GS700 stability

[rasndas]

I have an interesting situation with my 1985 GS700ES. when riding at higher speeds (70MPH) or higher the bike will twitch from side to side like it was hit by a sharp gust of wind from the side. It is not head shake as there is no decernable bar movement and it is not a constant oscillation. this only happens at higher speeds and is somewhat unnerving even though the bike hasn't done anything evil as of yet. I have checked the head bearings and there is no decernable slop or stickiness. Tire pressures are correct. Hoping someone out there might have an idea as I am stumped. I have quite a few different bikes and this is the only one that does this.

[posplayr]

I have an interesting situation with my 1985 GS700ES. when riding at higher speeds (70MPH) or higher the bike will twitch from side to side like it was hit by a sharp gust of wind from the side. It is not head shake as there is no decernable bar movement and it is not a constant oscillation. this only happens at higher speeds and is somewhat unnerving even though the bike hasn't done anything evil as of yet. I have checked the head bearings and there is no decernable slop or stickiness. Tire pressures are correct. Hoping someone out there might have an idea as I am stumped. I have quite a few different bikes and this is the only one that does this.

Welcome aboard. Not sure what condition your forks/shocks are in and obviously not exactly sure what the "twitch" is really like. However, when I was resurrecting my 81 GS750, it rode well except when I got over about 50 mphs. They it had a sorta twitch, that was like the front was very sensitive to grooves in the pavement even when there did not seem to be any grooves.

Anyway, after changing the fork oil and getting them matched to the correct level much of the twitch went away. Later i did the Progressives springs and fork brace which helped more. I felt pretty stable up to about 65-70 mph even on the freeway with many grooves. After that got a used set of Hagons and I was able to push up closer to 85 mph. With new Avons , it goes still faster

Point is that restoring these various elements allowed the bike incrementally improve to about as well as the stock bike would go. It may not be just one thing. The best thing with the old bikes is to make sure that all these things are in good working order.

So how bout:
front springs,
Fork oil
Rear shocks
swingarm bearings?

Another thing to do is NEVER trust your PO unless you would trust them with your life. There are plenty of screwed up repairs especially if yours is a hand me down bike.

A couple of my favorites are:

15mm ID front wheel bearings with a 17mm OD axle.

Welded But joint for a upper shock mount bolt that just twisted off with minor torque.

It is safest to make sure you know what is going on in every corner of your bike.

[rasndas]

Thanks for the reply. I will change the fork oil and have a look at what comes out. I believe I did change it when I got the bike but am not positive. I am also not running any air assist in the front forks so that could also be an issue. Will set that up to manufactuers spec also. I just found it strange that out of the 23 bikes I own this is the only one that acts like this. The twitch is hard to explain but is very much like being hit with a side gust of wind that causes the bike to lean but not change direction when traveling in a straight line.

[posplayr]

Thanks for the reply. I will change the fork oil and have a look at what comes out. I believe I did change it when I got the bike but am not positive. I am also not running any air assist in the front forks so that could also be an issue. Will set that up to manufactuers spec also. I just found it strange that out of the 23 bikes I own this is the only one that acts like this. The twitch is hard to explain but is very much like being hit with a side gust of wind that causes the bike to lean but not change direction when traveling in a straight line.

Wow that doesn't sound like the twitch i was referring to. I would do a string wheel alignment to to be sure the wheels are close to aligned and also make sure that the tires are properly pressurized.

I have had a a "lay down" type motion, but it would happen when the rear of my bike was overloaded (camping gear), and I was going through a sweeper turn at about 75-80mph. As the rear when up and down, the bike would lay over in unison with the rear bounce. Stiffer rear springs helped that. My theory was that the added weight on the rear caused more rear wheel side slip angle and cause the layover (almost as if the rear end was swinging out as the rear shocks compressed.) It was predictable but disconcerting nevertheless. It is gone now with stiffer springs and GSXR 18x4.5" wheel and matching radials.

Getting back to the forks, different oil levels in the forks, then one side compresses more than the other and causes the weight to shift side to side.

Maybe someone else has ideas for easy checks first.

P.S. make sure axle and swing arm bolt are "tight"

[Steve]

If checking the forks does not fix the problem, check the swingarm bushings/bearings.
Slop there will let the swingarm move around, causing some interesting handling quirks.

.

[spyug]

I agree with the guys. Its backend related and is most likely swingarm bearings. My XS did something like that prior to changing to bronze bushings ( they're stock with plastic bushings that wear out).

Check the side to side play on the swingarm and the alignment/tracking of the back wheel and chain. Its back there somewhere.

Good luck and let us know what you find.

Cheers,
spyug

[tone]

As above but also check wheel bearings for play

[rasndas]

Thanks for the input. Will be a couple of weeks before I can check this givin my cueent wor schedule but will deffinatly check the swing arm for play and let you know.

[Sunburn]

Maybe too simple but if this is the first time ridding this bike? If the front tire tread pattern has a grove the distance around the tire in the middle with cuts going off the side (older tires) At freeway speeds only, the front end would dance when it catches the natural grooves in the freeway/ road. It would feel like a random twitch to one side or the other. The center groove in the tire acts like a rail. When going slower you will not notice it.

Scary at first. I've never purchased a tire like that again. I think it was a Metzler tire made in the 80's and 90's i had.

[Mysuzyq]

If you've done any recent work at the rear end, it would be worthwhile checking the wheel alignment too (with a straight edge, not the hash marks)...out of alignment wheels also cause vague handling issues, in straight line cruising, and definitely in cornering.
Tony.

[BassCliff]

Greetings and Salutations!!

Hi Mr. rasndas,

After all of this good advice, all I can do is say "Hi" in my customary manner...

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[kingofvenus]

What is the size, brand and condition of the front tire?

[rasndas]

I believe the front tire is a Bridgestone BT45 110/90-16 and has very little wear. I just replaced the back tire which was a bridgestone BT45 130/70-17 with a Kenda K657 130/90-17. The manual says the original size 100/90-16 for the front and 120/90-17 for the rear. The PO installed the other tires. One thought I had was the factory rear tire is 2.1 inches larger in diameter than the front. The tires the PO had installed were approximatley the same diameter front to back so rake angle would have been affected. With the new rear tire the back is 2.2 inches larger in diameter than the front and is more in line with what the factoy set up would be. The twitch is still there however so it didn't solve the problem

[posplayr]

I believe the front tire is a Bridgestone BT45 110/90-16 and has very little wear. I just replaced the back tire which was a bridgestone BT45 130/70-17 with a Kenda K657 130/90-17. The manual says the original size 100/90-16 for the front and 120/90-17 for the rear. The PO installed the other tires. One thought I had was the factory rear tire is 2.1 inches larger in diameter than the front. The tires the PO had installed were approximatley the same diameter front to back so rake angle would have been affected. With the new rear tire the back is 2.2 inches larger in diameter than the front and is more in line with what the factoy set up would be. The twitch is still there however so it didn't solve the problem

Should not make a lot of difference, but the BT45 130/70-17 will have a stiffer side wall than the K657 130/90-17 just due to side wall height. More flex in the sidewall in the rear gives an uncertain feel. You have them boned up right?

[rasndas]

Not sure what boned up means. The tire was installed and balanced at the local bike shop and I set the presures to the factory recommended.