Yes, you are right. I had meant, I thought the TR6 speedos were always 1000
with the J-type. I was not positive if they had differing drive gears for
the A-types or not. On the earlier cars with the A-types, the drive ratio
was always the same (10:15, I think).
I have not torn down a J-type my self, and it has been a few years since I
did my A-type. At least on the A-type, I thought the speedo drive gear was
able to be removed from the outside (MUST be removed from the outside) in
order to dismantle the OD. Also, on the A-type, there is a scroll (10
lands, I think) on the OD output shaft to turn the speedo drive gear, and
this is not able to be altered (at least without exchanging the entire
part). I presume that there were different OD drive gears than the
"standard", whatever that was (15 teeth, I think).
Were there different speedo drive gears ("driven gear", as you more properly
called it), or were they always the same? I'd have thought it would be
easier to change these plastic doodads from the outside and keep the same
scroll on the "drive gear". (it would also allow a slightly finer ability
to alter the ratio. I presume that since the adjustment is SO coarse when
altering only ONE of the gears that they BOTH must have been able to be
altered....
-Tony
----- Original Message -----
From: "Randall Young" <ryoung@navcomtech.com>
To: "Anthony Rhodes" <spamiam@comcast.net>
Sent: Friday, June 11, 2004 8:13 PM
Subject: RE: Speedometer error with overdrive
> > For some reason I thought that all the TR6 speedos had the same
> > calibration:
> > 1000.
>
> Nope, early TR6 worked just like the earlier TRs, the drive ratio in the
> tranny was fixed and the speedo head was changed to match tire size &
drive
> ratio.
>
> Not sure of the exact change point offhand, but it was about the same time
> as they switched to J-type instead of A-type ... the drive gear in the
> J-type is removable, unlike the A-type that has it machined into the
output
> shaft/annulus.
>
> However, I'm pretty sure that John has managed to buy a J-type OD that
came
> from another car. There have been quite a few sellers around (including
> Rimmers) selling ODs from other cars as fitting TR6 ... but generally
those
> other cars used different drive ratios. The problem can be fixed by
> swapping the drive and/or driven gears ... but usually the drive gear is
> wrong & it takes a complete tear-down to fix it.
>
> Randall
|