Construction of brake drums.

Post by **wanderinstar** » Mon Nov 17, 2008 7:19 pm

Can anyone tell me if the piece of the brakedrum that faces up to the hub is cast iron, same as the actual drum itself.

Post by **Dean** » Mon Nov 17, 2008 7:50 pm

Do you mean the backing plate? As far as I'm aware it's pressed steel, quite substantial steel if it's an original one.

Post by **wanderinstar** » Mon Nov 17, 2008 8:10 pm

Thank you Dean. I didn't think it was made from cast, Don't suppose you know how thick it is, offhand?

Post by **aupickup** » Mon Nov 17, 2008 8:12 pm

backing plates are indeed pressed stell

can i ask why u want to know

Post by **bmcecosse** » Mon Nov 17, 2008 8:38 pm

Backing plates - the part with the cylinders and the shoes - are presed steel. The brake drum - the part the shoes rub against - is cast iron - all of it! And quite fragile so don't hit it too hard!

Post by **wanderinstar** » Mon Nov 17, 2008 8:48 pm

No, I dont mean the brake backplate. I mean the part of the brake drum that fits over the studs and with the 2 recessed holes in that the screws fasten the drums to the hub.

Post by **bmcecosse** » Mon Nov 17, 2008 9:02 pm

^^^ Cast iron !

Post by **Peetee** » Mon Nov 17, 2008 10:13 pm

No, I dont mean the brake backplate. I mean the part of the brake drum that fits over the studs ....

The part that rotates with the wheel (the dish shaped drum) is a single piece.

Post by **Dean** » Mon Nov 17, 2008 10:29 pm

Yes, it's a single piece of cast iron. You can lightly machine it to true up the bore that makes contact with the shoes, but do not attempt to weld it. Cast is brittle and the grain structure does not possess the properties that give a good adhesive weld.

Post by **Kevin** » Tue Nov 18, 2008 3:48 pm

but do not attempt to weld it. Cast is brittle and the grain structure does not possess the properties that give a good adhesive weld.

I agree Dean but why would someone even attempt to weld a brake drum.

Post by **alex_holden** » Tue Nov 18, 2008 4:48 pm

Kevin wrote:why would someone even attempt to weld a brake drum.

Have you ever watched Scrapheap Challenge?

Post by **Dean** » Tue Nov 18, 2008 5:14 pm

Kevin wrote:
but do not attempt to weld it. Cast is brittle and the grain structure does not possess the properties that give a good adhesive weld.
I agree Dean but why would someone even attempt to weld a brake drum.

What's the betting someone has tried it.

Post by **wanderinstar** » Tue Nov 18, 2008 7:12 pm

OK,OK. I hold my hand up. Made a slight miscalculation with wide wheels. The tyre are just rubbing on top trunnion.

So I thought if I could find my old rear drums I could take them to an engineering shop and have the drum bit parted from the flat bit. Instant spacer.

That is the theory. Unless someone knows otherwise?

Post by **PSL184** » Tue Nov 18, 2008 7:14 pm

In theory it would work but spacers are usually made of alloy and you would of course need longer studs I would think...?

Post by **wanderinstar** » Tue Nov 18, 2008 7:20 pm

I haven't measured how thick they want to be yet (dark when I get home) will do that on Sat.am. But am hoping I may get away using existing studs.
If not i thought about contacting Birmingham Morrie Centre. If they do alloy wheels surely they must do longer studs?

Post by **PSL184** » Tue Nov 18, 2008 7:22 pm

Yes, they do along with most of the other suppliers. Not difficult to change but obviously vital if you reduce the amount of thread you have available for your nuts!

Post by **bmcecosse** » Tue Nov 18, 2008 7:27 pm

Longer studs are easy - sold for Minis all over the place. Just make your spacer from flat plate - how much depth do you think you need Ian ? If only 1/8" then probably ok with standard studs - anything more - better fit longer!
http://www.minisport.com/acatalog/Mini_Wheel_Studs.html

Post by **wibble_puppy** » Wed Nov 19, 2008 8:45 am

I have a couple of spare spacers hanging around, if your studs are the standard Minor spacing - you'd be welcome to them if any use to you?

Post by **alex_holden** » Wed Nov 19, 2008 9:01 am

wibble_puppy wrote:I have a couple of spare spacers hanging around, if your studs are the standard Minor spacing - you'd be welcome to them if any use to you?

If you take Wibble up on her offer we should be able to get them to you without postage too.

Post by **wanderinstar** » Wed Nov 19, 2008 12:57 pm

Thank you very much for your kind offer Wibble, I will take you up on it please. Thank you as well Alex.
Ian.