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Thread: progressive springs ?

  1. #1
    Grammarian no, Rider yes ISAMEMON's Avatar
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    progressive springs ?

    friend has bike he is 3rd owner.86 rs. It has a "works"rear shock. IN doing a fork oil change got all kinds of black goop out. which led to a discussion, I wonder what springs are in the front if the rear has been replaced with a "performance" shock. Is there a way to tell if the bike has stock springs or progressives when they are pulled out ?

  2. #2
    sumran
    Guest
    The windings on progressive springs are not evenly spaced. There is a different resistance level depending on which part of the spring is being compressed.

  3. #3
    TGHSMITH
    Guest
    most stock springs are progressively wound... the black goop could be due to age or brand of fork oil(there is fork oil out that is black with additives when new) put in new fork oil,check for stiction, see how it rides to decide if to replace springs...(ps a dead give-away is that a piece of pvc is used as a spacer is often used with progressive brand springs)

  4. #4
    I've accumulated about 4+ sets of R90 forks in the past few years and found a mixture of PVC inserts of various lengths as well as custom machined inserts of various lengths to adjust the preload with stock BMW springs. Just because there is PVC in there doesn't mean you have Progressive brand springs. (I think you need to be clear on "Progressive", its a type of wind for springs previously described and also a Manufacturer...) Because of the front end dive associated with the soft BMW springs (at least on the R90) I think a lot of users "back in the day" added PVC to boost the preload simply because its a cheap and easy to cut to length. As mentioned, PVC inserts also are provided in the box with Progressive brand springs (at least they were in mine) and are recommended for preload setting by Progressive in the instructions.

    I did a total front end overhaul last week and learned the following: BMW "Heavy Duty" springs from the dealer have a white paint splotch on one end of the spring. The parts guy told me that is how BMW differentiates the HD springs from the regular. The Progressive brand springs I installed were an inch or so (guestimate) shorter than the HD BMW springs I replaced, and I think I read in some other post that the Progressive brand is a bit shorter than the factory. It sure looked like it when I compared them, but I have no clue what effects wear had on the replaced set.

    Again, I'm no expert, and this is just what i've learned for the R90, not sure about the later bikes.

    That crud could also be disentegrated damper "bump stops" or whatever they are called. They are made out of rubber or urethane and just turn to mush (or rock) over time. For my bike there are black ones in the lower fork leg and smaller ones inside the upper fork tube. If your friend is so inclined and doesn't mind doing all the work, he could replace all the bump stops, crush washers, seals, and springs for not much $$$. I did not find it to be that difficult on my bike. If your friend has no idea when it was last done, its not a bad thing to consider. I did all of that and steering bearings and I was happier than a pig in poop this morning riding to work. $$$ well spent.

  5. #5
    TGHSMITH
    Guest
    yes as I've said before a complete rebuild on the pre-81 forks is one of the best things you can do, in this case we have an 86 which no longer has all the wonderful internals the the earlier bikes had. They don't seem to ride as well either.(bet they where a lot cheaper though).... still wondering if my 83 sliders (brembo brakes)would work with pre-81 tubes and internals

  6. #6
    Quote Originally Posted by tghsmith View Post
    yes as I've said before a complete rebuild on the pre-81 forks is one of the best things you can do, in this case we have an 86 which no longer has all the wonderful internals the the earlier bikes had. They don't seem to ride as well either.(bet they where a lot cheaper though).... still wondering if my 83 sliders (brembo brakes)would work with pre-81 tubes and internals
    well i'm not sure, but i definitely have a bunch of extra sets of fork tubes and sliders from the mid 70s forks. let me know!

  7. #7
    TGHSMITH
    Guest
    the only real differance is the base of slider, when I get that unobtainable free time going to see if I can't machine up an adapter plate. I remember a cycle mag article from the late 70's Deslopping your sliders, it had a page for every major brand and the fixes to make the forks better.. when it came to BMW it had two sentences, these units are built like fine machines even having piston like rings, change the fliud as recomended....

  8. #8
    Grammarian no, Rider yes ISAMEMON's Avatar
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    out of the factory, according to the parts manual, the bike had an aluminum spacer.
    I guess there is no way to know for sure as a set of stock springs I have for a 78 have tighter windings at the ends also

  9. #9
    TGHSMITH
    Guest
    not unless you put a new pair of stock springs in

  10. #10
    Littleleroy38
    Guest
    Wilbers now makes springs for both twin shockers and monoshockers. Years ago, I went with Progressive brand replacement springs for my monoshock RS. They are pretty stiff and uncomfortable over rough pavement. Were I to do it again, I would try the Wilbers.

    In fact, I ordered a pair for my twin shock '84 from Ted Porter's shop a few weeks ago. He said that the Wilbers' were in between the stock and the Progressive springs. Plus, unlike Progressive's springs, these are made specifically for the BMW fork. Progressive recommends the same spring for a number of different marks, hence the use of PVC.

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