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MG MGB Technical - Overdrive on 2nd

When driving an MGB there always seems to be a bigger gap between 2nd and 3rd than on any other gear change. Many Triumph cars had overdrive on 2nd gear.

Has any one had experiance of modifying a B to use overdrive on 2nd?

Is it possible to do this without getting overdrive on 1st as well?

Clearly through relays triggered by the reversing light switch one can avoid overdrive on reverse.
David Witham

I've been using the reverse light to power a cutout relay on my B for over 20 years with no ill effects. As long as you don't overdo it in the lower gears, the od won't suffer any ill effects. I use od in 2nd all of the time and the only repairs needed over the 20 year span was a replacement of the od solenoid coil that was way past its prime. I wrote an article on this, in the early 90s, and it was well received. In fact, I've seen it posted many times on the internet, minus my name. RAY
rjm RAY

Thanks Ray. Any links to the article?
David Witham

The AMGBA should have it in their archives. I wrote it in '93. I might have a copy lying about, but it could take a while to locate. RAY
rjm RAY

Just love the idea of over drive on all forward gears. 8 gears!
I'm thinking it's a particularly good idea if you have a supercharger fitted that boosts the BHP. Non overdrive for lots of torque (sport mode) , switch in the overdrive on all gears for efficient driving.
The only risk is that you msut not engauge reverse in overdrive or you'll destroy it. Rays idea ensures this doesn't happen. very smart.
Peter Sherman

You would have to modify the linkage to give OD on 2nd but not 1st, similar to how the factory did it on V8s to give OD on 4th but not 3rd. Triumphs had OD on 2nd because they had a stronger unit, and the extra torque of the V8 was why they had to remove it from 3rd after warranty claims. OD 2nd on a 4-cylinder car is likely to suffer from the same problems if used exuberantly.

Simply using a relay with a normally made or a changeover contact would do the job electrically, but personally I would never rely on it as you are dependant on a relay plus wiring and connections *as well as* a switch to ensure OD is disabled in reverse. It *is* a bit of a big step from 2nd to 3rd, but I've only noticed it on hills, and I just rev higher in 2nd before changing up so it doesn't struggle in 3rd, or if steep enough simply hold it in 2nd at a slightly slower speed.
Paul Hunt 2010

Moderate driving has put no extra wear on my LH overdrive in the 20+ years that I have been running my bypass system. As Paul notes, putting the overdrive under a heavy load, in the the lower gears, will definitely shorten its life expectancy. I recently changed my od filter, for the first time since '98, and it was like it had been installed yesterday. There were no particles of metal in the sump either. I do not simply rely on a switch to prevent an accidental engagement in reverse. When I move the shift lever into the reverse gait, there is an audible click, from under the dash, indicating that the relay has opened the power circuit go to the overdrive solenoid coil. RAY
rjm RAY

Maybe Ok when you drive it, but we have our cars driven once a year by someone else!
Paul Hunt 2010

It doesn't answer the question, but as an alternative which avoids the big 2nd-3rd gap...

I have an electronic o/d switch that, once you drop to second automatically switches the o/d "off". So when changing back up from 2nd you go to "regular" 3rd, then hit o/d (or go to 4th and then o/d)
Michael Beswick

Same here, but I think the original question related to the rather large gap that is evident even when OD hasn't been engaged. OD being left on does make this even bigger, but the thing that used to bug me was the unexpected jolt when OD engaged shortly after changing up to 3rd, the struggling in OD 3rd having just changed up from 2nd, and another jolt when switching OD out again. After 15 years or more of this I built a circuit that locks OD out when changing out of an OD gear, until you manually turn the OD off and on again. This doesn't affect changing between 3rd and 4th, unless you allow the gear lever to move across to the 1/2 gate whilst in neutral.
Paul Hunt 2010

Yes OD coming in on its "own" on the up change from 2nd is a pain. My current B has OD on the stalk so it is much easier to flick it out quickly in those cases than my old B which had a dash switch.

Michael and Paul your switches sound quite clever.
David Witham

You can find details of mine at http://www.mgb-stuff.org.uk/wn_gearsframe.htm and click on 'Overdrive Sequencer Relay'.
Paul Hunt 2010

As I am not so confident with electronics, I bought mine! - Andy Capy advertises in EMG (June p87-(£17.00) (01582 832305)) Mine is mounted under the dash near the original o/d switch but I think he does one that mounts on the centre console just aft of the gear stick.
Michael Beswick

This thread was discussed between 10/06/2010 and 18/06/2010

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