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Tracer 900GT Front Disc Bobbins


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So, a friend of mine and I both have 2019 Tracer 900 GT's which we have had since new. My friend has a few more weather miles on his than mine and has just had his annual MOT test which came back with an advisory for slight brake drag on his front discs. The dealer said this is not serious but will be down to seized or sticking disc bobbins!

So, my question to you guys is, do you take steps to clear and clean them, and is the nut and bolt trick (ie through the bobbins tighten and then free up with a spanner or power tool) safe and advisable to do and if so how often do you do your?

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5 hours ago, Seawatcher said:

... an advisory for slight brake drag on his front discs.

My first thought would be to clean the caliper pistons (remove them, clean seals, all new fluids)

They are designed to extend during braking, then retract (and crud build up may be inhibiting that)

I don't think the bobbins require maintenance. 

Edited by Lone Wolf
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1980 Yamaha 850 Triple (sold). Too many bikes to list, FJ-09 is next on my list
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I've never done the ones on the Tracer, but I had a Triumph Trophy that had to have them cleaned every 4,000 miles or so to reduce brake "surging". 

I used an ezy-out in a cordless drill to do mine. Insert the ezy-out in the bobbin, spray generously with brake cleaner while spinning it with the drill. You'll be amazed at the "gunk" that comes out of them! Make sure to cover as much of the wheel as possible to lessen the clean-up time.

Just my .02!

2020 Tracer 900GT /1978 Suzuki GS750E /1978 Suzuki GS1000 /1982 Suzuki GS1100E /1999 Honda GL1500SE

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20 minutes ago, 2and3cylinders said:

What the heck are "disc bobbins"?!

Inquiring Yanks want to know!

They are the round "disc" that hold the outer brake disc to the inner hub, so they "float", if that makes sense.

2020 Tracer 900GT /1978 Suzuki GS750E /1978 Suzuki GS1000 /1982 Suzuki GS1100E /1999 Honda GL1500SE

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3 hours ago, 2and3cylinders said:

What the heck are "disc bobbins"?!

Inquiring Yanks want to know!

Best to go to the source here. Meanwhile this is one example. The "bobbins" allow the floating disc rotor to ... float, i.e. move in and out. If they are binding they can also cause rubbing friction at the brake pads.

Silver-Bobbin-angled-1.png

Regards, Grumpy Goat | 2019 Yamaha Tracer 900 GT & 2016 BMW R1200RS

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The reason I have asked for your views is because there are videos on Youtube of owners (various bikes) using power tools to spin the 'Bobbins' with a locked nut and bolt whilst spraying them with brake cleaner and I just wondered if that was a step too far?

I must admit I had not realised that the disc was supposed to actually 'float' on the bobbins so obviously if they get seized up the discs wont move very much. I have tried moving one with a locked nut and bolt and initially it was stiff to move but a few turns seemed to loosen it off. 

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2 hours ago, Seawatcher said:

The reason I have asked for your views is because there are videos on Youtube of owners (various bikes) using power tools to spin the 'Bobbins' with a locked nut and bolt whilst spraying them with brake cleaner and I just wondered if that was a step too far?

I must admit I had not realised that the disc was supposed to actually 'float' on the bobbins so obviously if they get seized up the discs wont move very much. I have tried moving one with a locked nut and bolt and initially it was stiff to move but a few turns seemed to loosen it off. 

What is this crud that is causing the bobbins on a floating disc rotor to seize such that it cannot float anymore and requires these tricks to unseize them?

To me, the root cause of the issue is to see what is fouling the operation of the bobbins, and to remove that root cause. I have never come across any need to do any maintenance on the rotor bobbins on any bike I own, and as far as I am aware this is not a maintenance item beyond normal cleaning of the bike, including rotors.

This thread has me slightly intrigued ... 🤔

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Regards, Grumpy Goat | 2019 Yamaha Tracer 900 GT & 2016 BMW R1200RS

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3 hours ago, Seawatcher said:

The reason I have asked for your views is because there are videos on Youtube of owners (various bikes) using power tools to spin the 'Bobbins' with a locked nut and bolt whilst spraying them with brake cleaner and I just wondered if that was a step too far?

I must admit I had not realised that the disc was supposed to actually 'float' on the bobbins so obviously if they get seized up the discs wont move very much. I have tried moving one with a locked nut and bolt and initially it was stiff to move but a few turns seemed to loosen it off. 

Yes if you do a lot of rain riding, cleaning and lubing is prescribed generally as you described.

I have done it, especially on older high mile bikes.

If done carefully it won't cause damage.

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3 hours ago, Grumpy Goat said:

What is this crud that is causing the bobbins on a floating disc rotor to seize such that it cannot float anymore and requires these tricks to unseize them?

To me, the root cause of the issue is to see what is fouling the operation of the bobbins, and to remove that root cause. I have never come across any need to do any maintenance on the rotor bobbins on any bike I own, and as far as I am aware this is not a maintenance item beyond normal cleaning of the bike, including rotors.

This thread has me slightly intrigued ... 🤔

I agree, I have heard of this but never had a situation where I need to do it myself, but I also don't regularly ride in the wet or ever on salted or chemically treated roads in winter. `

***2015 Candy Red FJ-09***

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Had a problem with my 2020 Tracer 900 GT.  Almost felt like the rotors were warped.  Cleaned the bobbing/buttons carefully did not spin them, got some stuff out but not that much.  I stuck a screwdriver thru them and slightly stilted to wobble them a small amount.  Scrubbed the rotors with scotch brite and brake cleaner and maybe isopropyl alcohol.  Replaced the pads at that time.  Brakes worked perfectly.  Bike had 19,000 miles on it at the time and ow has 27,000 miles.  Ridden in all kinds of weather except snow and ice.  

Talked to a Galfer rep about the rotors.  He said warped rotors will make a pulsating feel in the brake lever at speed.  Mine did none of that so cleaned the rotors and they are good.  No clue what caused it.  

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58 minutes ago, PhotoAl said:

Scrubbed the rotors with scotch brite and brake cleaner and maybe isopropyl alcohol.  Replaced the pads at that time.  Brakes worked perfectly.

... No clue what caused it.  

One of the potential causes is when someone brakes hard and comes to a complete stop, there can be a deposit of brake pad material at that point on the rotor (where someone stopped completely). That can cause a pulsating feel in the lever.

If someone really wanted to nail down the cause, they would do one thing at a time (for example leave the bobbins alone, and just see if doing the disc clean and new pads made the pulsing go away).

Guidance when bedding in new pads is to do several controlled braking cycles but DON'T come to a complete stop, for this reason. Especially important when transferring fresh pad material to a fresh rotor (or cleaned rotor).

Once bedded in, we should be able to come to a complete stop without putting a gob of pad material down, but if they are pulsing that is one of the remedies to consider to fix it.

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1980 Yamaha 850 Triple (sold). Too many bikes to list, FJ-09 is next on my list
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