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Author Topic: Front end wiggle when downshifting  (Read 181 times)
Igor900
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« on: August 01, 2020, 04:51:00 PM »

Hey friends. I got a '98 M900. He's got about 64k miles on him.
I've noticed that when I downshift, especially when he's rev'd up pretty high, I get a pretty good wiggle in the front end. I don't wiggle any other time, I can do 75+mph and he stays nice and smooth, can take my hands off and everything. Just when I downshift and let off the clutch, he's definitely got a good wiggle to him.
I've replaced the fork oil/seals earlier this season, just put on new front rotors, and I've been trying to adjust the steering stem nut (the bearing was replaced about 25k miles or 5 years ago). Any other things I should think about checking? Anybody else experience this before?
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Buhgaboo
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« Reply #1 on: August 01, 2020, 09:03:07 PM »

Start with checking your suspension sag numbers
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Charlie98
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« Reply #2 on: August 02, 2020, 05:47:07 AM »

How is the condition of your front tire?

My old CBR1000F was very sensitive to front tire profile, it would headshake just like you describe when the front tire was worn.
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Dennis

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koko64
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« Reply #3 on: August 02, 2020, 01:54:48 PM »

You need to run a close eye over all those components that can hurt you if they mis behave, because that don't sound right. I mean you ain't stomping on the shifter with both heels and upsetting the bike, so check the following:

Chain slack for a whiplash effect
Tyres for uneven wear and correct pressure (or damage)
Steering head bearings
Wheel bearings and rim condition
Axel nuts
Suspension sag and bolts, etc as DP said
Swing arm pivot area for case cracks, loose bolts, anything looking wonky
Anything else our brethren here can think of.

Also are you letting the revs fall enough before downshifting? It's not an in line 4, so allow for that as you need to allow a greater drop in revs before clicking it down or you'll be asking a lot of your slipper clutch if you have one. Your model came with a regular clutch and those big pistons can chirp the rear sending a shudder through the front if you change down too early. You come off a 4 cylinder bike previously?

This is most likely but giving the old girl a going over with a keen eye over a few beers is worth it.
« Last Edit: August 02, 2020, 02:05:56 PM by koko64 » Logged

1999 M750.    "Scrambler"
2013 M1100 Evo    Street
2004 GSXR 750     Track
Igor900
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« Reply #4 on: August 02, 2020, 04:39:14 PM »

I’ve checked mostly everything that you all have said.
The front rim is used, had to replace after a near accident last season (someone cut out in front of me I had to brake hard and the wheel bearing which was worn and needed replacing pushed into the rim enough to replace the rim) so I don’t know the history of the replacement rim (eBay find)
The tire itself looks clean and even. Only have two season on it.
I have been pushing the bike more in the last couple of years, and probably always had the wiggle when downshifting, but I’ve been doing it from a higher rev. I’ll be sure to slow him down and not push him so hard.

I started with my Monster. He’s been my first and only bike for the last 6 years.
During quarantine I picked up an old Ninja 500 to build for my boyfriend, and a 1985 Suzuki gs700es to restore back to original form.

I’ve experienced a rear wheel wiggle before based off of what is the usual suspects, but never the front wheel/handlebars until this year.
Just wanted some good starting points to look into.
Thanks guys Smiley
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Charlie98
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« Reply #5 on: August 02, 2020, 05:44:28 PM »

What kind of tires are you running?
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Dennis

2013 M796 ABS
1993 XR650L (the Torque-a-Saurus)

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S21FOLGORE
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« Reply #6 on: August 02, 2020, 06:46:35 PM »

,SNIP>
Also are you letting the revs fall enough before downshifting? It's not an in line 4, so allow for that as you need to allow a greater drop in revs before clicking it down or you'll be asking a lot of your slipper clutch if you have one. Your model came with a regular clutch and those big pistons can chirp the rear sending a shudder through the front if you change down too early. <SNIP>

This.

To OP,

Can you downshift WITHOUT clutch?
(Yes, you can shift up AND down WITHOUT clutch, if you know how the transmission works, and know how to shift.)

My guess is, (assuming that you don't have problems with the bike itself) your riding style is causing front end wiggle mostly, or entirely.

So, ... let me ask a few questions.

Can you shift up WITHOUT clutch ?
(Meaning, you can do that any time you want, you can do that all day long. NOT that you can do 1 out of 10 tries.)

Can you shift DOWN WITHOUT clutch ?

If the answers are no, ...

Are you pulling in the clutch lever completely?




If your "hard downshift" goes like this ...

1. going fast on the straight line

2. see the corner coming, wait as late as you can, then brake HARD ! (all the weight (of the bike and you) is pitched forward, loading the front forks to near its max capability)

3. pulling the clutch lever in, completely

4. Twist the throttle, revving up the engine high, let the clutch lever go ...


... then, try to shift without the clutch, both up AND down.
That (clutch-less shift) will force you to shift properly (and ride smoothly).
Then, most likely, the problem would be solved.
(And no, clutchless shift won't hurt your transmission.
You can cause damage to constant mesh transmission in 2 ways.
One is by shifting slowly. This will damage dogs.
Another is force shifting while dogs are strongly engaged by the torque or back torque.
This, you'll end up bending shift fork.
You don't damage anything by not using clutch.)

Also, try to shift with pulling in the clutch lever only 2 - 3mm, not all the way in. (Both shift up & down).


Another thing you can do, is
to flip the shift lever upside down, to make shift pattern 1 up 5 down.
Adjust the shift lever height (and clutch, brake lever) at the same time.



« Last Edit: August 02, 2020, 08:24:25 PM by S21FOLGORE » Logged
koko64
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« Reply #7 on: August 02, 2020, 08:10:47 PM »

You can ride these bikes hard for sure, just let the revs drop down a bit more before downshifting. You can also try riding in a gear taller when going hard and use the torque , you'll be amazed how much quicker you can go on tight twisty roads when using the "grunt".

It's a great sport, you never stop learning new things even when you're older and experienced Smiley
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1999 M750.    "Scrambler"
2013 M1100 Evo    Street
2004 GSXR 750     Track
S21FOLGORE
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« Reply #8 on: August 02, 2020, 09:36:48 PM »

You can ride these bikes hard for sure, just let the revs drop down a bit more before downshifting. You can also try riding in a gear taller when going hard and use the torque , you'll be amazed how much quicker you can go on tight twisty roads when using the "grunt".

It's a great sport, you never stop learning new things even when you're older and experienced Smiley

This is also a very good point.

Wider ratio transmission, more reciprocating mass make downshifting more difficult.

And, using "lower RPM" allows you to go round the corner faster ...



Typical air-cooled 2V Ducati's (like 900SS, M900) power output is like this ...



The peak of power output is just around 8K rpm.
So, you may think you need to rev up your engine that high, but ...




look at the torque curve


If you are revving your engine high, using 6 - 8k rpm during the cornering,
you are actually slower than someone on the same bike but using 4 - 6k prm.

Yes, using 4 to 6K rpm allows you to go round the corner(s) faster.

So, before going out for a ride next time, think about what RPM range to use when going through the corners, in which gear.
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