Thanks  Andy West

[L.A.B.]

15/12 is just another way of saying 1.25:1 (15 divided by 12 = 1.25).  

[TBS]

speedo / gearbox ratio drives to remember
speedo ending in 1000      15:12
speedo ending in 1600         2:1

[L.A.B.]

I cannot say for sure, but I think from what info. I can find, that the BG5330/168 drive box would be correct for '68 Triumphs as well.


 
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Addition


The '68 factory parts book shows the same unit used for both standard and QD wheels (part D637).

But the Len Craig 650 Triumph parts list shows the QD wheel to have a '164' drive, and the standard wheel drive is shown as '168', so you may have to investigate further, as I believe you have the QD type wheel?  

[TBS]

The difference between the QD and Non QD wheel speedo drive is the size of the spindle hole. On the Non QD it is large to accommodate the thicker spindle, whilst the QD drive has a small hole (which if necessary can be re-sized on a lathe).

[andyw1260]

Thanks LAB & TBS for a prompt reply, Ive only been into classic bikes for 6 months after 40 years biking (bought up in the Jap age just,  most girls did not like going on the back of british bikes then).
  Yes you are right I have a QD wheel, when I first got the bike from the  Essex restorer!!  I noticed the speedo was 25 MPH to fast at 30 MPH, I have just dug the drive out of the garage and seen it is a 2.1 which has BG5330/24 stamped on it, the centre has been filed out badly so you are correct in thinking there are different sizes, I did tell the restorer at the time but he said he could not understand it! literally I think.  

I have a Repro 1.25/1 in it now which is ok but I am after a Smiths stamped Drive and I got confused by all the numbers, it dont take much.
This restorer lark is a joke maybe they should be BSI or ISO or have a customer satisfaction score.
Thanks again and the top of the year to you both.

                             Andy West