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Old 08-03-2020, 12:59 PM   #1
modelacarman
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Default Rear brakes

Rear brakes. Iíve had my rear brakes turned twice and they are still out of round. Iíve had them turned by two different shops same results. Is it the shop thatís turning them not doing them right or am I missing something,can anyone help donít know what to do!Any help would be appreciated, thank you.
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Old 08-03-2020, 01:02 PM   #2
Mike Peters
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Default Re: Rear brakes

Do you mean you had the brake drums turned?
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Old 08-03-2020, 01:07 PM   #3
modelacarman
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Default Re: Rear brakes

Ground or machined donít know what else to call it
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Old 08-03-2020, 01:36 PM   #4
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Default Re: Rear brakes

They are hard to get right. It takes a very good shop to make them true. The shop should know if they are round or not.
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Old 08-03-2020, 02:09 PM   #5
1931 flamingo
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Default Re: Rear brakes

Bite the bullit and get NEW ones !
The originals were not meant to be turned. JMO
Paul in CT
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Old 08-03-2020, 02:52 PM   #6
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Default Re: Rear brakes

Quote:
Originally Posted by 1931 flamingo View Post
Bite the bullit and get NEW ones !
The originals were not meant to be turned. JMO
Paul in CT
It is mentioned in the Service Bulletins not to turn the original brake drums.
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Old 08-03-2020, 03:22 PM   #7
modelacarman
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Default Re: Rear brakes

Did not mention in my post that these drums were cast-iron replacements from snyder’s
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Old 08-03-2020, 04:51 PM   #8
Patrick L.
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Default Re: Rear brakes

What type of shop is doing this work ? Brake shop or machine shop ?

I'm wondering why 2 different shops are not turning them correctly.

What makes you think the work isn't correct ? If its because when you manually turn the drums when installed they catch/stick/contact at certain spots and turn free at other spots, thats normal.
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Old 08-03-2020, 06:48 PM   #9
modelacarman
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Default Re: Rear brakes

Automotive machine shop done the work two different ones and when you press the brakes to stop you get a pulsation in the break pedal. And the shops may have done it right but what am I missing is there something else wrong?
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Old 08-03-2020, 07:52 PM   #10
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Default Re: Rear brakes

I agree with Patrick L on this one. Brake drums on any car will "seem" to have high/low spots or be out of round when you spin them by hand. That doesn't mean they have been "turned" out of round. There are many variables. For example, when wheels are mounted, tightening of lug nuts will effect this situation as the tightening pulls on the studs and, therefore, pulls on the drums. Spinning the drums (or drums with wheels mounted) by hand cannot begin to approximate what happens with the weight of the car on the ground nor can it approximate what happens when the car is going down the road when brakes are applied at speed. Perhaps you need someone else's eyes or feel to determine if you actually have a problem. In any event, determine if there IS a problem before going further. Continuing to have the new drums "turned" is defeating the purpose of having new drums.

Good luck, Bob Bader
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Old 08-04-2020, 06:04 AM   #11
Patrick L.
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Default Re: Rear brakes

Well, if the brake pedal pulsates then thats a classic sign of warped drums. So I'm assuming you're sure its coming from the rear and not the front. I'm not sure what to tell you now.
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Old 08-04-2020, 06:29 AM   #12
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Default Re: Rear brakes

If your wheel is not setting flat against the drum, it can pull the drum out of round. I had that happen when a small bit of weld was proud to the surface and it was fine until I tightened the lug nuts. It was an old welded wheel.
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Old 08-04-2020, 07:28 AM   #13
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Default Re: Rear brakes

Maybe a bent axle.
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Old 08-04-2020, 07:32 AM   #14
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Default Re: Rear brakes

OK, let's back-up a bit on this. Many shops do not have the equipment to do this task correctly, -and there in itself can be things that will exacerbate the problem just as you are describing. When you describing pulsating, I am willing to bet the problem originated in the hub(s).

To begin with, before the new drums were ever installed, the hub itself needed to be checked. Often times, the hub is not (re)usable due to the hub race inside the drum being worn. I have a machined slug that we use to slip into the race area. You can visually see if the hub race is out of round. Our test is to put our finger over the small end of the hub and remove the slug. It it pops due to the vacuum, it is a good hub. If it won't pop, then the cost to restore exceeds the cost of a new hub.

Now even if the plug pops, this only checks concentricity of the race surface however the hub bearing race also needs to be parallel with the centerline of the hub. If this is not repaired, the drum will not be riveted on exactly perpendicular to the centerline axis of the hub. This will cause pulsation.

Next, if the shop used a cone on the mandrel to center the small end, they could have missed it there as often times the ends are damaged from the axle shaft nut. I use the centerline of the hub to reference off of, and when I machined my mandrel, I have a live center pilot hole on the small end of the mandrel. I mount the hub on my mandrel which centerlines off of the machined taper where I can true the flange so that it is parallel to the centerline. Then, when the drum is riveted to the flange, I know the shoe surface of the drum is parallel with the centerline. The machining of that shoe surface then is only needed to ensure concentricity of the centerline.

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Old 08-04-2020, 08:09 AM   #15
modelacarman
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Default Re: Rear brakes

Thanks Brent I’ll bet you’re right!
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Old 08-04-2020, 08:16 AM   #16
Jack Shaft
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Default Re: Rear brakes

Pretty easy to see a drum not true on the lathe...did you check the front drums?Im with Deuce,jack up the car and spin the wheel see if it runs true
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Old 08-04-2020, 08:51 AM   #17
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Default Re: Rear brakes

How would a bent axle cause brake pulsation?
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Old 08-04-2020, 11:37 AM   #18
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Default Re: Rear brakes

Quote:
Originally Posted by edzaha View Post
How would a bent axle cause brake pulsation?
A rear could.
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Old 08-05-2020, 09:18 AM   #19
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Default Re: Rear brakes

I had my hubs installed into my new drums and then the drums trued by a shop. When I checked them after I got them back I found that they were no true. One was actually pretty bad. The way I fixed the problem was to insert the old bearing races in the hubs and then mount the whole brake drum / hub assembly in the lathe between centers using the old bearing races as the reference surface. In my case this, this allowed me to turn the drums concentric to the center line of the bearings.
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