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MG MGB Technical - over drive

hello ive had a problem with my over drive for a while ,its now stopped working ,can any one give me any ideas what to do to repair or fault find thanks daren
daren

The first check is to ensure that you haven't lost the 12v supply to the solenoid circuit. That happened on my TR6 but was easy to spot since the fuel and temperature gauges, which are fed from the same fuse, also ceased to indicate.

Good luck,

Barry

BJ Quartermaine

Daz
Yep, check for power at the solenoid before taking things apart.
If you have power take off the square plate - 4 bolts - and check the plunger inside the coil by applying 12 volts of power. There will be virtually no pressure on the plunger when power is supplied but it will be noticeable.
If this is ok check out the condition of the two "o" rings - one on the pointy end of the plunger and the other that sits in the top of the assembly that surrounds the solenoid coil. The assembly is cylindrical with a slot half way down the side and a plate on the top with a conical centre and an "o" ring in a recess around the cone on the flat of the plate.
The condition of these two rings is critical to the operation of the unit.
Also, ensure that you replace the tiny steel ball on the top of the plunger when you reassemble things.
Peter M
Peter M

Also check the oil level in the gearbox. If this has dropped then maybe there is not enough pressure. Does your car have the switch on the gear lever? It's common for the wiring to break there, a neigbour here had this with an LE GT
Stan Best

thanks my over drive is on the gear stick ,when you say check the solenoid is that at the gear box under the car .sould there be a supply to the solenoid only when it put in to over drive and can it be tested with out the engine running thanks daren
daren

In my many years of wrenching B's, as a gnarly geezer older than dirt, I've yet to see or hear of an MGB OD failure that is other than no oil or dirty oil/screen, or, usually,the solonoid/wiring.
Start at your shift switch. Betcha that's where it is on the switch poles having corroded where the 2 wires insert switch back. Luck though, and let us know. Vic
vem myers

Daren

You can check for voltage at the solenoid without the engine running. You need to be in fourth gear (due to the inhibit switch that precludes the OD engaging in first second and sometimes third) and have the ign switch on. Actuating the OD switch on the gear stick should result in a nominal 12 volts at the solenoid.

Barry
BJ Quartermaine

This thread was discussed between 09/07/2007 and 10/07/2007

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