The return of the Oscillation

[misterprofessionality]

Well, the Oscillation in the front end of my CB has returned. It's going to the shop very soon, don't worry, I am not going to try to fix this myself.

Small recap: Last year I replaced my front brake discs because i was feeling a rythmic oscillation in the front end under low speed front braking. This is a classic sign of a warped brake disc. after replacing them both, I was happy to report that the oscillation went away. However, over the course of many months the oscillation slowly returned. It's been less than a year at this point and it's already back, leading me to believe there's now something wrong with the bike itself that's re-warping the new discs. Everything I know how to measure seems to be aligned with regards to the front forks ect, but then I don't know much. Another interesting symptom I noticed is that one of the four brake pads in the front calipers is wearing out much faster than the other 3...even though they were all changed at the same time. odd.

As said above this is definitely going to a shop because everything I work on is a disaster, but I'm still curious. What does the knowledge base at large think could be causing these discs to warp?

 

[GoldOxide_imp]

Are the discs discoloured? Heavily glazed?

 

[misterprofessionality]

nope. they look like normal discs with around 10k miles on them.

 

[The Gecko_imp]

the bleedback hole in the master cylinder is partially blocked.. (the little one when you look in the reservoir) OR,(more likely) the lever isn't allowing the master cyl to return all the way. I have seen both situations before on other bikes, especially when a replacement lever was used. there needs to be a few thou of clearance between the lever and the piston on the master cyl (0.002"-0.005" minimally) or it will always have residual pressure that can cause this exact issue. 0.02

cool m in sc, makes a lot of sense (and I wouldn't have found that explanation). At the same time I wonder, could it also be that a quality problem (e.g. with none OEM pads) ?

 

[max]

Three questions;
1; has the bike been put away with water between the pads and the disk?
2; did the wear on one pad occur in the previous situation?
3; are the pistons in the affected caliper with the most worn disk moving back freely ( flexible seals ) from the disk after releasing the brake lever ?

My honda hornet developed some uneven braking after the bike was put indoors with rain water under the pads and developed slight rusty patches overnight.

 

[emptysea]

I get weird stuff happening with brakes - oscillations, squeaking, etc. I have my shop guys look at it to be sure it's nothing major and that it's safe to ride and then I just go back to riding. If the bike stops, I figure my bikes works better than most Harleys and I just keep on riding it. I wish I could be of more help. Hopefully, your mechanic will set things true.

Also, wasn't 'The Return of the Oscillation' the 3rd studio album for the Zombies?

 

[GoldOxide_imp]

I get weird stuff happening with brakes - oscillations, squeaking, etc. I have my shop guys look at it to be sure it's nothing major and that it's safe to ride and then I just go back to riding. If the bike stops, I figure my bikes works better than most Harleys and I just keep on riding it. I wish I could be of more help. Hopefully, your mechanic will set things true.

Also, wasn't 'The Return of the Oscillation' the 3rd studio album for the Zombies?

lol - not quite, but can see the point.

More impressively, few people can relate to The Zombies.

 

[misterprofessionality]

the bleedback hole in the master cylinder is partially blocked.. (the little one when you look in the reservoir) OR,(more likely) the lever isn't allowing the master cyl to return all the way. I have seen both situations before on other bikes, especially when a replacement lever was used. there needs to be a few thou of clearance between the lever and the piston on the master cyl (0.002"-0.005" minimally) or it will always have residual pressure that can cause this exact issue. 0.02

Ok...this all actually sounds really plausible EXCEPT the master cylinder was taken apart and cleaned thoroughly and a rebuild kit was applied (new seals and new piston and such) at the same time as when the discs were replaced. I actually didn't mention that in the original post because I didn't think it was relevant until I read your post. The brake pads were also replaced at that time and of course the lines were thoroughly bled and all that. It seems like that procedure would have cleared a blockage or funny business in the master cylinder would it not?

Three questions;
1; has the bike been put away with water between the pads and the disk?
2; did the wear on one pad occur in the previous situation?
3; are the pistons in the affected caliper with the most worn disk moving back freely ( flexible seals ) from the disk after releasing the brake lever ?

My honda hornet developed some uneven braking after the bike was put indoors with rain water under the pads and developed slight rusty patches overnight.

1) no not in recent years. The bike was taken out of typical commuter rotation before all this started happening.

2) now that you mention it i believe it did.

3) they are. They were moving ok with the previous discs and at that time they were even taken apart and cleaned out and reassembled with new rings. They are currently moving smoothly near as I can tell.

I get weird stuff happening with brakes - oscillations, squeaking, etc. I have my shop guys look at it to be sure it's nothing major and that it's safe to ride and then I just go back to riding. If the bike stops, I figure my bikes works better than most Harleys and I just keep on riding it. I wish I could be of more help. Hopefully, your mechanic will set things true.

Also, wasn't 'The Return of the Oscillation' the 3rd studio album for the Zombies?

Yea im definitely not gonna let it go. The oscillation only occurs at low speeds but that doesnt mean it's hot happening at higher speeds. The frequency is just too fast to feel. It's causing some undue stress on at least one of the brake pads by my observation and more than that its just bugging the heck out of me when I stop.

 

[dave]

When was the last time you had your front tire replaced? Did you do it yourself? If a shop replaced your tire there's a chance they bent your rotor(s).

 

[misterprofessionality]

I dont change tires myself. Last time i tried thati nearly diedof exhaustion.

This was what I thought caused it last time, but they haven't been replaced since the discs were replaced the first time, so a tire change has not had the opportunity to bend the discs this time around, meaning it likely wasn't the cause the first time either.

 

[max]

On my hornet the oscillation was slowly changing, it seemed that the "sticky patch" was getting bigger ( longer ) and less apparent, so it seemed to fix itself over time.

You could feel it when applying and maintaining the brake lightly whilst pushing the bike forward through the cycle.

What fixed it in the end ( to my surprise ) was a change of pads:celebrate:

So something simple to try is to replace the pads or swap them around and write down what went where so it can be traced back later, just an idea, the shop sounds good too.

Something else that happened to me was the forward cup of the master cylinder was oversize in the master cylinder and was not clearing the small breathing hole in the master cylinder ( dragging ), took me a while to find that but a new cup fixed that, probably not your problem but worth knowing.

Thanks for bringing up the subject MP.

 

[jtopiso_imp]

Check if the caliper pistons are retracting properly. Or check if the front calipesr are heating up after a ride, even if you brake with the rear.

I had the same problem on an old car: it warped a set of discs, replaced, and did the same to the next set. It ended up being too much fluid on the reservoir, so when the system was heated the liquid expansion was enough to apply some braking all the time, leading to overheating the discs and warping.

Or just check fluid level and make sure it's not over the "max" mark.

 

[misterprofessionality]

Small update: the fluid level is normal, the lever doesn't seem to have excess play against the piston, but I did try an experiment by riding home from work today without using the front brake at all. When I parked I took my glove off and felt each disc, one was cool, one was hot. Not crazy hot but definitely hot. Of course, this is the one that's on the same side as the one brake pad that's more worn than all the others.

Conclusion: yea one of those calipers is dragging slightly at all times.

 

[GoldOxide_imp]

... excellent. Glad you were able to safely arrive home Mr. P. with just the rear brake.

 

[misterprofessionality]

Its not so hard.

 

[1973cb750]

i weigh 235 and i run about 6 more psi in my front and the cupping has almost been eliminated i think a cupping tire causes your issues

 

[Tev62]

I take it the front wheelbearing is in good order and that there isn't a little play giving rise to a little one sided lean on the wheel and hence the rotor?