Pre Unit Triumph CLOSE RATIO 4-speed Swing Arm gearbox for production racers – SOLD

Pre Unit Triumph CLOSE RATIO 4-speed Swing Arm gearbox for production racers – SOLD


Pre Unit Triumph Close Ratio 4-speed Swing Arm gearbox for production racers.

For 500cc / 650cc Pre 1960 Triumph Bonneville, T110, T100 etc.

It’s very difficult to find a close ratio racing box. So, it’s nice to be able to offer one.

I didn’t rebuild it. But I was informed that it had been rebuilt. Please come and open it up for yourself and do your own inspection. Please inspect the images.

This Pre Unit Triumph Close Ratio 4-speed swing arm gearbox is probably not originally a factory version. I have had one of those. It was stamped “CR” in the correct position. This is the one that sold in 2021. This gearbox is not stamped with any numbers. Not that it matters from a document / machine dating perspective.

Condition of this pre unit Triumph Close Ratio 4-speed swing arm gearbox

speedometer drive hole has been plugged

As you can see from the images, it has been altered to suit a race bike. The kick start has been removed and plugged. The speedometer drive hole has been plugged (correctly – see parts list below) and some parts are lock-wired.

The outer cover has some old pitting on the leading edge (shown). There is some chafing on the outer casing just under where the drive output is. (Shown). The drive end of the shaft is good. The threads are fine. The gear change shaft splines are OK too.

It turns smoothly and it’s very clean inside.

I have got as far as just checking layshaft LOW gear. It is 28T, as it should be. I could see this one through a hole in the inner cover. I didn’t want to remove the inner cover as that would involve re-assembling the gears/ shafts. I have no reason to doubt that this gearbox has the correct gears for a close ratio gearbox.

However, if you would like to come and take it apart (and then re-assemble) the gearbox just for your own reassurance, you are very welcome. 

The outer cover fixings are finger tight and I have bent the tabs back inside already. Note if you buy this gearbox, please bend the tabs back in place before you use it. (See one of the pictures)

Pre Unit Triumph Close Ratio 4-speed swing arm gearbox gears

I had a look at some parts lists. Here is the information that I found regarding close ratio gearing as supplied by Triumph to all 500cc and 650cc Pre-unit models in 1959. That includes: 6T, T100, T110, TR6, T120.


  • T1117 – 18T – Mainshaft and Low gear
  • T1383 – 24T – High
  • T955 – 21T – 2nd
  • T1179 – 23T – 3rd


  • T959 – 22T – Layshaft and High gear
  • T961 – 28T – Low
  • T963 – 25T – 2nd
  • T964 – 23T – 3rd

OTHER PARTS supplied by Triumph

  • T983 – Plug for speedometer drive
  • T948 – Washer for plug.

I have a few standard Triumph Pre-unit swing arm gearboxes but this is the only close ratio one that I have. The others are a combination of swinging arm / rigid frame gearboxes. Please see the selection of Triumph gearboxes here within the rest of the pre-unit parts..

Buyer notes

Shipping is charged ON TOP of the price for the itemThere are too many variables to include shipping in the checkout, so please contact me before you buy and I will give you a shipping price.

I usually ship to most destinations.

International shipping available. Let me know where you are and I will send you a price for shipping with tracking

Combined shipping available. 

Viewing: Please come and check it over before you buy. It is at PE28, near St Ives in Cambridgeshire.

Collection: If you don’t want it shipped, I have plenty of space. If you can’t collect for a while, it’s not a problem. However, I will need to be paid very soon after the sale. Thanks.

Payment: Good old fashioned money on collection is preferred. I can accept payment through PayPal or by bank transfer as well. I can accept EUROS. Please ask. 

Import Taxes: Please note that IMPORT DUTIES are not something I can control. If you are buying from outside the UK, there is a chance that you will have to pay import taxes. Import taxes vary from country to country. If there are charges to pay, it is the buyer’s responsibility to research the cost and pay the duties. The price that you see on my advert is for the item and not the item plus whatever taxes might be due.

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