Unusual brake problem on 900GT

[John_D]

I have a Tracer 900GT which I bought about 18 month ago.  Late last year, on a 1500 mile trip to and around Scotland, the braking performance gradually deteriorated.  Gone was the sharp, instant braking achieved with just one or two fingers.  I found myself using my whole hand to brake.  It got to the point where I didn't feel happy riding in traffic at any speed.  Gone was the sharp, instant braking achieved with just one or two fingers.  The lever didn't feel particularly spongy or have excessive travel but it needed much more force than before.  The ultimate braking force was seriously compromised and stopping distance was way more than it had been.

I called the dealer and explained the problem.  A week later they had the bike in their workshop on a rolling road and ran their diagnostics.  The mechanic came out and said he couldn't find a problem and said that the brakes seemed OK to him.  I was invited into the workshop where he re-ran the diagnostics including the ABS system test so that I could see for myself that everything was OK.

I left the shop feeling unhappy that they hadn't found or fixed the problem.  However as soon as I started to ride home I could feel that the brakes were back to normal. They had obviously done something that had fixed the problem, even if they didn't know it.

Unfortunately, after a few hundred miles of riding, the brakes began to deteriorated again and they are now as bad as they ever were.

Has anyone else had or heard of this problem?

Is it possible that the ABS is reducing brake performance all the time, not just during extreme braking?

 

 

 

Edited May 18, 2020 by John_D
Removed a duplicated line

[roadrash83]

@John_D First thing I would do would do is bleed the brakes and activate the ABS to flush out the system. Also replacing the rubber hoses with braided lines is a big improvement. Do both of those thing at the same time and save some aggravation.

[betoney]

4 hours ago, John_D said:

Is it possible that the ABS is reducing brake performance all the time, not just during extreme braking?

The ABS pump is inactive until needed, the fluid just passes through.  When the wheel sensors detect a skid and the wheels get out of sync then the ABS solenoids activate.  If you pulled the fuse for the ABS, your brakes would still function normally, except the anti-lock function.

Is your brake issue happening to both the front and rear?  I don't know if you have salts and corrosives on the road surface but I would check the cleanliness of the caliper pistons.  Buy a can or 2 of brake parts cleaner and some green kitchen scrub pads, not the red ones as they are too abrasive.

Remove the calipers one at a time, pump the brake lever to extend the pistons (careful not to extend them too far) and gently clean the crap and corrosion.  The entire sliding surface of each piston should be shiny.

Also pull the slide pin for each set of brake pads and make sure it is clean and smooth with no grooves for the pads to hang up on.

[skipperT]

Any idea if the tech at the shop took the bike for a ride before performing tests, etc?

you need to bring it back when it’s symptomatic and ask the same guy to ride it again. Then he will see that there’s something going on. explain that it was all fixed for a period of time and then became a problem again. Tell them how long approx it took to develop the problem again so they can duplicate the issue. 
-Skip

[BBB]

I would change the brake fluid completely, a full flush. The fluids are hygroscopic and your symptoms could be due to too much water in the fluid which boils under heat and compromises the ability to get a hard feeling lever.

Try also cable tying the front lever hard to the grip overnight and see if the responsive feel comes back. Sometimes the accumulation of tiny bubbles compromises the brake feel and keeping pressure on makes the bubbles smaller so they can make there way back to the reservoir more easily.

[John_D]

21 hours ago, roadrash83 said:

@John_D First thing I would do would do is bleed the brakes and activate the ABS to flush out the system. Also replacing the rubber hoses with braided lines is a big improvement. Do both of those thing at the same time and save some aggravation.

Thanks for the quick reply.  I'm not convinced that bleeding will help because the dealer didn't bleed the brakes and yet the problem went away for a while.  Also, I'm a bit reluctant to do anything myself until I've at least spoken to the dealer again which is a bit of a problem  at the moment because of Covid-19.

[John_D]

20 hours ago, betoney said:

The ABS pump is inactive until needed, the fluid just passes through.  When the wheel sensors detect a skid and the wheels get out of sync then the ABS solenoids activate.  If you pulled the fuse for the ABS, your brakes would still function normally, except the anti-lock function.

Is your brake issue happening to both the front and rear?  I don't know if you have salts and corrosives on the road surface but I would check the cleanliness of the caliper pistons.  Buy a can or 2 of brake parts cleaner and some green kitchen scrub pads, not the red ones as they are too abrasive.

Remove the calipers one at a time, pump the brake lever to extend the pistons (careful not to extend them too far) and gently clean the crap and corrosion.  The entire sliding surface of each piston should be shiny.

Also pull the slide pin for each set of brake pads and make sure it is clean and smooth with no grooves for the pads to hang up on.

Thanks for your comments. 

After I posted I went for a ride to see if I could get the ABS to activate, again.  On a slightly dusty road I managed to get the rear to pulse a few times by applying really heavy presure to the pedal.  I'm not sure if the performance of the rear brake has changed because it has always been next to useless so it could probaly fail completely and still have minimal effect on stopping distance.

I applied as much pressure as I dared to the front which just confirmed that the stopping distance was a lot more than I would like.  Given the poor deceleration, I'm not surprised that I didn't get the ABS to activate.

The caliper pistons are fine.  This is no surprise because the the bike has only done 5000 miles and has been ridden rarely on salty roads.  Haven't checked the slide pin yet.

As I said to roadrash83 , the dealer made things better, for a while,  simply by running their normal diagnostic tests and then measuring brake performance on their rolling road.  I don't think that would fix corrosion or wear problems at the brake caliper.

I take your point that normally the ABS is inactive until needed but what if the ABS unit is faulty, e.g. a sticky solenoid or a leaky valve?  Could that result in reduced fluid pressure in the caliper?  Is it possible that a faulty ECU or sensor results in the system being in a constant anti lock state, again applying only reduced pressure to the brakes?  These are the sort of things that might be fixed, at least temporarily, by the diagnostic tests and associated system reset.

 

 

 

 

 

[John_D]

20 hours ago, skipperT said:

Any idea if the tech at the shop took the bike for a ride before performing tests, etc?

you need to bring it back when it’s symptomatic and ask the same guy to ride it again. Then he will see that there’s something going on. explain that it was all fixed for a period of time and then became a problem again. Tell them how long approx it took to develop the problem again so they can duplicate the issue. 
-Skip

He rode it a short distance from the car park to the workshop entrance at the back of the shop but he didn't give it a proper test ride.  My understanding is that first he ran tests with the  Yamaha diagnostic unit and then verified the brake performance on the rolling road.  He didn't find any problems so I can understand why he didn't feel the need for a test ride.  He was sufficiently confident to re-run the diagnostics in my presence to give me confidence that the bike was OK.

I was already thinking as you are.  Late yesterday I did manage to get the dealer on the phone.  He agreed that he'd have another look.  I suggested an initial test ride and he readily agreed.  Unfortunately I'm not sure when that will happen because of covid-19.

 

 

 

[John_D]

18 hours ago, BBB said:

I would change the brake fluid completely, a full flush. The fluids are hygroscopic and your symptoms could be due to too much water in the fluid which boils under heat and compromises the ability to get a hard feeling lever.

Try also cable tying the front lever hard to the grip overnight and see if the responsive feel comes back. Sometimes the accumulation of tiny bubbles compromises the brake feel and keeping pressure on makes the bubbles smaller so they can make there way back to the reservoir more easily.

Thanks for your suggestions.

Cable tying the lever was the first thing I tried.  It worked wonders for my old VFR800 on several occasions but made no difference at all to the Yamaha.

I'm confident that the fluid is OK because the standard Yamaha diagnostic tests fixed the problem, if only for a few hundred miles.  If the fluid had absorbed water then the only way to fix it would be to replace it.

 

 

 

[skipperT]

John- do you have aftermarket levers or anything else installed on the bars? How about the grips? Have the wheels been off since you purchased the bike?

-Skip