Hi Randall
I realise this was the case, but I thought it would be possible to work
back, the cars I generally deal with are the six cylinder saloons, and I
know these are the same, in that they seem to use the different heads and
same gears before a date, and 1000 turns calibration and different gears
after that date. They make life easy by stamping the number of starts for
the drive spiral of the speedo on the rear of the o/d housing, using this
and the pinion you can work out the ratio then having the difference between
the 3.7 and 4.1 you can work out the number of teeth required, If I remember
right I couldn't get close using the original spiral (6 starts) as there was
not a suitably toothed pinion so I had to go to a 5 start spiral to get the
ratio right. I think the same could be done on the straight 4 speed boxes
using gears from later cars if the boxes are similar, this is where my
knowledge of the problem breaks down as I don't know if the 4A used a box
common to other models.
Also, ORS referred to in my last message is Overdrive Repair Services,
http://www.overdrive-repairs.co.uk they carry most bits for the
overdrives, I just fitted a very comprehensive O ring kit from them in my J
type od.
Graham.
----- Original Message -----
From: "Randall" <randallyoung@earthlink.net>
Cc: "Triumph List" <triumphs@autox.team.net>
Sent: Saturday, October 27, 2001 8:23 PM
Subject: Re: Speedometer Calibration
| A word of clarification might be in order here. Until sometime in the
| 1970's, the TR series of cars all used the same speedo drive pinion gear
| in the transmission. Differences in final drive ratio and tire size
| were accomodated by different speedometer heads. So, a 4.1 TR4A had
| exactly the same pinion as a 3.7, only the speedo head changed.
|
| There is a 4-digit calibration number (in cable turns/mile) printed on
| the face that distinguishes, it's typically around 1180 for 3.7 gears,
| and 1350 for 4.1 gears. Sometime mid-TR6 production, that changed, and
| later TR6 all used a speedo head calibrated to 1000 turns/mile; with the
| drive pinion altered to suit tires/ratios. I'm not sure how, or if,
| this applies to other S-T cars (or TR7/8).
|
| Randall
|
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