How soft should stock forks feel? upgrades?

[Guest]

I just rebuilt my forks (1979 GS750EN), as the seals were torn up and I didn't know the history of the maintenance. Everything got a through cleaning, and 15 weight fork oil and new seals were used on reassembly. I checked the springs and the lowers (the long ones) are worn and about a half inch short. Fluid level was measured as precisely as I possibly could, and triple-checked. I've rebuilt forks before and never had a problem, but these still feel incredibly soft, and there is still some oscillation and wheel hop over large bumps. I realize that these probably weren't the highest-performance forks around, but I have a hard time believing that this is how they should act. I can get them to bottom fairly easily under hard braking. There is some rust on the shafts, with maybe 2 little spots on each side, so the seals probably won't last long, but at this point they don't seem to be leaking.

Are GS750 forks just really soft? Springs don't affect damping, but I don't want to put the money into fork springs if there is something else going on.

That said, are there other forks out there that are a direct fit if the rust becomes an issue and these still are too soft for my riding? I'm not a particularly heavy guy, and there is no way I want to be overwhelming my forks. Not too confidence-inspiring.

I know GSXR swaps are pretty common, but I just don't have the money for that right now.

The bike needs new head bearings anyway, so I wouldn't rule out a front end swap using different trees, forks, bearings, etc.

[BassCliff]

Hi,

Progressive springs, or Sonic springs, are not that expensive and will firm up the front end quite nicely.


Thank you for your indulgence,

BassCliff

[gearheadE30]

yeah, definitely. I was going to buy some Sonics to go in, but the forks are literally so underdamped that I think the springs would just overwhelm them. It typically does two full compression/rebound cycles before calming down again. My CM400 from about the same era feels very composed and doesn't have any hop or oscillation at all over bumps, and it has roughly the same unsprung weight, 33mm forks, and the same 15wt oil in the forks. I just can't believe that it's supposed to be that way...

[TheCafeKid]

Did you make sure your damping rod was clear of any crap?
And those springs are sacked out brother. It's hard to damp forks that have no support from the springs.
Good springs will make that bike handle better than you think. And make sure you've set your sag correctly as well.

[elrico]

Fork oil measurement taken w/the springs and spacers removed and legs compressed all the way in vert. position..air above the oil is part of fork's overall spring rate.Using the correct/recommened oil level and still mushy,etc.Maybe try slightly higher oil level,which results in a smaller air space above the oil which can/may reduce front end dive when braking and produce a firmer ride. But...if springs are sprung,$pring for good/new ones..what about that front tire,condition and air pressure,check it before ride/test,it could be low and soft,slow leakdown that could get by you,Fork caps..perfect seal, o-rings good?

[gearheadE30]

Yeah, I'll probably be putting new springs in soon. But the seals are leaking already, which I don't really understand... I've probably done 7 forks in the past and never had one leak. Granted, these have a few rust spots, but I don't think that would be enough to do it. So it looks like I might be looking for some non-rusty forks or uppers anyway.

fwiw I did measure the oil with spacers and springs out and legs compressed and all that, and I understand the air being additional spring rate. I thought about adding some oil, but since they're leaking, the seals obviously can't take what little pressure is there with the factory level, so I don't want to push it. Tires is new, pressure is good, fork cap o-rings are new and seal fine.

[TheCafeKid]

Pitting (rust) in the fork will leave a bit of a burr usually which can nick up the new seals and cause them to leak quickly. Taking the edge off of the pits with a small Jewelers file is a good idea. But the pits themselves will also invite leakage as it gives a place for oil to move around the sealing lip of the seal.
You can try to fill the pits in with a hard but sandable epoxy resin (couple of threads on that here) or hunt up new upper stanchions.