Overdrive Shift Knob/Covers for Triumph, MGB, Leyland, others

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Overdrive Shift Knob/Covers for Triumph, MGB, Leyland, others

In the course of restoring my late brother's GT6 I found an overdrive shift knob in one of the bins.

Apparently this is what he desired to install, but the knob had the wrong shift pattern for reverse on the cover. I suspect he purchased this used and it was from an MGB.

I decided to make the model for the cover with the correct shift pattern and 3d print it. Using OpenSCAD I made the text configurable to have the reverse positions in all four corners. So, I have generated models here for each of those cases. In addition, there is a blank cover with no shift pattern, this would be for the case where you are looking for a cleaner, simpler, look or if you wish to employ a decal.

After going this far I decided I did not like the original white metal shift knob that I had. So I made a fairly decent model of the knob. More importantly I made a "core". The "core" allows you to more easily turn a wooden or metal knob on a lathe (like my wooden one in the photo). So long as you bore a hole 37mm in diameter (of proper depth) in your turned knob, you can then insert and epoxy glue the core which will then allow you to accept the Lucas switch and the cover. This saves you from having to do the complicated machining inside the wooden knob, which would probably not be possible.

The knob (or core) is easily printed on an FDM printer. I suggest ABS printed with 100% infill. You may wish to optionally perform ABS acetone vapor smoothing on the knob. No support is required when printing on FDM.

I only made a 1/4" pilot hole in the base of the knob. The assumption is that you would be drilling out to install some sort of metal threaded insert. I used 1/2-18 coarse threaded rod. I then center drill it and the tap the threads for the 5/16" shift lever.

I recommend printing the cover with a UV liquid resin printer. Especially if you wish to accurately reproduce the in-letted shift pattern text. You need to use a resin that is not brittle once cured and has some amount of flexing as is encountered during installation and use. You could print the non-lettered cover with an FDM printer.

I ended up mixing resins. I added about 25% Resione flexible F69 to RichOpto Standard Black resin. However you might wish to try some of the more durable resins such as Siraya Tech Blu. Cracking the cover is something that you may encounter so gang print several covers at a time on your UV printer in case you break one.. There is always printer specific variances, shrinkages, etc. So be prepared to do a little sanding or filing to make things go together more easily. The Lucas switch screws are challenging, I cut the screws down slightly and you will have to clear the holes out on the UV printed cover.

You can then paint the cover with a paint of high durability. Like a gloss epoxy paint.
Afterwards you can "wipe in"/"wipe off" white paint to fill the shift pattern and lettering.

Alternatively, you could FDM print the non-patterned cover and then optionally use a water slide decal. Then do a final clear coat.

All parts are interchangeable with the original Leyland components. So if your cover is broken you have a solution here.

The Lucas OD switch for knob is available from Moss for around $10.

I am not releasing the OpenSCAD file, but if you see a problem let me know in the comments section.

Revisions:
3/15/2026
I've added four additional models that permit the use of alternative switches,
od_knob_alt.stl, od_knob_core_alt.stl have opened up interiors to accommodate a deeper and larger switch.

od_shift_empty is a blank cover that you can drill or cut for whatever switch you want to use.
od_shift_cover_22.stl has a 22mm hole for use with common round switches.
I suggest printing these two covers in FDM.