Rear brake disc intermittent rubbing on caliper bracket


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kerravon
Posts: 28
Joined: Tue Dec 29, 2020 6:15 am
Location: Sydney, NSW, Australia
Motorcycle: GL1500 1990

Rear brake disc intermittent rubbing on caliper bracket

Post by kerravon »



I've been following the DIY articles to get a new to me 1990 wing back on the road for months and there is one final step that has me beat. I rebuilt my rear brake calliper, replaced the swing arm bearings, rear wheel bearings and brake pads. But when I put the rear wheel back on and tightened everything to the factory torque spec, the rear brake disc is intermittently rubbing on the rear brake calliper bracket and making a grinding noise when I turn the wheel by hand. The noise is not continuous - it only happens for about 1/5th of the total wheel revolution. The wheel still easily turns by hand. There are no obvious scratches on the disc, but it is definitely not a normal "disc rubbing on new brake pads" sound. The sound goes away when I loosen the axle bolt.

My first thought was warped brake disc. Using a dial gauge, I checked the rear brake disc and rear wheel rim runout. The disc and rim runouts are identical, varying by about +/-0.1mm (0.003 inch) consistently with the sound starting and stopping.

Because the disc and rim runout are identical, I guess it is not a warped disc, and that either the rim is warped (I don't think it is) or more likely, the whole rear wheel is askew / not mounted straight for some reason.

So, I removed the rear wheel and checked that:
- all brake disc mounting bolts are torqued to spec
- both wheel bearings are fully seated into the wheel hub (verified with Vernier callipers)
- the rubber dampers inside the wheel hub are pushed fully into the wheel hub
- the 5-pins (it's a 1990 model) of the flange (that connects the wheel hub to the final drive) are pushed all the way into the metal inserts inside the rubber dampers. When doing this, I found that if I lightly tapped one corner of the flange with a rubber mallet to make sure the pin on that corner was fully seated into the rubber damper, it made the opposite pin rise out of the damper by 1mm (0.03 inch). And when I tapped the other side, it caused the side I had just tapped in to rise back up by 1mm (0.03 inch). Not sure if this is normal. Tried to address it by gently tapping the centre of the flange so all pins bottomed out at once.

I put the wheel back on and did my best to make sure that the flange was fully seated into the final drive teeth. I then spun the wheel but the same intermittent grinding sound is there.

The only other thing I can think of is that when I rebuilt the rear brake calliper, one of the calliper pistons still had a bit of pitting / rust even after sanding it with 1200 grit paper and following the DIY article. This made it hard (but by no means impossible) to push it back into the calliper that easy. But the piston is in the calliper, the brakes are working, and the calliper is not leaking. And I guess if the calliper piston was the cause of the problem, the rubbing noise would be continuous, not intermittent.

I am now stuck for what to do next.


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Rambozo
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Re: Rear brake disc intermittent rubbing on caliper bracket

Post by Rambozo »

There should be a lot more than 0.1mm gap between the disc and the caliper mount. If that is all it takes to rub, my guess is that you don't have the proper stackup of spacers on the axle. Perhaps a previous owner mixed up a flat washer with the spacer?

https://www.partzilla.com/catalog/honda ... rear-wheel
kerravon
Posts: 28
Joined: Tue Dec 29, 2020 6:15 am
Location: Sydney, NSW, Australia
Motorcycle: GL1500 1990

Re: Rear brake disc intermittent rubbing on caliper bracket

Post by kerravon »

Rambozo wrote: Sat Dec 11, 2021 4:55 am There should be a lot more than 0.1mm gap between the disc and the caliper mount. If that is all it takes to rub, my guess is that you don't have the proper stackup of spacers on the axle. Perhaps a previous owner mixed up a flat washer with the spacer?

https://www.partzilla.com/catalog/honda ... rear-wheel
Thanks Rambozo - to clarify my post - I am not saying there is 0.1mm space between brake disc and calliper mount. What I am saying is that the brake disc runout (amount of warping of disc) is 0.1mm when you measure it with a dial gauge. I have not measured the distance between the disc and the caliper bracket yet.
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Rambozo
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Re: Rear brake disc intermittent rubbing on caliper bracket

Post by Rambozo »

I understand that. However, if you are saying that with a runout of .1mm the disc rubs the bracket, then that means that the gap is .1mm or less, or it couldn't rub.
Do you know exactly what is touching and where?
Also is that runout axially or radially?
kerravon
Posts: 28
Joined: Tue Dec 29, 2020 6:15 am
Location: Sydney, NSW, Australia
Motorcycle: GL1500 1990

Re: Rear brake disc intermittent rubbing on caliper bracket

Post by kerravon »

Rambozo wrote: Sun Dec 12, 2021 12:19 am I understand that. However, if you are saying that with a runout of .1mm the disc rubs the bracket, then that means that the gap is .1mm or less, or it couldn't rub.
Do you know exactly what is touching and where?
Also is that runout axially or radially?
Thanks Rambozo, what you say makes good sense. The runout is axial. I will get some feeler gauges and poke around and try find exactly where it is hitting and how much clearance there is between that point and the disc when it is not hitting.


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