Author Topic: KX500 Frame rear brake lever pivot  (Read 61 times)

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Offline k9Mike

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KX500 Frame rear brake lever pivot
« on: October 11, 2019, 05:19:32 PM »
I was wondering if anyone has replaced the rear brake lever pivot on their KX5?  I just had my frame bead blasted, and it appears the pivot has worn a bit.  I test installed a new brake lever on it and there is a little side to side play (although in the brake lever are 2 pressed in bushings which are not perfectly smooth. Not sure if one bushing has an intentional raised ring to locate it on the frame pivot shaft. Perhaps the bushings are more responsible for the wobble than the pivot.)

Frame is about to get gusseted so that would be the time to replace it (if necessary). Just not sure if the pivot was perfectly flat along its length when new (or if it had a very small step to match the bushing).

Thx.

Offline cwtoyota

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Re: KX500 Frame rear brake lever pivot
« Reply #1 on: October 12, 2019, 11:50:19 AM »

Frame is about to get gusseted so that would be the time to replace it (if necessary). Just not sure if the pivot was perfectly flat along its length when new (or if it had a very small step to match the bushing).

Thx.

Mike, I'm sure they were a constant diameter cylinder with a 12mm diameter.

As a machinist, I'd just whittle out a new pin with the appropriate internal threads and replace that worn pivot, but another idea came to mind as well.

The current model Yamaha YZ's use a large shoulder bolt. 
The bolt has an 8mm threaded section that goes into a flat surface on the frame, then it has a 14mm smooth cylindrical section that serves as the pivot.
The beauty of that system is that a new bolt means you have a fresh pivot surface.
The bolt goes all the way through the tab on the frame and the tip of the threaded portion is drilled for a keeper clip (or safety wire).

The YZ bolt would be too large (14mm diameter), but perhaps another bike like a Suzuki or Honda uses a 12mm shoulder bolt on the brake.

Also, if you can find a metric shoulder bolt with a 12mm diameter smooth shoulder, you could drill and tap the frame and set it up like the Yamaha.
When the shoulder wears out, you replace it.   It's much less likely to wear though, as most industrial shoulder bolts are hardened and ground.

This product from McMaster Carr Supply is on the right track, although the head of the bolt is pretty tall:
(The threaded portion is M10-1.5mm, the shoulder is 12mm, and the length is 25mm).
Any supply house like Tacoma Screw Products or Fastenall, or Grangier, or the local place should be able to get a metric shoulder bolt.


https://www.mcmaster.com/92981a404

If none of that makes sense, check out this diagram for the Yamaha system on the 2005-2019 YZ250 and YZ125 at the link below:
Items #2, #3, and #8 are the pivot-bolt, o-rings, and the retention clip.

https://www.motosport.com/dirtbike/oem-parts/yamaha/2010/yz125/stand-footrest



Offline k9Mike

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Re: KX500 Frame rear brake lever pivot
« Reply #2 on: October 12, 2019, 01:07:48 PM »
That is a great idea! I'm not a fan of non-replaceable / serviceable parts that have the potential to wear pretty significantly.  To be able to replace that pivot would be a huge improvement.

I think I saw a video of someone replacing the KX5 pivot by simply grinding off the weld in back, and pushing the pivot pin out, so perhaps there's already 12mm hole in the frame that would just need to be cleaned up and tapped (my forte is making electrons do my bidding... not chips of metal, so I don't know if a 12mm ID hole can be tapped for a 12mm bolt.)

I'm going to do some research on parts to see if something off the shelf will work. Meantime, going to ask the KX guru that's going to work on my frame if that's something they would do for me.

Thanks for the idea! Planning on doing this unless some practical issue that prevents it.

Offline k9Mike

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Re: KX500 Frame rear brake lever pivot
« Reply #3 on: October 12, 2019, 02:50:35 PM »


Since the tab that the brake pivot is welded to is only .125" thick, I guess a threaded sleeve would need to be welded to the tab to provide enough support for a shoulder bolt.  I think there is plenty of clearance behind the pivot bolt (it's in the swingarm linkage area), so I don't think a sleeve protruding .5" or so would be a clearance issue for anything.

Offline cwtoyota

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Re: KX500 Frame rear brake lever pivot
« Reply #4 on: October 12, 2019, 03:29:00 PM »


Since the tab that the brake pivot is welded to is only .125" thick, I guess a threaded sleeve would need to be welded to the tab to provide enough support for a shoulder bolt.  I think there is plenty of clearance behind the pivot bolt (it's in the swingarm linkage area), so I don't think a sleeve protruding .5" or so would be a clearance issue for anything.

I just looked from the left side of the bike, behind the stock pivot on my 1990 KX500.   
That stock pivot is drilled all the way through for the factory M6-1.0 thread fastener.   (I can't see if the threads go through, but the hole does).
There's really no good reason you can't just cut off the stock 12mm peg, enlarge the hole with a tap-drill and thread it to work with a shoulder bolt.
That would be the simple way  to avoid any welding.

Of course, you'd have to do some fairly precise grinding work, or use a spot-facing cutter to make that area flat after you saw-cut that stock pivot.