Rear disc rotor 1980 GS850G

[Totallyforked]

Hi all, I need to replace the rear brake rotor on my gs850g as it is less than 6mm thick and has gouges in it.
I bought a new rotor but it didn't include the center piece. It looks like the old rotor is fixed to the centre piece with 9 steel rivets.
Does anyone know the procedure for fixing the new rotor to the old centre piece?
I'm sure I can get the old rotor off the centre piece by drilling out the rivets. But I'm not sure after that.
For instance what sort of rivets do I use and what size? Do I use a big rivet gun or are they a shrink fit with heat?
The Suzuki parts fiche only shows one item which includes the centre piece attached to the rotor. And it costs over $500!!
I couldnt find any YouTube videos or any threads in this forum.
Any advice would be appreciated

[Grimly]

Pretty sure there was a hub change design and the flat disc just bolts straight onto it.
Should be able to pick up a later wheel complete.

[bwringer]

Interesting... do you have a source for metric rivets in the size needed? (Or if the holes are 8mm, 5/16" would be close enough.) You'd need the appropriate riveting air hammer and a nice solid hunka steel for a bucking bar, but it's certainly do-able.

There may not be enough room for the thread engagement needed to use bolts and nuts.

As Grimly says, the later models had a rotor bolted directly to the wheel; if that's the same rotor, then getting a wheel from a later model might be just the ticket.

[Syd]

Someone please correct me if I'm wrong for this particular year and model. I thought the original factory Suzuki rotors were solid, non vented discs that have a minimum thickness of 6mm. When the later vented rotors became the norm, I'm fairly sure the minimum thickness is 4.5mm.

Do your rotors have a minimum thickness marking stamped into them somewhere?

[rphillips]

Looking at parts diagrams it looks like the GS850"s, through "81" had the rotors like in forked's top picture (smaller center hole), Tha "82" GS850G diagram has one that looks like the lower picture (larger center hole). "79" GS850 diagram shows a solid rear rotor, the "80" diagram shows a slotted rear rotor.

[Totallyforked]

Pretty sure there was a hub change design and the flat disc just bolts straight onto it.
Should be able to pick up a later wheel complete.

Hi Grimly, yes that's a possibility but it's not that easy to source a complete wheel where im located (Sydney Australia). If i could find one it would probably cost more than the price of a new rotor

[Totallyforked]

Interesting... do you have a source for metric rivets in the size needed? (Or if the holes are 8mm, 5/16" would be close enough.) You'd need the appropriate riveting air hammer and a nice solid hunka steel for a bucking bar, but it's certainly do-able.

There may not be enough room for the thread engagement needed to use bolts and nuts.

As Grimly says, the later models had a rotor bolted directly to the wheel; if that's the same rotor, then getting a wheel from a later model might be just the ticket.

Thanks bwringer, the hole size on the new rotor is 6mm. I can source 6mm solid steel rivets but I've never done this before. I will do some research and see if it is doable. Maybe I will take it to a shop and see if they can do it

[Totallyforked]

Someone please correct me if I'm wrong for this particular year and model. I thought the original factory Suzuki rotors were solid, non vented discs that have a minimum thickness of 6mm. When the later vented rotors became the norm, I'm fairly sure the minimum thickness is 4.5mm.

Do your rotors have a minimum thickness marking stamped into them somewhere?

Yes Syd, they are definitely stamped 6 mm. My rotor is just over 6mm on the edge and just under (5.8mm) toward the centre. I'm considering just leaving it and seeing how it works.
It would be a bit of a shame though as every other part of the braking system has been refurbished including braided steel lines, pads, pistons and seals.
My local Suzuki supplier has 8 discs in stock so it must be a fairly common issue.

[peteGSX]

Have you tried Metalgear at all? The same situation exists for the Katanas and I'm pretty sure they offer a service to swap the internal part to a new rotor. Not sure if they only do that for their own rotors or not but might be worth a try? This is their 850G listing.

[Totallyforked]

Hi Pete, no I haven't heard of them. This is great news! I was sure there must be some place that does this but i had no idea where to look. I'll try them tomorrow, thanks 😀

[peteGSX]

Cool, I get all my brake gear from them and some sprockets/chains as well. I haven't had to get a rotor swap done like that myself but have had good results with everything else. I've been running their discs and pads on the 450 and pads on the Kat for years (it still has original discs).