Fishtailing on hard braking

[NOLAGuzzi]

My breva has recently decided this is a fun behavior. I don't agree. It scares the crap out of me. My tires are good, and properly inflated, so they should not be to blame. What is the most likely culprit here?

[GT-Rx]

Assuming there was no change in how you apply pressure(?). If not, I advise checking over the caliper as perhaps the pistons have begun to seize or some foreign matter has lodged into the pads/disk? Just a guess, but a good place to start. Will you do the trouble-shooting, or will a shop or dealer?

[NOLAGuzzi]

I'd like to do the trouble shooting, but as I am somewhat limited on tools and knowledge it may wind up with a local shop.
I don't understand what you mean by a change in how I apply pressure.

here is a little more info though. I noticed this last time I really needed to stop quickly. I have on more than one occasion locked up the rear wheel to avoid t-boning cab drivers and oblivious drivers etc... Every time (at least a dozen) that has happened my bike continued to track a pretty straight line. I had an oh shit moment the other day and now it fish tails which is different than my previous experience. I tried a few more controlled hard brakes and it is easy to repeat.

I'll check the pistons, pads, and disc. in anycase. I can handle that task.

[rossw]

I'd like to do the trouble shooting, but as I am somewhat limited on tools and knowledge it may wind up with a local shop.
I don't understand what you mean by a change in how I apply pressure.

here is a little more info though. I noticed this last time I really needed to stop quickly. I have on more than one occasion locked up the rear wheel to avoid t-boning cab drivers and oblivious drivers etc... Every time (at least a dozen) that has happened my bike continued to track a pretty straight line. I had an oh shit moment the other day and now it fish tails which is different than my previous experience. I tried a few more controlled hard brakes and it is easy to repeat.

I'll check the pistons, pads, and disc. in anycase. I can handle that task.

What about swingarm bearings and wheel bearings?

[john zibell]

The big mistake is locking the rear wheel. Better technique is a firm progressive (increasing pressure gradually) on the front light to lighter on the rear. You can get 100% braking force on the front wheel (stoppie) but normal hard braking should be in the 90% range. If you do lock the rear, as long as you are looking straight ahead, it should continue to track straight. If you look to either side, then you will get the sideways motion. This is what I think is happening and subconsciously you are trying to correct the slide resulting in the fish tailing. Another though is you aren't looking far enough ahead and you are getting surprised by traffic resulting in the need for frequent (as you say about a dozen times) hard braking.

[NOLAGuzzi]

I agree that locking the rear wheel is not ideal. That does not happen every time I brake hard, but it does happen on occasion. I guess what I was trying to convey that I have experienced the spectrum of needing to slow down quickly up to the point of locking the rear wheel and have not experienced fishtailing. Now I do and I can reproduce the effect without locking up the wheel by braking hard. Something feels very different about the way the bike handles. Thanks for the reminder to keep my eyes up.

[Paxo]

I expect these are too obvious but might possibly hold a clue. When was the last time you checked your tyre pressures, the wheels and tyres (front and rear) for any wear or damage, tightness of the wheel axle nuts? John is right though, you should never be regularly travelling so fast that every stop is an emergency. If you are then sooner or later there's a hospital bed with your name on it! Take it easy and have more fun.

[ghezzi]

Firstly, the camber of the road can have an impact. Initially the rear wheel will want to drift down hill, then your (over) correction may bring it back etc. etc. If you want to test it, find a dead flat surface ..........................

Not knowing your level of experience this leads me to make 2 recommendations.
1. Have your bike checked out for everything from steering head bearings to loose spokes by a reputable Guzzi specialist, then have your suspension dialled in for your weight & riding style.
(in reality, any possible serviceing issue/part failure that may cause fishtailing should also be recognizable by other poor handling traits)

2. Book yourself into an advanced "Road craft" riding school and hone your skills and understanding of the dynamics of motorcycling.

I only say the above because in any situation "if you cannot place the motorcycle precisely where it needs to be, YOU are out of control". Once you have locked a wheel, or begin to slide you have lost control.
Supermotard, MotoGP etc are excluded here as we are talking road riding. It is totally normal for a rider/driver to lock the brakes of their vehicle in an emergency, but normal doesn't mean best practice or safest technique. That's why ABS etc has been invented because most of us are incompetent and panic in these situations.

Knowledge and lots of riding practice will bring the experience we all need.

[NOLAGuzzi]

First thanks for the concern about my riding abilities, but don't misunderstand what I am saying. I have, but do not routinely do it, experienced the joy of locking up my rear wheel when someone threatened to or actually pulled out in front of me. I don't routinely come sliding up to stop lights and the like. If I went to an MSF course on my bike right now and did the quick stopping drill the instructors would likely tell me there is something wrong with my motorcycle.

Now let me again try to explain what my issue is more clearly.
I ride on urban surface streets every single day. I'm not talking about broad thoroughfares, but camera enforced 35-45 mph pothole pocked surface streets. In the seven years I have engaged in this activity I have needed to use hard braking/evasion, which I learned in both the basic and advanced MSF courses, on about a dozen occasions. If that seems unreasonable, then you (no one in particular ) are not remotely familiar with urban motorcycling. I am not talking about slamming on brakes from 60+ mph. Always less than 50 and very rarely that fast. The scenarios which concern me are like
1) oh shit that cab driver is looking right at me but I see his front wheel moving forward, I'd better stop.
2) I'm not going to make it through that intersection without having my picture taken either speeding (which I'm not doing to begin with but would be to make it through the light) or running the light so I need to stop.
3) There are mardi gras beads or gravel or sand or drunk people wearing mardi gras beads all over the intersection, I'd better stop.
4) That new pothole may go all the way to China and spans both lanes! I'd better stop.

These are examples of plausible reasons to need to stop quickly other than bad riding habits and excess speed which may be encountered on ANY given day on my commute. I'm not saying I don't have any bad riding habits but speeding and following too close are not among them.

In the past when I have encountered these situations and needed to stop quickly I have not had worries or issues with the stability of my bike. Now things have changed and it sucks and I would like to fix it.

Now, that being said. I truly appreciate the replies and will check out the Steering and swingarm bearings. I could not find any issues with the operation of the brakes but there is nothing fouling the pads or disc and the pistons move freely. The tires only have a little over 1000 miles both front and rear and I check the pressure regularly. The breva has alloy wheels, no spokes, and YSS rear shocks and Hyperpro progressive springs dialed into my weight plus luggage and the bike has NEVER exhibited the fishtailing tendency until last week. I can easily reproduce the problem in a level parking lot by quickly stopping in a straight line, without locking the rear wheel, from no more than 30 mph. Having a bike to commute on makes one of the most dreaded parts of my day, the commute, one of the high points but I need to have confidence in the behavior of my bike, especially when I encounter an oh shit kind of moment.

[Paxo]

Sorry if you felt your riding abilities were being insulted but it just wasn't clear from your post what your level of riding skills are. For what it's worth I learned to ride a bike in the centre of London and did courier work for a while as well as commuting in one of the world's most congested cities, so I do understand where you're coming from!

Back to the problem....it does seem that your bike has developed a major and potentially dangerous fault which could be anything from shot wheel bearings to a broken frame member. Whatever it is, I doubt very much anyone can diagnose the fault via the internet and you really need to get your bike checked over. Sooner the better. Metal is easier to fix than bones.