Help With Rear Comet Hub Shim Clearence

[Steve Burden]

I am a complete novice to shimming the rear drums for clearance. This is my first Vincent. During my due diligence I noticed a scrapping from the rear drum. Having removed the wheel and taken apart both hubs I noticed a clear rub mark bordering a gouge on the right hand side of the wheel. At first I thought it had been shimmed incorrectly. I have managed to shim one side up with out any problem but the scrapping side I have to shim up so much that the nut will no longer go on the end of the hollow axel. I have spent a couple of hours trying to pinpoint the problem swopping things about and trying it identify a bad part. The drum does not seem warped. the actual brake plates look ok and when I swop them from left to right the drum that had been rubbing does not catch on the opposite side. the Axel is straight. When I read the riders handbook it indicates that I am only applying shims to stop the edge of the brake plate catching the drum it does not mention any thing about clearances on the actual cam mechanism. Any help and advice would be helpful. I will attempt to upload the photos I have taken. Thanks Steve

 

[Steve Burden]

Sorry I have no idea how to upload pictures. It goes up to 100% and tells me it failed. They are jpeg and only 4ook in size.

 

[tatty500]

Steve,

The plates are not very strong and get bent for all sorts of silly reasons.

If one is that far out it might be a good idea (except you'll be messing with the nicely regreased bits) to remove the hollow axle from the wheel, and with no shims between the bearings and plates, just bolt it all together in fresh air.

You can then measure the distance apart the plates are at different positions around the circumference and I'll bet you'll find the problem. Bend it back.

You can also pop this hollow axle and brake assembly onto the tommy bar spindle. Holding the spindle in the vice the plates can be rotated the see the wobble caused by bent plate(s).

Regards

Tatty

 

[Steve Burden]

Thanks Tatty I will give that ago tomorrow. It's all clean and dry at the moment. I did put the brake plate with the brake shoes still on placed on a flat mirror and it looked straight but will check again

 

[vibrac]

You mention the cam mechanism do you mean the crown of the cam is rubbing on the brake hub inner face?

 

[Steve Burden]

I wish I could get my pictures up. They say a thousand words. What is dragging on 50% of the bottom of the drum is the cam that pushes the brake shoes out against the drum. Part number H10 of the spare parts list. It screams out something is not straight but I've double checked it all with straight edges and flat surface but nothing is looking wrong.

 

[Bill Thomas]

Hello Steve, It's been said before, Make your reply a half page, Then make your photo half page, Then Drag and drop, It's not your fault, There is a problem with the Forum. Good Luck, Bill.

 

[Steve Burden]

Yes thank you have been told this also tonight. Problem is only have s desk top at work so will have to do this tomorrow. Thanks for advice

 

[chankly bore]

You mention the cam mechanism do you mean the crown of the cam is rubbing on the brake hub inner face?

View attachment 16094

Just another small thing to worry about. Are you sure that the drum is not fouling the bends of the outer spokes? A lot of spokes have too great a radius after exiting the spoke flanges. Result, cracked drums.

 

[greg brillus]

Steve, Just make sure the brake cam is fully home, if the serrated washer and brake arm are not attached it is possible the cam can be held out somewhat by the shoes themselves if they have a small bend in them, quite common. If the shoe linings are bonded on the clamping applied In the process can distort the shoes as they are quite weak simply be their size alone. Cheers ................Greg.