Author Topic: Notchy gearbox  (Read 309 times)

Offline Oggers

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Notchy gearbox
« on: June 08, 2021, 09:47:30 AM »
Chaps

1966 Triumph T120 Bonneville is proving to be an occasional pain in the neck when changing gear - especially from 3rd to 4th. Here it basically does not engage into 4th and finds neutral instead. Compared the other bikes, the gearchange just does not seem positive in selection and seems over-light - for want of better words. The throw of the gearlever between changes is also very small, and finding neutral from 1st or 2nd is a very fine art. The delicate tap required at the (standard) gearlever to find neutral is almost imperceptible.     

Of course I realize this may be all perfectly normal and that I need to adapt my right foot to the circumstances, but it does seem a little "light"

Things I have done fairly recently

Fresh gearbox oil - to the spec as per the manual - filled with correct amount
Fresh engine oil - to spec
Various adjustments at clutch nut - the one concealed behind the chaincase
Various adjustments of the clutch cable at both the lever and at the gearbox ends
Cleaned up the clutch plates/basket
I change up at around 4000/4500 rpm with a slight whiff of throttle.

It may simply be an attribute of the gearbox - which I understand to be original - but all thoughts welcome, particularly from other T120 owners.   

Offline iansoady

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Re: Notchy gearbox
« Reply #1 on: June 08, 2021, 10:56:44 AM »
I'm not familiar with the gearbox but this kind of problem is often caused by slight clutch drag. You seem to have done most of what would be needed however, although your descriptions are a bit odd - eg "Various adjustments at clutch nut - the one concealed behind the chaincase".

Is it easy to get into first from neutral at a standstill? When in gear does it feel as though it's trying to move off with the clutch fully disengaged?

Different bike I know but I briefly had a unit 500 Triumph and hated the short gearlever. If I'd liked the rest of it I would have lengthened it.
Ian
1952 Norton ES2
2008 Yamaha X-Max 250

Offline Oggers

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Re: Notchy gearbox
« Reply #2 on: June 08, 2021, 11:37:47 AM »
Ian

My poor description perhaps. Clutch nut  = clutch operating rod ajustment. The slotted rod held by locknut behind the cap in the centre of the outer primary chaincase.

It's not particularly difficult to engage first from standstill, nor does it move much with the clutch lever fully pulled back.

For sure it has a short gearlever, considerably shorter than my other British bikes - Ariel VB and Velo MSS - and indeed I did  think of swapping it for something longer. I just wished to clarify that there is not something I could do to improve things before I did so. Mine is also unit construction....

Offline Oggers

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Re: Notchy gearbox
« Reply #3 on: June 08, 2021, 05:44:09 PM »
Ian

I stand slighty corrected. When on the main stand and in neutral, the rear wheel rotates quite quickly suggesting a little clutch drag. I'll try and adjust things further. Just took it out and I moved the gearlever a notch over the spline. Seems slightly better....   

Offline Rex

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Re: Notchy gearbox
« Reply #4 on: June 08, 2021, 06:54:13 PM »
If it's in neutral clutch drag doesn't come into it. The rear wheel always rotates when on the stand because of oil drag between the main shaft and sleeve gear.
It's personal choice, but I've always rated the light and short Triumph gear lever action. Is this a recently-purchased bike?

Offline R

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Re: Notchy gearbox
« Reply #5 on: June 09, 2021, 05:22:06 AM »
You should be able to just tread on the brake pedal and the rear wheel will stop (in neutral).

I see you've done the fresh oil in the gearbox.
That has worked for me with other bikes.
You'd wonder why it should make any difference, but it certainly can.

After that, all I can suggest is you check that the primary chain is not too tight.
The final drive chain also, come to that.

Offline Oggers

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Re: Notchy gearbox
« Reply #6 on: June 09, 2021, 08:16:04 AM »
Slight tweaking of the clutch actuating rod (winding it out @1/4 turn) and the rear wheel has almost stopped rotating when on the main stand. For sure there is no real drive there and it is easily be stopped by the rear brake. Chains - hadn't thought of that, will check. Many thanks

Offline Rex

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Re: Notchy gearbox
« Reply #7 on: June 09, 2021, 09:23:00 AM »
The length of the clutch push-rod has no bearing on the rear wheel rotating in neutral as the mainshaft (through which the push rod goes) is rotating too.
A quarter turn would be a miniscule dimension anyway.

Offline john.k

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Re: Notchy gearbox
« Reply #8 on: June 10, 2021, 02:28:01 AM »
If the clutch is actually dragging ,first thing to check is the pressure plate at full lift.....does it wobble as it turns.......may be that new springs in a matched set are needed,or just adjusting the spring nuts to level the plate at full lift...Another thing to check is primary chain tension.....check at the tightest spot in several rotations..........neutralizing or jumping out of top gear will quickly damage the whole box with steel chips ,not to mention the gears involved....Likely cause is excessive endfloat in the box somewhere,either selectors or even ball bearings.