Front forks, springs

I notice on the bike, when i brake, the suspension goes down almost all the way. Only few cm over first part, and shakes the last few kmh befire full stop. Today i put in new oil, correct amount. Old oil was dirty but amount was ok. So if i understand correct, the problem is too soft springs?

 

The suspensions on these bikes are pretty soft and the fork valving is crude, so they do tend to squish at stops. Shaking is not normal. You'll have to give a better description of what is shaking. More likely to be brake rotors or stem bearings than forks. Which model bike? Aggressive stops or slow stops?

 

Oh sorry. Its a 1997 XJ600N.

The shaking happens in hard braking, but only on very slow speed - below 20kmh, when forks are sqashed. The bottom of the forks is visibly going back-forward. Bike has been standing still for couple of years, before that it had a new disc rotor. On the brake handle, vibration is not felt (like would on car with bent rotors).

 

Steering head bearings. Put the bike on the centre stand grab the fork legs a push and pull on them. They should not move back and forth and the forks should turn easily with no tight spots lock to lock.

Do you have a dial gauge to check the discs for runout?

 

Yes that was what i think of first. But there is no "air" in them (sorry dont know the real english word - i mean they are tight as they should be - and they turn nice).

No, sadly dont have runout gauge.

 

What condition is the front tyre in? What viscosity is the oil you put in the forks?

 

Don't discount stem bearings even if they feel good. Too loose, too tight, divots formed in the neutral position. I'm not familiar enough with the 600N to know if you have a center stand, but I assume you've got the front tire off the ground when doing the checks?

 

I have a center stand, i used it to remove forks, but before that i checked the stem for air. It turns nicely with no effort and has no visible air with fork on or off.
I used recomended 10W oil by liqui moly.
Tyres are new.

 

Did you pull the lower fork legs and push them? Any movement? Check it with someone sitting on the pillion seat to keep front wheel off the ground or a heavy bag on pillion seat.

 

No feelable movememt in forks. By some instructions, the steering was little to loose so I tightend a litlle with no change in shaking.

My plan is as folows: first change rotor and pads (was going to change pads any way), then try with spacers for spring pre load (recommended or not?), then change bearings in stem.

Now that I think of it... First time i noticed the shake was after a long descent drive with hairpin curves. The heat could have bent rotor maybe.

 

The solution of shaking was bent rotors. Now it is fine. I also put 2cm spacer in forks, so it is little more hard suspension. Its not perfect, but ok it is. Any one using alternative springs and witch ones?