suspension questions

[Brian]

It seems to me that the fork on my 82 vision is quite soft. I think it is bottoming out over some bumps, giving me a pretty hard "thunk" going over speed bumps in parking lots and coming into my driveway. I have replaced the fork oil with new, and it may have helped some, but...?
A friend of mine runs non-detergent 30wt oil in the forks on his 78 suzuki GS750. It made a huge difference in his forks, but his bike (and he) are much heavier. I dont want to make the forks too stiff. Any other oil ideas?
I have also seen that some people drill the fork caps and add air valves to adds some pressure to the forks. How much does this change the ride?
Thanks
Brian

[George R. Young]

I've installed air forks and it makes a tremendous difference, you can easily adjust the ride height without affecting damping or spring rate.

The valves are from scrapped cast wheels, courtesy of your favourite motorcycle junkyard. Once you install the caps, you can use the handle (bash out the nut) from that fantastic screwrdiver in the toolkit to install the fork caps. And if you're really desperate for a screwdriver, you can always reinstall the nut.

Also, I use nominal 15W oil in the forks, mixed half and half 10W30 and 20W40.

[Lucky]

I'd  be a little suspicous of a "thunk" over bumps.  You might have loose or worn steering head bearings.  if you put a jack or blocks under the front of the engine while the bike is on the center stand, (to raise up the front wheel) Grab the forks by the bottoms and try to move them forward and back.  you shouldn't have any movement like this at all.  also, slowly turn the bars from side to side and feel for any bumps in the steering.  either condition indicates further inspection of the steering head bearings is needed.

there are tapered bearing replacements ava that are much better than the stock '19 ball' style.  this is one area where you want things in top notch shape (pardon the pun)
--Lucky

[Rick G]

As far as I'm concerned air forks are the answer. I tried adding a longer spacer (about an extra 1/2 inch) to mine and it just made the ride harsh. With the air it rides as softly as it does stock UNTIL you hit a bump and the it helps the suspension cope with the bump. I use ATF. Do as Lucky says and check your front end you need to eliminate that concern first.

[Brian]

Thanks for the info, I am thinking that air is the way to go. As far as using ATF, it seems like that would be thinner, and therefore offer less damping than even 15 wt fork oil. True?

 I did check out the bearings in the head tube, and all is fine in there, no slop or notchy feeling at all.

Thanks
B

[Rick G]

Hi Brian,  Your right, atf  (which varies in viscosity by brand, but  is around 7.5 wt ) will produce  less damping. I tried  the recomended 15 wt fork oil  and , in my opinion the ride was way too stiff. Every expansion joint in the hiway,  felt like it was going to dislocate my sholders so I went to  atf, anyway I'm happy!