NEW! 4-speed gearbox to Nimbus developed in Sweden!

A 4 speed gearbox to Nimbus has been developed during the winter of 2003 and spring 2004. The gearbox could be described as a pull-wedge box and has 4 pairs of wheels constantly engaged. Both shafts has dismountable wheels but on the driving shaft, the wheels are permanently locked to the shaft. The driven shaft is hollow and under each wheel are three locking balls, engaged by a sliding wedge that runs inside the shaft. When the head of the wedge is directly below a wheel, the locking balls are pressed outwards and locks the wheel to the shaft for that particular gearing.

Types:

Two different types of gearboxes are avaliable, namely 'Sport' and Touring'.

Sport is a harmonic case where gear shifts take place at torque/effect maximum. 1:st and 2:nd gear corresponds with the 1:st and 2:nd of the original case while the 3:rd gear is slightly geared down and the 4:th geared up compared with the 3:rd gear of the original box. The Sport gearcase is suitable both for side cars as for solo machines and makes better use of the Nimbus engine's modest performance than the original gearbox. The new box gives faster acceleration, a higher top speed and lower fuel- and oil consumption.

Touring is a speciality box for side car riding.

1:st to 3:rd gear corresponds with the old box while the 4:th corresponds with the 3:rd of a solo (provided that the solo final drive is mounted). The thought is that a sidecar rider could use his rear wheel with the lower gear ration even for speeds of a higher geared solo machine. The first three gears are used for normal riding while the 4:th could be used when the side car is dismounted or when you have the wind in your back and light cargo in the side car.

The boxes can be fitted in the original housings that are, preferebly, sent in for a bearing job and fitting of the new inner workings. The newest type of housing (with a fork shaped clutch engagement lever) can be used directly with no modifications but the old type of housing (with a bar shaped clutch engagement lever) has to undergo a slight internal milling process. This modification does not affect the function of the old box though. Both the old and the new box can easilly be restored with their original contents.

Test rides:

The box has been tested in more than 6000 km without any noticable wear has been evident. Even though the box is unsynchronized, it is so easy to manouver that with careful riding it is easy to do totally noisless shiftings both up and down. As a matter of fact, it is quite possible with a little training to change gears both up and down noislessly without the use of the clutch. The box is exceptionally quiet and the Nimbus now sounds more like a motorcycle and less than a fire alarm.

From a safety point of view the Sport box is in a league of itself since you can keep a more traffic adapted march speed as well as be able to do swifter overhauls.

The Touring box also permits that the average march speed will be faster since side car riders usually has light or no cargo and thus can utilize the 4:th gear frequently.

Particulars for stick shift Nimbii:

Adaptation of the box to stick shift is thus carried out as follows:

  1. Fabricate a pin, slightly longer than the hollow bolt that holds the spring and locking ball for the gear shift shaft of 8 mm diameter. Make one end into a short, conical point.

  2. Fit the pin into the hollow bolt above.

  3. Lock the gear shift shaft in third gear with the bolt and pin.

  4. Adjust the stick so that it lays against the front edge of the notch for the 2:nd gear and fixate it by fastning the bolts that holds the stick.

  5. Unscrew the bolt with the pin to release the gear shift shaft and move the shift back so the notch for the 2:nd gear is visible through the threaded hole for the bolt. The stick is now slightly ouside and forward the neutral notch.

  6. Lock the gear shift shaft in 2:nd gear with the bolt and pin.

  7. Using a sharp file, file the neutral notch longer so that the stick precisely can fall in place against the forward end of the neutral notch.

Gears are now located as follows:

Particulars for foot shift Nimbii:

The external Ric-rac system for foot shifting has to be rebuilt so that it can index four steps instead of 3. This means that a new banjo plate has to be made, the secant in the lower portion of the housing has to be modified and the end stops. The modifications are not irreverisible though and this housing can also be reconverted to its original shape and function. Modification of the rick-rack system will be offered to those who so whish.

Production:

The box will be produced in series of 25 and order lists are already set up. The boxes are manufactured by Folan Technics in Sweden and will be sold through JC Nimbus in Copenhagen. The price for a gearbox will be approximately 8500 DKK for parts and rebuild of the original house. Costs for modification of the rick-rack system will add to this though and the price for that modification is not yet decided.

Orders and/or questions:

Contact Rune on J.C. Nimbus in Denmark at (+45 35 83 13) or drop an email to: nimbus@allitnil.df.lth.se. Observe! Denmark is in the timezone CET (GMT+1)! If you west or east of Europe, make sure that you call during Danish working hours!

The function of the 4-speed gearbox to Nimbus

FunktionComponents