What's the BUZZ from the overdrive solenoid

[BrianN]

When the dash switch is closed and the gearbox switch closes, the OD solenoid buzzes and does not actuate the OD. Then when the dash switch is opened (turned off), the condition remains the same, the solenoid still buzzes when the gearbox switch is closed.

Do I have:

A. A bad solenoid internal switch or low power holding coil is not functioning properly?

B. A bad throttle relay? (Seems to work OK. Cuts out the buzz when the dash switch is opened and the throttle actuated sufficiently).

C. A bad overdrive relay?

D. A solenoid adjustment issue?

Has anyone else encountered this problem?

 

[Ed_K]

Hi Brian,
It sounds like either the solenoid is out of adjustment or something has changed inside of the o/drive and the plunger can no longer reach the end of it's travel because of a mechanical bind of some kind.
If the solenoid adjustment arm is loose, then a solenoid and operating valve lift check/adjustment are what you need to do.
... But it is possible that the buzzing is just the result of not enough current available to actuate the solenoid. Some electrical checks are in order for the circuit down to the solenoid. If it checks out OK electrically, then do the solenoid and operating valve lift adjustments.
Ed

 

[Healey 100]

I experienced severe buzzing in my solenoid when the holding coil opened up. The solenoid would actuate on the pull-in coil but when it reached the end of its stroke and switch to the holding coil it would fall back to the off position. Then it would reacactivate, the whole thing buzzed like a cheap doorbell. I could hear it inside the car with the transmission cover on. The OD would not engage either.

The only cure for that problem was a new solenoid.

There may be some buzzing from the holding coil if the pull-in coil fails to energize fully, due to dirty contacts on that reed switch. This is a very common problem with these solenoids, sometimes you can get them going again by cleaning or filing that little reed switch under the top cover.

A poor ground can also weaken the pull-in coil so it can't lift the plunger off the bottom. The pull-in coil is very low resistance, just a fraction of an ohm -- so it does not take much resistance from a poor ground or dirty connectors to really weaken it.

Good luck
Bill

 

[Ed_K]

Brian,
A quick check to see if you have a electrical problem with the solenoid, 3/4 switch, ground connection, and the interconnecting wiring;
Disconnect the wire from the overdrive relay that goes to the 3/4 switch then on to the solenoid. I don't have a wiring diagram handy but you should be able to find it.
Attach a lead of your ohm meter to that wire.
Attach the other lead to engine ground.
You should see around 6 ohms or less when your shift level is in 3rd or 4th gear.
If you see more than 12.5 ohms, then either the pick coil of the solenoid is not in the circuit ( open coil or the internal switch contacts in the solenoid are not making ) or the 3/4 switch contacts are getting so bad that it is only working marginally. In any case if you measure more than 12.5 ohms from that disconnected wire to engine ground then you will have to ohm out everything in the path. As Bill said, The solenoid should be around .5 ohms if you check it alone out of the circuit. If it is above 12.5 ohms then either the pick coil has burnt open or the internal switch contact is not making for
some reason. If the solenoid is above 12.5 ohms while still installed on the o/drive but if removed shows the correct .5 ohms then something is preventing the solenoid plunger from moving all the way down to the bottom rest.
One other quick check is to put one lead of your ohm meter on the little ground wire to the RELAY on the firewall. Put the other lead on the engine( a nut without any paint or rust). If you don't see close to zero ohms, then you have a poor ground connection from your engine to your overdrive relay. On a BJ8, it is a screw on the firewall that has several black wires under it, with a star washer between the bottom wire and the firewall. The paint should be scraped off of the firewall under that washer, ( not something folks want to do after painting the car to perfection but necessary for a good ground )!
Lets us know what you find .
Ed