Author Topic: Why have bungs in brake caliper pistons?  (Read 898 times)

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Offline Brockett

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Why have bungs in brake caliper pistons?
« on: October 01, 2020, 20:19:55 »
Regarding my VX800 the front brake caliper ( yes just one)  is grotty. The surface needs a repaint and the gubbings inside was not good. ( no dust seals and very worn pressure seals.  I have sourced a service kit which includes stainless steel pistons. However in the original pistons there is a plastic bung which does not fit in the replacements which have a slightly thicker wall and are a tad too small for the bungs to be inserted. The bungs bear on the pad to apply the brake.
1/.- Should I trim the bungs so they fit or not bother to fit them?
2/.- I can clean up the surface of the caliper but then before applying VHT paint do I need to apply a primer or will the paint adhere to the bare ally surface ?
This doesn't last forever, so do it while you can.

Offline kwackboy

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Re: Why have bungs in brake caliper pistons?
« Reply #1 on: October 01, 2020, 20:32:36 »
Regarding the piston Inserts.

I've always wondered why some calipers have them and some don't but to answer your question, you'll notice they sit a little proud of the piston, I'm pretty sure they're to keep the piston centralised in the event of abnormal pad wear and they help with heat dispersion.

Do you actually need to put them into your new pistons ...? I would if they were there in the first place however, your brake should work perfectly well without them .
Chief trouble maker 🙂

Offline Brockett

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Re: Why have bungs in brake caliper pistons?
« Reply #2 on: October 01, 2020, 21:08:08 »
Yes KB. As you say they sit proud of the piston so without them the piston would have to protrude further out to operate. They may act as an insulator the keep the brake fluid less hot.
This doesn't last forever, so do it while you can.

Offline Mr Nick

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Re: Why have bungs in brake caliper pistons?
« Reply #3 on: October 01, 2020, 23:58:16 »
And perhaps reduce the chance of brake squeal by removing a metal:metal contact? However, plastic is more compressible than steel so there will be a reduction in force transfer: if you trim them down you would reduce wall thickness if they're hollow and that would increase compression & reduce force further. If they're solid, then the effect is far less.
Seems pearl asbo orange is faster after all....

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Offline Brockett

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Re: Why have bungs in brake caliper pistons?
« Reply #4 on: October 02, 2020, 01:29:11 »
Not solid - the cross section is a "+" All I have to do is to trim the sides of the "+" and maybe a little off the circular top.
This doesn't last forever, so do it while you can.

Offline Mr Nick

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Re: Why have bungs in brake caliper pistons?
« Reply #5 on: October 02, 2020, 10:43:03 »
That's easier to deal with than a cylinder then.
Seems pearl asbo orange is faster after all....

'Don't believe all the quotes in forum signatures' - Aristotle

'Ehh, good enough' - Mediocretes

Orange Bikes Matter!