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Baffled by preload knobs...

  • Thread starter Thread starter Frog
  • Start date Start date
F

Frog

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Can I just say that I'm so happy I found this delightful corner of the internet? It's helped me out a lot so far and will hopefully help me forever more.:)

I have recently acquired an '83 GS750ES and I'm confused as to how, exactly, the two knobs on the left side of the bike by the swingarm affect the suspension. One is small and has the numbers 1-4 (#1 is red) on it and only clicks clockwise. The other is a metal dial-like thing and has 1-5 marked on it, but won't turn no matter what I do to it (stuck maybe?).

My problems are:

I have no idea if the small one that I can turn is affecting the preload at all. I'm 185 lbs. and I don't notice a difference between the settings...even riding 2-up.

I can't figure out what I'm supposed to do to the bigger knob to even make it turn for me. :o
 
The one you can turn is the rebound damping. 4 is the hardest, 1 is the softest. If you feel like the bike bounces off bumps, increase rebound damping.

The one that's stuck is the preload. 5 is the stiffest. Looks like it might be broken. Others might have tips for how to fix it, I decided to go with a new shock from Hagon with remote preload. The combined rebound/compression damping is on the base of the shock. Works very well, but they don't give them away for nothing.
 
The bigger knob is the preload knob,it can be turned both ways.It effects preload hydraulically. There's also an sliding indicator on the side.

Here's a pic of a shock out.
 
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Thank you! Looks like I have a little more research to do. If anyone knows what might be going on with the preload adjuster please, let me in on your secrets!
 
I don't think the manual the rebuild of the unit but it can be done. The preload is accomplished by hydraulic pressure and it takes place in the base of the unit. Essentially it's a solid piece of aluminum with valuing and separated by o rings, which are replaceable, but you have to source them yourself. When I rebuilt the one on my 1150 I found them at a heavy truck repair shop that also specialized in hydraulics. After you take apart the shock you will see 3 o rings in the base, and they are different thicknesses so keep track of where they go. I took mine to the shop and with a micrometer and a catalog the guy identified what needed to be ordered and I had them in a few days. Popped 'em in, refilled the shock with fluid, and voila, preload worked! I did have a bit of a time with filling the fluid without air, but by working the adjuster knob, and using a syringe, you can basically fill it and burp it, then finish the fill. Something like that. Use hydraulic jack oil. I used brake fluid, which I think was a mistake since it absorbs moisture, but it can be changed out I guess. Hope all that helps, PM me if you have any questions about what I did.
 
Yea, that's what I was assuming as I was taking a real good look-see at the shock. I'm planning on getting a new one installed in the near future, but that can wait for now. The preload seems to be set around where it needs to be for someone my size so it's not a huge issue at the moment. Now to go figure out why it's not idling without some choke :dancing:

Thanks for the help everyone!
 
If the preload knob is stuck it is probably stuck at the shock where the base meets the bottom of the spring. Try using some gentle leverage with channel locks and a rag on the knob and see if you can turn it
 
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