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Rear drum groove?


jsgun
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Both of my rear drums have a groove down the center. Is that a Buick thing? I've never seen that before. I originally though it was a wear mark, but both drums match.

 

Also, anyone know the wrench size for the bleeder screws front and rear? I'm going to get a angled bleeder wrench, but I don't want to craw under the car right now. 

reardrumgroove.jpg

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The groove may be there on SOME disc brake rotors, BUT NEVER on drums that I've EVER seen.   In your defense Winston looking at it 1st. glance it does ALMOST does look like a rotor, BUT he also said drum.

The drum needs to be measured for I.D.  IF enough material,  .060" to .090" oversize MAX, from 12" original starting dimension, it can be turned.

Most/many shops today do not have the proper machining equipment. Stuff is so cheap from China it doesn't pay to waste your time & one can make more $$$$$ by replacing.

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A wear indicator makes sense, because it's exactly the same on both drums. The first one I pulled, I thought something had gotten into the shoe and scored it. But the other is exactly the same. The front drums don't have this groove. A previous owner had rebuilt the brakes, they look damn near new. Even the drum surfaces.

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Chances are there was something on the brake shoes that scored the drums when an older set of linings wore out.  Of all of the 1st generation Rivieras  that I've owned, parted out, and helped work on, these pictures are the first I've seen of scored drums.  Probably what alerted the owner that he needed new brakes.

 

Ed

Edited by RivNut (see edit history)
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Had an identical mark on a set of drums. I had a set of riveted shoes and one of the rivets wasn't fully seated.  After the shoes wore a bit, that high rivet started scoring the drum.

 

In any event, I've never seen that mark on original drums -- but I wouldn't worry about it if the drums are otherwise good.

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Some replacement brake drums came with a groove to indicate throwaway thickness. I've seen drums like these before.

Agreed that Buick did not build them with drums like that. Also I have seen brake rotors with the same type of groove down the middle

to indicate when they are worn out.

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The replacement drum makes sense, it goes along with the brakes being rebuilt. Thanks for the info!

 

Also, any guesses on what the bleeder screw size is? Is it the same on the front and rear? Not able to get under the car until the weekend.

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If you don't already have a set, get one.  "Flare nut " wrenches.  Don't get the ones that are beveled, make sure they're flush on the entire surface.  

 

Like this

 

husky-flare-nut-wrenches-hfnw6pc-64_1000.thumb.jpg.94bb00086817611021b5fa0fcf6e6b30.jpg

 

 

 

Not this

 

61d8iVNyoeL._SX425_.jpg.69b6aabe12198cdf4ef5c9e3360f199d.jpg

 

Sometimes the nut is so small, it only reaches into the bevel, and into the hex part.

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I picked up a few of those last week actually. My dad is a retired diesel mechanic, I grew up around a great set of tools. Learned early on the importance of having good wrenches. He had a few 90 degree bleeder wrenches, those were awesome. Gonna find a 5/16 - 3/8 bleeder and make life easier.

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