M620 Went Down After Brake Lockup

[Kegan]

Hey everyone, you may have seen my previous post regarding the front end work I had to do after a run in with a curb. Now to add to my exemplary riding history, I laid my 2004 620 down while decelerating at a stoplight. I'll replay what happened as I remember it, but I don't understand why I went sliding down the road. Any help figuring this one out would allow me to address the issue and get back on the Monster.

1. Clutch in, engine brake (gradually) down to 2nd
2. Brake smoothly with about 60% on the front and 40% on the rear
3. Clutch in, downshift to 1st traveling not faster than 20mph

Okay, here's where problems start. I believe the clutch was in the friction zone when:

4. Braking, braking, lockup, screaming tires, bike violently throws itself to the right
5. I go down, on the right, and so does the bike.
6. I pick the bike up, it's in 1st, and the handlebars are floppy, sliding in their clamps on top of the triple (Speedymoto).

Now I KNOW i torqued everything down before riding after the repairs. I had ridden the bike at least 50mi before this had happened, frequently encountering the exact same conditions. The road surface was without oil, gravel, or other traction robbing material. I made no sudden movements. I'm trying to figure out why I went down; if the front brakes had locked up that would have been one thing, but for the bike to throw itself to the right was unnecessary and odd. I suspect the forks were bent prior to this whole incident, but not by much. Any ideas?

[BK_856er]

Not sure how hard you were braking, but if your forks were seriously low on oil you might have bottomed them out and washed out the front?  Frame and or forks tweaked from your previous incident could cause all kinds of whacky handling behavior.  When you torqued the bars did you do it 1-2-1 with a good torque wrench not at its range limit?  Could the bars have come loose first, rotating and causing abrupt front brake application?  Does sound like an odd spill.  Bike does not sound safe at all!

BK

[rockaduc]

Does the 620 have a slipper clutch?  If not, i think your problem was the downshift to 1st.  Not that you did it wrong, but 1st gear is primarily for accelerating from a dead stop and parking lot stuff.  I never down shift to 1st when i am coming to a light.   It is probably better to skip the downshift to 1st (leave it in 2nd)when coming to a stop and just pull in the clutch while using both brakes.
just my $.02.

[zooom]

2. Brake smoothly with about 60% on the front and 40% on the rear

1st mistake....generally 75+ % of your braking comes from the front and the rear is generally just a small added in portion of braking for stabilization

3. Clutch in, downshift to 1st traveling not faster than 20mph

2nd mistake as previously noted by rockaduc

1st gear is primarily for accelerating from a dead stop and parking lot stuff. 

3rdly...when you downshifted, did you fan the clutch out with any throttle or just pop it?...more than likely...the latter....which when you did so, lurched the bike more forward onto the front end moreso than you already were in braking...during that extra bit of unintended compression, you released traction adhesion from the rear and thereby started the "screaming tires" as you locked up the rear....I am guessing that when the rear locked and the chassis was settling back, you had the bike's rear end start to come around just slightly which started to pitch the front end over as if it would fall into a turn, but you had too much braking force for that sidewall traction and BOOM...."down goes Frazier" as Howard Cosell used to say

but this is all a subject for the "Riding Techniques" section IMHO and not "Tech" as you have posted it...

[battlecry]

If I'm not mistaken, I think the M620 got the slipper clutch in 2004.  I have a 2003 M800 w/o the slipper and due to my probably bushleague technique, I avoid downshifts to first when in motion because it is easy to make it abruptly.  Even when coasting to a stop with the clutch in, I get a clunk on the box, so I time it just before a stop at the light so I can find N. 

Hard to say, and I'm sorry it happened, but perhaps you were close to the rear tire traction limit when braking and the downshift to first overwhelmed the rubber.  I use rear brake a lot on the dirt, but try not to on the street.  I replaced the rear disk on the M800 with one of those petal shaped ones to further reduce it's effectiveness in case I press too hard. 

[CDawg]

Hard to know for sure, but here are some thoughts:

1) If you heard screaming tires then you did lock up the wheels.  Do you remember if it was the front or rear wheel or both that was locked up?    I would tend to agree with the others and guess you locked up the rear.  If you were 60% front and 40% rear and you increased the amount of front braking, then you would loose braking traction on the rear wheel as it unweights further.

2) Assuming the rear did lock up, did you release the rear brake?  I did this once and the bike buckled like a wide horse and flung me off the bike as the rear regained traction and snapped back in line.

3) If you do not have a slipper-type clutch, the rear would shimmy/chirp if you down shift without matching revs.  It's never been so bad for me as to throw me off the bike.  Your experience may vary.

I will echo others and say that downshifting into first from 20 mph is pretty fast and would require matching revs on a S4RS.

Good luck!

[Langanobob]

Regardless of riding mistakes or not riding mistakes,  the thing that sticks in my mind after all this discussion is the bars being loose and sliding in the in the clamps.   I'd sure take a close look at that and come up with a plausible explanation for how it happened.   I've bent bars before but they were always tight in the clamps afterwards and I'm struggling to grasp how they could be loose and sliding, if indeed they were tight before the wreck?

If your forks were bent from the previous accident, braking could have twisted the bike to one side, then if the bars came loose during the twist to the side, I think I may have instinctively grabbed even more brake.

All happens so fast it's hard to piece the sequence all together.  I guess I don't need to suggest to make sure the bike is absolutely mechanically sound and have another set of eyes and hands check it out before riding again.

Glad you are OK.

[BK_856er]

Just to add to my post further up...is there any possibility that the front tire contacted the horizontal cylinder head?  You said you installed new triples after your previous crash.  If the forks were sitting significantly higher (not all top triples are designed the same) you could end up with diminished tire clearance.  Combined with your seriously corroded fork tubes and potential for fork seal damage/leakage/low level, you could run into trouble under hard braking.  Just a thought...

BK

[A.duc.H.duc.]

I'm not really trying to knock all the responses so far as I love the guys on this forum, but I find it hard to believe that locking the rear would cause this. Nor do I think it would have anything to do with it being a slipper, etc. If you're braking in a straight line, not leaned, you can lock the rear all day long and the bikes not going to wash out on you. Letting the clutch out like a neadrethal isn't going to send you pitching over the bars either, it'll just chirp the rear a little bit till the engine slows down. Even if you had a hamfisted front brake, and you brought the back end off the ground you're only going to end up with a little squiggle, so this has to be front end related, well, or the road surface screwed something up, but you already said the road surface was normal. Since it doesn't sound like you were emergency stopping, and you didn't mention anything about poor tire condition, I too have to assume this has something to do with a previously damaged front suspension. If your forks were bent it's conceivable you bound up the front wheel as they compressed, even without the tire hitting the horizontal cylinder head.

   Any news on the bars? did you find out what's made them loose? Damage from the drop, or are they really just simply loose?

Justin

[DarkStaR]

http://www.ducatimonsterforum.org/index.php?topic=50010.msg915364#msg915364

It may be possible that you had leftover damage from nailing the curb in the previous accident causing this incident, or something was not put back together properly.

[bikepilot]

Its hard to lock the front tire on decent asphalt when its already loaded up from braking - near impossible I'd say (you'd endo before you ran out of grip) without something physically locking the wheel.  I'd guess the rear locked - maybe you didn't let up on the rear brake when you banged it down into first and the extra engine braking was enough for it to lock, then maybe it stepped out a bit and then maybe you let up or the clutch started slipping a little, it gripped and tossed you into a high side. 

Also, maybe your clip-on slipped before you crashed and that's what threw the bike to the right.  If you had a bunch of weight on them during braking and one gave way, you'd probably steer the bike really abruptly.

Any obvious brake or wheel malfunctions when you picked the bike up?

[Kegan]

Thank you to everyone who replied. It's really helping me sort out what happened. I agree with moving the thread, I'll do that when I figure it out.

I'm beginning to think I must have locked up the rear based on everyone's input. I think A.duc.H.duc. hit it on the head in his analysis, and furthermore I'm technically understanding how the accident could have occurred. The forks needed to be replaced anyways (thank you for linking my other thread with pictures from my retarded curb incident), and could have contributed greatly to the issue. It is possible the bars came loose while the bike was locking up, causing instability as I leaned during the forward pitch and thus me falling, although I, in hindsight, think they probably got knocked loose from impact.

There were no brake or wheel malfunctions after I got it up and running. Out of poverty (not stupidity), I did baby the bike back home without incident. Everything was sound enough to limp home, but the handling felt unstable and I was wary of going too fast or changing lanes. The steering assembly (bars, triples, instruments, etc) was not straight even when the bike was traveling in a straight line, leading me to believe the forks are definitely extensively damaged. New ones are in the mail.

The consensus seems to be that downshifting to 1st too fast + bent forks + possible improper braking technique + gremlins from the first incident = me going down. Right?

I feel like a complete idiot after all this. Granted, I'm brand new at riding, but I paid attention at and easily passed the MSF course, am not reckless, and cringe when I see some asshat on a Ninja going 90 with no gear on. Is there something I'm missing?

[DarkStaR]

Maybe you locked the front on either slick painted road surface, or the oily center portion of the lane that accompanies stop light intersections?!?!?

[H-2 CHARLIE]

  If the bike has a slipper clutch then a fast down shift the 1 st  might not have ben the problem but if your not using a organic rear pads , it could  have locked up fast and  these could be it ,  its hard to controll a rear skid for more then 15-35 feet  if even that .

[RAT900]

The only other thing I can think of would be if you re-bled/changed out the brake fluid when you pieced together your front end again

and used Brand X brake fluid made in some Chinese Mainland Mouthwash factory

swollen seals/low boil point etc etc