[dburnash]

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Hi everyone. well after about a month of blood, sweat and tears, and practically LIVING in the garage I finally got the 84 interstate with 20,000 actual miles that had been sitting for several years to actually go down the road. when i got the wing from the P.O the back tire was bald with the cords showing and the front tire had VERY little discernable tread and was so badly cupped it looked like a giant circular saw blade. the front shocks had fifteen psi in them and the back had none. I drained the fork oil and filled with spectro 10 w. fork oil. reduced the psi to 6 lbs. in the front and put 30 lbs in the rear. I installed a new set of bridgestone spitfires and had the front tire and rim spin balanced. the rear tire was acceptable spun by hand and the high points checked aftereach spin. First ride starting at about 25 MPH and gradually getting worse till about 35- 40 MPH the bike hops/ bounces at about a frequency of two times a second. Like going over a section of washboard. I removed the front tire and had it spun again. it was right on. drained the fork oil. added kerosene pumped the shocks and drained. did this till the kerosene was crystall clear. when moving the shock sliders up and down on the fork tubes they go up and down smoothly with no binding. Pulled the anti dive units and dissasembled them. cleaned everything with kerosene. blew them out with air. coated everything with ATF. reassembled them and flushed the shocks with ATF pumping the shocks several times and draining the ATF. did this several times... Added 10.9 ounces of ATF to each fork tube and reinstalled the caps... With the handle bars straped down, grasped the forks at the bottom and tried to move them for and aft. No movement or play. tried to twist them back and forth. no play. go for a ride. same thing. bounces hops at 25 MPH worsening till about 40- 45 MPH. Not sure if it goes away after that or just becomes much less noticable. tried 40 psi front tire and 40 psi rear tire. tried 34 psi front/ forty rear. seems a little less noticble at 40 PSI front. tried anti dive units at all settings. same.... with dial indicator straight on to front tire in the middle, out of round .050"... tire side wall run out .025"... rim run out .006 "... right disc run out .009 "... left disc run out .005... Dial indicator straight on to rear tire in middle, out of round .050"... rear disc run out .005"... rear rim runout .005 "... rear tire sidewall run out, .055 Sorry for the long post but if anyone has any ideas, suggestions, or advice I would be very greatful. Hell at this point I'd even take a muffled chuckle or a stern " so ya just had ta have a wing now did ya boy?" Thanks all,Mike

 

[johnmac]

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Mike,
At first thought, I wonder if you have a bad spot in the front tire, like some bad cords inside the tire.
On the other hand, I wonder if the cupping on the old tire might give a clue.
What I'd do to check for the bad spot: if you fill the tire just enough to make it look full, and push the bike slow while someone watches for a spot where it looks a bit "flatter", at the ground.
For the cupping, has any other members had front tires cup out bad?
Just a few thoughts, good luck!

 

[axelwik]

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There's a couple extensive threads on this subject. Go to the top of the page and enter, bouncing front end, in the search engine.

 

[GilbertGL]

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I followed your thread and the others on this bouncing business. It seems that many of us have it to a greater or lesser extent. My '83 1100 gives a small fast frequency hop and slow speeds but seems to smooth out at faster speeds. Just like an out of balance tire or a slight washboard road surface.

I have new tires, and recently overhauled forks. Just changed the front wheel bearings and steering stem bearings.

The old tires wore out perfectly evenly and the wheels were balanced both before and after the new tires.

I am beginning to think that this wobble/bounce/hop, or whatever it is called, is built in to the design.

If anybody manages to fix it (by accident or design) please post it!!!

Gilbert

 

[axelwik]

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Don't know about your 1100s, but my GL1000 has absolutely no bouncing or handling issues.

 

[wingdawg101]

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My GL 1100 is steady as can be from 0 to 100 and I didn't even balence the front tire just told them put it on and if it needs it i'll come back, didn't need it ! Rides much better than the last tire that was balenced?! (Dunlop):baffled:

I know you say the wheel is "Hopping" but check to see if the bike is "Tracking" front tire over back tire, i've seen bad tracking make bikes do a few different things that I didn't think it would cause ?

 

[ccsailor]

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my 1200 is rock steady at all speed I can let go of both bars and cruise straight (not that I do for long max was about2 min

Neil

 

[wexy]

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Whats the bets it is your rear tyre and nothing to do with your front tyre ,,happened to me on a 1500,,and all along it was the rear tyre ...so check it out ..ciaran

 

[twisty]

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dburnash wrote:

Hi everyone. well after about a month of blood, sweat and tears, and practically LIVING in the garage I finally got the 84 interstate with 20,000 actual miles that had been sitting for several years to actually go down the road. when i got the wing from the P.O the back tire was bald with the cords showing and the front tire had VERY little discernable tread and was so badly cupped it looked like a giant circular saw blade. the front shocks had fifteen psi in them and the back had none. I drained the fork oil and filled with spectro 10 w. fork oil. reduced the psi to 6 lbs. in the front and put 30 lbs in the rear. I installed a new set of bridgestone spitfires and had the front tire and rim spin balanced. the rear tire was acceptable spun by hand and the high points checked aftereach spin. First ride starting at about 25 MPH and gradually getting worse till about 35- 40 MPH the bike hops/ bounces at about a frequency of two times a second. Like going over a section of washboard. I removed the front tire and had it spun again. it was right on. drained the fork oil. added kerosene pumped the shocks and drained. did this till the kerosene was crystall clear. when moving the shock sliders up and down on the fork tubes they go up and down smoothly with no binding. Pulled the anti dive units and dissasembled them. cleaned everything with kerosene. blew them out with air. coated everything with ATF. reassembled them and flushed the shocks with ATF pumping the shocks several times and draining the ATF. did this several times... Added 10.9 ounces of ATF to each fork tube and reinstalled the caps... With the handle bars straped down, grasped the forks at the bottom and tried to move them for and aft. No movement or play. tried to twist them back and forth. no play. go for a ride. same thing. bounces hops at 25 MPH worsening till about 40- 45 MPH. Not sure if it goes away after that or just becomes much less noticable. tried 40 psi front tire and 40 psi rear tire. tried 34 psi front/ forty rear. seems a little less noticble at 40 PSI front. tried anti dive units at all settings. same.... with dial indicator straight on to front tire in the middle, out of round .050"... tire side wall run out .025"... rim run out .006 "... right disc run out .009 "... left disc run out .005... Dial indicator straight on to rear tire in middle, out of round .050"... rear disc run out .005"... rear rim runout .005 "... rear tire sidewall run out, .055 Sorry for the long post but if anyone has any ideas, suggestions, or advice I would be very greatful. Hell at this point I'd even take a muffled chuckle or a stern " so ya just had ta have a wing now did ya boy?" Thanks all,Mike

dburnash, without riding that bike it is hard to diagnose your problem over the Internet. It sure has all the signs of slightly sticking front forks.

It's possible you have a stiction problem on the fork bushings or even the seals are sticking slightly on the fork tubes.

One place you might look is at the amount of fork oil added. IF, your forks have had Progressive springs added at one time or another the oil quantity needed will be different than stock springs.

You could also have sticking upper fork bushings or a slight bend in the forks.

If you can see through the upper fork area (I can on my 1200) see if the forks look locked up as the problem is happening. Or ride along side & watch the forks in action.

If your problem is only there on somewhat smooth roads but goes away on bumpy roads I would sure suspect fork stiction.

You might try much more & much less fork pressure to see if you can effect the problem.

You might also try running about 24 psi in the front tire to see that effects the problem.

Your problem really doesn't sound like a wheel balance problem but there is always the chance you have a tire uniformity problem (common in automobile tires).. That would be a force variation in the tire carcass that would leave a stiffer or softer spot on the tire body (almost impossible to see in action but easily measured with the correct equipment.

Twisty

 

[dburnash]

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Thanks everyone for the replies. I will try raising and lowering the PSI in the forks and the tires and report back. Twisty, what could be the causes leading to the fork stiction? the bike only has 20,000 miles and the fork tubes appear to be straight as far as I can tell. Is there any way i can check the upper fork bushings or do the forks have to be dissasembled to check them. would I notice the stiction when sliding the sliders up and down on the fork tubes by hand with the springs removed, or is that something that would only show with the springs in and the forks weighted? I dont think the springs have been upgraded because they are two piece and still have the washer between the two. thanks again for the help, Mike

 

[L8ndeb]

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Mike,

For what it's worth, I vote with wexman. I'd recheck the balance and do a spin balance if possible on the rear tire.

 

[twisty]

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dburnash wrote:

Thanks everyone for the replies. I will try raising and lowering the PSI in the forks and the tires and report back. Twisty, what could be the causes leading to the fork stiction? the bike only has 20,000 miles and the fork tubes appear to be straight as far as I can tell. Is there any way i can check the upper fork bushings or do the forks have to be dissasembled to check them. would I notice the stiction when sliding the sliders up and down on the fork tubes by hand with the springs removed, or is that something that would only show with the springs in and the forks weighted? I dont think the springs have been upgraded because they are two piece and still have the washer between the two. thanks again for the help, Mike

Mike, there are a lot of causes of fork stiction.

Any added side load on the forks (make sure the front wheel is cenetred & not forcing the forks together or apart).

Any additional fore/aft load (like bent forks, extended forks past normal ride height)

Dry rubber seals or old hard seals or something slightly sticky on the upper fork tubes like car wash soap residue).

Fork oil with additives that attack the fork seal rubber or swell it up (Harley recommends different fork oil for their old or newer fork seals due to different seal material).

Too much air pressure forcing the seals to grip the tubes tighter.

Worn upper fork bushings that allow bushing material to jamb up slightly.

Grab the front brake & hold it on then gently roll the bike fore/aft to see how easily the forks stroke up & down. After a hard stop does you bike's front jump up as you accelerate away from the stop? If so the forks are probably sticking down slightly.

Twisty

 

[Tonys96]

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dburnash wrote:

... what could be the causes leading to the fork stiction? the bike only has 20,000 miles and the fork tubes appear to be straight as far as I can tell.

...would I notice the stiction when sliding the sliders up and down on the fork tubes by hand with the springs removed, or is that something that would only show with the springs in and the forks weighted?

1) The leading cause is misaligned or bent suspension pieces from the top triple clamp to the axle, anything that places binding forces on the smooth movement of the forks.

2) You may notice an issue as you describe, that would be a galling or indentation on the fork tubes where the seal normally sits at rest.

You can check the fork tubes by disassembling and rolling on a flat surface, glass works well for this.

You can do a little checking for stiction while the forks are in the bike with zero air pressureby, with the help of a friend.

1) Push down on the front of the bike and release, mark the forks (Felt tip pen such as Sharpie) where they come to rest.

2) Lift on the front end and release, mark the fork.

These two marks should be within 0.5" of each other, if at a distance greater than 0.5" you have an excessive amount of stiction and need to determine the cause.

Air pressure in the forks Will increase stiction as it forces the seals tighter against the fork legs.

Another test for stiction while riding is to monitor the fork movement, they should almost never stop moving while riding, small movements 1/8" - 1/2". That's a little harder to do.

 

[dburnash]

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Thanks guys for all the info. Took the bike out this morning and released all the air pressure in the forks. seems to be about 25% better. ran the front tire at 40 PSI and then dropped it to 24 PSI. that Didnt really seem to make a difference. Cant really tell for sure ( hard to ride and stare at the forks throught the opening below the fairing) but the forks dont really seem to be real active when the bouncing occurs. The problem is definetly very pronounced the smoother the road is. seems to subside quite a bit on the more rougher irregular roads. the problem doesnt seem to be a solid constant. sometimes it seems to skip a beat or two and then repeat. Do you think that the P.O putting 20 PSI in the forks could have caused any damage? The fork seals dont leak at all though. Can anyone explain a complete set up or know of a link for the adjustment procedure for aligling everything ( forks, wheel, handlebars ect.) I,d like to try that before i dissasemble the forks on the chance that something may be out of align causing some binding as tony stated. I will get someone to help and check the forks to see if they are sticking in different spots when bounced. Thanks again everyone I really appreciate the help, Mike

 

[exavid]

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Does it make any difference if you are coasting out of gear?

 

[twisty]

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dburnash wrote:

The problem is definetly very pronounced the smoother the road is. seems to subside quite a bit on the more rougher irregular roads. the problem doesnt seem to be a solid constant. sometimes it seems to skip a beat or two and then repeat.

Mike, that sure points to some sort of stiction in the front suspension (in the auto industry that is called smooth road shake). One of my current projects at work is trying to eliminate that in new cars & trucks. Problem is: in automobiles it isn't just one single thing (or we would have eliminated it easily by now). It usually a combination of many things. I currently have a couple of patents pending onsmooth road shake elimination in front wheel drive vehicles but they wouldn't be useful in motorcycle fork applications.

What happens on the rougher roads is the forks are kept in motion most of the time so they don't stop long enough to stick. On smooth roads they stop often so tend to stick when a slight bump it is contacted, then the entire front end tends to jump at resident fork or tire frequency until bigger bump is hit that overcomes the forkstiction.

Do you think that the P.O putting 20 PSI in the forks could have caused any damage? The fork seals dont leak at all though. Can anyone explain a complete set up or know of a link for the adjustment procedure for aligling everything ( forks, wheel, handlebars ect.) I,d like to try that before i dissasemble the forks on the chance that something may be out of align causing some binding as tony stated. I will get someone to help and check the forks to see if they are sticking in different spots when bounced. Thanks again everyone I really appreciate the help,

No, I doubt putting 20# of air in there did any harm. Possibly the bike sitting for a long time with the seals inflated tight to the forks caused some damage there.

As far as a complete set up? That would be so long it would take a novel to explain. Get a service manual & go through the basic set up & alignment.

A couple of things to try..

Try removing the fork oil & trying some 10W30 Mobil 1 as that is pretty slippery stuff & might loosen the stiction a little.

Try working some Mobil 1 or other high end oil down the top of the seal protectors.

Try adding a little front wheel imbalance, that might keep the forks in motion so they don't stick as easily.

Try different forkair pressures until the best rate is found.

Ride the heck out of it on a rather rough road to see if it will loosen up a little on it's own.

Obviously check for abnormal fork installation or other front end part damage,

Twisty

 

[johnapool]

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When you said it sort of skips a beat it sounds like oscillation, not vibration. Are your wheels true in their seats, and how are the bearings? Sitting for long time can do strange things to bearings.

I also had the same problem with new tires on a truck once. Turned out the mold halves were slightly offset when the tire was made. The tire could be balanced, but it was OUT OF ROUND on each half by about 1 MM. Never ran right until I replaced the tires. JP

 

[dean_3326]

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Hey dburnash:waving:Is there any way you could ask the Previous owner if there was a similar problem before he stopped riding it? If he was then you could elimanate the tires for sure.If not then it seems either the new tires or sticking forks. I only run 1 lb of air in my 84 gl front shocks, and 25-35 in the rear with 2 riders. I think Twisty"s idea of riding it on a washboard type road might help if the shocks are sticking. Sometimes new tires have problems that are not obvious. I wish you good luck figuring it out.



:12red:

 

[dburnash]

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Hey guys, thanks for all the new info. I will try all the suggestions first thing in the morning and report back. as far as talking to the previous owner I dont think that would get me anywhere. I try to make it a habit of not critisizing others but this guy is just a pure, unadulterated idiot. I'm sure he mounted the bike more than once facing the rear tire. (trust me on this). Thanks again all for the help. Oh yeah I tried coasting in gear with the clutch in, coasting out of gear, and coasting with the engine off and that made no difference. Mike

 

[wexy]

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I still reckon its the back tyre ......not the front end at all .....the vibration will come through the front and it can fool you into thinking it is the front ....Ciaran