Front wheel hop feeling????

[TommyT]

When my OEM shock wore out, it bottomed out in potholes and was a hard ride in general. Is this hop occurring at predictable intervals within that speed range or is it random?

Yes it is at predictable intervals and within a speed range, I start to feel it at 30 (slight), at 35 it is more noticeable, gets worse as the speed increases to 45 and after that it starts to disappear going to 50, at 55 -65 I do not notice it at all. coming down from 55 to 45 it starts back up to the point I can tell what speed I am going without looking at the speedometer. It does it in 2, 3, or 4th gear. I would think a shock bottoming out is more a function of the spring rate and the load on the swing arm and less the damping action of the shock. I was told the spring on the shock is rated at 230-345 lbs/inch.

I took the shock off, lowered the spring collar down all the way. I have about 4 inches to move the shock shaft without the spring, it is kinda easy to push down, one handed, a little harder to pull up but I can do it one handed (i am not really strong). Question how hard should it be to move the shaft up and down? BTW I have it set at "level 4" the hardest damping setting, but then again level "1" feels only a little easier.

[Laitch]

The spring should contact the collar with its wide end and the mount at its narrow end.. Is that how it is adjusted right now?

[TommyT]

The spring should contact the collar with its wide end and the mount at its narrow end.. Is that how it is adjusted right now?

The spring was properly installed, I disengaged it to test the damping of the shock.   


What I was asking about was how easy should I be able to move the shock shaft up and down without the spring, i.e. how should the damping of the shock feel? I am thinking that it is moving too easy, that the gas/oil in the shock is low or worn out and that is letting the spring oscillate.

[Laitch]

. . . but I can do it one handed (i am not really strong).

I am thinking that it is moving too easy . . ,

If it's the shock's action that's being discussed here, it sounds like it's time for a replacement shock.

[TommyT]

If it's the shock's action that's being discussed here, it sounds like it's time for a replacement shock.

Well.. I put the shock back together, went to put it back on the bike and the bottom bushing pop'ed out when I tried to slide it on the swing arm stud. The rubber part is all chewed up. I don't know if this could be part of the problem but I am ordering a new Progressive Suspension 412-4015B shock today. Once I get it on and ride the bike I will update the status here. It may be a week or more as I have a trip next week and will not be back for 2 weeks.

Till then... thanks all for now.

[TommyT]

greetings...

are the tior rotation arrows showing proper rotation...


j o

Yes they are. still waiting for the new shock to arrive, looks like it will not make it before I leave for a trip. Will update status in 2 weeks. BTW when I had the shock off and the rear wheel, I tried to check the swing arm for play, I could not feel any side to side and it felt smooth up and down. I do not know if that was really a good way to check.

[Laitch]

I tried to check the swing arm for play, I could not feel any side to side and it felt smooth up and down.

Let us know what difference a new shock makes when you return. It seems certain that one that was mounted was at the end of its useful life anyway.

[TommyT]

I got back from my trip this weekend and yesterday I went for a long ride. The new shock help the overall ride of the bike but the hop is still there. Not sure what to do next, the bike feels good over 50. I was cruising at 65 and felt fine. I have a friend locally that has a k75, I may see if he is willing to swap wheels, one at a time to see if it is a wheel/tire thing. The back wheel has 40g of balancing weights on it and a very slight (1 to 2mm) high spot. If I can't get my friend to swap wheels, I will take the wheel back and have it remounted, checking the true of the wheel and tire. How often is a new tire made out of round? These are V rated Michelin tires, I am not a V rated rider but I was thought a V rated tire would be better quality and went through better QC processes.

[Laitch]

I am not a V rated rider but I was thought a V rated tire would be better quality and went through better QC processes.

Quality control will be at the same level in all grades. Consumer safety and legal liability are overarching considerations for manufacturers. The higher speed-rated tire might have greater durability in addition to enhanced performance.

[aces59]

Hi. Just picked up on this topic - Don't know whether the problem got solved but I have almost exactly the same symptoms. Low speed 'patter or bouncing Definitely from the front end. Bikes been through new tyres new rear shock and new head bearings with no change to this - I haven't stripped the forks yet - It's getting high on the to-do list - Going to put Castrol 10W synthetic in.
My personal guess is that its stiction in the forks
TommyT - Did you get round to changing the fork oil?
Laitch - do you think it might be anything to do with Tyre pressure?
Has anyone tried the low friction (PTFE?) fork seals I've heard both good and bad reports about them but haven't used them myself
Steve

[Laitch]

Hi. Just picked up on this topic - Don't know whether the problem got solved but I have almost exactly the same symptoms. Low speed 'patter or bouncing . . .

When an old bike with an unsupported maintenance history or a history of neglect is purchased, the difficult fact to face is that all its systems need examination. Fork condition might be at the root of the patter or bouncing that is being felt by members writing in this thread.

Tires incorrectly balanced, tires incorrectly inflated, tires with factory imperfections, faulty rims, excess fork fluid et. al. might contribute to producing these symptoms but disassembling, cleaning and examining the fork tubes and their components for wear and checking their alignment are essential to eliminate the fork as the cause for bounce, patter and wobble in a bike that is being reclaimed.

[TommyT]

I did change the fork oil, it did look crappy. Use 5 wt as called for in the manual, but I have 7.5w I want to try and as dirty as the oil looked it would not hurt to do another flush I think.


Yes I agree that it is getting time to take a serious look at forks and the rear bushing. If I can get my friend to swap wheels and they do not eliminate the hop, then it must be in the suspension. I would be a little surprise the problem lays there as this seem only only happen at certain wheel RPM and not at all times. I really suspect there is something going on with the rear wheel/tire.


Overall the biked been taken care of (expect the old tires) rear drive and tranny oil was fresh, the rear drive shaft splines were well lubed and showed little wear. Burns little oil, shifts well. no rust anywhere. I am going away again this weekend, when I get back I will see if I can try my friend's wheels.


Thanks all for the tips so far, to be continued....

[aces59]

Well I'm going to change the fork oil for new Castrol 10w.  There's a good spreadsheet online which lists a heap of different fork oils and their actual viscosities. It's obvious from that that you can think you are doing something sensible and actually be way out.
Also looking at fork seals. I may try putting some slippy PTFE stuff on the seals to see if it makes a difference. SKF make fork seals and claim they are low friction so I am trying to find if they do ones for the K75 - I'm more inclined to believe SKF than some far eastern Snake Oil seller with a fancy name :-)
Also - Really quick thing I can try - Going up/down 5psi on the front tyre. May do that tomorrow.
Steve

[Martin]

Front wheel bearing can feel fine, but can the source of the problem you are having. I read something a while a go about a bike with the same problem eventually he changed the front wheel bearings and this cured it. Once the bearing were removed he could feel a tiny rough spot that could not be felt before the bearing was removed. It's a bit of a long shot and I can't find the post.  :dunno
Regards Martin.

[TommyT]

Well I'm going to change the fork oil for new Castrol 10w.  There's a good spreadsheet online which lists a heap of different fork oils and their actual viscosities. It's obvious from that that you can think you are doing something sensible and actually be way out.
Also looking at fork seals. I may try putting some slippy PTFE stuff on the seals to see if it makes a difference. SKF make fork seals and claim they are low friction so I am trying to find if they do ones for the K75 - I'm more inclined to believe SKF than some far eastern Snake Oil seller with a fancy name :-)
Also - Really quick thing I can try - Going up/down 5psi on the front tyre. May do that tomorrow.
Steve

I am still waiting to get with my local k75 owner friend to try a wheel swap.


Ace did any of your efforts fix your problem? If my problem seemed to occur on a smooth road and after hitting a bump I would think that my front forks were oscillating due to a lack of dampening of the spring action due to weak or too light weight of fork oil. BUT my problem seems to be a rotational issue, it happens at a given speed range. When I swap wheels I will know more.

[aces59]

Not had time to try anything yet - Getting the bike ready for a trip to Chimay this weekend so may at least get a chance to do the tyre pressure experiment. Will keep you posted
Steve

[Laitch]

Be circumspect with your throttle. At speed when bumps are hit, oscillations can become wobbles; wobbles can become tank slappers.

[aces59]

Thanks for the warning.
Also - the guys who changed the front fork steering head bearings took out the damper.
Steve

[Laitch]

Thanks for the warning.
the guys who changed the front fork steering head bearings took out the damper.

Maybe he felt his ceramic dog collection was complete and he's diversifying—dampers from around the world.

[TommyT]

I did change the fork oil, it did look crappy. Use 5 wt as called for in the manual, but I have 7.5w I want to try and as dirty as the oil looked it would not hurt to do another flush I think.


Yes I agree that it is getting time to take a serious look at forks and the rear bushing. If I can get my friend to swap wheels and they do not eliminate the hop, then it must be in the suspension. I would be a little surprise the problem lays there as this seem only only happen at certain wheel RPM and not at all times. I really suspect there is something going on with the rear wheel/tire.


Overall the biked been taken care of (expect the old tires) rear drive and tranny oil was fresh, the rear drive shaft splines were well lubed and showed little wear. Burns little oil, shifts well. no rust anywhere. I am going away again this weekend, when I get back I will see if I can try my friend's wheels.


Thanks all for the tips so far, to be continued....

Well I finally caught up with my K75 friend. either I did not notice or he did not notice, but we failed to notice that he has a drum brake rear wheel and I have a disk one. So no wheel swap.


It is still happening, but the bike feels really good at 55+ mph. I am about an hour away from Max BMW in Tory, I may see if they can check the bike. I really think one of the wheels were not balanced right. I am changing the fork oil again. going to try 10wt oil instead of 7.5wt and see if that helps. I did try increasing the tire pressures both front and rear, but it did not really help.




 

[johnny]

greetings...

its the tiors... have the installer of your new tiors put another set on there... if thats it thats it... if not you gotts a spare set of tiors...

j o

[Motorhobo]

greetings...

its the tiors... have the installer of your new tiors put another set on there... if thats it thats it... if not you gotts a spare set of tiors...

j o

+1 what johnny said

[TommyT]

Just to close the loop on this problem, recently I had to get the front tire worked on. It had seam leak. I told to re balance the tire when they were done. Hop was gone when I took it out. I guess the shop that "balance" the tire the first time did not do a very good job.

[Soggz]

Fork springs. I replaced my rear shock with a YSS one with upgraded spring. Bike still hopped a bit, but loads better than it was. All bearings are fine and new Avon Roadriders. New progressive springs are on their way. It’s a 32 year old bike. Nothing lasts forever, no matter how tidy it may look, it’s always the bits you can’t see that fail.