77 GS750 fork upgrades

[Chuck78]

I'm looking to find a donor bike to get at the very least a dual front disc mount on both fork tubes. I thought that in the process, I could potentially swap out the front suspension off of a slightly newer/better handling bike, perhaps a GS1100 since I already have the aluminium swing arm off of a GS1100. I want to retain my stock spoked wheels, so I think that may rule out the GSXR and other popular USD and modern shocks.

I had read that an early GS1000 is a good donor, but the triple trees and everything need to be swapped out due to being larger diameter.

I remember reading about the GS850G that their forks were tuned softer for more comfort. I may be getting the top half of an 81-83 GS650G engine for my wife's GS550, and noticed that the GS650G parts bike had dual front discs and they were the standard axle layout (not leading axle). I could get these forks off of that parts bike, but not sure if they would be an upgrade or if they are set up for a more comfortable ride rather than sporty high performance handling.

I wondered if I should just stick with the stock GS750 dual disc forks or whatever fork legs I could get - such as this 650's (non-leading axle model), and just swap to a stiffer progressive spring - but I'd need help with spring model/spec suggestions. I read that Sonic makes a 25mm diam. spring that fits our bikes, but not sure what specs I'm after. Also read a little about RaceTech cartridge emulators for about $165 that allow independent dampening adjustment of the compression and rebound. Still wondering if there was a complete fork that would be a substantial suspension upgrade, and a direct bolt in to my GS750 frame and my stock front wheel - especially if I would be good to go with the springs and dampening system in a complete fork setup.

I am also seeing a lot of people recommending getting a 35mm fork brace. When I clicked on the link on one, it looked like a brace that connects both fork tubes, not the lower part that the wheel mounts to like I had suspected (a horseshoe type stiffener between the two legs to keep the suspension from deflecting sideways and binding). Where do these go, and what is the benefit?

[Chuck78]

That GS650G also had a complete dual disc setup along with slotted/drilled rotors front and back. I wonder if the offsets on the rotors and everything would swap directly to my 750, or if the triple trees on the 650 are wider to accommodate the duals? Might be worth offering to buy the whole bike for the forks, dual discs, and the top half of the engine as well!

So after some geeking out on thegsresources.com and caferacer.net, I am looking at the following:
*Get dual disc 35mm forks from another GS750 or the GS650G & full brake setup from the 650
Will the 650 lowers swap directly onto the 750 for tubes? will my current triple tree spacing work fine with dual discs mounted up? The GS650G forks are 3/8" shorter height, this is the big reason I asked about swapping just the lowers - because I love the way it steers currently, although new springs may raise the front and change the steering angle from it's current state.
*25mm dia. progressive rate springs from Sonic
any tips on length or stiffness rating?
*Race Tech 35mm cartridge emulators
(these seem to be billed as for Harley's, am I looking at the right ones?)
*Hagon 2810 rear shocks (or used external reservoir CB900F shocks to rebuild)
*new bearings for my GS1100 box aluminum swingarm swap, 530 chain conversion since the old 750 swingers are 35mm shorter
*Shinko 230 Tour Master tires for much improved handling
What is the widest tire I can fit on my GS750 rear rim? I know 120 is recommended, I'd go 130 if it isn't going to balloon out and cause sidewall flex and cornering problems (wife's GS550 has a 130, looks so much fatter/appealing...), maybe try for 130/80-18 if this is going to handle as good or better
*should I be looking into upgrading my steering bearings, or just verify that my OEM's are in good condition?

So much for keeping my bike around $2000 invested! $650 more to upgrade the top end to 920cc's & 9.8:1 compression, easily $800+ with all of this brake/suspension/tire upgrading... Whew... This will be the last bike I ever buy I guess, more of a fun money pit than my house rehabbing! So far it's looking like about $2700 and growing! It will be a really really awesome ride when I'm getting progress made on it. Time to do some more side jobs to not break the bank!

[tarantulahed504]

I've been researching about swapping a gs650 front end setup onto my gs750t..stumbled across this old post and was hoping to get some info.. What setup did you end up going with? lowers? fork brace.? springs?.Did the smaller for tubes decrease handling at all.
Thanks
Andrew

[Chuck78]

They arent any smaller, just lowered the ride height 3/8" in front. Got a little bit of headshake now between 40-50mph only, but a needle bearing conversion kit will fix it. You shouldn't have that problem with the one you're working on (t='82? Probably has needle bearings already).

If you have 37mm legs and not 35's, stay with the larger.

Swapped uppers & lowers as matched set, reused triples, longer of the gs750 springs (2 per side oem) plus spacer to replace short springs. Emulators, tarozzi brace, AllBalls fork seals, 15w oil, mikesxs emulators at 2.75 turns in on valving preload.

[Chuck78]

Steers faster with shorter forks, btw.

[tarantulahed504]

I understand the basics of bike geometry and steering. I guess what I meant to ask was if it negatively affected the ridability..Any clearance issues with the bike lowered. Did you go with the hagon shocks?..where'd u pick up the tarozzi fork brace from?? Thanks for all the help chuck78

[Chuck78]

Not at all, Fork brace was acquired at fastfromthepast.com , wanted ahagon Nitro's but they dont come with a clevis lower mount, but the comparable YSS Z362 does. I scored a vintage pair of GS1000 piggyback Fox Factory Shocks that are quite a vintage gem. Neeeing fully rebuilt & shaft replaced, but still will be awesome once rebuilt & tuned.

[tarantulahed504]

So I got a set of stock rebuilt gs650g forks off a forum member.. I have been looking at different springs(progressive and stock cut) options and emulators. I see racetech.com seems to have a lot of parts and info and also saw this mikexs name come up a lot as well.. I want a good performing feel on the road, I will not be road racing just an aggressive street ride. Could you offer me any advice or direction on parts ...thanks a lot chuck

[Chuck78]

Use the spring rate calculator on the sonic sring site. How heavy are you with gear? Any mods to lighen the 550lb bike (4-1 exh., center stand delete, etc.)? .90, 1.0, or 1.1kg//mm spring and appropriately sprung $200-300+ rear shocks from hagon or progressive. Mikesxs.com emulators at 2-3/4 or 3 turns dampening valve preload with 15w fork oil. That's based on my experiences. Spend more on rear shocks if you can afford ut, $400 for some rebuildble Ikons or $500 for some Works Perfrmance or YSS Z-362's. Buy a tarozzi fork brace when you can afford it, shocks are crucial, fok brace is an easy future add in.

[tarantulahed504]

I'm at 170/ 175. No weight reduction mods but will eventually be doing both 4 to 1 header and center stand delete. Clip ons, etc... spring rate calc said 1.00 kg/mm. Have you personally used the sonic springs? ....unfortunately I will not be able to cough up 400-500$ for shocks. 300$ is realistic tho. Will be looking at the hagons or progressives..will search ikons as well.. The mikesxs emulators are same quality as the race tech...thanks again for all the as knowledge chuck

[Chuck78]

Yes, Dan on here critiqued them quite a bit and seems to think that they are a better design than the racetech's, similar but opposite engineering setup on the valving. I plan to get Sonic springs eventually, many people on here run them with great results.

[tarantulahed504]

Hey chuck. Any recommendations on SS brake lines? I've seen spieglers but they are quite expensive... I will be able to use my 750t Master cylinder? Will just need a longer, dual port banjo bolt?

Thanks as always

[tarantulahed504]

Or use a distribution block or y-fitting up to the M/C

[Chuck78]

I got the Earl's diy compression banjo fittings and Speedflex stainless steel hose w/clear coating, I believe the size was -3. There is a thread on here with a title something like "stainless steel brake lines video" - check that out, or search on here for Earl's Speedflex or ANPlumbing.com Speedflex. AN Plumbing sells the stuff, among others. There are lists of what parts work best, angles of fittings and adjustable vs nonadjustable fittings. You are much better off for cost and performance to just run two lines off of the master.

I never installed my lines yet because the Kawasaki double banjo that I got for my 2005 Ninja master cylinder had the holes drilled for different thicknesses of banjo fittings, so I was unable to use it and just assembled my bike with some spares for the big road trip.

Also take note that I believe Suzuki uses a finer (or was it coarser?) thread than all the other big 4 Japanese bike makers for their banjo bolts. If you are using a Suzuki master for dual disc, make sure you get the correct thread banjo and correct double banjo bolt spacing. I think the fittings were thinner if I remember. If AN doesn't sell the Suzuki, the dual disc late model ninja master cylinders with the plugged off mirror thread hole in the top and the rectangular master reservior are awesome.

[Chuck78]

You're going to run around $90-105 for the Speedflex hose set for dual disc fronts if I remember correctly.