Hi Bud,
Those numbers look fishy. 4th gear should be 1:1, e.g. turning the input shaft
one turn should yield one turn of motion at the output flange. The lower gears
would turn the output flange less than one turn. A 1.33:1 overall third gear
ratio would see the output flange turn 3/4 of a turn per one turn on the input
shaft. Similarly, a 1.75:1 2nd gear would result in slightly more than half a
turn (.57 to be exact) of the output flange per turn of the input shaft. Note
that 1.33 and 1.75 are random numbers shown to illustrate and not actual gear
ratios. I think the GT6 used 1.78 and 1.25 for 2nd and 3rd. At least the Mk3 GT
had those ratios.
What you reported seems to be the opposite of my example.
It is possible that you are seeing some sort of "sticktion" where gooey oil in
the gearbox is coming into play. But the key is that 4th should always be 1:1
unless there's an overdrive and that O/D is engaged.
But the only way to know for sure of what the ratios are is to count teeth and
"do the math".
Can you remove the top cover and count the teeth on any of the gears on the
main shaft? That should make it easier to identify what gear clusters are in
there. You probably only need to count the teeth on the main shaft but I know
squat about GT6 gearbox internals other than they are more Spitfire-like than
TR-like so the lay shaft gear ratios may be fixed? as they are on the Spitfire.
The point being that there are only so many ratios available that would? fit in
the gearbox, so it should be fairly easy to figure out what you have there.
Regards,Bob Lang
On Wednesday, January 10, 2018 9:09 PM, Bud R via Fot <fot at
autox.team.net> wrote:
Listerati,
I?ve been trying to figure out what gear ratios I have in the gearbox that came
with my race car but don?t know how to? do the proper math. The PO told me it
was a close ratio GT6 gearbox but one never knows until you actual check.
I at least took some ?data? while it was out so I?m hoping someone can tell me
how to figure out the gear ratios and if it is indeed close ratio GT6 gears or
whatever it might be.
When the input shaft was turned one full rotation the output shaft turned the
following amount.
1st gear it turned 1/4 turn
2nd gear it? turned 1 1/8 turns
3rd gear it turned 1 5/8 turns
4th gear it turned 1 3/4 turns
Any help on how I should do the math is appreciated.
Also does anyone know what happened to the minty lamb gearspeed website? It
does not appear to be up any longer and I used to play with it a lot. Very
useful site that now appears gone.? Waaahhhh.
Thanks
Bud Rolofson
Extreme Parts Racing (more than just a haircut)
71TR6 CC57365 (Good 6)
71 Spitfire MK IV Race Car #3
69 Spitfire MK III (back up FE engine/dinghy car)
93 Minnie Winnie Race Support Vehicle
77 Z-50A Hardly Davidson Honda Mini-Trail Bike (Triumph Pit Bike)
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