There’s a lot of confusion over Post-War Norton gearbox numbers with G Prefix GB21 G101 G102 etc. I don’t claim to be an expert. However, through my own need to understand the numbers, I have gathered together some information that I found useful. Rather than keep it to myself, I offer the information here as a “guide”, rather than the last word.
I realised that I had collected together many Norton gearboxes. I divided them into pre-war (Upright, Dolls Head) and post-war. This page is all about Post-War Norton gearbox numbers with G Prefix GB21 G101 G102 etc. This includes Manx Norton and 5ooT gearboxes.
Of course, you have variations, with Wide Ratio and Close Ratio versions. There were works ones too. This page just covers the basics. You will often find that the ratios are sometimes stamped on the back face of the main shell.
Burman gearboxes made the G-prefix transmissions, cases and covers. They were made under contract to Norton. The only obvious Norton identification is the small inspection cover with “Norton” inscribed.
Burman also made gearboxes for many other vintage British motorcycle manufacturers. This included AJS / Matchless, Panther, Vincent and many others.
As the Dolls Head gearbox was supplied with pre-war and post-war bikes, it’s worth looking at the post-war Dolls Head identification.
Post-war “Dolls-head” gearbox numbers:
| Prefix | Model | Year |
|---|---|---|
| G5 | ES2, 16H, Big 4 | 1946-1949 |
| G15 | International, “Garden-gate” | 1946-1952 |
| G16 | Manx, “Garden-gate” | 1946-1950 |
| G55 | Daytona Manx | |
| G56 | 500t, Poss rare 350T | 1949-1954 |
| G110 | 500t, Poss rare 350T | 1949-1954 |
Post-War Norton gearbox numbers with G Prefix GB21 G101 G102
The Post-War Norton gearbox numbers with G Prefix GB21 G101 G102 etc covered many models. They are all basically the same shape. However, some had different length shafts, different, kick start parts and different widths to the frame mounts. If you are looking to get the right box for your bike, please take special care to get one with the right frame mount widths.
| Prefix | Model | Year |
|---|---|---|
| G82 | Model 7 with plunger frame | 1949-1951 |
| G101 | Side valve & OHV singles with plunger frame | 1950-1952 |
| G102 | Model 7, side-valve & OHV with swing-arm frame | 1952-1956 |
| GB8 | Model 88 & 99 with featherbed frame | 1952-1956 |
| GB21 | International with featherbed frame | 1953-1957 |
| GB9 | Manx with featherbed frame | 1951-1957 |
| G18 | Daytona Dominator 88 using Inter close ratios with K/start and Daytona Manx 1st gear. Only 8 made | 1957 |
NOTE:
Instead of the usual The Post-War Norton gearbox numbers with G Prefix GB21 G101 G102 etc, there are also oddities, such as the stamping “G56A” . This appears to have been stamped on transmissions for the 500T.
From 1946, Norton appear to have used ‘G’ but also ‘M’ , ‘K’ and ‘A46’ as stampings. I still have to work this lot out.
The usual obvious caveat operates here. Please use this information as a guide. Probably verify your needs with the Norton Owners Club. They are the experts.
Norton gearboxes for sale.
I have a few. If you don’t see the one that you need, please ask me here. Here is the page of Norton gearboxes.
