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Thread: Fork Issues

  1. #1

    Fork Issues

    Hi All. New to airheads. I have a 1971 (12/70) R75/5 project. Did not run and was in quite a state. I now have it running and have taken it around the block a couple times. During this ride I noticed that I was feeling every bump. Not enjoyable. Upon inspection, my forks were still compressed(as indicated by the boots). I was able to pull the forks down but there was not rebound. Ah! Stiction I thought. Loosened the 4 points from the triple tree to the axle . Once loosened, the rebound improved but the forks were still sticking albeit not as bad (some rebound vs none). I removed both forks and tested the rebound off the bike. Left one is ok and the right is worse. Since I dont really have a baseline for this model I'd like to know, what height should the fork be assembled and off the bike, how much should it compress and return? The forks were rebuilt using a rebuild kit.

    Thanks

    Adam

  2. #2
    Liaison 20774's Avatar
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    Welcome to the forum! The specs suggest that the front fork spring travel is around 8.2 inches. Sag should be around 1/3 of travel when you just sit on the bike with normal weight. You can put a zip tie around the fork tube with the front tire off the ground, then carefully take it off the center stand and then sit on the bike. The zip tie will end up at the point of sag.

    The best process for checking fork alignment is using the Randy Glass method as outlined here:

    https://w6rec.com/204-2/

    In order to prevent stiction, you need to tighten the fork clamps from the top down, with some cycling of the forks between each tightening. Ideally, you would have the forks out of the tubes, removed at the top. Then tighten the lower fork brace. With the axle put into the bottom of the sliders, you should be able to manually slide the sliders up. Then tighten the next level down on the fork...slide the sliders up. Keep repeating to the point where the axle and wheel are finally installed.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Airmarshal-IL James.A's Avatar
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    I have seen this. Please check the bolts that hold the horse shoe fork brace to the fork sliders. Those threaded holes that the brace is fitted with/by are not bottomed, and the ny-lock nuts can push the studs in to the tubes, creating a bind. It happened on one of my bikes. Please make sure this is not the case with your front forks.

    This is a possibility specific to the /5 front forks. It might also apply to the US models of pre-1970 bikes which have, essentially, the same forks.
    1973 R75/5

  4. #4
    Registered User ebeeby's Avatar
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    Quote Originally Posted by James.A View Post
    I have seen this. Please check the bolts that hold the horse shoe fork brace to the fork sliders. Those threaded holes that the brace is fitted with/by are not bottomed, and the ny-lock nuts can push the studs in to the tubes, creating a bind. It happened on one of my bikes. Please make sure this is not the case with your front forks.

    This is a possibility specific to the /5 front forks. It might also apply to the US models of pre-1970 bikes which have, essentially, the same forks.
    +1......Also, the forks can leak out those stud holes in some cases. I had to seal one side with blue locktite during a fork re-build which also served to help ensure the studs were not driven too deeply in which to cause a bind
    1973 R75/5

  5. #5
    Thanks, took a look and the stud on one was shorter than the other. I backed it out and got better performance. Cant believe those holes go all the way through. I back them out on both forks and now have return. Tell me, should I feel ANY parts contacting each other during the action? I dont feel anything during compression but feel parts slide past each other on return. Not a constant contact, just near the end of the travel.

    -Adam

  6. #6
    Quote Originally Posted by adamw View Post
    Thanks, took a look and the stud on one was shorter than the other. I backed it out and got better performance. Cant believe those holes go all the way through. I back them out on both forks and now have return. Tell me, should I feel ANY parts contacting each other during the action? I dont feel anything during compression but feel parts slide past each other on return. Not a constant contact, just near the end of the travel.

    -Adam
    Once you are happy with the position of the stud mark it. Then remove and apply thread locker and return to the marked position.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

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