Screeching sound from Trident 900

Whilst doing the Lewes bypass yesterday morning (having just emerged from a
miserable few miles of freezing fog) on my '93 Trident 900, at about 80mph I
became aware, above the wind noise, of a screeching sound coming from below,
not unlike a small electric motor being over-revved and its bearings
complaining.

This has happened a few times before, but it's extremely difficult to tell
exactly where the noise is coming from, because it doesn't happen at lower
speeds and I can't very well lean down and listen more closely when
barrelling along at fairly high speed. It definitely seems to be related to
road speed rather than engine revs, because the noise continues if I shut the
throttle and declutch, but stops when I get below 50 or 60 mph.

I'm wondering if it might be the speedo cable or speedo drive?

Has anyone else encountered anything like this and can offer wise counsel?

Thanks...

 

Sounds a likely culprit. The speedo drive gear jobbie on my Morini
rumbles a bit when you spin the front wheel on a stand, but you can't
hear anything for the row from the 2:1 pipe once under way. Is the
speedo wheel or gearbox driven?


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+-------------------------------------------------------------------+
| Pete Fisher at Home: |
| Aprilia Shiver Yamaha WR250Z/Supermoto "Old Gimmer's Hillclimber" |
| Gilera GFR * 2 Moto Morini 2C/375 |
+-------------------------------------------------------------------+

 

Does the note tone rise and fall linearly with speed (gearbox etc ?) or
does it just rise or fall in volume (aerodynamic whistles).

 

Alternator [1] bearing?

[1] Dunno if your trumpet even has an alternator, but I had this happen
many years ago on a 1977 Honda Civic. Took ages to find the culprit;
it was completely seized.

 

Thus spake Pete Fisher () unto the assembled multitudes:

Wheel. Two years ago I sliced through the cable when I (*blush*) forgot
that I had a disk lock attached to the front disk. Drivers were beeping me
and frantically pointing at the hanging cable on my way home, thinking that
it was my brake

 

Thus spake () unto the assembled multitudes:

Bit of both, but not by much. The sound, once it starts, is a fairly
constant note and it's not often immediately apparent because of wind and
engine noise. And below a certain speed, it just stops. It only ever seems
to be that stretch of road where it happens, but I know that's a bit of a
daft correlation. At that point I have done 13 miles from home, so I'm sure
it would happen anywhere else at a similar speed after a similar distance;
it's just that riding it to work is my most frequent journey.

 

Either speedo drive or wheel bearing getting squeaky when hot. Try
popping the speedo cable off & squirting some spray grease in the drive
hole. If it takes longer for the noise to appear, there's your answer.

 

Highly unlikely given the above. The standard failure mode for early
Trumpet alternators is a rattle[1] not a squeal.

[1] Known as 'DAR' - Deathly/Deafening Alternator Rattle.

 

If it's cable driven, why not leave it disconnected completely while you
test it?

 

Thus spake Krusty () unto the assembled multitudes:

I should add that the noise is not quite a squeal, but not really a rattle
either. And as I said, it's related to road speed rather than engine revs so
surely is unlikely to be the alternator. I bloody hope not anyway. Very
difficult to describe really. It's a bit like the sound of an elephant
trumpet (how appropriate!), and maybe like the sound of a loud brake squeal
like you often hear from large trucks or buses. Just imagine it as a long
drone rather than a short burst of sound. If only I could record it and put
it online somewhere...

 

Thus spake Oily () unto the assembled multitudes:

I'll try both of these approaches, but my strongest suspicion is the speed
drive, so disconnecting the cable might not actually help with testing,
unless of course the problem only happens under load.

Thanks to everyone so far for your thoughts and advice.

 

Sounds rather like a partly- seized bearing, then. Once the housing has
warmed-up it allows the whole bearing to rotate, whereas when cold, the
shaft spins in the centre.

 

I think the suggestion was to disconnect it at the bottom not the top...

 

Sounds like wind noise to me.
Have you fitted any accessories for the wind to hoot around ?.
Any cracks or loose fasteners in fairings, mudguards etc ?

It is very easy to create an organpipe effect if air flows
the wrong way, it only takes a small slot or a narrow gap between
two items to get it started.

Do you have a nice handy wind tunnel ?

 

I know someone who's got one, but with the best will in the world (and
lots of lubrication)...

 

It was.

 

Checked tyres for pressure, wear, cuts or foreign objects lately?

 

Thus spake Mark Olson () unto the assembled multitudes:

That's how I read it. My point was that the symptoms might not occur if
there is no cable to drive, i.e. the speedo drive box was just spinning by
itself. With the cable connected then the drive is under some load. But then
again trying both would be a useful control.

 

Thus spake () unto the assembled multitudes:

I know what you're getting at, but no, I'm pretty certain it's mechanical noise. I've
heard the same sort of noise from a small electric motor that was spinning too
fast (i.e. above its rated voltage).

Nothing changed in the last couple of years.

 

Thus spake Mike Civil () unto the assembled multitudes:

Yep. The noise cannot be anything to do with the tyres. Famous last words... ;-)

I've just had a request from a student who wants to make a sound recording of
our server room. Perhaps I could get him to record my bike too ;-)