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Instability at high speeds

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    #16
    Originally posted by oldGSfan View Post
    In everyday legal speed riding they were OK.
    Limiting a turbo 11EZ to "everyday legal speed" ought to be against the law.
    1982 GS1100E V&H "SS" exhaust, APE pods, 1150 oil cooler, 140 speedo, 99.3 rear wheel HP, black engine, '83 red

    2016 XL883L sigpic Two-tone blue and white. Almost 42 hp! Status: destroyed, now owned by the insurance company. The hole in my memory starts an hour before the accident and ends 24 hours after.

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      #17
      All good info above.

      If it was me, and I'm assuming it's a bike that's new to you, I'd start by confirming the frame is straight using string-lines. If it's tweaked, nothing else you do will compensate for this. And repair will be necessary. This one below has the steering head is twisted anti-clockwise (seated on the bike).



      Then I'd check that the fork tubes are straight by taking them off the bike, clamping them in a vice by the caliper lugs, setting up a static pointer and rotating the stanchion tubes, if bent this will be obvious.


      If the frame and forks are straight, I'd make sure the have the correct oil at the right level

      Then I'd check the tapered roller steering head bearings replace if wear is evident, regrease if they look good. The stem nut needs to be torqued down 29.0 - 36.0 lb-ft, seated by rotating the stem once or twice and the nut backed off a 1/4 to 1/2 a turn. There should be some resistance to rotation, but it should be smooth; it shouldn't rotate under its own weight. This is important as the preload on the steering stem bearings provides some steering damping and so impacts stability and resistance to the resonance that sets up dynamic instability of wobble/tank-slappers.

      The other critical chassis part is the swing arm pivot. The cross-bracing around the swing arm pivot means that shimming the swingarm pivot is a better way of removing end play on the swing arm, as the tension on the pivot can't deform the frame to close this up to any great extent. If you look at a parts diagram, there are shims either side under the needle bearing dust caps. If you can squeeze another one in, then do it. Even if you need to tap the swing arm in with a mallet. Definitely replace the bearings and sleeves as these never get greased and are likely to be shot.

      ​​​​​​Correct preload at the pivots is critical to make the GS chassis handle.

      Assuming the shocks are good, lowering the rear end should improve stability as it increases trail on the front wheel.

      Tire pressure should be what feels good to you. Less pressure is a bigger contact patch, more grip, more heat, more wear and more tread squirm/slightly heavier steering more feed back. Higher pressure gives a small contact patch, less grip, less heat, less squirm/lighter steering and less feedback. I run about 29/32 it works for me.
      Last edited by KiwiAlfa156; 07-06-2024, 04:00 AM.


      "Johnny the boy has done it again... This time its a scrubber"
      Dazza from Kiwiland
      GSX1100SXZ, GSX750SZ, GS650GZ All Katanas, all 1982

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        #18
        quick update i did put the stock suspension back on and although they are old and feel terrible for bump dampening as expected with 42 year old shocks, i did feel a bit more stable at higher speeds.

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          #19
          another update, ride to work today was about 40 degrees out, and i didnt even realize i was past my usual rpms, so the cold helped my instability a little. usually i dont push past 6500 (not sure of exact speed since speedo stops at 85) but today i was pushing 7500. maybe ill revisit my tire pressure and recheck my air pressure in the forks just to be sure.

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            #20
            Dang stupid 85 mph speedos... Ball park figure, most big GS's run appx 15 mph. per 1000 rpm., so appx #'s, at 7500 you're near 112 mph... Check your bike, hold steady at 3000 in 5th gear and check your speed, if you're doing 52 mph. divide that by 3 and you're doing 17.3 mph per each 1000 rpm.. Keep us updated, I've had a couple of big GS's that with age got a little insecure. I changed everything I could think of, but never got them back to how they were when new.
            1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

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              #21
              I did not see this mentioned, so, do you have a fairing of windshield of any kind on the bike?

              Depending on model and design of these items higher speeds can lift the front a bit.

              My 1100G had something similar when the front lifted slightly as wind got under the Vetter fairing.

              Turned out time and the extra weight had considerably weakened the springs so when the fairing lifted the springs were doing almost nothing and it actually was almost floating.

              A new pair of Progressive springs and fresh fork oil improved everything.


              Also....check front-rear wheel alignment. This should always be a part of the checks when you install bearings, especially swing-arm bearings..
              Bertrand Russell: 'Men are born ignorant, not stupid. They are made stupid by education.'

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                #22
                Originally posted by wilsonsandy07 View Post
                quick update i did put the stock suspension back on and although they are old and feel terrible for bump dampening as expected with 42 year old shocks, i did feel a bit more stable at higher speeds.
                This points to an imbalance in the suspension, front vs back.
                I suspect your shocks are too stiff and the forks are too soft

                Better shocks and upgrading your fork springs should cure your issues
                1978 GS 1000 (since new)
                1979 GS 1000 (The Fridge, superbike replica project)
                1978 GS 1000 (parts)
                1981 GS 850 (anyone want a project?)
                1981 GPZ 550 (backroad screamer)
                1970 450 Mk IIID (THUMP!)
                2007 DRz 400S
                1999 ATK 490ES
                1994 DR 350SES

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                  #23
                  Originally posted by Big T View Post
                  Better shocks and upgrading your fork springs should cure your issues
                  I did that (progressive front and back) and tried multiple combinations of dampening and preload. Same.........



                  82 1100 EZ (red)

                  "You co-opting words of KV only thickens the scent of your BS. A thief and a putter-on of airs most foul. " JEEPRUSTY

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                    #24
                    UPDATE:

                    got about 4k of my own miles on the bike now, certainly ridable and i have pushed it about as far as itll go without further tuning/jetting carbs. it could feel more stable, but i can feel when the bike is fighting and back out when needed.

                    However, went on a longer run recently and was just checking some levels/psi and found my fork air pressure sitting at 30 PSI! not really sure how it happened since i serviced it to 7 like the manual says but it is what it is. dropped the pressure and it feels way better but i think my front tire is out of balance. im using balance beads and i couldnt notice it before as there was so much pressure on the front it was pushing the wheel down hard, but as i get up to highway speeds i can feel the vibration from the front tire and see it consistently jumping. its not coming off the ground but i can see it vibrating.

                    nice to finally put eyes on an issue

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                      #25
                      You might try eliminating the air assist forks. Don't really need the air if you have upgraded the springs and you are positive that the correct level of 10 wt. fork oil is used.

                      And while we're at it, what is holding you back from putting your bike info in your signature?
                      Larry

                      '79 GS 1000E
                      '93 Honda ST 1100 SOLD-- now residing in Arizona.
                      '18 Triumph Tiger 800 (gone too soon)
                      '19 Triumph Tiger 800 Christmas 2018 to me from me.
                      '01 BMW R1100RL project purchased from a friend, now for sale.

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