Looking for fork oil advice

[Keith Lane]

1980 GS1100E
My scooter has developed a leak on the left fork leg, with oil seeping from the dust boot at the top of the slider. I have acquired the seals and new dust boots, and now that the weather is pretty bad for riding, I want to pull the forks and replace the seals/dust boots/oil. The local parts guy at the Suzuki/Honda/everything else including UTVs and ATVs dealer in't even as old as the bike, and said they ONLY have 5 weight, and he has no idea what is called for. I only have the Clymer manual and there is no specification that I can locate.
What is the recommended oil? Also, the Clymer book claims 25PSI for air pressure, which seems pretty high(?)...
Thanks in advance.

 

[dgates1]

Owners manual says 7.1 psi on the forks and 238ml of oil in each, but does not specify a weight.

https://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/GS1100E_Owners_Manual.pdf

Service manual says the same on air pressure and mentions "Front fork oil #15" if that means a 15w oil...? Suppose it depends on your preference of ride. Thicker oil will ride stiffer but better on the highway.

https://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/80-83_GS1100T-LT-EX-1000SZ-EZ-SD-ED-ESD.pdf

 

[Grimly]

In my 850 I last filled the forks with SAE 10 Belray, or something. Not that important.
It rides fine, but it's not exactly standard.
In my XJ I used 5w40 synth motor oil. It rides fine, and it's totally standard.
Suzuki originally recommended home diy-ers to make up a mix of ATF and 20w50 motor oil, might have been 50/50 ratio, but I unrecall.
I'm utterly sure that worked fine, too.

If you're not a track star, you probably won't notice it.

 

[first timer]

jump on amazon and get some maxima 10wt or 15wt.

If you are a +200 guy go with the heavier oil, the heavier the oil the more rebound dampening.
These old damper rod forks don't really care about oil as much as the newer cartridge style forks. Hell you could even use ATF fluid and it will be fine.

 

[chuck hahn]

Save your money and make your own. 1 quart 30wt oil and 1 quart ATF. Makes 15wt oil. Service manuals have the recipie in them.Make half gallon for 9 bucks where things like Belray is 18 a quart.

 

[salty_monk]

10wt is good for most. Weird thing about fork oil is there is no standard so a 10w in one brand could be slightly different to a 10w in another.
If they feel harsh or slow after drain and go to 5w or got the other way if you’re a big guy.
with our low tech forks you’re unlikely to notice though!
personally for me it’s 5w or 7.5w with a cartridge emulator. With those the oil weight is controlling the rebound damping whilst the emulator adjustment controls compression. They are interconnected so an adjustment of the fork oil weight needs an emulator tweak too.

im about 170lb. Most important for our forks is to get the right weight springs and setup the static sag. Minimal preload is technically best if you can get the right spring.