Hi Manuel, welcome back.
The overdrive circuit on your BN1 is somewhat more complex that that used in
the later cars. It uses 2 relays, a throttle switch, a centrifugal switch, a
top gear switch, an overdrive solenoid and a manual dash switch.
To identify exactly what the problem is I think you will have to do some
more diagnosis.
First I would check that power to the operating solenoid, on the overdrive
unit is actually being interrupted when the overdrive disengages. Overdrive
units with low oil pressure can produce symptoms similar to those you
describe so you need to determine if the problem is with the unit itself or
with its controls.
To save you the trouble of removing the tunnel a preliminary test can be
done by connecting a test light between the C2 terminal of either relay and
ground (these relays are above the driver's knees). If the light goes out
when the overdrive kicks out the fault is with the control circuit. If it
does not the fault is most likely internal (you actually need to test at the
solenoid if this is the case just to ensure that there is not a poor
connection between the relays and the solenoid).
If the light does go out the fault is in the control circuit.
Because the fault appears to be both speed and throttle switch position
sensitive I would start by first installing a jumper on the throttle switch
to see if that makes the problem go away.
If that changes things I would suspect the throttle position switch is
incorrectly adjusted. (The clamp on the arm can slip and cause this).
If jumpering the throttle switch makes no difference you can remove the
jumper from the throttle switch and fit it between the two terminals of the
centrifugal switch (you have to remove the tunnel to do this).
If this resolves the problem the centrifugal switch is misbehaving (many
BN1s run around with this switch bypassed but, with much patience and access
to a variable speed drive system for set up they can be repaired).
Hope that helps.
Michael Salter
100S (1955)
3000 Mk111(1965)
100 (1953)
AHX12 (1953)
Bugeye (1961)
http://www.netbug.net/blogmichael/
-----Original Message-----
From: owner-healeys@autox.team.net [mailto:owner-healeys@autox.team.net] On
Behalf Of Manuel Formosinho Sanchez
Sent: June 8, 2007 8:23 AM
To: healeys@autox.team.net
Subject: 100 BN1 overdrive problem
Hi everybody I have been absent from the list for some time but here I am
again and as usual I need your help. My overdrive has some unexpected
reactions that I will try to explain the best I can:
I am running with the overdrive engaged at around 75 mph, the OD switch is
on,
now I press the accelerator full throttle and at this moment the OD
disengages
(OD switch still on), I lower the speed and the OD engages automatically.
This
has never happened to me before and I believ that it is not normal. Any
ideas
how to fix it?
Thanks
Manuel Sanchez
55 BN1
58 Sprite
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