Hi Tim
On the early Rootes products the speedo drive gear can be easily removed, it
is retained by two small bolts and just slides out, changing the other gear
on the gearbox output shaft requires a the gearbox to be dismantled.I
haven't got a later series gearbox to look at but feel that it should be
fairly similar.
I would be very surprised if the hard nosed Rootes brothers had different
speedo specs between overdrive and non overdrive cars.
So if the tyre size and rear end ratio is the same the logical assumption is
that the gears fitted to your overdrive are compatible.
If your roads authorities don't mark out speedo check distances on a highway
near you there is another alternative :-))
Mark a rear tyre where it touches the ground and roll it forward till it
completes about ten revelutions. Measure this distance as accurately as you
can. By measuring over ten turns the errors are minimised. This will give
the distance travelled per wheel revolution. Divide this into your main
distance, I guess miles in USA, using the same units(ie inches or feet) to
give wheel revs per mile. Multiply this by the rear end ratio, 3.89 is
common one in Rootes products, and you have engine revs per mile. Some easy
non calculator math :-)) that figure is rpm at 60mph ( 1 mile per minute
:-))
Often these figures are in the workshop manual, but remember they are
accurate only when using the original specification wheels and tyres.If it
is easier take the wheel off the car and just roll it along the sidewalk,
but in this case without the weight of the car on it the distance will be
slightly in error (longer) but should still give you a working idea.
If you are still afflicted with that cold wet stuff on the ground you can
put the rear axle up on stands start the engine (it is a good idea to open
the garage door first :-)) engage top gear and run the engine up to rpm that
indicate say 60mph and compare speedo and rev counter. If you don't feel
comfortable running the car that fast on stands you can use lower rpm and
work out the correct speedo indication. I am quite concerned about my own
safety when pulling this little trick and tend to not only chock the front
wheels securely but also nudge the front bumper against an old tyre on the
garage wall to prevent unplanned movement of said car.
I use this little trick to track down driveline vibrations as it is a little
tricky to crawl under the car when driving down the road.
Had a look at your original message from your Northern location I would say
you are still waiting for the big thaw :-)) So being able to check this
without braving the stuff your road maintenance people throw about during
the winter is probably a better option :-)))
Had my Hillman out to an all makes gathering at Cleveland yesterday
(Cleveland Queensland that is :-)) Lots of hot rods and big USA cars only a
few Rootesmobiles. apart from my Californian an Alpine, Hillman Hunter and a
1964 Vogue. Best car of the show was a very nice Triumph 1800 roadster of
early fifties vintage. Forgot to put on the sunblock so have a slight red
hue today :-))
Keith
55 Californian
Original Message -----
From: "Tim Stiffy" <tstiffy@pulsenet.com>
To: "Alkon" <alkon@bigpond.com.au>
Sent: Monday, February 10, 2003 5:16 AM
Subject: Re: Overdrive Speedometers
> Thanks Keith. I'll wait until the weather warms up a little and try your
> test. How hard is it to change the overdrive gears?
>
> Tim
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