Author Topic: Brake Drum Dust Seal  (Read 146 times)

Offline Athame57

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Brake Drum Dust Seal
« on: July 03, 2026, 08:37:50 PM »
I finally decided to fit the dust seal and washer for my rear brake drum. Alas, it caused so much trouble when I went to put everything back together I gave up with it. It was stopping me from getting the brake arm fit in a way that let the securing bolt pass through the recess in the brake shaft. Is this unusual, is it really important anyway? :-\
« Last Edit: Today at 02:27:35 AM by Athame57 »
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1978 CB400F2 named Elen.

Offline McCabe-Thiele (Ted)

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Re: Brake Drum Dust Seal
« Reply #1 on: Today at 08:05:50 AM »
As you will know the specially shaped washer is also a basic wear indicator,, the felt washer is to help keep out dust and water. Personally I think you should fit them both.

It's a fiddly job made difficult as the brake lever splines will be tight from the clamping of the bolt, worse if overtightened in the past. I would ensure the splines are clean on the shaft, rust free.

As you will have found out as you slide it in place the shaft moves into the hub. I had one of those tools that is like a screwdriver except it's a  pointed tapered end. I was able to push the tapered point into clamp bolt hole and this pulls the shaft out of the hub as the taper meets the bolt recess part of the shaft.

It might help to ease open the lever arm if it's a very tight fit in the shaft.
If they are available a new lever arm might be needed if it's been continually overtightened in the past,.
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Offline Athame57

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Re: Brake Drum Dust Seal
« Reply #2 on: Today at 09:02:48 AM »

As you will have found out as you slide it in place the shaft moves into the hub.
That is exactly what happened Ted, I even wondered if this was a fault in itself. I'll have to find  something I can press into service to help with that.
I brake for animals!
1978 CB400F2 named Elen.

Offline K2-K6

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Re: Brake Drum Dust Seal
« Reply #3 on: Today at 09:31:33 AM »
If its a felt seal (often the case from this era) it's ultimately to stop ingress of moisture by oiling the felt periodically. 

Stops them corroding from wet, road salt etc in the pivot, then seizing to stop brake working.

Much easier with wheel out as spindle can be supported from other side to push brake arm on.

The brake arm is ordinarily positioned with dots matching on arm & spindle to give correct system setup and adjustment range.

Offline K2-K6

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Re: Brake Drum Dust Seal
« Reply #4 on: Today at 09:41:57 AM »
There's often a "blank" spline area on the spindle to prevent the brake arm being moved incorrectly to another part of the tooth engagement too.

Prevents both wrong assembly position or someone trying to compensate for knackered shoes by moving the arm  :)

Offline Athame57

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Re: Brake Drum Dust Seal
« Reply #5 on: Today at 09:56:16 AM »
There's often a "blank" spline area on the spindle to prevent the brake arm being moved incorrectly to another part of the tooth engagement too.

Prevents both wrong assembly position or someone trying to compensate for knackered shoes by moving the arm  :)
Yup, I noticed that.  ;)
I brake for animals!
1978 CB400F2 named Elen.

Offline Bryanj

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Re: Brake Drum Dust Seal
« Reply #6 on: Today at 03:09:46 PM »
Was a common practice to file one spline out of the arm so you could move it round and use up the brakes shoes, brake shoes were expensive!

Offline Athame57

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Re: Brake Drum Dust Seal
« Reply #7 on: Today at 04:52:42 PM »
Was a common practice to file one spline out of the arm so you could move it round and use up the brakes shoes, brake shoes were expensive!
LOL! The last time I had mine changed the mechanic said I was doing it too soon.  8)
I brake for animals!
1978 CB400F2 named Elen.

Offline exvalvesetdabbler

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Re: Brake Drum Dust Seal
« Reply #8 on: Today at 05:31:50 PM »
As you will have found out as you slide it in place the shaft moves into the hub. I had one of those tools that is like a screwdriver except it's a  pointed tapered end. I was able to push the tapered point into clamp bolt hole and this pulls the shaft out of the hub as the taper meets the bolt recess part of the shaft.

That's what I have managed to do, I removed the wear indicator to re plate it and I wasn't going to faf around removing the wheel and hub just to get a finger on the other end of it. A small Phillips screwdriver or length of welding rod will do.

If it's been missing the dust seal it probably wouldn't hurt to remove the shaft , clean and re grease while you are at it.

Regards
Dave

Offline K2-K6

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Re: Brake Drum Dust Seal
« Reply #9 on: Today at 06:03:20 PM »
Was a common practice to file one spline out of the arm so you could move it round and use up the brakes shoes, brake shoes were expensive!
LOL! The last time I had mine changed the mechanic said I was doing it too soon.  8)

They make it with the splines like this exactly to prevent wearing the shoes down far enough such that it would allow the brake cam turn fully square on to the shoes, which risks locking the wheel unintentionally, that being quite dangerous  :o