What happens when belt breaks?
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Hooked
Joined: 06 Oct 2013
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Thu Jun 06, 2019 10:48 am quote
Motovista wrote:
Bueller wrote:
https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/#post-26854294

https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/#post-37291909

https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/page-2#post-37300688

It can happen. It’s not all that common, but if the pieces jam the clutch bell badly enough you will get a lockup.

One thing I learned during the three decades I worked as a master auto tech, shop foreman, and almost 10 years with Harley - just when I think it’s not possible, someone proves it is!
If you have a good scooter, with good parts that are in working order, and everything has been put together correctly, the odds are significant that a broken belt will not lock up the rear wheel.
That applies to any vehicle. For scooters in particular, if everything is assembled correctly and in good working order why would a belt fail at all?

Why is it such a stretch to believe a belt could break, wad up between the clutch bell and the case and lock the wheel? While I agree it is not common, it has happened and still does happen on occasion. Personally I’m not cheap enough to try to push belt life. I change them as recommended (In fact I think I bought my last one from Scooter Parts Co) because I don’t want to have to deal with being stranded or with potential safety issues.
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Thu Jun 06, 2019 11:20 am quote
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Thu Jun 06, 2019 11:37 am quote
Motovista wrote:
If you have a good scooter, with good parts that are in working order, and everything has been put together correctly, the odds are significant that a broken belt will not lock up the rear wheel.
Now that I can agree with.
Molto Verboso
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Sat Jun 08, 2019 1:16 am quote
SoCalGuy wrote:
WEB-Tech wrote:
OR
Your doing 70 on a wide bend in the road and the belt breaks, gets jammed in the clutch, locks the rear wheel up and you do cart wheels in the median for 100 feet ....
Huh? Care to explain how exactly a broken belt can get “jammed in the clutch” and “lock the rear wheel up”?

You can't lock up a CVT scoot for the same reason you can't bump start it. The engine must be turning roughly 2,000 RPM to engage the clutch. If a belt breaks the clutch disengages. It doesn't matter how fast the rear wheel is turning, with no belt, the clutch is disengaged. A broken belt is less likely to “lock up the clutch” than it is to sponantously cause your hair to catch on fire.
I was dyno'ing a Honda Silverwing when the engine seized at indicated 65mph. The rear wheel locked temporarily, which on the road would have almost certainly thrown me up the road. You'd expect the clutch to immeditately let go and allow you to coast, but it doesn't always work that way. Of course the bike was tethered so nothing much happened. Now when a belt breaks, it can have the same effect. The rear wheel can indeed lock if the belt breaks as I found out on a customers bike. Of course, the wheel may not lock, it just depends on what bike, how the belt breaks, what speed it happens at...etc etc
Molto Verboso
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Sat Jun 08, 2019 1:21 am quote
SoCalGuy wrote:
Hold on, you’re talking about two different things.

A “locked clutch” isn’t a “locked rear wheel”.

Sorry, but I’m not even sure what you’re referring to by a “locked clutch”. Are you saying a broken belt can cause the clutch to not disengage? Or not to spin? Either way, it wouldn’t lock the rear wheel. Even a seized engine wouldn’t cause the rear wheel to lockup.
The belt strands can get into and around the clutch bell and jam the clutch in the engaged position causing the rear wheel to lock solid. I've had this happen on a customers bike with me riding it. Not nice! Most belts breaks don't lock the rear wheel but some do indeed cause this, as I experienced.
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Sat Jun 08, 2019 8:58 am quote
[quote="SoCalGuy"]
Quote:
Believe it or not, Piaggio’s engineer’s actually thought about this. They anticipated that people may not change their belt as frequently as they should, and that many belts would break while people were riding. The transmission is designed so that a broken belt will not cause the rear wheel to lock up.
What they thought is, "how does the transmission in these Honda 250cc engines we bought work?..."
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Sat Jun 08, 2019 12:03 pm quote
How timely! Just this morning, my husband helped a friend whose 150 stopped driving yesterday at 60 mph. She said the scooter came to a gradual stop. My husband investigated and found that the belt shredded and disintegrated into little bits and pieces. The carbon fibers were wrapped around the engine pulley and neighboring parts.

F3123726-1D8F-4040-A47A-6DFB3CF465D6.jpeg

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Sat Jun 08, 2019 1:49 pm quote
Thinking of places and times I've ridden....
And a member here's scooters lost drive 7 times. 4 belts, 3 nuts.
Man, I'd rethink my service schedule......and
use a new mechanic!
O.S.
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Sat Jun 08, 2019 6:11 pm quote
What? The rear wheel will lock when the belt snaps and gets wedged between the backside of the rear fixed torque driver and reduction box cover! Usually when you ride wheelies on a modded (or stock if ya got skills) Zuma 50cc 2 stroke. When it gets wedged between those 2 parts, not only does the wheel lock but it usually cracks the reduction box cover, bends the primary drive shaft and warps the fixed side of the torque driver. Ride wheelies to experience it for yourself! Burnouts can do it also! Factory belts are much more forgiving than aftermarket kevlar belts when they snap. My friend had it happen doing a nice wheelie. He left a skid on the pavement and he said he left a skid in his underwear to! I stink at riding wheelies on anything, so Im safe.
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Sat Jun 08, 2019 9:57 pm quote
So the clutch bell is splined to the primary drive gear. A chunk of belt between the bell and the case will indeed lock it up. Saw the 30 foot skid on the road when my wife LX190 belt disintegrated. Experienced it my self when my LX190 broke a belt. So thats 2 lock ups in my house hold. Anecdotally a friend on a GT200 riding with his dad as a passenger suddenly decelerated from freeway speed due to heavy traffic suddenly slowing in front of him. Rear wheel locked up solid. pulled to side of road and it had released. everything looked good when he got it apart. the thing must have folded before the driven pull could close up and take out the slack from the drive pulley opening up. It can and does happen, I assure you. FYI in both of our broken belts, Malossi brand. After multiday tours and on days when ambient temp exceeded 100 degrees F. I use OEM only now and change them early
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Sun Jun 09, 2019 12:51 am quote
Two broken belts and both times the rear wheel locked up. That is incredibly rare and unfortunate.
Were the Dr. Pulley sliders in OEM or aftermarket variators and was it the first time you had installed belts or sliders?
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Sun Jun 09, 2019 6:59 am quote
Sometimes oem is thebest.
Molto Verboso
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Sun Jun 09, 2019 8:30 am quote
Motovista wrote:
Two broken belts and both times the rear wheel locked up. That is incredibly rare and unfortunate.
Were the Dr. Pulley sliders in OEM or aftermarket variators and was it the first time you had installed belts or sliders?
Being some years ago I don't remember for sure but probably my first two belt changes. I was shown the correct way to do it by a friend who was a Vespa dealer at the time( with regards to seating the belts deep in the driven pulley so the drive pulley nut is not pinching the belt). Stock variators, probably was using Dr. Pulley or at least lighter rollers for sure. Both times first ride after 700+ mile "weekends". Both on 100 degree plus days. On my scooter lock up was momentary, though my muscle reaction was to pull in the left hand lever. The excellent riding around here tends to wear stuff fast(near constant on/off throttle). I've taken to replacing belts at 5k miles and find my variator bushing is out of spec by 10k and needs replacement of both halfs(grooves in faces). I recall one belt had 1500 miles at the time of failure. I think heat and inferior aftermarket were the culprit in both cases. I haven't lost a belt since.
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Sun Jun 09, 2019 8:35 am quote
Lift
Or a Torque Wrench ?

Listen to advice also ?

Bill x
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Sun Jun 09, 2019 9:05 pm quote
scootermarc69 wrote:
... probably my first two belt changes...., probably was using Dr. Pulley. ...
Quite a few broken belt stories share one or both of these elements. You might not know this, but where the Malossi belt uses Kevlar, the Piaggio belt uses polyester. Kevlar is said to hold up better to heat than polyester, so the Malossi belt just might be worth the extra $11.
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Sun Jun 09, 2019 9:12 pm quote
But won’t a broken Kevlar belt have more chance of locking the real wheel due to its superior strength?
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Sun Jun 09, 2019 9:25 pm quote
znomit wrote:
But won’t a broken Kevlar belt have more chance of locking the real wheel due to its superior strength?
I just watched a documentary series about the people where you live, titled Fresh Eggs, and I asked myself, "Which one of them rides an LX190?"
IF you read some of the stories about broken belts taking out your transmission, it is easy to come to the conclusion that you can break diamonds with glass.
"The belt was broken and my clutch was a mangled mass of metal", doesn't mean the belt broke and destroyed your clutch. Given the materials the belt is made of, even Kevlar, and the materials everything else is made of, and the mass and momentum of all the components involved, and the force required to lock up the back wheel of a moving scooter, it is possible, but not likely, that you could have a very momentary lockup. But a lot of times you open it up and whats left of the sliders are chunks of melted plastic, or the clutch has broken shoes or the pulley has separated at the weld. The belt did not do that.
If broken belts really locked up the back wheel, do you think scooters would be allowed on the roads? If you look at what happened with Big Red, and kids ATVs, I don't think any of the Japanese companies would still sell scooters in the US if this was an issue.
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Sun Jun 09, 2019 11:22 pm quote
It's worth remembering broken belts are not very common either. Yes it happens but often to poorly maintained bikes. Owners often check a belt and because it looks ok and is still in spec regarding measurements, they put it back. They don't consider it's age. An 8-10 year old belt with 9000 miles on it will break if not changed at or near the recommended time interval. That is especially true if the bike has done an amount of two up riding. Probably one in 10 broken belts will cause a rear wheel lock up. So not many and in most cases the lock up is brief...however as with my customers Silver wing 600, it could have you off.

When we ride or drive our cars we all take risks. If anything goes wrong with engines or transmissions the motor can lock. These thing happen everyday. But mostly good maintenance prevents most bad things from happening.

Helicopters & planes crash but no one suggests the makers stop selling them!
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Sun Jun 09, 2019 11:48 pm quote
Motovista wrote:
If broken belts really locked up the back wheel, do you think scooters would be allowed on the roads?
CVT lockups may be rare, and belt only lockups even more so, but I had one early last year.

There were about two seconds of coasting after I lost power and had released the throttle. I didn't even realize what the problem was yet and I was right in the middle of a 'WTF' when my rear wheel locked up hard. I rode out the slide from 45-50 mph to a dead stop. Then I dragged my GT sideways to the median (I was in the left lane) to let approaching traffic go by. A little bit of rocking loosened up the wheel and I was able to push my GT to the right side of the road. Even then it did not roll easily.

I'm back up and running a year+ now with a just a clean out and regular CVT service. No twisted metal, no melted rollers. I installed a Malossi belt and variator tuning kit that I got from you. I also cleaned and re-greased the clutch when I installed the torque converter but the only parts I replaced in the CVT or clutch were "consumables"; rings/seals, slides, rollers, belt, etc.
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Mon Jun 10, 2019 2:06 am quote
I'm guessing your belt wrapped itself around the outside of the clutch drum and jammed against the inside of the transmission case, which seems to be the most often reason for a lock up. It explains why the bike coasted for a couple of seconds and then as the belt was wrapping up the clutch drum, it jammed the clutch solid for a few moments causing the back wheel to lock. Glad you were ok.
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Mon Jun 10, 2019 2:25 am quote
SoCalGuy wrote:
WEB-Tech wrote:
OR
Your doing 70 on a wide bend in the road and the belt breaks, gets jammed in the clutch, locks the rear wheel up and you do cart wheels in the median for 100 feet ....
Huh? Care to explain how exactly a broken belt can get “jammed in the clutch” and “lock the rear wheel up”?

You can't lock up a CVT scoot for the same reason you can't bump start it. The engine must be turning roughly 2,000 RPM to engage the clutch. If a belt breaks the clutch disengages. It doesn't matter how fast the rear wheel is turning, with no belt, the clutch is disengaged. A broken belt is less likely to “lock up the clutch” than it is to sponantously cause your hair to catch on fire.
Ask Jess HE witnessed it during the 2008 Cannonball Run, Unless you are calling Jess a LIAR???
So I guess a belf can lock up a rear wheel.
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Mon Jun 10, 2019 6:55 am quote
Motovista wrote:
scootermarc69 wrote:
... probably my first two belt changes...., probably was using Dr. Pulley. ...
Quite a few broken belt stories share one or both of these elements. You might not know this, but where the Malossi belt uses Kevlar, the Piaggio belt uses polyester. Kevlar is said to hold up better to heat than polyester, so the Malossi belt just might be worth the extra $11.
Not true. The Mitsuboshi belts that Piaggio supply have an identical para-aramid to Kevlar, if not the actual branded product. Possibly Twaron?
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Mon Jun 10, 2019 9:32 pm quote
jimc wrote:
Motovista wrote:
You might not know this, but where the Malossi belt uses Kevlar, the Piaggio belt uses polyester. Kevlar is said to hold up better to heat than polyester, so the Malossi belt just might be worth the extra $11.
Not true. The Mitsuboshi belts that Piaggio supply have an identical para-aramid to Kevlar, if not the actual branded product. Possibly Twaron?
Not for the 50 or the 150. Piaggio belts for the 50 and 150cc scooters have polyester cords, just like the OEM Honda, Yamaha and Kymco belts. None of the OEM belts from major manufacturers in those displacements use Kevlar or Aramid fibers. I don't know how the rumor that all Vespa belts are Kevlar belts started on MV, but it's not true. There seems to be a lot of misinformation out there about belts in general, and Kevlar belts in particular, and a lot of belts are sold as Kevlar belts that aren't. Kevlar belts are better, particularly the way we use scooters in the US, but I don't think most people know how or why.
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Tue Jun 11, 2019 2:49 am quote
Don't see a lot of 50 and 150 belts breaking posts on here, so maybe it isn't an issue.
If Honda and others aren't either maybe it's not needed.
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Tue Jun 11, 2019 6:09 am quote
WEB-Tech wrote:
Don't see a lot of 50 and 150 belts breaking posts on here, so maybe it isn't an issue.
If Honda and others aren't either maybe it's not needed.
With a stock bike, and typical use the scooter is designed for of short trips in stop and go urban traffic, it isn't. The advantages of Kevlar, for our purposes, are it's ability to better withstand the shock from hard stop and go throttling of a modified engine or heavier loads (such as myself), and it's ability to withstand heat better, like the kind that builds up in the transmission from holding it wide open for five miles at a time.
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Wed Jun 12, 2019 5:14 pm quote
i've untangled my fair share of shredded belts and been the recipient of two letting go at speed. i'll say from experience that one let go and coasted and the other locked up due to getting wrapped up in the bell.

the chances of a lock up are small, but do exist.

and i'll tell ya, nothing sucks worse than pushing a bike with a locked up wheel.

-g
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Thu Jun 13, 2019 7:53 am quote
Thanks for weighing in g. Do you remember what scoot that happened on? On some non-Piaggio scoots, I can see how it might be possible for a belt to shed into just the right size bits and the shredded bits could possibly manage to wedge themselves between the cover and the clutch bell in such a way that could possibly lock the wheel. I think the odds of that happening on something from Pontedera are crazy small due to the particular design of the cover/case/bell. The shreds would basically have to fly sideways.
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Thu Jun 13, 2019 8:40 am quote
Predicting what will happen when a belt breaks is like dropping a glass and trying to predict how many pieces it will break into and where they will land. There are way too many variables in play to make an accurate prediction. In a case like that, I ask "what's the worst that can happen?" The answer to that is the rear wheel locks up. Since that can make you change your shorts on a good day, and end up in the hospital (or worse) on a bad day, I'd take the approach of replacing the belt per the recommended schedule or sooner if you think there is a reason to be suspect about it's condition.

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