Overdrive Oddness

[Mj17]

The longer I spend with the big blue sofa the more it confuses me!

It's a '72 MG... Mk2 2.5PI so should have left the factory (if optioned) with a J-type overdrive if I understand things correctly - and a J-type doesn't need a relay in the overdrive circuit because of the electro-hydraulic solenoid (unlike the A-type).

In which case - why does my car have it's J-type wired up via a relay?


Currently the O/D works now and then but I get intermitten and franetic clicking from the relay.  Sometimes this trips the O/D in and out.

I'm guessing the relay is on it's way out and breaking/remaking the connection.  Sometimes this happens so quickly the O/D doesn't actually loose oil pressure and disengage, other times it is off long enough for the car to lurch out/back in to O/D.

But how to fix it...

Replace the relay (that it doesn't need) or cut the relay out of the circuit?

[Russell]

My '72 2000 has an A-type overdrive, so an A-type for your '72 PI might be normal. The '74 2500TC I had, was a J-Type.

Your problem definitely sounds electrical though. Could be something simple like a loose spade on the inhibitor switch.

Russell.

[andy thompson]

Most 72 cars seem to have A Types originally... but things are pretty random especially after 30+ years of fitting S/H spares... if you have the Relay wiring but a J Type.. i'd bet it was originally an A Type... I have a Dec 72 Stag with J Type but my brother had one a few weeks older and it had a A Type....

L reg is the transition though... never seen a A Type M- Reg and never seen a J type K -reg of any variation 2000 or Stag

Oh yeah... if you have a J Type just by-pass the relay......