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Holden rear drum backing plate damage (will apply to Torana as well)


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#1 yel327

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Posted 12 September 2019 - 12:47 PM

After finally getting hold of a set of HQ-WB rear backing plates to rebuild for the HK (damn things used to be throw away, try and find them now), when I pulled them apart I noticed the trailing shoe spring clips were a bit loose, and also the self adjusters which are located on the same pin were a bit sloppy. I thought it was just the springs had gone soft but once they were apart I noticed the hole in the backing plate were the pin head sits was concaved not flat like the other one. I looked at all the HK-HG backing plates in the shed and they were all similar. Found two more pairs of HQ-WB and a Torana set today and they were the same. As these backing plates are pressed symmetrical, and then have the handbrake and adjustment slots added afterwards, they should be the same on both pin holes.

 

What I had to do with mine was get them on an anvil and use a 12mm drift to bash them flat again. Otherwise the pin would sit maybe 2-4mm further towards the shoe which would mean the trailing shoe would be loose and so would the auto adjuster. I still think after the bashing that the steel is still about a mm or so shallower than it was originally, so I will probably put a washer under the pin head on that trailing shoe pin.

 

So when you go to rebuild your brakes next look at the rear pin head from behind. If it isn't flat like the front one and the steel under it flat you have the same damage as mine.

 

I bought all new pins, springs and clips for it. What does everyone use to free up the screw adjuster and keep it free? Is normal grease OK or should it be never seize or something similar?



#2 claysummers

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Posted 12 September 2019 - 05:13 PM

I use copper coat or neverseize. Just don’t let it near the rubber components of course.


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#3 S pack

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Posted 12 September 2019 - 06:50 PM

After finally getting hold of a set of HQ-WB rear backing plates to rebuild for the HK (damn things used to be throw away, try and find them now), when I pulled them apart I noticed the trailing shoe spring clips were a bit loose, and also the self adjusters which are located on the same pin were a bit sloppy. I thought it was just the springs had gone soft but once they were apart I noticed the hole in the backing plate were the pin head sits was concaved not flat like the other one. I looked at all the HK-HG backing plates in the shed and they were all similar. Found two more pairs of HQ-WB and a Torana set today and they were the same. As these backing plates are pressed symmetrical, and then have the handbrake and adjustment slots added afterwards, they should be the same on both pin holes.

 

What I had to do with mine was get them on an anvil and use a 12mm drift to bash them flat again. Otherwise the pin would sit maybe 2-4mm further towards the shoe which would mean the trailing shoe would be loose and so would the auto adjuster. I still think after the bashing that the steel is still about a mm or so shallower than it was originally, so I will probably put a washer under the pin head on that trailing shoe pin.

 

So when you go to rebuild your brakes next look at the rear pin head from behind. If it isn't flat like the front one and the steel under it flat you have the same damage as mine.

 

I bought all new pins, springs and clips for it. What does everyone use to free up the screw adjuster and keep it free? Is normal grease OK or should it be never seize or something similar?

Byron, the backing plates are not worn, I think they are made like that to compensate for the added thickness of the self adjuster. That's why every backing plate you can find will have that hole pressed deeper than the other.

The backing plates on my LJ are the same as what you describe.

 

I just use a smear of high temp bearing grease on the adjuster wheel thing.



#4 yel327

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Posted 12 September 2019 - 07:15 PM

These were not normal, a few of my HK ones are slightly recessed but these are way more. The way they are now I reckon that pin will still set a mm or two further in than the other, will see how they go when I put them back together, it will be easy to adjust.

Grease on the thread? Sounds like a plan.

Edited by yel327, 12 September 2019 - 07:20 PM.


#5 S pack

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Posted 12 September 2019 - 09:20 PM

Yeah, I made sure the threads engage & run freely and just applied a smear of grease to the first 5mm of the male threaded piece and screwed them together to work the grease through the threads.

I also put a smear of grease on the smooth spigot before fitting the slotted cap piece that engages with the shoe.

 

Found this pic of a pair of UC Torana backing plates on ebay. The hole for the pin that holds the shoe and self adjuster assy (yellow arrow) has a very pronounced conical stamping compared to the hole for the pin that only holds a shoe (red arrow) which appears to be almost flat.

 

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#6 yel327

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Posted 13 September 2019 - 06:20 AM

Mine were like that, and the way it had recessed the hole had gone oval. Others I had here were nowhere as pronounced, the recess was just enough for the in head to be flush. The whole shoe and adjuster were loose on both of the pair. Will see what is is like when they are back together, if too tight will only take a small whack to create a small indent.

#7 S pack

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Posted 13 September 2019 - 06:37 AM

I'm surprised there could/would be that much movement at the head of the pin to cause so much wear in the backing plate.



#8 yel327

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Posted 13 September 2019 - 07:54 AM

So was I. Dr Terry told me he has seen it with warped drums before.

#9 S pack

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Posted 14 September 2019 - 08:20 AM

A pair of LJ backing plates. Thanks for the pic in your build thread Marty.

 

 

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#10 yel327

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Posted 14 September 2019 - 08:43 AM

Geez that is random. I saw some a few days ago sitting in about 1mm, those are probably near 4mm. There is no way the shoe and adjuster will sit tight with the pin head in that far. At least those LJ holes are round, mine were oval and the pin head only just stopped pulling through. The pin heads were pulled concave also.




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