Tampering with the Jaeger Speedo/Tacho
Assuming your tacho is reading
correct, just cruse along at 2.000 revs in 5th gear and see if
you need to increase or decrease the speedometer. When you
have verified the discrepancy, go back to you garage and
remove your speedo. There are two nuts to undo at the back of
the instrument before you take the whole Jaeger unit out from
the dash. OH, the early original
Jaeger tacho has the trip km above
the needle and the total under. Later Jaeger tachos had the
total over the needle and the trip below. So you know if it is
This is how I do it. The procedure is
for the Jaeger instruments, common on AR Spiders. I have
however not tried this on Veglia Borlettis, but I know
that they are very similar. Here is a good Pdf file about how
to do it, a general description but very useful.
Take a thin bladed knife and carefully
press around the rear where the ring is crimped to seal. An
ordinary screw driver will do too. Do not press too hard, 'cuz
you do not want to stress the glass and crack it, oh no. Once
the ring is pried far enough all around, the ring and glass
will come off. Here's a photo of a dismantled speedo.
Now comes the tricky part. Use a small
screwdriver and undo the screw holding the reset cable. This
goes for the old Jaeger speedometer, used on Duettos and early
1750 Veloces, pre 1968. Use some detergent if the screw is
stuck. On later Jaeger speedos there is no screw, they made
some improvements. If you pull your reset knob, you have a
screw, if you press you have the "modern" type
without. Good. You need to remove the reset cable arrangement,
otherwise you won't get access to adjust the mechanism.
Time to get the mechanism out. Remove
the two screws supporting the mechanism to the case and remove
the unit. Be careful and work with clean hands so you don't
end up with fingerprints for the F.B.I. all over the gauge. It
is amazing how the sun makes every spot so visible.
Go out in the kitchen, yes, in the
kitchen, and borrow a suitable electric whisk. I got my hands
on one with two beaters, one of them was reversing. You may
also use any electric motor as long as it has constant revs
and is reversing. Attach a flexible cable or hose between the
motor and the speedo cable connection.
Place the speedo in a vice grip or
have your 'spouse to hold it firm and start the motor. Check
the speed at the certain rev and remember it.
Now, time to calibrate.
There is a screw, red arrow, to the left of the reset-cable
connection. If you turn it clock-wise, speed increases and
anti-clockwise the speed will decrease. The picture shows the
mechanism taken out from the housing. You don't have to do
that, this is just to make it easier top understand. This is
how it works:
I used a regular fork and a pice of
thick paper to remover the needle. Be careful and place the
fork where you have support from the mechanism. The screen is
made of rather weak aluminium.
This photo shows a rev counter andd
. . . and some of my speedos,
they are all Jaeger The one with two warning lights,
Generatore and RFiscaldatore is from a "Bertone".
They are the same except for the warning lights. The Duetto
had only one, Riscaldatore. Nobody will notice anyway. The
Jaeger in the photo has the total above the needle, that means
it is a later Jaeger.
This is my Jaeger tacho in my
Duetto. 2018 March 15. Nice You may see that the trip odo is
above the needle, this is a very original and old Jaeger on my
I have LED bulbs to illuminate my
Jaeger gauges. Nice.
The crimping of the bearing supports
the tachometer (rev counter) needle.
This adjusts the distance of the aluminium disk from the
spinning magnet and hence the force by the eddy current.
As the bearing wears (or slips on the
shaft), the distance decreases, more torque, higher reading.
When the distance increases, less torque, lower reading
Start your electrical whisk at the
same revs and check the speed. Then re-adjust the screw until
you're satisfied. My first Jaeger started reading 55 kph and
after two turns on the screw it was reading 40 kph. The second
Jaeger started at 50 kph and needed one turn to drop to 40
kph, so you may need to do it by trial-and-error.
Since I had my instruments apart, I
drilled a hole in the case to get easier access to the
adjusting screw. Do not use the drill unless the instrument is
Reassembly is the reverse of removal.
Now it's time to put the speed back
again. Do not waist your time at this stage, just connect the
cable to the instrument, start the engine and make a test
drive. If everything is OK, then connect the wiring etc. and
tighten the nuts. If the reading is still inaccurate, do it
all over again.