Topic: '71 CB500 rear brake drum out of round

[idahoblueskies]

Putting the finishing touches on my CB500, and found that my rear brake drum has a few high spots in the drum liner, causing a pulsing when the rear brake is applied.

Of course I didn't know this before removing the hub, polishing it, and re-lacing it into a new rim.
I don't know anyone with a big lathe to turn the high spots out.  There doesn't seem to be any cracking, just slightly out of round in a couple of spots.

I'm wondering if anyone has tried putting course emry cloth on the shoes, and then running the wheel with the brake applied for a bit to sand down the high spots?

I have another hub, but didn't want to start over just yet.

Looking for sage advice on fixing it first, if it's possible.

Thanks in advance,
Pete

[bryanj]

That drum is cracked, its the only reason for high spots.
Not enough meat to turn a bit out, you need somebody who can turn it all out and fit a new liner to spec

[idahoblueskies]

There aren't any visible cracks.  It looks more like there is rust forming between the liner and the hub, causing the liner to bulge out a bit in spots.   The bike sat for over 40 years since it was last registered, in who knows what conditions.

I'm going to give sanding a try, and see what happens.  If that fails, I'll just replace it with the spare hub I have.

Pete

[MauiK3]

The rust is a bad thing, it likely won't stop warping the inner liner.

[Don R]

  Is it possible the spokes have a tight area pulling it out of round?

[idahoblueskies]

Possible I suppose, but the hub does not look out of round at all when it is rotating on the bike.  I think it's just the liner.

[idahoblueskies]

  Is it possible the spokes have a tight area pulling it out of round?

Yep, likely to continue to get worse over time.  Hoping for a quick fix for a riding season or so, while I get the spare hub polished and ready to relpace into the wheel when I have some time to dig into it.

[bryanj]

I have had quite a few hubs relined, the problem is finding a cast car drum of appropriate size, if rust behind the liner has forced it inwards it will have cracked, the fact they aint visible doesnt mean they aint there.
I had a batch relined several years ago but unfortunately the man with the big lathe, could do complete wheels, has retired so cant get any more done.
If you have a liner done it need to be pegged at the joint as the original hub was cast arround the drum

[scottly]

There aren't any visible cracks.  It looks more like there is rust forming between the liner and the hub, causing the liner to bulge out a bit in spots.   The bike sat for over 40 years since it was last registered, in who knows what conditions.

I'm going to give sanding a try, and see what happens.  If that fails, I'll just replace it with the spare hub I have.

Pete

When iron rusts, it does swell some. Rather than rusting between the liner and hub, is it possible the rusting was between the brake shoes and the liner during the 40+ years the bike sat?

[HondaMan]

One other possibility (that I saw once on a 750 rear wheel): if the rear wheel bearing on the brake side is internally damaged (usually from rust, caused by sitting for decades) it can make the brake-side of the axle assembly wobble a little bit, making brake marks like those. It happens when the rust in the bearing has shrunken a few of the balls on one side (which was the bottom side when it sat 40 years) and the bike was put back in service.

While hard to detect this, I did it by slowly turning the wheel on the axle and [listening and] feeling the drum and bearing with fingertips to see if it 'wobbled' or 'ground' a little bit: when I pulled out the wheel bearings, both of the inner ones had lots of rust in the grease. New wheel bearings fixed it eventually by having a 'shuddering' brake pedal for a couple of months.

--note: this was the kind of stuff we did for "poor college kids" in the 1970s, who seldom had two $1 bills to rub together for bike maintenance: your maintenance quality may vary--

[idahoblueskies]

I decided I had nothing to lose and gave the sand paper a try last night.

I bought a $3 pack of self adhesive paper that had various grits, and stuck a strip of the paper on each brake shoe.

Put it back on the bike, and ran it on the center stand in first gear, and slowly applied the brake.  I could feel the sand paper start to work down the two high spots that were in the drum liner.

I added more pressure to the brake as the spots wore down, until there were no more pulses in the brake pedal.

I repeated this with a finer grit paper to smooth out the drum surface after the heavy grit, and in less than 10 minutes I was left with a smooth drum with no high spots or pulsing in the brake pedal.  The brake works like it should, smooth and no issues.

No doubt that the liner will likely move more in the future, if the rust in-between the liner and the hub is expanding.  But it took 40 years to get to where it was, so I think I have some time to just ride it as is for now.  If it gets to be an issue, I can either sand it again, or replace the hub with a spare that I have on hand.

For now, I'll call it a win.   

I took the bike out for it's first real ride since the 80's, and it was awesome.

Pete

 

[Kelly E]

Great idea.

[bryanj]

Well done, i have seen many cracked but never one like yours, bulged but not cracked.
I hope it lasts for you but i always worry abou brake failure, especially after i had an 18 wheeler going down hill where i had brake failure, luckily a farm track went off to the side!

[HondaMan]

Very clever, a home-drum-turning tool!