Frontal nightmare

[crayonjota]

All was going well with the new improved GS, the GSX exhaust made a world of difference, more torque and power across the board. Like riding a new bike.. Oh, its a 1980 GS1000E with twin vented disks..

Then during some heavy brakeing I got a thump come up through the bars, and thought hmm, a rock... Next day it got worse and worse. The local experts said it was the headstock bearings, so I replaced the bearings even though to my eye they both looked in good shape, if not a little slack in adjustment.

Took it out for shakedown, and nice all well, though not enough air in the fork. Took it out again with the requisite 20psi and the front end feels real weird, especially after the superlight thumper and the spinejarring lump is still evident, especially under braking, but anytime there are undilations in the road surface. It feels like its coming from the frontend, but the shockwave gets the whole bike and to be honest I am afraid to get silly on thing till its sorted out.

Stationary jumping up and down on the bike produces nice fluid suspesion movement with no odd noises. The rear swingarm may have a little play in it, but surely not enough to cause such a violent reaction thoughout the frame..

As ever your assistance is greatly appreciated.

CJ

[jimcor]

Could it be a warped brake rotor?

[Travellin' Jones]

First of all, I don't think it's a good idea to overlook any known fault, such as the swingarm bearings being loose. A rear suspension fault can cause more handling problems than a front. To see what I mean, drive your car in reverse at 40 mph and twitch the steering wheel a little.

But it sounds like your next step should be to disassemble and inspect the forks. You may have a broken or loose damper rod. Even if everything looks ok, it would be a good idea to replace the damper rod seal rings and the slider bushings while it's apart. As an aside, I like to replace the damper rod bolts whenever I remove them. They're easily damaged during removal, and while you can reinstall them, subsequent removal can be difficult.

Of course, you don't want to overlook the wheel bearings and brake caliper mounts.

[Anonymous]

I had this problem with my GS400E. It would thump whenever I tried jumping a steep curb. I never did figure it out by I think it was probably the gauges smacking the headlight or something. I'd had the forks apart a few times freshening them up and didn't see anything unusual.

Another thought is that your preload pins have broken off and are moving around between the fork caps and free pistons. My bike used to have 3 preload settings upfront but when I was changing the fork oil I found that both of the nubs were AWOL. They must have broken off at some point and then gotten removed during a service.

Steve

[Sandy]

The suspension on the GS1000's is really prone to bottoming out easily and while the air helps they just have really baggy springs. Also if there is an oil cooler installed make sure the front fender is not hitting it. You can tell because there will be a dint or scraps on the front fender. The fact you can pump the suspension up and down shows that the forks aren't bent and are probably aligned properly in the triple clamps. If this doesn't find the problem then you'll probably have to take it apart until you find the problem unless someone else here has any more ideas. Good luck CJ.

[argonsagas]

An interesting problem.

Let's see....you first had the problem under heavy braking, so weight would have been transferred forward, and compressed the front suspensio, while both brake rotors would be warmly and firmly hugged by the calipers, making wheel bearing movement minimal, due to the force exerted by the brake pads.


The effects came sharply, which suggests something gave way, shifted, or broke.

Loose head bearings could cause that, but this seems not to apply, as you replaced them.

A weak spring would not change suddenly, but one could break, or a spacer could split, resulting in uneven damping between the forks, and, while you say jumping up and down when stationary produces only a fluid motion, this could still be a problem, although not likely the main cause of concern right now.

Where does it say 20 PSI in the front forks is required? You are likely better off with longer or additional spacers to increase spring tension, or replace the springs....and still use spacers.



Loose calipers could allow some twist and grab of the disks, but sharp thumps seem unlikely.

A warped brake rotor would cause uneven braking, and some unwanted tremors, but repeated thumps seem less likely, and they would not happen solely because you were riding on an undulating road surface

Forks that are not tightly clamped could also produce something like this.
With the head bearings having just been replaced, you would likely have attended to this, but the lower clamps could be checked.


I have no experience with broken pre-load pins, and so offer no comment.

You get strong, sharp thumps, and they appear to have gotten worse during your successive rides.

A loose front axle could cause that.


Of course, a bent front axle could also cause that, but that implies you hit something, which does not appear to be the case.

A broken wheel would cause that.

If all else seems good, I would look closely at the front axle , and, while down there, take a VERY close look at the front wheel to see if it has cracked..








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[feelergaugephil]

Here's how I cured my Thump!! I installed new fork oil, and installed a dual air line on both forks and put them at 12psi.
I also installed a fork brace and torqued the rear swing arm bolts, (mines a shaft)
It stops in a straight line and doesn't woble over white lines.

[crayonjota]

Thanks for all the advice. Its not the axle or brakes as it does it over the innocentest of bumps either on or off the brakes, so I am thinking that something broke in the forks somewhere. Lovely.

Going to haul it all apart and see what the hell is going on before it throws me off...

Cj

[crayonjota]

Let me update and see if anything more concrete comes up. I double checked the headstock bearings. Everything is fine, flushed the fork oil and refilled to SUZUKI (like they know) specs. Looked over the rears and checked every nut bold and washer on the bike for tension.

Set off for a run only to get the thump thump thump as I went across the expansion joints on the concrete road from my house. Its worse on the brakes but still aparent as I crash over every lump and dip. I wind the sucker up as I am not best happy and it all comes together and smooths out at around 120kph and stable as a rock at 230kph (and because I didnt disconnect the speedo I wasnt about to go any faster as at 240 or more the cable breaks), though the bigger of the bumps throw my butt from the saddle and threaten my footing. Yes the suspension I have is very stiff, but then I hate the wallowy floaty disconected feeling of anything less than err, taut. OK, ballbreakingly stiff.

Does this help anyone finetune the advice or should I just be done with it and tear the forks down? Some, perhaps 50% of the lumping comes up from under my seat, the other crashing through the bars, but aparently only at legal or below, speeds

CJ

[first timer]

tear the forks completly apart so you can check your springs length and replace your teflon bushings, and seals. it' will be a little bit of a pain in the ass but the bike probly needs a good frond end rebuild. also pull your swing arm it's not that hard and see about replacing the bearings there to, it will do you good and give you a peice of mind to atleast knowing these are back to right off the show room floor 1980 condition. the parts will probly only be like 50 bucks for every thing, i know you are in panama but you should stiull be able to get bike bandit or ronayer to ship if you get in contact with them. if you need shipping help email me and we can work sumtin out.

it is real hard to say what could be the problem the only way to figure it out is start replaceing some of the simple stuff first and see if that helps, or atleast digging in and see if there is somthing right there.

-ryan

[jimcor]

CJ, any chance that new exhaust is banging around? Did you get a proper hanger for it yet?

[KEITH KRAUSE]

It is funny how the problem seems to have started after the new exhaust was installed.
If it's not the exhaust, have you checked all frame welds?

[crayonjota]

I am pretty sure it started before the new exhaust, and it handles oddly right now suggesting suspension woes.. If l let go of the bars they begin to shake from side to side, which seems to scare the crap out of other motorists!!!

As to a proper hanger, no, no time.... I didnt even get Sunday off to look at it. Stupid little thumper just keeps on going, covered in sand and mud with lovely compliant suspension. Kinda the opposite to the GS really. I will be looking at the swingarm bearings after I have fixed the stuff my wife has listed on the fridge, so sometime in 2006 the way things are going.. CJ

[jimcor]

If that was a Concours your steering stem bearings would be too loose and the front tire would be 'cupped', scalloped shaped wear on the sides.

I had the same trouble, without the thumping, tightened the bearings and replaced the front tire, eventually. Problem cured.

[crayonjota]

Today I took the rears off and replaced the stock jobbies. It was raining a full on tropical storm so I had a bit of time. Going to see what goes from there. Replaced the fork oil again too, REPSOL 10W20, on the 5th bike shop I tried. Nobody it seems, even the bike mechanics use fork oil other than 5w, here in the tropics....!!!

CJ