Drum brake resurfacing

[John_Mc]

In my rear end refurbish, I noticed that my R side brake drum looks pretty scored, like a vinyl record. L side looks fine. Can I take just the R side to the machine shop or do I need to take both? Any advice appreciated. Thanks.
I already have new shoes from BPNW waiting for reassembly.

 

[TR3driver]

No reason you can't turn one without the other; the resulting difference in braking is too small to matter.

However, there's a good chance it's already too worn to turn safely. Don't be surprised if the shop refuses to turn it. The maximum diameter should be cast into the face of a TR6 drum.

 

[Geo Hahn]

...The maximum diameter should be cast into the face of the drum.

I've never been able to find that number on a 10" TR3A drum -- any idea what the max is on those?

 

[Don Elliott]

I had a clutch and brake shop re-line the shoes for the rear brakes on my TR3A and I asked them to turn the ID of the drums. They told me that the drums should be turned so that the linings on the shoes will sit properly all around. In other words, they matched the linings on the shoes with the drum ID. I assume they did that because they work fine.

 

[John_Mc]

...The maximum diameter should be cast into the face of the drum.

I've never been able to find that number on a 10" TR3A drum -- any idea what the max is on those?

I just took my drum to the LAPS and we couldn't find the number on my drum either. Anybody know? I'll check Haynes...

 

[TR3driver]

Ok, I went and dug a TR6 drum out of the pile : it's marked max diameter 9.040".

I agree the TR3 drums are not marked, and I've never seen a specification for them. My WAG is that "max dia" is a concept introduced during the late 60's and was simply left to the mechanic's discretion in the 50's. But certainly the TR6 allowance of .040" would be very conservative ... those TR3 drums are massive !

In other words, they matched the linings on the shoes with the drum ID.

"Back when" that was considered part of the job. The lining thickness was not that well controlled during manufacture, nor was the shape of the shoes perfect. So the drums would be measured and the shoes "arced" to match the drums, on a special machine.

 

[martx-5]

In other words, they matched the linings on the shoes with the drum ID.

"Back when" that was considered part of the job. The lining thickness was not that well controlled during manufacture, nor was the shape of the shoes perfect. So the drums would be measured and the shoes "arced" to match the drums, on a special machine.

When I first started swinging wrenches back in '70s, the place I worked for had one of those shoe arcing machines. Basically a drum sander that you put the shoe on and adjusted the pivot point to get the proper arc. Yes sir, just watch all that asbestos dust fly around the shop! Fortunately, I never used it, and only saw it used two or three times on some really stubborn cases. Most of the time, if you kept within the drum cutting specs, the shoes fit pretty good.

 

[TR3driver]

Most of the time, if you kept within the drum cutting specs, the shoes fit pretty good.

And if they don't, they will wear fairly quickly until they do.

But I have to say it was a real eye-opener the first time I installed "arced" shoes on my first car. The difference in braking (it had drums all round) was remarkable.

 

[70herald]

When I first started swinging wrenches back in '70s, the place I worked for had one of those shoe arcing machines. Basically a drum sander that you put the shoe on and adjusted the pivot point to get the proper arc. Yes sir, just watch all that asbestos dust fly around the shop! Fortunately, I never used it, and only saw it used two or three times on some really stubborn cases. Most of the time, if you kept within the drum cutting specs, the shoes fit pretty good.

I had new brake shoes made up a few months ago. The shop put on extra thick friction material and then used one of those sanding machines to trim the shoe to the proper arc. Of course nowadays the friction material no longer has asbestos, and there was some sort of high powered vacuum cleaner sucking up the dust. Still kind of messy.

 

[Guest]

What do machine shops charge now a days to turn a drum? New TR6 drums are very reasonable through places like Ebay for less than $50 each.

.

 

[TR3driver]

It's been a few years, but last time I had it done, they charged me $10/drum.

And not all Triumph drums are as cheap as TR6 ones. With shipping, a Stag drum is over $150. 10" TR3 drums were unobtanium for many years, tho I see Moss has them now for $100 (plus shipping). And a pair of original 10" Alfin drums brought nearly $1000 on eBay not too long ago.

Personally, I'm not big on turning drums, certainly not as a matter of course as most shops do. If they are only lightly scored, I run them "as is". Out of round or heavily scored means discard. For drums in otherwise good condition, I just break the glaze with crocus cloth then wash & dry them thoroughly.