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MG MGB Technical - Overdrive switch - move to gearlever

I am looking at moving my overdrive switch from the dash ( ‘73 BGT) to the gearlever using the Brown and Gammon silver overdrive gearknob. I think it is far more ergonomically natural for me to have the switch there and apart from that, I think they look great.

It will of course be suitably fused (it already is) given the slightly increased risk of damage to the cables.

I suspect it could be just a simple matter of attaching the White and Yellow wires on the dash switch to the red and black on the new switch? It looks like I can re-route them back into the engine bay and down the side of the loom that runs along the gearbox – I will put the cables in some temperature resistant sleeving which I am a bit of a fan of anyway.

Is that the best route or can I do the join nearer to the overdrive, noting my preference for not cutting into the loom wherever possible! But I need the power (white) from somewhere?

Mike

Mike Dixon

PaulH and others will be able to advise you.

Having owned a '73 as a daily driver I think what you're doing is a very good idea, otherwise some changes are both hands off the steering wheel too.

I don't know the B&G overdrive o/d switch knob but if it's made especially for them it'll probably be good. But if it's just bought in then I've had them work on my car and got parts from them, like all the major suppliers, a few of their parts I had from them were poor quality so don't just think because they're a name in the business they're perfect, do check.

And I'll ad my usual bit for using o/d, whether changing in or out of o/d you don't (fully) lift off the accelerator pedal, or dip the clutch pedal, as the o/d unit relies on load to it, have a look at the Driver's Handbook and see what it has about operating the o/d (not that I can remember now).

What are you going to put on the hole in the dash where the o/d switch was?

What about an o/d warning light if you're forgetful or to avoid the even wider gap from o/d third down to second, already potentially a wheel-squealer or slide out of o/d. 😉
Nigel Atkins

Mike, I've got on OD switch on the gear knob but I've retained the dash switch as well. Both switches are wired in parallel so either has the ability to operate the OD but you must use the same switch to disengage it. I find the gear knob switch useful for driving in warm weather, it seems natural to operate the OD from there. The issue I have with this switch is in cool/cold weather with the top down (although you don't have this issue with your GT) I like to wear gloves, this make the gear knob switch difficult to operate, this where the dash switch come in, it's not as convenient but it's easy to operate with gloves on.

Bob
R.A Davis

The other way round, when it's hot a metal gear lever knob, in a closed or open car, can get uncomfortably hot to use. Especially with a BGT that's has been parked up in the sun with all 6 windows firmed closed, the solar gain from the roof and other metal panels on top of all the glass area on the car can make things hot with direct sunlight on to a metal ball that you have to touch to drive off.
Nigel Atkins

For me the column switch on my V8 is the best as it anticipates paddle switches. The only advantage of having the switch on the gear lever is it;s easier taking it out of OD when changing between 3rd and 4th. But on the roadster a finger-tip reaches the dash switch to take it out of OD if needed, and the V8 with OD on 4th only has the torque for it not to be needed anyway.

To add a gear knob switch you can either run a pair of wires down to it from the dash switch connections, but make sure the switch is in the white there, not the yellow or in the engine compartment.

But easiest to insert the switch between the gearbox harness and gear lever switch. Doesn't matter which of the two wires on the gearbox switch. Fuse marginally better between the white and yellow where the dash switch was than in the engine compartment, but not much.
paulh4

Mike
Yep do as you indicated in your first post but when you get back near the gearlever leave enough slack or even a loop in the wiring so that the wiring can move nice and freely during gearchanges otherwise the wiring will end up failing
I had a Triumph Dolomite Sprint knob on mine and as Bob mentioned with your race gloves on you can't actually feel the switch but the Dolomite one was a slider with grooves so it was just a case of sliding it, you didn't really need to actually feel it the gloves moved it ok
I actually ended up turning my knob around a quarter of a turn as it felt wrong to me-had so it had on to the right off to the left--it felt a lot better crosswise so you just brushed your thumb accross it instead of trying to move your thumb back and forwards while trying to have a good hold of the knob---just another weird me thing
willy
William Revit

Correction: "To add a gear knob switch you can either run a pair of wires down to it from the dash switch connections, but make sure the FUSE is in the white there, not the yellow or in the engine compartment. "
paulh4

Thanks - picture of the one I am fitting attached as fitted to Ron Gammon's 66 B in period. There should be no problems using the switch, gloved or not. I did ponder the 2 switch solution but I think I might just end up forgetting which one I used.

I will move the fuse from where it is in the engine compartment on the yellow to the white.

Paul - sorry to be dim but where is the best place to get at the gearbox harness - where it joins the gearbox or in the engine bay? I need to get under and have another dig around

Once happy, I am pondering using the spare hole for a fuel pump switch as a safety/security thing - I suspect the existing switch might work, 'hidden in plain sight'? I do wonder about a light though - might put one in the centre console to distract the navigator....



Mike Dixon

On a 73 don't put the fuse in the white as that feeds the fuel pump not the overdrive. Or rather, put one there where it connects to the rear harness as well! Both my cars and some I have worked on have had shorts at the pump damage rear and main harnesses.

Remove the gear lever surround and tunnel cover plate and the connections to the overdrive switch on the gearbox can be accessed relatively easily (more so on a 3-synch tunnel).

Easier though is where the yellow from the main harness joins the yellow/red from the gearbox harness in the engine bay, having done a bit of grovelling to get the wires down from the lever and up there. I suggest you use insulated twin flex such as for 2-wire mains appliances, not individual wires, for better protection against chafing If you leave the fuse in the engine compartment it should stay where the yellow from the main harness connects to your new wire going down to the gear lever switch. However it's better behind the dash as the white has to be connected to the yellow there anyway, protects more wiring, and the fuse just needs two male spades instead of bullets to interconnect them.






paulh4

I wouldnt do it personally, the dash o/d is very easy to use I find. I had to fix the wiring of the o/d on an LE GT where it had frayed due to flexing where it enters the gear lever. Luckily it went open not short.
Stan Best

I think the simplest is, as you say run some sheathed twin core connected to the wires from the original switch - I will probably move the fuse from the engine bay to behind the dash as you say and connect everything in that area

Something like the attached.

As I say, I recognise the potential issue of fraying but with the cable physically protected and fused I will give it a go. Just makes so much more sense to me to do all the gear changing with the same hand in the same place.

We shall see!



Mike Dixon

My Triumph has the O/D switch on the gear knob and it is very handy there. I prefer to the dash switch on my '71 MGB.
Mike Howlett

Yeah, on the knob's the go-
If you're scooting round some bendy stuff steering and changing through the gears there's just not enough hands to go around to operate a dash mounted switch ---
William Revit

Mike - that should do it.

One possible route up from the gear lever is under the carpet then behind the console and across the back of the dash. But getting past the trim ring needs to be thought about - not squashing the flex and causing a short.
paulh4

I agree it seems silly, not to mention awkward, to change some gears with your left hand (RHD cars) and some with your right (OD switch on the dashboard).
However, at least in my opinion, without drilling a hole up the centre of the lever, or having a shift lever boot extending up to and over the bottom of the gear lever knob, it is always going to look an untidy amateurish owner modification or afterthought to run the wire for the OD switch up along the side of the gear lever to the knob; (which of course is exactly what it would be).
Perfectly OK for a gutted out track car, but potentially untidy in a properly trimmed and finished road car.
T Aczel

I think with the wires you either have them on full display at the gear lever of fully hidden at the gear lever. Just a different gear lever gaiter would hide most of the wires and a short bit of black sleeving for the last bit.

What I was wonder is whether the switch itself turns so that it's either horizontal or vertical and then whether up or down or forward or back is o/d in. I suppose you'd get used to it but I'd struggle especially with left hand.

I suppose you can just swop over the wire to reverse the switch operation.


Nigel Atkins

On the Triumph the switch slides forward and back. Forward is off and back is on. It is so simple to use and is clearly marked IN and OUT in case you want to glance down and check. I've fitted a warning light low down on the console as a belt and braces reminder. I 3D printed a small hood for the light which I can turn round to prevent it being a nuisance at night.

I have seen photos of competition MGBs where the OD switch is a plain toggle fixed on the shaft of the gear lever up near the knob. That would work well too, but wouldn't be so attractive to look at.
Mike Howlett

The attached is my hoped for endstate, albeit on a Healey. The period pictures of MGBs are not, I have to admit so tidy but we do use the car a bit for regularity rallies as well as touring and have Brantzs etc fitted. I suspect I will end up somewhere between he 2 in terms of aesthetics.

I will have a look at at the via the trim ring route, I have some spare sheathing that might add an additional layer of protection.



Mike Dixon

looks good to me Mike
IF you're going to use them plastic wire ties like that, don't over tighten them, as with a bit of time and heat they can squeeze the insulation on the wiring and cause a short, also when you cut the tails off the wire ties, pays to trim them right back flush with the blob of the wire tie with something like a razor blade, otherwise there's a really sharp little end there waiting to slice you to pieces,
William Revit

Thanks for the photo Mike, I was only thinking of the switch being at the side (despite 360 being available). Any position would be beyond my limited mental and physical dexterity.

Good advice about cable-ties, usually the sharpest ends are in a location that's very difficult to get the cutters too let alone blade and Sod's Law they're the one that get at your skin.
Nigel Atkins

Mike. The RB gear shift lever will fit into the earlier trannies, but not vice versa. Why not simply pick up an assembly from a RB car and have a factory style system? Les
Les Bengtson

The 77 and later gear lever can be fitted to earlier gearboxes if you replace the left-hand (top in the attached) locating pin with a blanking screw. The ball in the later lever only has one locating slot to prevent the lever being fitted the wrong way round. It will also need the later slotted retaining plate.


paulh4

Just done a test fit and I think its going to be just right for me. All gear changes with the left hand and the switch falls neatly between 2 fingers, a good tactile reminder if the overdrive is in or not and my hand is in place to sort it out if required.

Cable routing next - I like the under the carpet interior run. 2 options to get round the trim ring: Either drill a hole in the cover plate or what I think is better, cut into the fibreboard ring that sits under the trim ring? Nice straight-ish run from the gear lever with little risk of pinching.

I do not think there will be much need for wire ties - its neatly held in place by the trim with luck.

The only downside I can see is getting the gear knob and trim off later should it be needed will be a bit of a faff, but no more than a later car?
Mike Dixon


Mike, great idea, and very practical, however, being a bit particular about finishes on restored MG's, and as Les suggests, I will use the 77 gearstick option, and keep the wiring hidden, when I get to completing my 73 GT restoration.

Maurie P
R M Prior

This thread was discussed between 06/05/2021 and 10/06/2021

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