Topic: 400f front forks

[Frenchmike]

Hi all i,m new to your forum and i,m also new to my 1977 400f , my question is , I have replaced the front seals and used 10 grade fork oil , but the ride feels quite hard and not much dive under braking is this normal ?

[MoMo]

try ATF instead....Larry

[grcamna2]

It'd be good also to check the straightness of your fork tubes by loosening up the tubes in the triple clamps while all assembled and try slowly turning each fork tube by hand thru 360 degress and seeing if they'res any resistance while you do this.The upper tubes should turn in the clamps w/ no resistance; & check the alignment of your triple trees by eye to see if they're bent while the forks are in there.The only other thing could be your seals may still be a bit new/stiff...or your fork springs could be 'out of spec'.

[camelman]

The previous two posters nailed it. Excessive fluid will have an impact too. How'd you measure the amount of fluid you put in?

Camelman

[grcamna2]

The previous two posters nailed it. Excessive fluid will have an impact too. How'd you measure the amount of fluid you put in?

Camelman

+1`

[Frenchmike]

Thanks for your replies, oil quantity as per manual, it was the first ride after overhaul, and not very far, but you could feel ever small bump in the road but it could be ridden with hands of the bars, so may be I should do a lot more kilometer be for making any changes.   

[grcamna2]

Mike,
Did you try what I recommended ? if the forks & triples are not bent,you may be experiencing 'stiction' between your fork tubes and seals.

[chewbacca5000]

I rebuilt a set of 1971 or 72 cb750 forks and filled with an extra 30 cc of 10 weight fork oil and they are pretty stiff.  I wanted it to be a little stiffer anyway.  Manuel called for 230 cc I put in 250 cc.   Would that extra 30 cc of oil make that much of a difference?

Does not seem like that much at all.

[strynboen]

yes over 250 ml it  vill vent stone hard...there need to be some air floting in the valve..overfill make it hard..even with thin oil..that just mine idea..

[chewbacca5000]

yes over 250 ml it  vill vent stone hard...there need to be some air floting in the valve..overfill make it hard..even with thin oil..that just mine idea..

Thanks will drain a few cc!  Appreciate the quick reply.

[Jasondo]

I have recently rebuilt my 400f forks. I believe 160cc is all it took. Its a small amount but extra is not better! Also if your tubes are straight I would then take them apart and clean the damper orifices on the piston. They may be clogged up?

[Frenchmike]

Having ridden for about 60 miles to day, just to see if it would sort itself out , but still the same, but better over 70mph ,and at slow speed like riding over corrugated roof sheets

So i'm going to strip the front end down tomorrow and look at everything again

[grcamna2]

Mike,
They have the amount of fork oil specified in the manual for the CB400F to be 145-150cc after a routine oil change and 160-165cc after full rebuild.

[Frenchmike]

Yes thanks for that, I have tried the oil levels as you said as well, right at the beginning

[grcamna2]

Mike,
You may just be experiencing the stiffness of new seals;what brand seals are you running ?