Topic: Fork Oil change question

[Jugghead]

Hey everybody.
I just drained and refilled my forks on a 73 CB350F. I would say this is the first time in 35 years this was done, but there was Teflon tape on stripped/sheared threaded drain screws, so this was probably the second time it was done.   Anyways, The stuff that was in there was black and NASTY! yuck!
I did it all according to the shop manual, including putting the specified volume of oil (ATF-type F) via graduated syringe in there. (105cc)

I actually put 110cc in there because I let it drain a while and did some pumping to spooge the old crud out.

It could be my imagination, but the front forks seem spongier than before. I now have no problem fully compressing the front end when the bike is off the stands and I am standing over the front end.

My process was to stand flat footed, both kick stands retracted, apply the front brake, and pump the forks.  I had no trouble bottoming out the forks. 
1) Will this improve over time as the oil refills the bottom passages?
2) Is the amount of ATF too low? (should I add up to 15cc?=125cc for complete rebuild)
3) Is this too loose/soft for the front suspension?

It just seems a little weak on the dampening.  I would hate to hit a Philly pothole, have the forks bottom out, and damage some component. Or worse, encounter a handling problem (esp. while braking) that would cause a loss of control and a crash.

Is there an oil fill line in there somewhere? or a standard measurement as to how far from the top of the tubes the ATF should be? I refilled as per the manual and now have decreased damping performance?
From reading the posts "re: fork oil level," it seems there should be an air space in there, but how do I get the fluid level back to spec without removing and rebuilding the forks?

Thanks for any and all responses!

[750goes]

I'd pump the forks and then empty them again, this time refill them each with a measure and the right amount..then make sure you have the drain bolts installed before you refill them....forks should not bottom out by just pumping them.. about 4-6 inches by hand pumping is lots of movement in a real pot hole situation.

[Jugghead]

make sure you have the drain bolts installed before you refill them....forks should not bottom out by just pumping them.. about 4-6 inches by hand pumping is lots of movement in a real pot hole situation.

I agree. The impetus for draining and refilling was that I reached the 12K mile mark, and also very recently was cruising a 4 lane divided highway at about 65MPH, hit a gnarly road imperfection, and heard a nasty THUNK! as I felt the front forks bottom out for the first time ever.
I did make sure to have the drain bolts secure before refilling, and like you said, I found it odd I could bottom them out just by pumping them.
 I will recheck in the morning, but am still curious if there is a way to fill to a certain distance from the top of the fork tubes.

[bwaller]

If the oil was really bad there will be lots of crud in the bottom of the leg. If you choose not to disassemble you can drain your fresh oil again, add 200cc's of diesel fuel, work the forks some to flush out some crap.

From the 350/400 Honda shop manual I have it asks for 145-150cc after draining, and 160-165cc from dry.

[kuyarico]

What weight fork oil is standard for your bike? If memory serves me correctly, I believe that ATF has a viscosity of a 5W oil. Your bike may require a heavier weight. I would try running a 10W to see the difference.

[Jugghead]

bwaller:
I will drain again like you and 750goes suggest, just to flush it one more time. seems like a good idea.
BTW I am not sure about your shop manual, but here are the oh-so-detailed instructions for this straight forward procedure.


Kuyarico:  The honda shop manual says use any ATF fluid.  I used ATF type-F, red stuff from the local store.
If the re-drain/refill doesn't solve the sponginess, I will indeed switch to 10W fork oil.


SO, it seems a redrain and refill with the required cc of ATF will return the oil level to normal.
thanks for the help. any other opinions/experiences are welcome!

[jaknight]

Hello Jugg,

     If you change to fork oil............ I have always been happy with 10W that has teflon added to it......... Perhaps you could jump up to 15W and give it a try........... but, again, I would go for the teflon additive....... always given me a better "feel & seal".........

     ~ ~ ~ jaknight ~ ~ ~

[crazypj]

Dont use the quantity, (except for initial filling) use oil level from top of tube, forks compressed and springs out.
The trapped air acts as a spring on last 1/3~1/4 of travel.
 Start with about 5" from top.
 If still too soft fill to 4" from top.(and if too hard, remove some oil)
 Works on any bike and any diameter of fork tube
 Don't go too thick with oil as it can lead to forks 'packing' if you hit a series of ripples/bumps. ( unless you drill out damper rods, stick with 10 weight, full synthetic is best but also most expensive)
PJ

[RSV12K]

Measuring from the top works best.
I don't think 15W is too much. If you think it might lead to a problem use fork oil (Belray or some other). 15W Belray is what I use and it works for me.
Some aftermarket springs (Progressive's, for example) require your using spacers. Don't think that applies here, but I figured I mention it. I needed them for my CB750--you might too, to get the right amount of preload.

[TwoTired]

Did you measure the fork spring length while you had it apart?  The springs can fatigue and compress with time.  If shorter than 18.84 in., they should be replaced.

The oil you removed may not have been ATF.  Could have been a thicker weight.

Cheers,