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Thread: fork spring dilemma

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    Registered User 6659's Avatar
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    fork spring dilemma

    I have a 1978 R100/7 that was originally equiped with a Luftmeister fairing long since removed. The front end has a rather harsh jarring effect. I am thinking this bike was equipped with a heavier duty spring? I had another person tell me his 78 R100 does the same thing. Now, If I buy Progressive springs, will that smooth out the jarring or should I look for an old OEM pair to install from say, a /6?

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    Administrator 20774's Avatar
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    I have the same bike but still have the Lufty on it and I can say my front end doesn't do that. I'm pretty sure the springs are original, but I'm second owner and don't really know. I'd look into a refurb of the existing front end before I popped for new springs. It's possible that you have some stiction with the sliders as they ride up and down on the fork tubes. Or maybe the fluid has so much debris in it that the damping holes at the bottom of the forks are plugged. Or maybe the fluid is too heavy weight or there's too much fluid in the forks, both of which could produce a stiff front end.

    I'd first start with a fluid change of the weight and volume and go from there.

    Kurt in S.A.

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    Polarbear Polarbear's Avatar
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    My /7 too

    My Progressive springs have been in there for some time and they are stiff springs, vs stock ones. I had the Jammer heavy fairing on it way back when with the stock springs, but wanted better performance in the handling, so I went with the Progressive ones. I don't know how to soften them and have tried everything under the sun. I use a much lighter Scout fairing these days at only about 5 lbs.. I'll read on for what pops up here, too! Randy13233

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    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    You could remove the cap from the top of one fork leg and see if there is a plastic spacer on top of the spring. If so, it's possible that shortening it to reduce the preload on the spring may help. Then remember to do the same thing to the other side.
    F.O.G.Rider, Rounder #6,
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  5. #5
    Registered User 6659's Avatar
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    I used to put a spacer in there to help with the extra weight of the fairing. Are you saying a spacer will make it smoother without the fairing or if they are in there they should be removed to soften them?

  6. #6
    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    Depending on the length of the spacer, you may want to put a shorter one in. You could go to the hardware store and get some PVC pipe of the same diameter and make shorter spacers in, say, 1/4" increments and see how the ride is.

    When was the last time the oil in the forks was changed? And what weight oil is in there? And how much? It all works together. Too much oil, or too heavy, can make the forks harsh.
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  7. #7
    James.A
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    Y'know, Randy, I agree with a good fork service as a starting point. But, the term "jarring" suggests to me a fork binding situation.

  8. #8
    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    I guess the question might be, does it occur on the compression stroke, or the rebound?
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  9. #9
    Registered User 6659's Avatar
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    Cool

    Its hard to tell. I just know that when I drive it seems very jerky. I had an R90/6 that I just sold and that one was very smooth over the same roads.

    I think it would be best to start with an oil change, The fork oil has not been changed as far as I know and it is 29 years old. It only had 9800 miles when I picked it up last year. I bought some 7.5 wt oil and will do that first. I will repost after I get that done and let you know how that goes. It might take me a month to get to it since I set this as a low priority.

    I also was looking at Max BMW and under 1978 R100 they show 2 different springs available. The first is called compression spring and the second is compression spring reinforced. So something is going on here. And they are listed for up to Sept. 1980 as optional equipment. The mystery continues. I'll be back.

  10. #10
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    "Jarring" sounds to me like a hydraulic problem, not a spring problem. Even if the springs were substantially stiffer than stock they would still compress.

    There were some issues with plastic parts in the dampers that could fail and jam the valves/orifices.

    I suggest that its time for a fork rebuild.

    It is possible that someone stuffed in a spacer that's much longer than needed, which could cause the springs to "coil bind" on compression. It's easy enough to pop off the caps and extricate the springs for a look-see. (bike on centerstand, please)

    And, with the springs removed, you can slide the front end up and down and see if it's binding.

    pmdave

  11. #11
    Registered User 6659's Avatar
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    It's been a couple of weeks since I first brought this up. It's a cold Saturday here in Atlanta and a perfect time to delve into the forks.

    First, I had a helluva time just loosening up the fork tube tops. I was lucky that I just happen to have a 36mm socket that I had bought for a Triumph project. Never thought I would use that tool again until now. That with a 3 foot extension helped pry the fork crown off. I used a smaller handle for the rest of the removal. When the top broke free it almost flew off. I found a 2 inch spacer in there. That was a lot of compression! So I removed them and put in a one inch spacer. I was able to put the crown back on with very little difficulty.

    Now as soon as the weather warms up I will take it for a test drive. If it is still too harsh I will try without any spacer.

  12. #12
    Grammarian no, Rider yes ISAMEMON's Avatar
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    if it is like my bike, it had no spaceers with the stock springs. the progressives did use spacers, could be that the spacers were put in by someone else trying to stiffen up the springs.
    do/did the springs have a painted stripe on top.
    If I remeber, the stocks have a painted stripe, the progressives do not
    I could be wrong on the paint thing


    and if it is raining, etc, why not change fork oil while your in there, it is supposed to be done every few years

    also excessive play in the 3ple tree bearings can give you some jaring and jolts

  13. #13
    Registered User boxerkuh's Avatar
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    Fork oil weight?

    I personally like pretty stiff springs and originally used 15 weight fork oil. When asking around I was advised to use 7.5 weight and add a little more oil and that would stiffen it up. I just changed my fork oil again and only had 5 weight around. I drained out 250 cc and I added 250 cc. My Master Mechanic told me that my bike calls for 2.5 weight and only 230 cc.
    I like the change much better. The front end now absorbs bumps much easier than before. I thought it would be exactly opposite, since I switched from an S fairing to an RS fairing. Shows what I know... NOTHING>>>
    Keep the rubber side down!!
    1986 R 80 RS
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  14. #14
    Registered User 6659's Avatar
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    Just to let anyone who wants to know. By replacing the 2 inch spacer with a one inch spacer made all the difference. Now I still get somewhat jarring but much muted and can live with that. It is 70% better. I would think without the spacers it would be perfect but after 30 years of being pressed by the 2 inch spacer, it has caused a sag in the spings. If I wanted to go further I would just get a new set of Progressive springs and not use a spacer. Maybe later on when I feel rich enough to spluge.

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    Rebuild advice . . . .

    I am replacing my fork springs. I have a 1 inch pvc spacer from the old springs. Is it correct to rebuild from the top down? In other words, do I fill the fork tube from the top and then drop in the threaded fork top cap and then the snap ring?
    What is the purpose of the small vinyl "piston ring" that is so hard to install?
    Thanks,
    Campbell Tellman II
    '93 R100RT

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