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Rear brake dragging


jstehman

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I just noticed today after a good long ride that my rear brake may be dragging. The rotor was hot to the touch.

 

Realizing that the VFR has linked brakes, I touched the left front rotor and it was warm. Right front rotor was cold.

 

I would expect the rear to lock if there was a fluid return blockage.. it has not.

 

Rear brake master cylinder fluid level was at the maximum, almost touching the rubber insert.

 

Front brake master cylinder fluid level is I'm assuming completely full, I can see no bubble in the window and the fluid is copperish in color.

 

Maybe I'm just using the rear more?

 

Also I can hold the rear pedal down and cannot wiggle the caliper. When I release, I can wiggle the caliper so the fluid return must be ok

 

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Pop it up on the center stand. Does the rear wheel spin freely?

You may be right in saying you might just be using the rear more. I've noticed with my 8gen non linked brakes that with just normal riding with a balanced normal use of both front and rear braking, the rear gets incredibly hot compared to the front twin discs that have a good flow of air over them. The rear disc being blocked off from cooling air via the wheel rim.

I was so concerned for the rear brake disc temp that I went on a ride and only used the front brakes, the rear disc was cool and no dragging evident when spinning the wheel on the center stand. Even with light use of the rear brake, it's disc seems to get very hot when comparing to the fronts.

Cheers.

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I thought I felt it dragging when I had the wheel off for tire change.

 

But I've never had a SSSA before so I'm not sure what to expect as far as how many revolutions or how much freewheel there is to be expected. Also with a cold chain

 

I can hear normal pad/rotor rub

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Left front brake seems to make more rub noise than the rest.

And that's the one activated by the rear brake correct?

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3 minutes ago, jstehman said:

I thought I felt it dragging when I had the wheel off for tire change.

 

But I've never had a SSSA before so I'm not sure what to expect as far as how many revolutions or how much freewheel there is to be expected. Also with a cold chain

 

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Try running your bike in 1st gear whilst on the center stand. Pull the clutch in and the wheel should slowly come to a stop or very near stop, if it stops quickly then suspect a dragging brake.

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1 minute ago, jstehman said:

I'll try the centerstand test tomorrow.

Should I be concerned with the front master being overfilled?

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General rule, shouldn't ever overfill any master cylinder brake or clutch.

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Yeah I thought that was the rule.

I took a few mls out of the rear master since it was full full. Looks like I will take some out of the front tomorrow also.

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11 minutes ago, jstehman said:

Left front brake seems to make more rub noise than the rest.

And that's the one activated by the rear brake correct?

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Rear brake pedal also operates Front Left Caliper center piston.

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Front master

 

There was fluid all the way up to the diaphragm. Probably ok but jeez there's a lot 5a3dc9b49e58b4aa3dbaa57a09ff284d.jpg

 

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I have the same issue with my 2006. I just replaced the pads front and rear recently and did clean up the pistons a bit. It was so hot on the rear I ended up taking a laser temperature sensor with me. Over 150 degrees without using brake in the rear at all. I can barely spin mine rear wheel on the center stand.

I took the rear wheel back off, removed the caliper and looked. It seems like the center piston that is linked to the front is not retracting all the way. I pushed it in, put it back together and the wheel would spin way freer than it was. But then after a ride, the rear is dragging again.

 

I too have pretty full fluid on both front and rear (this is all new stuff to me). I'm wondering if there is something else that needs to be bled a bit to reduce pressure?

 

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I put the bike on the centerstand and clicked her into first gear. Let out the clutch then pulled it back in.

The wheel kept spinning for maybe 10 revolutions then slowly came to a stop. I do not believe I have a dragging caliper.

Just weird this linked brake system. I will probably pull the calipers off anyway to clean off the seals and lube the sliding pins and the backs of the pads.

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The main causes of pistons not retracting/pads staying in contact with the disc are either sticky piston seals (trapped dirt or corrosion on the piston), poor movement in the caliper slide pins (lack of lube) or fluid pressure not releasing. If you can release the pad binding by cracking the bleed nipple, then it most likely is the latter.

 

You may need to check the secondary master cylinder to ensure that the pushrod is moving in/out freely i.e. not seized. Then there are some very small ports in the master that can clog and these will trap fluid pressure and cause brake drag. In the SMC there is also a plastic one-way valve/filter that has another tiny port that can clog. If you remove the hose fitting where fluid enters the SMC you will find that one-way valve and also the compensation port.

 

Here's a link to the ST1300 owners site, these bikes use a very similar brake arrangement and have all the same issues as VFR800's.... https://www.st-owners.com/forums/threads/st1300-photos-of-dismantled-smc.157318/#lg=post-2000958&slide=21

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3 hours ago, jstehman said:

Front master

 

There was fluid all the way up to the diaphragm. Probably ok but jeez there's a lot 5a3dc9b49e58b4aa3dbaa57a09ff284d.jpg

 

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That fluid is really dark and needs to be changed.   New fluid has a hint of a golden hue  but is practically clear.  When it gets dark it has  absorbed moisture and / or deteriorated.   There is an excellent thread in the maintenance section on how to accomplish that task.  I just did a fluid change on mine this w/e and added a comment to the thread.  Use only DOT 4 fluid, not 3 or 5.  Be sure to do the clutch while you're at it.

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Well I'm sure I can look forward to at least a good bleed of the system. Got some reading up to do on that procedure..

I will probably lube the calipers while I'm there

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Rear caliper dragging may generate so much heat that it catches on fire... it happened to Marv's 4 pot Brembo on his ZX7R...

 

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Got through the fluid change/bleed.

Also cleaned up the rear caliper before install.

I think the brakes feel much better than they did before

Rear rotor still getting warm.. pistons are definitely releasing.

Still have at least 4mm of pad material.

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  • 2 weeks later...

Another update to this thread..

I had her up on the centerstand today to lube the chain and gave the wheel a good spin. Got around 1.5 revolutions before it slowed and stopped.

I believe there is no brake dragging and the wheel felt very free to spin.

I lubed the chain and parked her for tonight.

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