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Brake drum measurements
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jcpatrickharrison
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PostPosted: Sat Apr 17, 2021 3:01 pm    Post subject: Brake drum measurements Reply with quote

Hey,

I’m trying to figure out if I need to buy new brake drums. They look pretty decent. How do I know if they need to be turned? Is there an easy way to tell if they are out of round? I was thinking I could measure the wall thickness with a digital caliper. Would this work?
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Cusser
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PostPosted: Sat Apr 17, 2021 3:29 pm    Post subject: Re: Brake drum measurements Reply with quote

I'm in Phx AZ, and the big parts stores here don't have adapters to turn old VW drum these days; so maybe a old-fashioned machine shop or a VW shop can help there. I'd guess the parts stores could measure for you.

So what do I do? Even though I "think" a local VW machine shop could turn these, if my own drums feel grooved like an old record, I likely would replace them. I don't generally replace even/smooth drums (or rotors) and jsut do brake shoes (or pads). So that's my 2 cents.
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modok
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PostPosted: Sat Apr 17, 2021 3:54 pm    Post subject: Re: Brake drum measurements Reply with quote

brake drum measuring tools... some are calipers with extended anvils, others are...more difficult to explain, like a ruler with two sliding arms on it.
In any case the reason it's a special tool is t be able to reach in and check the size without going through the middle.
Because in the middle is the hub, or arbor,.....have to reach around that. Measure runout with a dial indicator.
You can feel free to invent your own ways to do it if you understand the principles.
OD minus wall thicknesses would be fine, but is that easier? It is if you can do it.

Any place that deals with brake drums I expect would measure them for you, for free, but who knows.
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61SNRF
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PostPosted: Sat Apr 17, 2021 4:40 pm    Post subject: Re: Brake drum measurements Reply with quote

Look where the shoes wear in the middle, if you see a raised lip around the edge or as Cusser mentions any grooves you can feel with your nail those are indications they need to be turned.

New they are about 9.065" Max inside diameter is 9.115" so there is not a lot there to turn.

Being they are cast iron you really can't get an accurate measurement using wall thickness and besides there are no specs for this.

They make special drum gauges with a dial indicator read-out but they are specialty tools. If your local FLAPS advertises drum turning they probably have one.

You can get a fair measurement with an inside micrometer but those take care and experience to get an accurate reading
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Eric&Barb
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PostPosted: Sat Apr 17, 2021 8:53 pm    Post subject: Re: Brake drum measurements Reply with quote

This and lots more is explained in the workshop manuals:

https://www.wolfsburgwest.com/cart/DetailsList.cfm?ID=book1

Get one that is applicable to your year of beetle ASAP. Yes, the above is out of stock, but there are other VW suppliers that should have it available. Also do check thesamba classifieds. They do show up from time to time in good used shape for less $$$.
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scrivyscriv Premium Member
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PostPosted: Sat Apr 17, 2021 10:01 pm    Post subject: Re: Brake drum measurements Reply with quote

jcpatrickharrison wrote:
...Is there an easy way to tell if they are out of round...

Not really, but the quickest way to check for out of round is mount it in a brake lathe and either check runout with a dial indicator, or actually start cutting. You'll see the wear pattern as you go.
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EVfun
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PostPosted: Sun Apr 18, 2021 9:24 am    Post subject: Re: Brake drum measurements Reply with quote

If someone made a pushrod that was 230mm long you could get a decent check for round and basic diameter with feeler gauges. You couldn't reach the outside face but you measure at several points around in about the center of the area where the shoes run.

I bought a pair of '58-'64 drums, a low swap meet price on used VW originals, hoping they would be good based on looks. They were to large to run, even though smooth and the lip from previous shoe wear was not very large. I suspect they had been turned years ago and then run through several more sets of shoes. I ended up buying new drums. I was trying to avoid that because rear replacement drums for '58-'67 Bugs are 6mm wider than original '58-'64 drums.

Bug drums should have a new diameter of 230.1mm and an maximum diameter of 231.4mm according to my cheat sheet on brakes.
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jcpatrickharrison
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PostPosted: Sun Apr 18, 2021 3:29 pm    Post subject: Re: Brake drum measurements Reply with quote

Thanks everyone!
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stevebaz
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PostPosted: Mon Apr 19, 2021 12:16 pm    Post subject: Re: Brake drum measurements Reply with quote

https://www.amazon.com/Westward-1EKA5-Brake-Resett...mp;sr=8-24
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toxicavenger70
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PostPosted: Mon Apr 19, 2021 12:53 pm    Post subject: Re: Brake drum measurements Reply with quote

I though my drums had a imprint on them stating how much they can go before they are garbage. So check and see if you have nay numbers on them.
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