3 Sep 2011

Trykit 2WD maintenance

I had been running an 8 speed Shimano cassette but the time came when it and the chain were too worn to continue. I decided to invest in a 9 speed Sram cassette and matching Sram chain.


Replacing the cassette provided a handy opportunity to examine the Trykit 2WD freehub "innards". Just to see how it was coping with almost daily use. Particularly after a very long and hard winter. The Trykit 2WD free-hub and new half shafts were fitted exactly one year ago.

Poor old Mr Higgins is showing his age. The carrier clips and the bags, which previously adorned the seat stay triangle, have rubbed away the rather soft paint.

The Trykit 2WD freehub floats on its oversized, sealed, journal bearings between the two half shafts. The shafts (or axles if you prefer) are located in their own journal bearings. Removal of the outer bearing cups allows both Trykit axles to be withdrawn outwards. This leaves the inner bearings in place in their specially machined, bottom bracket cups. The freehub and mounted sprocket block cassette can then be lifted free of the Higgins axle reinforcement loops.

Here is a partially cutaway Trykit 2WD freehub borrowed from the Trykit website. Only one pair of the 3 pairs of right  side pawls and their internal ratchet are shown here. These would drive the right side axle only. There are six drive pawls in total per side. Twelve in total. Three more pairs of pawls and another support bearing are hidden on the left inside the remainder of the 2WD freehub. The drives to each axle are thus completely independent of each other in a remarkably compact, standard format, Shimano freehub. Allowing any Shimano/Sram cassette to be fitted.

The adjustable lockring allows a range of cassette widths depending on the number of sprockets. All journal bearings are rubber sealed to avoid water ingress. A common problem with standard cup and cone bearings typical of older trikes. The freehub body is machined from tough, hardened steel. Promising a very long life.

First I removed the saddle pin and carrier and then lifted the trike onto the work stand. Wheel removal from the Trykit axles is very simple. Requiring loosening the wheel-retaining, track nuts. Then a few gentle bangs on the side of the rim with my palm. Once free the nuts can be removed and the rear wheels slid off the axles. Leaving the nuts on but loose, saves the wheels from flying away if they come unstuck rather suddenly.

Having donned thick rubber gloves I removed the old chain (with a chain link extractor) and set it aside as a spare.  The worn cassette was released from the free-hub with a chain wrench and the splined, Shimano, lock-ring, removal tool. 

Pushing the journal bearings out of the freehub didn't take much effort. There is a push fit, sealed bearing at each end of the freehub. Then come the pawl carriers. With a light alloy disk separating the two, independent, pawl carriers. The bearings and their rubber seals protect the pawls and their carriers.

Though the original clear grease was blackened with use it was still in good (greasy) condition. In the absence of the recommended de-greaser I had to use petrol. This was used to wash all the components in a small glass jar only just large enough for take the special, freehub body. The freehub was carefully brushed through with an old toothbrush to remove any possible metal dust. The rest of the components had a quick bath in the petrol and were set aside to dry in the warm sunshine. All the components were given a final polish with a clean cloth.

Examination showed that there was no visible sign of wear to the pawls or freehub ratchets. They looked as good as new! As did the journal bearings. I reassembled the Trykit freehub components using thin, Castrol LMP grease. Trykit recommend a thin grease. I'm not sure whether the Castrol grease is thin enough but is very soft.

Image showing a trial assembly of the pawl holders in the freehub. Note how they are self-centering on the sprung pawls. Naturally, they need to be inserted the correct way around to take up the drive from the chain/ sprockets and transfer it to the axles via the hex socket in the pawl carriers. The ratchet teeth are actually, slightly asymmetrical which ensures the pawls won't be put in back to front.  One just has to remember that the freehub drives the pawls. (as indicated by the arrows)

The pawls and their springs are self retaining. So there is no danger of things flying away if the Trykit free-hub is dismantled. Everything was thoroughly clean and then well greased before it went back together. Such an apparently simple mechanism but a true work of  mechanical genius!

The new 9sp cassette was then fitted to the Trykit freehub. The 9sp is wider than the 8sp so there is not so much visible thread beyond the Trykit locking ring. Though I still used my thick, brass spacer ring. I think it looks smarter with the lock ring almost flush with the end of the freehub. A 10sp would not need the brass spacer ring but my bar-end gear levers are limited to 9 speeds. 

Front of Sram 12-26T, cassette showing the high gear, splined locking ring. This holds the 12T top gear in place. The sprockets are sandwiched between this ring and the rear locking ring. I torqued down on both simultaneously to ensure all was tight. The sprockets won't fall off or slip because of the splines but they don't want to be loose or they might cut the splines of the free-hub over time.

The Sram cassette sprockets are well cut away making for a remarkably light assembly. The designer went the extra mile and matched the cutaways to produce an attractive geometric arrangement. The rather "techy" cut-outs have their own character rather than being simple radiused arcs. I haven't had to do it yet but it looks much easier to clean than a Shimano cassette.

I deliberately made the chain one link longer than the last time to see if it affected anything. Removing another link (if necessary) is very easy with a modern link extractor. As usual I allowed enough chain to use the largest sprocket and the largest chainwheel at the same time. Not a normal occurrence out on the road but it offers complete safety and confidence in a hurried gear change when I suddenly need a low gear.

(Note: the overlong chain proved to be  complete waste of time and caused all sorts of problems! Make the chain the correct length every time! Wrap the chain around the largest sprocket and largest chain-wheel and bring the ends together so they overlap. Use one free end as your marker at the overlap then add one link. Break the chain at that point. Use a modern link extractor with an adjustable stop screw or you will damage such a narrow chain! I used a cheap, chain link extractor designed for normal 1/8" chains. The chain broke a couple of times while I was a long way from home! It was my own fault! I have now invested in a modern, Spectra chain link extractor) 

It reached 74F this afternoon. A bit warm for me standing out there in the sunshine.

The chain is much too long! This is on the smallest chain-ring. Middle sprocket. The chain still jumps in some gears. No chain tension!

View from the other side. Not how Shimano has saved money on the protective finish on the less visible parts of the Tiagra gear changer. I shall have to remove another chain link. Perhaps two.

I removed one more link but the chain is still jumping on hills and when I stand on the pedals. Still not enough chain tension. I'll take out another link before I go out again.

One link less: Better, but still not enough tension.

And yet another link but still skipping. I should have been more ruthless at the start. Setting the chain length to match the largest sprocket and biggest chain-wheel plus one link. Just allowing the chain to pass safely through the changer rollers without the chain going completely tight.

See important note about correct chain length above!

Also remember to tighten the wheel nuts properly after any maintenance work!  

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