MK II Rear Brake Drum Circlip Dislodging

Dan1950 · Nov 1, 2021

Anyone have any idea what might cause this? I'm thinking someone substituted a similar yet slightly off size circlip as it doesn't seem to be bottoming out around the entire perimeter. If I put pressure on the stub axle from the backing plates side, it will pop loose. There doesn't seem to be any damage to the groove in the brake drum.

I do have valve spring shims that are the proper O.D and I.D. to space the stub axle from the backing plate, but I don't see how that could affect the circlip. (.015", .030", and .060" thickness)

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kommando · Nov 1, 2021

Happened to me, well the circlip broke into 2 pieces, had the bike 30 years and replacing the circlip was the first time going in that far expect for changing brake shoes.

HoveToo · Nov 1, 2021

I had to grind my circlip down on an oilstone when I replaced the rear brake drum. The groove was too tight to allow the circlip to bed in properly.

zotz · Nov 1, 2021

I had the same issue. I got the clip in but it was very tight. I had to help the clip seat properly by tapping it in with a screwdriver. Make sure the bearing is completely seated.

ashman · Nov 1, 2021

My second rear drum was a cast iron drum and after about 20 years or more the whole drum jammed my back wheel 4 miles from home the outer casting that held the C clip in had broken and was only about 30mm left and the circlip was not in place, the sprocket was still good but I ordered a new sprocket from RGM but while I was waiting I was able to put the drum on the lathe and using a small boring bar was able to machine the circlip grove deeper and put a circlip 2 sizes bigger to hold everything in, 15 minutes to set up on the lathe and 15mintes to cut a new grove, that was over 8 years ago and the drum is still on my Norton and the new drum is still sitting under my work bench.
The new drum is steel and not cast iron, it was such a easy job to save the old one from the bin and a bit of thinking and a $1 circlip.

Ashley

Dan1950 · Nov 2, 2021

ashman said:
My second rear drum was a cast iron drum and after about 20 years or more the whole drum jammed my back wheel 4 miles from home the outer casting that held the C clip in had broken and was only about 30mm left and the circlip was not in place, the sprocket was still good but I ordered a new sprocket from RGM but while I was waiting I was able to put the drum on the lathe and using a small boring bar was able to machine the circlip grove deeper and put a circlip 2 sizes bigger to hold everything in, 15 minutes to set up on the lathe and 15mintes to cut a new grove, that was over 8 years ago and the drum is still on my Norton and the new drum is still sitting under my work bench.
The new drum is steel and not cast iron, it was such a easy job to save the old one from the bin and a bit of thinking and a $1 circlip.

Ashley

I have been contemplating having the groove recut if a new circlip doesn't cure the problem.

HoveToo · Nov 2, 2021

I had a new circlip with the new brake drum and still had to thin it on the oil stone. If you have access to a lathe then you could go the re-cutting the groove route. I didn't and spent a few minutes wearing my finger tips off but it did the trick.

Torontonian · Nov 2, 2021

I've experienced the same circlip issue of it leaving it's home hub slot/groove. Resulted in an uneven rubbing sound from the hub. Everyone knows circlips have a sharp side cut and the outer side is ever so slightly rounded. This is part of the circlip stamping process , and the sharper cut side must fit outboard to prevent any drifting and retain the bearing well in place.
Yes to machining a deeper groove , new larger circlip to stop this known issue.

Dan1950 · Nov 2, 2021

Torontonian said:
I've experienced the same circlip issue of it leaving it's home hub slot/groove. Resulted in an uneven rubbing sound from the hub. Everyone knows circlips have a sharp side cut and the outer side is ever so slightly rounded. This is part of the circlip stamping process , and the sharper cut side must fit outboard to prevent any drifting and retain the bearing well in place.
Yes to machining a deeper groove , new larger circlip to stop this known issue.

Well, it's reassuring that this is a known issue.

Dan1950 · Dec 7, 2021

Update;

I got my rear brake drum back from the machine shop and they did a bang up job. The deeper groove and slightly larger circlip now securely retains the bearing. In fact, I had to upgrade my snap ring pliers to get the bearing out of the drum.

MK II Rear Brake Drum Circlip Dislodging

Dan1950

1974 MK II Roadster

Comp Cams 4753 Valve Spring Shim Kit 1.250" OD; .814" ID; .015"; .030" | eBay

kommando

HoveToo

zotz

ashman

Dan1950

1974 MK II Roadster

HoveToo

Torontonian

Dan1950

1974 MK II Roadster

Dan1950

1974 MK II Roadster

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