Out of round drum

[Tom and Maria]

Just spent the afternoon double, double checking that this really is the problem and it is. New drum bought only a few months ago. About half a mil difference in the diameter depending where it is measured. It is a rear one. Has anyone else had this?.

Had never noticed myself but was picked up as a slight knocking, when either hand or foot brake were applied, by the mot man. Only reason for failure so not too bad really!

Can anyone please pm the name of somewhere they have bought an okay drum from? I use one of the main suppliers but, with a limited time for a free re-test (Friday) I don't want to get another duff one.

Alternativey (yes, I suppose this bit should go in the wanted section) if anyone in the Exeter area has a nice old rusty one that they don't need I'd be glad to hear from them...

Tom

[Dean]

Do you have a toolroom nearby that could just lightly take a scim of material out? A decent turner could do it in five minutes for a pint of beer?

[bmcecosse]

I would be very surprised if it is out-of-round! How would anyone make it like that? The rubbing surface could be off centre to the hub mount - but it WILL be round...... Fit an old drum to get through the test!

[mike.perry]

Logically the rubbing of the brake linings should make the drum round.
I am still running (stopping) on 60 year old brake drums

[Tom and Maria]

The old drum which it replaced had cracked along the outer edge and so was thrown away. Shame, as I doubt the mot man would have noticed the crack. I've no doubt that it would even up over time but as it has been noticed im going to have to sort it. All the others are original.

I originally thought that it must be eccentric rather than out of round, and so spent the afternoon tinkering with the small amount of play available in the four wheel stud holes, it really is not round. A length of metal that will fit one way across the diameter and will not fit the other. Can't think how it happened.

I work in the engineering dept of a university so will get it sorted after the test as a spare, just need something quick before the mot re-test.

Ideas?

[Dominic]

I know that cast iron can distort slightly over time, especially the first few months after casting.
For that reason, I would never buy a new woodworking plane when I was making violins, as they are machined "flat" almost as soon as the casting has cooled enough to handle. Ideally, they should season for 6 months or so prior to machining, after which they should remain stable.
I remember hearing when I was a student that cast iron cylinders for motorbike engines always used to be left outside in the factory yard for months before being machined. So yes, "green" cast iron can change shape slightly.
You'd be very lucky to wear them round in use, as the shoes would merely follow the variable internal diameter, wearing more or less evenly, with the resultant vibration being felt through the pedal or hand brake.
Of course it may merely have been an apocryphal story put about by the engineering dept. boss who took us for metalworking classes...

[bmcecosse]

The store outside story is true enough. It must have distorted somehow - can you not get it machined on Monday and retested on Tuesday? And lesson to learn - never throw anything away!! Must be someone nearby who can lend you a drum? Post up an accurate location - 'north west' suggests Ullapool ??

[Tom and Maria]

I'm down in Exeter, not the north west!

[Dominic]

I'm the one in the North West Roy! Near Blackpool.

[bmcecosse]

Oh sorry - Blackpool?? Hardly 'north' but certainly west

[Dominic]

coming originally from Brighton it most certainly is North!

[bmcecosse]

Pretty much in the 'middle' of the UK........ We haven't abandoned you yet....

[Tom and Maria]

New drum arrives from CW tomorrow...

[Tom and Maria]

Well, the new drum arrived and sorted the problem.

Retest tomorrow, fingers crossed.

I'll try to post some pictures of skimming the warped drum when I do it.

Tom

[MarkyB]

I wonder if the last one got damaged in transit or even from being knocked about in the factory, cast iron is tough but it isn't indestructible.

[Dominic]

I would think that any "knock in the factory" would only result in a crack rather than distortion, cast iron being a fairly brittle substance.

[Matt]

when I was working in the motor factors we got discs/drums back which were distorted out of the box on a ~6 monthly basis. It definitely does happen!

[MarkyB]

To get a crack I think you'd have to hit it with a club hammer or something, there must be scope for distortion before it crack surely, drive a forklift over it perhaps?

[Tom and Maria]

Itsdefinitely a wobble rather than a dent. I guess it'll be quite obvious once I get it on a lathe. I only hope the distortion is evident when held by the central hole, otherwise it'll mean making up a four-bolt clamp to secure it via the wheel stud holes.

I'll keep you posted...

[bmcecosse]

You can't rely on the centre hole! Why don't you just send it back for credit!! ?