Out of round drum

[Tom and Maria]

Passed the mot today!

[bmcecosse]

Great success.....!

[Dominic]

Excellent news!

[lee_rob]

I have two drums sat in my boot which I had to remove as they fouled the brake shoes due to them being out of shape. These too were from a reputable supplier...
I am now on the old drums again which have been previously heavily skimmed hence why I wanted to replace them, even with new shoes I am on the last adjuster and the pedal is very low....

[bmcecosse]

You can easily fit a shim under the tail of each shoe to hold them out nearer the drum.

[IslipMinor]

I think I may have a similar problem. New rear drums a little while ago and no apparent problems. MOT in August this year and the tester reported that there was some grabbing on the rear brakes, so I removed the drums and made sure there was a good chamfer on the leading edges of the shoes.

I am now getting a slight shudder when applying the brakes, whoich I can replicate by just pulling on the handbrake only. Will do some detailed measuring when we get home in a week's time.

[Tom and Maria]

Finally got the drum on to a lathe today. The variance was about .35mm, easily enough to cause the brakes to grap.

It wasn't so much a dent as a general ripple right through the drum, no idea ghow it could have happened.

[bmcecosse]

What were you centering it up on? You can't use the centre hole - best to mount it on a hub and then apply dial gauge.

[Trickydicky]

It would be interesting to know how, when people have skimmed there drums, they have mounted them in a lathe and if they have been succesfull in keeping them "true" to the bearings on the hub on the car?
If the center hole of the drum is not true to the braking surface then you have no hope of removing the imperfections.

The only way I can think of ensuring it is correct is to mount it via the PCD of the drum in a lathe.(as it is mounted on the car but from the inside).Then skim the braking surface.

[MarkyB]

a general ripple right through the drum

Any pictures? I can't visualise what you mean by this.

The other possibility might be that they have speeded up production by missing out some curing time or machining them too hard and/or too fast.

Wouldn't it be possible to true the centre hole in some way?

[bmcecosse]

That's what I was thinking - with a used drum - first grip it and centre it all up on the old wear surface - then skim it. But with a new drum.....it really will need a mandrel to mount it accurately using the 4 stud holes...if you want to try to square it to the hub.

[Tom and Maria]

I did mount it on the lathe using the centre hole, but after checking that it really was in the centre by measuring it against the stud holes. Turned it upside down and drew around the holes on to paper then took the measurements, that all seemed square (or round) as it should be.

When I say a general ripple I mean it was like a wobble line rather than dented in one particular place. Very odd.

The proof of the pudding will be in the fitting, maybe I'll swap it over for the other old drum, which is pretty corroded, and let you all know how it goes.

Tom

[fussyoldfart]

I too have drums that have been skimmed too far and they were probably centred on the hole not the studs because "That's the way we do it."

On the advice of some others I went looking for a good used pair and fortunately located them on this continent (North America). I have yet to examine them but the seller took them off his car to fit disks and says they have never been skimmed. He sold them to me with a set of new shoes and included the snail cams for a bit less than new "replacement parts".

The notion that cast iron needs to cure is quite accurate. The original Lincoln automobiles would have the rough block castings thrown out in the weather for 6 months before they were machined.