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fork dive

Discussion in 'The Garage' started by gray am I, Aug 24, 2019.

  1. gray am I

    gray am I XS650 Enthusiast

    just got my 78 special back on the road after sitting for 20 years and noticing the front end is really soft. There was no apparent fork oil leakage before I started riding it, although there is a small weep on the rh side now so I will replace the seals. When I grab the handlebars an push and pull the bike up and down I get 90mm (3 1/2in) of travel, this seems excessive, any thoughts. Before I pull the seals can I check fork oil level by measurement or do I measure volume after draining.
     
  2. cafetools

    cafetools XS650 Addict

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    After doing seals and filling with oil everything will get better. I like 20w oil. It's thicker.
     
  3. 5twins

    5twins XS650 Guru Top Contributor

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    If the seals are just slightly leaking, it could just be dirt trapped in them causing it. I usually just clean slightly leaking seals and many times that solves the problem.

    Using slightly more than the specified amount of oil will greatly firm up the forks. Stock amount is just under 6 ounces. Put 6.5 to 7 ounces in there. I don't go any heavier than the stock 10 wt. Thicker oil will certainly stiffen the fork action but at the expense of reducing their responsiveness. They won't react to the little bumps as well, jolting you instead of soaking them up.
     
  4. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    I'm big on changing to Sportster springs. Seriously, just started riding Period Piece and was headed to find the best deal on a set this morning.
    PS thanks for this! I just scored a set on fleabay for $37 delivered!
    Big twin makes a replacement set, this search will find sellers. "24-0905 35mm"
    Did some measuring aways back and they are 15% stiffer than the stockers, and a titch longer, it's a bit of a wrestling match getting the caps back on, but worth it. I'm going to have to look for sure, I may have them installed with older fork caps that don't have the adjustable preload. (34mm fork caps are the correct fit for 35mm tubes also!) I tend to use 15 weight fork oil and like 5T use slightly more than the stock fill. IMHO The Minton mods are also an improvement over stock. Tho I'm old, I think I tend to ride more aggressively than most?
     
  5. Superjet

    Superjet XS650 Junkie Top Contributor XS650.com Supporter

    I too have changed up to the Harley springs as Gary noted above and they are super! I have the preload adjustable caps and have them set to the first notch. Dont think you can get them on 2nd notch (max preload) pretty stiff springs. I have been using 10w oil.
     
    gggGary likes this.
  6. arcticXS

    arcticXS XS650 Junkie

    Are those Sportster springs linear rate, or progressively wound? I got some stiffer, but still progressively wound springs from Heiden, which improved things a lot. But linear springs are supposed to work better with emulators.
    (For my RD350, I got genuine Racetech emulators and linear springs, which improved the fork considerably. As an added benefit, thr Racetech springs were lighter than the stock RD springs)
     
    Superjet and gggGary like this.
  7. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

  8. Superjet

    Superjet XS650 Junkie Top Contributor XS650.com Supporter

    That is why I purchased these HD springs as I plan on doing emulators this winter.
     
    gggGary and arcticXS like this.
  9. cafetools

    cafetools XS650 Addict

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    Will they fit in a standard?
     
  10. 5twins

    5twins XS650 Guru Top Contributor

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    Gary, exactly which set are you using? Your 1st post says the spring #24-0905 but the link in your 2nd post is for a #24-0906 spring. Will either work?
     
  11. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    good question may be different lengths? or even weights. Guessing here''s the fitments

    VT No: 24-0906 OEM No: 46052-80
    Fork tube spring set features high tensile strength, ground ends.
    XLS 1980-1982
    FXR 1982-1983

    VT No: 24-0905 OEM No: 45907-80[​IMG]
    Fork tube spring set 35mm feature high tensile strength, ground ends.[​IMG]
    XL 1980-1983

    To add to the mystery; an old link I have points to these.
    VT No: 24-0904 OEM No: 45408-75
    Fork tube spring set features high tensile strength, ground ends. Overall length is 19-3/4".
    FX 1976-1983
    XL 1976-1983
    Guess I'll report length of the one's I just snagged when they get here :shrug:
    Might be that fine tuning length is possible, desirable in any case.
     
  12. 5twins

    5twins XS650 Guru Top Contributor

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    19 3/4" would probably be a good length. The stock springs are 482mm, or about 19" long. I recently added 1" preload spacers to stock springs and it wasn't too hard to get the caps on. Spacer and washers in place, the "stack" came up flush with the top of the tube .....

    [​IMG]

    I install the caps using a 3/8" drive T-handle. It allows you to push down and turn at the same time.
     
    gggGary likes this.
  13. XSLeo

    XSLeo XS650 Guru Top Contributor

    Yes, you can check oil level before you tear them down. Pull cap and springs. Let the forks completely collapse.
    Find something that fits down in the forks. Put a mark about a foot up from the end.
    Now slide the whatever own into the forks till the mark lines up with top of fork. Remove, there should be some oil on the whatever. Measure from the oil up to the mark.
    A tape measure works well for this.
    I'm not sure just what the level is for a full stock fork. Probably somewhere around 8 inches or so. Never measured one.
    You may find there is no oil in the fork or that what's in there looks very dark. Both bad signs.
    At this point I would drain out what every you find in there.
    Actually I wouldn't measure, just skip to the draining. You May have to move the forks up[ and down to pump the old stuff out.
    Once the old is out, put about 6 to 8 ounces of kerosene or diesel fuel in each fork. pump up and down. Drain, repeat as needed to get so what comes out is as clean as what went in.
    Let drain over night to be sure the cleaner is out. The stock 5 or so ounces of oil is enough to absorb the road shocks and keep the tire on the road but a bit more will be better. In a lot of circles people have come to use the 6 inch down method to fill with oil.
    As before, remove springs, completely collapse forks, Fill to six inches down from top of fork tubes. This may sound a bit tricky but is easy. Get some clear tubing. A few feet at least. A vacuum pump is handy. Like a Miti Vac, but just mouth suction works. Place a zip tie around this tubing 6 inches from one end
    Select your oil. Put I about 8 ounces of oil. Slip this 6 inch end down in the fork till zip tie is at top of tube. Draw out any extra oil. Reinstall remove parts.
    This extra oil decreases the air volume above the oil. This increases the air shock action of the shock. Most have some effect but adding more oil increases this effect.
    It will improve the ride and handling a bit but most noticeable will be the decrease in fork dive.
    You can experiment with different oil levels but less than 6 inches won't gain much and may cause poor seal to leak more.
    You can try different weights of oil. Try a few different combinations to find what works for you.
    Leo
     
    JAX71224 and gggGary like this.
  14. XSLeo

    XSLeo XS650 Guru Top Contributor

    Almost forgot. I have the H-D springs in my 75 with 79 35 mm fork.
    I got mine from J&P Cycles. Item #230-584. How that lines up with the VTwin book I can't say.
    It was a while ago and the springs fit all the 35 mm Showa forks used then. XL and the FX used them.
    Mine are a linear spring. I have the adjustable caps. On the lightest setting I get about 25 mm of laden sag. On the middle setting I get about 12 mm of sag, I can't get to the highest setting.
    I have some flat caps somewhere around I thought I'd try them with several lengths of spacer to see how that works, just can't seem to find those darned round toit's
    Leo
     
  15. gray am I

    gray am I XS650 Enthusiast

    having to replace a fork seal I have stripped the forks down measuring each fork leg oil volume, 5oz in each side, I will try 6 when I reassemble with stock springs, noted that the preload caps were set on the last notch. I did notice that the steel sleeves just below the oil seal were a little scored , nothing on the fork tubes , just wondering if the is a wear limit on these as I was thinking of giving them a light polish, as there seems to be no replacement part for them
     
  16. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    Glad this thread popped back up; the VT No: 24-0904 OEM No: 45408-75 are direct fit slightly longer than stock at 19 3/4"

    The VT No: 24-0905 OEM No: 45907-80[​IMG]
    Fork tube spring set 35mm feature high tensile strength, ground ends.[​IMG]
    XL 1980-1983 I got off eBay came in at about 24" long so will need to be cut before installing. Period Piece is gone so it may be a bit before they go in a fork. The problem with cutting is the factory ends have a "tight loop where they are cut for a near full circle contact area, a longer spring, cut off won't have that. I'm conmsidering heating and bending the coil to be cut but that's another day, far better to get the 24-0904 set!
     
    Last edited: Sep 14, 2019
    grizld1 likes this.
  17. grizld1

    grizld1 Grumpy old man Top Contributor

    Usual practice is just to flatten the bottom coil on the grinder, but there's a more serious issue involved in cutting springs. This sounds counterintuitive, but when you shorten a spring, you increase its rate in direct proportion to the reduction in length. Example: if a 20" spring with 50 lbs./in. rate is shortened by 2", the rate increases to 55 lbs./in.
     
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  18. arcticXS

    arcticXS XS650 Junkie

    Exactly! So if the springs are too long, it may be a better option to shorten, or even completely remove the spacer.
     

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