Upgrading ‘78 GS750 dual discs to 1980+ GS850 setup

[mattd1205]

I’m considering upgrading my 1978 GS750 stock dual disc setup to the rectangular pad setup found on the 1980+ bikes. I’ve got a line on some ridiculously cheap calipers/slotted discs from a 1980 GS850G that I spotted but I’m wondering if they bolt up ok and not have any unforeseen issues as far as function goes.

thanks
Matt

[Grimly]

The later GS750s were fitted with dual discs, so you could find one and use it.

https://www.suzukicycles.org/GS-series/index.html?GS750.shtml~isoraami

I had a suspicion the earlier GS750 had a 35mm fork leg diam, and so it proves...

https://kiwavmotors.com/en/faq/about-fitment/motorcycle-fork-tube-size-chart

However, you could simply fit the entire 37mm front end from the 850 and Bob's yer Auntie.

[mattd1205]

I’ve actually got dual disc on mine now. It’s just that I have the crummy, squeaky round pad calipers now.

[Grimly]

I’ve actually got dual disc on mine now. It’s just that I have the crummy, squeaky round pad calipers now.

Oops, I should have read that more carefully.
Ok, on checking x-compatibility on partzilla, your existing calipers are not shown as being fitted to the 79 GS850, which is a bit of an obstacle. If they were the same calipers as the 79 850, you could likely easily replace them with the later ones, as I've done.
Here are the 750B front calipers...
https://www.partzilla.com/catalog/su...ripers-gs750ec
Here are the 850 calipers...
https://www.partzilla.com/catalog/su...front-caripers
The odd thing (and is probably confirmation) is the 79 850 calipers are not shown as fitting any other model.

Who knows, it's still a possibility. If you can measure up the bolt spacings I can tell you if they might be a fit for the later ones.

<edit>
Here's a huge obstacle - the disc size.
You have 244mm diam discs, the 850 has 274 or 275mm diam discs (depending on who was measuring). However, if the caliper bolt holes are in the same position on the fork legs and the disc fastening holes are the same PCD, you might still be able to do it. There's a very good chance that your bolt holes are in the wrong position on the legs, though.
Where possible, Suzuki were in the habit of re-using components, but it's quite possible the 750s were at the end of line for some road-going equipment and the next year saw the improvement of several things, brakes included.

https://www.suzukicycles.org/photos/GS/GS750E-articles/1978_Cycle_road_test/1978_GS750EC_Cycle5_800.jpg

[mattd1205]

No worries I really appreciate the help. I used to have a 1980 GS850 that had 1979 round style brakes paired with the later slotted rotors and never had an issue. I guess in theory the mismatch could’ve been problematic because the solid and slotted rotors are different thickness but it didn’t present an issue in the real world. I noticed they used different part number calipers between the dual disc GS750 and 1979 GS850 which could imply that there is some minute difference despite appearing identical to the naked eye. I did however get some encouraging words from a guy on one of the GS groups on Facebook who used late style GS850 calipers and rotors on his 8 valve 750. He said they bolted on with no issue and have been problem free for years. I guess I’ll give it a go and see what happens.

[93Bandit]

My 77 750 is single front disk, but a caliper from an 82? 650G bolted right up. Rotor was same diameter, not sure if the twin disk 750s used different rotors than the single disk. Unsure if this is useful information for you or not, but thought I'd add just incase.

[Reddog78]

I have a '78 GS750E which from the factory had dual discs with round pads. I converted to early to mid 1980's GS square pad calipers and slotted rotors. Bolted on with no modifications/no issues. Installed EBC semi-sintered pads and I am pleased with the conversion.

[salty_monk]

Yes as long as you use the matching rotors I believe you'll be fine... You could also use the Twinpot calipers & CBR rotors.