Need help diagnosing brake shudder please.

[Colemine]

Hi Guys

I am having an issue with brake shudder on my nc700 front brakes. I initially thought the brake disc was warped. So I bought a new disc and the shudder went away. For a few hundred km at least. Now it's back. As you can see on the attached photos there is strange patched discoloration on the old and the new disc. I took off the wheel and took it to a wheel repair center where they put it on a lathe and measured the disc with a dial gauge. They confirmed the the disc is not warped and running straight. I have also flushed the brake fluid and bled the brakes. This shudder has also continued across 2 pairs of brake pads. I am stumped as to what can be causing this. The bike will brake relatively smooth from high speed and once the speed gets around 30km/h the front will start shuddering. Anybody have any ideas?

 

[670cc]

I noticed the pattern on the disk in the upper photo shows 5 discolored areas, coinciding roughly between the 5 bolt mounting locations. I’ve never heard of such a problem, so I’m just speculating wildly. Could this have something to do with the right wheel axle spacer or the mounting lugs for the brake caliper? Could the caliper somehow be severely offset from the plane of the disk? Does the wheel spin freely when the brake is not applied?

 

[Colemine]

Yes it spins freely. I have looked at the caliper and cannot see anything wrong. If it was offset then it should be binding continuously if the disc is true. As I said, I am stumped.

 

[HarveyM]

Just spitballing but Piston sticking? Causes the pads to be out of parallel when engaging. Less disc flex were the bolts are = more pressure, friction there. Bent wheel/ bad wheel bearings (wheel runout instead of disc runout)? Head bearings bad?

 

[showkey]

I am with Harvey.........on the caliper piston not retracting.......... causes, piston sticking in the caliper bore, caliper seal issue, brake master cylinder not releasing pressure. By the discoloration of the disk it appears the pads are dragging once your riding. (The caliper piston seal is responsible for the piston retraction )

That discoloring looks like it’s getting really really HOT !!!!!!

Stock brake lever ? Aftermarket lever might be holding the brake on ????
Are the pads wearing evenly.......the caliper slides or floats on the caliper pins. Bent or stuck pins would cause the whole caliper to stick. Usually the piston pad wears more quickly and the one side of the rotor would show more heat or wear when compared to the other side.

Ride the bike under normal conditions for several miles.......stop, place on center stand and immediately check to see if the front wheel spins without dragging.

When the wheel was inspected and checked for runout ..........were wheel bearing were checked for smooth operation, no sticking or notchy feel, rust or sloppiness ?????????

If debris blocks the compensating port in the master cylinder , brake pressure will trapped or held in the caliper causing drag only when your riding.

 

[ld_rider]

I see two rotors and they are not the same. I would stick with an OEM part to eliminate one variable.

 

[TacomaJD]

I see two rotors and they are not the same. I would stick with an OEM part to eliminate one variable.

My thoughts exactly.

Also, sounds like the same exact problem another member was having on here. Was it Afan?

About the only other variable you could change would be the caliper. Maybe like mentioned before there could he a piston not functioning properly causing uneven pressure on the rotor, possibly warping it?

Or, maybe there is supposed to be a shim or something behind the back pad that isn't there anymore and like Greg mentioned, its causing more pressure on the outside than the inside, instead of even pressure on both sides, and this is causing you to be able to feel the 5 points around the rotor where it's mounted to the wheel.

This would make sense as to why it went away when you got a new rotor put on then came back. A new rotor would he hard, but as you used it more, the heat could make the rotor a bit softer and able to move more in between the mounting points.

Sent from my SM-G930V using Tapatalk

 

[BFair]

Should make sure brake discs are not glazed over, flush brake fluid, clean around pistons with tooth brush. And be sure wheel is installed correctly, meaning forks aren't binding when compressed by using a specific torque method, compressing the forks then tightening up axle punch bolts. Pads could be grabbing asymetrically. Make sure the disc is not overtorqued distorting the metal.

Once a pad gets contaminated it can be nearly impossible to get clean again. If you have a digital caliper, measure brake pads to see if they are wearing evenly and from front to back. Usually standard to replace pads with new rotors. The caliper is almost undersized for the rotor. Most will share braking duties with dual disks. That's another post sorry.

 

[Colemine]

Should make sure brake discs are not glazed over, flush brake fluid, clean around pistons with tooth brush. And be sure wheel is installed correctly, meaning forks aren't binding when compressed by using a specific torque method, compressing the forks then tightening up axle punch bolts. Pads could be grabbing asymetrically. Make sure the disc is not overtorqued distorting the metal.

Once a pad gets contaminated it can be nearly impossible to get clean again. If you have a digital caliper, measure brake pads to see if they are wearing evenly and from front to back. Usually standard to replace pads with new rotors. The caliper is almost undersized for the rotor. Most will share braking duties with dual disks. That's another post sorry.

Hi

Thanks for your reply

Here is what I have done. Replaced Rotor, flushed brake fluid 3 times. Disassembled and serviced the caliper, replaced brake pads, replaced wheel bearings, removed forks and made sure they were straight and checked fork oil level. Put them back again correctly. Replaced the steering head bearings. Checked the master cylinder. Put rim on lathe to check it and the rotor isn't warped. Replaced the tire and balanced the wheel. Checked torque on every bolt and nut on the front end to make sure nothing is too loose or too tight. I even took the front wheel with rotor off another NC and put it on my bike and the shudder was there immediately. I spoke to numerous mechanics about it they were all stumped. I am still stumped. I just gave up and sold the bike.

 

[BFair]

Colmine, thanks for the comprehensive followup. To often these threads go on and on with the basics. You certainly went over and above with diagnosing your problem. I would have gotten rid of the bike as well, not a typical Honda problem.

You eliminated all areas, wheel, brake, suspension, ect. If there is a flaw with this bike we can look for it now and know what it's not. How many miles when it started, to finish off the data?

The only item left could have been a faulty brake master cylinder intermittently not holding pressure. The ones Honda uses are quite universal.

I will look for it in my bike, I have found the brakes to be intermittently "squeaky." I'm not really impressed with the small 2 pot caliper.

 

[TigerDude]

I feel like the brake thing was a manifestation of the problem, not the cause. The bike shudders, so the wheel shakes against the pads.

I would start with the head bearing (Honda calls it the stem). Then I'd check the rear suspension. IIRC, the Harley death wobble started in the rear end but manifested in the front. So rear bearing, shock, swingarm, alignment.

 

[Colemine]

Colmine, thanks for the comprehensive followup. To often these threads go on and on with the basics. You certainly went over and above with diagnosing your problem. I would have gotten rid of the bike as well, not a typical Honda problem.

You eliminated all areas, wheel, brake, suspension, ect. If there is a flaw with this bike we can look for it now and know what it's not. How many miles when it started, to finish off the data?

The only item left could have been a faulty brake master cylinder intermittently not holding pressure. The ones Honda uses are quite universal.

I will look for it in my bike, I have found the brakes to be intermittently "squeaky." I'm not really impressed with the small 2 pot caliper.

It was aroung 20k miles. Yes I agree about the caliper. I was actually playing with the idea of buying forks and front wheel from another bike with the same diameter and twin discs and calipers and fitting them. Just never found a suitable set. Would be interesting though.

 

[BFair]

Show key's post #5 shows an excellent picture of the brake cylinder and describes the function of this well. Knowing how hard carb jets and orifices are to clean, it could be manufacturing junk in the compensating port. But my second guess would be the ball which acts as a valve was manufactured with a flat spot which could cause intermittent pressures.

Most of my brake cylinder failures were in that circuit where the brakes would not release causing drag and lockup. I could not get them to release even after a rebuild. Which leads back to that ball. Thanks for the picture.