Tank slapper bent my rear brake lever

[egleaves_imp]

I’ve read of it happening for a few common reasons:

Coming down from a wheelie
Bad head bearings
Bent rim
Tire out of balance
Sudden steering input

My tire is suspect #1 , but it seems really strange that it happened at relatively low speed, while decelerating, and under light braking. Basically everything you’re supposed to do in order to mitigate the wobble is what I was already doing. Still trying to figure out why it happened. I’m sure the bald front tire wasn’t helping, but I have a hard time believing it was the cause in this case.

[Lord Popgun]

I just took a look at my rear brake and I would not recommend kicking it back into position. You could bend the pivot mount or maybe crack the lever and not be able to see it. Looking at mine there seems to be a place it could crack and you not see it. Hard to tell.

I would remove it and bend it and examine it closely before re-installing.
I’d examine the switch and linkage too as you never know when a big shock occurs.

[egleaves_imp]

I just took a look at my rear brake and I would not recommend kicking it back into position. You could bend the pivot mount or maybe crack the lever and not be able to see it. Looking at mine there seems to be a place it could crack and you not see it. Hard to tell.

I would remove it and bend it and examine it closely before re-installing.
I’d examine the switch and linkage too as you never know when a big shock occurs.

Thanks, popgun. That's exactly what I was wondering about. I won't try to bend it back until I get home and can detach it.

[jtopiso_imp]

I just took a look at my rear brake and I would not recommend kicking it back into position. You could bend the pivot mount or maybe crack the lever and not be able to see it. Looking at mine there seems to be a place it could crack and you not see it. Hard to tell.

I would remove it and bend it and examine it closely before re-installing.
I’d examine the switch and linkage too as you never know when a big shock occurs.

Thanks, popgun. That's exactly what I was wondering about. I won't try to bend it back until I get home and can detach it.

I assume it is not made of aluminium. If it is, don't even try to bend it back: it will be brittle and unsafe to use even if you get it to look good.

If it is steel, probably you'll be ok, unless you can find some cracks.

[dave]

Did your front tire wear unevenly (like mine did), with high and low spots on the sides? If your answer is yes, then I suspect the tire caused the wobble. My CB1100 started to head shake when the tire wore like this, and I replaced it. I switched to a different brand (can't remember off the top of my head right now) but the head shake completely went away, and the new tire is wearing much better (I'm on the third front tire now). A friend of mine crashed his CB750 back in 1981 because of unexpected head shake. Luckily he survived, but he sold the bike immediately.

[jtopiso_imp]

Had a little scare this morning on the way to work. As I’m approaching my freeway exit I get over with plenty of time and fall in line with other traffic slowing for the exit. We had collectively slowed to around 50mph when my bike went into a violent wobble that must have lasted 2 or 3 seconds. My feet were thrown of off the pegs and the rear started alternately beating the insides of my legs while the bars whipped back and forth. I thought for sure I was going down, but I kept my cool and reacted without panicking. My legs are killing me, but I kept the bike up.

Speeds were about 50mph and slowing gently, no hard braking, no known road obstacles. It felt like the rear brake was locked up for the whole wobble. Riding the last mile to work felt odd every time I applied the rear brake….once I parked the bike I found that the rear brake lever is bent up and out which drastically changed its position relative to my foot. That’s why things felt different.

Could that lever have been bent (out and up) by my leg smashing into the side of the bike? It wasn't like that when I left the house. Think I can just step on it to bend it back, or would I be putting weird stress on other components that I can’t see?

I'm still trying to replay the whole thing in my head in the hope that I can determine the cause of the wobble. The bike has never done that, and aside from cars ahead and behind me conditions were pretty favorable.

I am trying to think on the causes:

-worn tyre means smaller tyre radiuis, so smaller steering trail.
-braking means bike dives, so lower trail too.

Still, I'd say this would mean the bike isn't as stable as it could be, but is that enough to cause a tank slapper... :-? I wouldn't think so!

Check your pressures (again: affect your tyre radius->steering trail), and check your suspension preload settings (rake -nose down attitude- will decrease trail too).

And, if you find the root cause, please let us know!

[the Ferret]

Just out of curiosity, when you slowed down to 50 mph you didn't sit up and let go of the bars momentarily did you?

[egleaves_imp]

Wow. Have you made any mods to your front end? Or raised the rear? I thought the rake on the cb1100 was long enough to make a tank slapper very unlikely.


Sent from my iPhone using Tapatalk

Just out of curiosity, when you slowed down to 50 mph you didn't sit up and let go of the bars momentarily did you?

I had a proper grip on the bars…..not too tight, firmly positioned, elbows bent slightly. Good thing too, or I don’t think I would have recovered it.

I checked the pressure this morning and it was down to about 27-28, so I brought it back up to ~35psi. It seems like I lose about 1 or 2 psi per month and have to top it off again. I do believe that more frequent checks are in order.

Did your front tire wear unevenly (like mine did), with high and low spots on the sides? If your answer is yes, then I suspect the tire caused the wobble. My CB1100 started to head shake when the tire wore like this, and I replaced it. I switched to a different brand (can't remember off the top of my head right now) but the head shake completely went away, and the new tire is wearing much better (I'm on the third front tire now). A friend of mine crashed his CB750 back in 1981 because of unexpected head shake. Luckily he survived, but he sold the bike immediately.

No scalloping, if that's what you mean. The profile is evenly bald out to the chicken strips.

[VLJ_imp]

Quote:The profile is evenly bald out to the chicken strips.
The same could be said of most CB1100 riders.

[emptysea]

What tires are you running?