four hundred four fork oil

Discussion in 'Classic Motorbikes' started by mark, Jan 9, 2009.

  1. mark

    mark Guest

    Will 15w be really horrible?
    /furtive glance at quantity of 15w in shed...
    mark, Jan 9, 2009
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  2. It would be a bit OTT, I think. The forks actually aren't soft: just
    oversprung and under-damped. 10w might be better.
    The Older Gentleman, Jan 9, 2009
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  3. mark

    mark Guest

    I thought that might be the case...
    /looks forlornly at 15w oil again...
    mark, Jan 9, 2009
  4. mark

    sweller Guest

    Get some ATF (Automatic Transmission Fluid) - it'll do for the vast
    majority of 70/80s mass produced machines.
    sweller, Jan 10, 2009
  5. mark

    Champ Guest

    Well, if they're underdamped, going from 10W to 15W might be a good
    Champ, Jan 10, 2009
  6. You'd think so, but with the hard springing you wind up with something
    that hardly moves. I tried 12w in mine: it wasn't a success.
    The Older Gentleman, Jan 10, 2009
  7. mark

    sweller Guest

    When faced with 70s UJM forks all I've ever done is a couple 2p's under
    the fork caps and the appropriate amount of ATF.
    sweller, Jan 10, 2009
  8. Oh yes, I forgot about the 2p pieces. I used that dodge on a CB550 when
    I put a full Rickman fairing on it.
    The Older Gentleman, Jan 10, 2009
  9. mark

    mark Guest

    That is the sort of experience I needed to hear about before trying it
    myself really :)
    I have plenty ATF. Might even have some 2p's.
    mark, Jan 10, 2009
  10. I really don't think that the 2ps would make any appreciable difference
    in the 400. As I said, I used them on a 550. That was because the added
    weight of the fairing was making the forks sag a bit.

    Heavier oil *will* improve the damping, yes, but you'll get forks like
    those on my Ducati - not much cop on anything other than smooth

    Basically, you're dealing with a fork design that is well over 30 years
    old. If you really wanted to make a difference to it, you'd take it to
    Maxton or somewhere and get it revalved: that's the only way to effect a
    noticeable improvement.

    Incidentally, the front forks on the 400 are exactly the same units as
    you'll find on the CB250G5, CB360, CJ250/360 except that the damping
    internals are revised. The stanchions and lower legs are the same (well,
    they matt-blacked them on the CJs).

    Well, the whole front end is more or less the same: 18" front wheel,
    same front brake, front mudguard. CJs used a different front mudguard.

    Incidentally, if you need a rear carrier for the 400 (and they are the
    proverbial rocking horse shit), a rack for a 250/360 uses the same
    fixing points and bolts straight on. So buying a totally dead 250 for
    £50, if it has a rack on it, is a Good Idea.
    The Older Gentleman, Jan 10, 2009
  11. mark

    mark Guest

    I wasn't looking for an improvement as such.
    I had just acquired a few bottles of 15w so was wondering which bike I
    could use it in :D
    The fork oil hasn't been changed for a while, the seals are weeping and
    one of the lowers needs changing.
    It has a crack near the top where someone has made a mess of changing
    the seals

    That's handy to know.
    mark, Jan 10, 2009
  12. mark

    Rusty_Hinge Guest

    The message <>
    Recommend you test the 2p pieces with a magnet, and select the older
    bronze ones...
    Rusty_Hinge, Jan 10, 2009
  13. I say, do you mind...

    (I had one, it was truly horrible)
    Austin Shackles, Jan 10, 2009
  14. mark

    mark Guest

    Hadn't realised this until the other day when I noticed which coins were
    stuck to the tank bag.....
    mark, Mar 28, 2009
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