Author Topic: CB550F1 rear brake drum revival  (Read 1263 times)

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Offline SteveUK

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CB550F1 rear brake drum revival
« on: April 21, 2015, 07:48:38 am »
I had a problem with the rear brake drum on my 1976 CB550F1 which was grabbing as the cast iron liner had cracked from side to side in a number of places and was out of round.
Given the lack of spares and the likelihood of any replacement being likely to go the same way I decided to see if the drum could be repaired.
I took the wheel to a local friendly engineer and he devised a solution he was prepared to try.

Using a precision milling machine he centered the wheel and removed the existing liner and just the corrosion from the alloy drum to leave as much alloy as possible.

For the replacement liner I did some research at my local motor factors by browsing their parts catalogues.  I found that the brake drum from a 1969 Mini 1100 provided the perfect base for machining a new liner.

The engineer turned the outside of the cast iron drum on a lathe to about 10 thou wider than the internal hole in the bike drum.  He then cut the ring from the rest of the drum to the same width as the original.

After freezing the new liner and only moderate heating of the drum he pushed the new liner in.  He used a lot of skill and experience to judge the amout of shrinkage onto the liner as if done excessively the alloy drum is liable to crack.

The inside diameter was finished on the milling machine, matched to a new set of brake shoes.
No need to unlace the wheel or find a lathe big enough to accommodate the wheel.

The results are perfect and the total cost was £11 for the brake drum and £140 for the engineer which is not bad given that the wheel was effectively a write-off.