Hey Guys,

I had some Sonic Springs (1.0 with 15wt oil, I'm 145lbs) put on over the winter and now that I've gotten a few miles on them I'm noticing a harsh ride over bumpy pavement. I've let out all the air without improvement. I went back to my mechanic and he said he cut the tube and added the oil per instructions and pretty much blew me off for any other help. Has anyone else come across this???  Maybe too much oil in them???  I'm trying not to have to take it apart to check his work (This is why I paid to have it done).  Is it possible to just let some oil out of each fork for a slightly softer ride???   Thanks for any help.

air???
pre 94 bike only, used air assist, in stock configuration, only for pre sag.... and any aftermarket spring and build technology that anyone could install, removes the "add air" necessity from the equation... whoever did the work, is a dufass...
if they added air, along with new springs and other stuff, its highly suspect to have been faulty install from the get go... just tossing this out there.


who did this work?

now, likely because he had no clue what he was doing, he added oil with the springs installed, again, on a pre 94 the oil level is checked with forks extended, and no springs.... and it should be at 355 mm from the top of the fork tube (14" works fine for metric impaired folk) and no less than 13-7/8".

My bike is a '87 with the air valve on the top of the right fork.  It also has the two drain screws at the bottom of the fork tubes.  So if I drain the oil out and replace it with 10w (Instead of the 15w).  I measure with the springs out and the forks compressed to 150mm (5.9 inches),  about how much oil should this be???

 MOB is correct, you dont use air with proper springs made for your weight unless your sag is too much which I doubt with your weight and 1.0s. What is your sag now?
On my C10 I had to go to 50W fork oil to get the rebound to slow down and it was still not enough. Granted I had 1.2 Sonic springs and gold emulators and that was the best setup I ever had for that bike.
It could really soak up bumps. It will never ever be close to a properly valved cartridge shocks but it is not a  slouch either. Maybe you should think about buying emulators. They really help.
Running thin oil in a damper rod shock  should   make it bounce around a lot with little to no damping at all (rough ride)-- I would think.
Are you sure your forks are not bound up?  Do you have a fork brace installed?

My bike is a '87 with the air valve on the top of the right fork.  It also has the two drain screws at the bottom of the fork tubes.  So if I drain the oil out and replace it with 10w (Instead of the 15w).  I measure with the springs out and the forks compressed to 150mm (5.9 inches),  about how much oil should this be???

ennnnnnnnnhhh...
stop.

pre 94 is measured with the forks fully extended, springs out..... do not compress forks...... measure the top to oil level with the forks fully extended....

not compressed...... fully extended..... springs removed...... measure the level with the forks fully EXTENDED.....

I gave the distance dimension in my other post....forget liquid volumn/quantity....  .go by the dimension...... 355mm, or 14" if that works...
now repeat this all again....

ok?

and to reiterate, do not add any air to the forks afterwards.....

Air is compressible, it'll act as a spring. Heavy rider, more air. That said...

Can't really fill the forks by volume as there's always a modicum of oil left in the forks when you drain them. As hard as you try.

So, jack the front of the bike up, get the front wheel off the ground at the very least. Remove the fork cap (may be harder on pre 94's?), and the spring if it's required. Wheel and fender (and stuff) can remain attached.

Now take a carpenters tape measure, extend it to ~17". Insert the tape into the fork tube to the 16" mark, remove. Subtract where the oil left a mark on the tape from 16, you now have the fork oil level.

If the damping is too harsh, use a lower viscosity oil.
If the damping 'locks up' or 'hammers' going over a bump, it's probably over filled. It will also blow the fork seal eventually.

Personally, I make sure I have oil in my forks, and the level is at or below the mfg's recommendation. I'm not real picky as to weight or quantity. Some owners will tell you that they can run over a dime and tell you if it's heads or tails. I'm so far in front of them that I don't really care.... It's only a dime

Rick

OK, so I got everything out and measured the oil.

Forks extended 17 3/4 to the oil.

Compressed 9 3/4 to the oil. Per instructions from Sonic Springs (150mm = 5.9 inches compressed) that's where I'm getting that compressed number.

I'm confused, I would've thought not having enough oil would've made it a softer ride???

OK, so I got everything out and measured the oil.

Forks extended 17 3/4 to the oil.

Compressed 9 3/4 to the oil. Per instructions from Sonic Springs (150mm = 5.9 inches compressed) that's where I'm getting that compressed number.

I'm confused, I would've thought not having enough oil would've made it a softer ride???

ok, I'm only going thru this one more time.
you have a pre '94 fork, the valving components differ from  post '94, and this is why there are 2 mothods based in difference of the valving components.
I feel the info you have been given is incorrect for YOUR fork. Sonic sells very few kits to pre 94, and when they do, I think they are giving out false and incorrect info...

ok.?

level in a post '94, taken with spring removed, and compressed fully, is 171 mm per oem spec, or close to 6-3/4"

you see what I'm getting at??
so forget the compressed fork readings, and stick with the oem method, you only replaced springs.... not the internal valve components the take care of damping and rebound rates...

now, as to "why" its stiffer, unless you fully understand the damper, and the effects on hydraulics, it makes no sense to you, but I'll say that in this case, there is air being trapped in the cartridge, and it is cavitating, and "hammering" the internal valving, the correct oil level keeps the complete valve section full, and will work smoothly and consistantly, add an air pocket within the same valve, and it will not work the same, once the air passes the control orifice and the oil hits it, it will slam. Thus the harsh feel.
Air in a closed valving system does not like to be compressed, ain't the same as the air just sitting in the void above the oil in a fork tube... it all has to do with the valving...the mixture also has a tendancy to encapsulate air into the oil, because it is being forced to mix in the valve, this will cause foaming and aerated oil, which is even more inconsistant to control flow rate.

so again, extend the forks, and make the level correct for the valve to work.
play with the oil viscosity all you want, this changes rebound rate and smoothness of function, but just use the correct oil level.....

I will also say this, Sonic does NOT diferentiate or sell springs on their site based on specifics of model year, for the Concours....
their instructions may say to make the spacer a different length tho, it sits on top of the spring...
all of this has absolutly no bearing on the required oil level  completely functioning the valving cartridge of the fork.

I'm done with this now, best of luck, I tried to give you intelligent and concise answers to the problem.
I can not explain this more clearly than I have already.

Man Of Blues,

Thank You, Thank You, Thank You. I appreciate you taking the time to help with this.

Back to the garage.

From the factory service manual for 86-89 models. 

Interesting oil weight 10w20.

Also, here is a thought - maybe the oem spring wire dia is slightly smaller than aftermarket springs.  Diff in oil height may be insignificant after springs are inserted.  Hmm, raises another question if using oem springs cause iirc one end of spring has tightly wound coils and other end doesnt so it might make a diff which end is down.

Found this to be very helpful seeing that I'm in the middle of changing mine out. I have a 98. Although, the Youtube DIY by Tito did not mention when to fill it up. I'm assuming that the forks go back on dry then you fill. This will take into account the rake angle. Or, is this why you fill when forks out and compressed. Any other thoughts on this matter??

Found this to be very helpful seeing that I'm in the middle of changing mine out. I have a 98. Although, the Youtube DIY by Tito did not mention when to fill it up. I'm assuming that the forks go back on dry then you fill. This will take into account the rake angle. Or, is this why you fill when forks out and compressed. Any other thoughts on this matter??

fill with forks installed, springs out, and compressed or extended dependant on model year, to the levels shown in the manual. oh, that kinda dictates being on the centerstand, maybe stick a 2x4 under the tire to kinda level the bike.... doesn't specify that in any book, but it won't amount to much difference.

your '98 forks will be 171mm oil level from top with forks compressed...( 6-3/4" works fine)