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O/D Woes ...Help

Darren Sharp

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Hi All I am having a massive O/D headache with OlaF my Mk 2 2500 Saloon. The Symptoms were a gradual loss of O/D over about 4 months with occasional trouble free eureka drives when it worked . I tried all the usual remedies involving Oil level and electrical gremlins but I have continuity at all the joins and everything is coming up as normal on the voltmeter. At this point I decided to check the filter and the oil was sieved out to check for metal . It was spotless so it was cleaned up and returned to its proper place. Despite this I persuaded myself that the Solenoid was most likely the problem and bit the bullet .... Wrong ! In desperation I rigged up a direct supply via a separate switch and hey presto! Instant overdrive whilst being carefully driven round the block. It was about now that I noticed that when the jury rigged connection was manually removed with the system live (Ignition on. O/D Switch on in 3rd or fourth) that there was an almighty spark ( it was dark by now) and I could also hear the solenoid engage. This does not happen when the system is returned to its correct wiring although the meter shows the same voltage at the solenoid as when its wired direct to live. Further investigation of the torturous wiring with most of the centre console and big rubber bung removed revealed that if I bypassed the inhibitor on top of the gearbox by removing and joining the wires then I enjoyed the big spark phenomenon again ( It was very dark now ). Am I on the right track please because I will have to drop the cross member to change the Damn switch as I do not have access to a double jointed midget!

Thank you

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UNdoubtedly a high resistance somewhere that is preventing enough current passing.

A type or J-type?

Is there a relay fitted?

If J-type and no relay then it could be just about anything, including the actual contacts of the gearlever switch or inhibitor switch.
If there is a relay (J type or A type) and the relay itself pulls in, then it has to be something in the power circuit (not switches just mentioned which are in the relay coil circuit) and could be the relay itself.


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its not uncommon for the contacts inside the inhibitor switch to be green and past it,  whilst is invisible its worth a check if you can get it out,  uncrimp the sa141 base plastic and all will be revealed ,  
you could try  to google a double jointed midget  ??

   on mine it had a mind of its own, that was a jammed lack of use solenoid piston   no sparks just did what it wanted with no controll just in out all by its self.
    just remove the circlip inside the end of the sol and extract the plunger , clean and replace,



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I have found the swtiches to be absolute rubbish, mine was buggered so i brought a brand new one from rimmer bros. It was getting so hot it was making the gearstick almost too hot to touch!!!! so yea big resistance there. I have my own new wiring harness with relay, changed the swtich and boom, all good. From what i have found with the headaches on mine is 99% of the troubles you will have with O/D are electrical.

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Greeks wrote:
I gave up with the original-style switch - too prone to breaking. Got one of these instead:


IIRC young Bancroft has one too

I now have one of these on Gertie as well.

It should be known though that these wont screw straight on to a Mk1 or Mk2 saloon gearstick. The Mk1 thread is 5/16th UNC, and this gearnob has a 3/8ths UNC thread. I had to find a 3/8 UNC bolt with a long shank and then had it welded onto Gertie's original gearstick.  :)

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Also agree with Greeks, never had much success with the original switch. Have replaced them on 2 cars with one in pic. Nice bullet proof Hella switch powering a relay, in turn powering the J type solenoid. No more problems. The S that I'm playing with at present has the original switch, o/d wasn't working when I drove her home but will reserve my judgement until I check the rest of it .This switch works across an ohm meter but terminals were loose on switch.

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Yes, Radders, had to tap it to fit. And also a smear of silicon on the cap stopped it from vibrating.

Weird that people get hot knobs, though. Mine stays as cool as a cucumber even on hot Austalian days... and don't just take my word for it, my wife's never complained.


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