1991 Yamaha XJ 900f Fork Oil

Hi XJ Owners

I read on the internet that people are using automatic transmission fluid in their motorcycle forks instead of fork oil. Has anyone done this and what were the results? My forks have 5wt fork oil but I want to try 15 or 20 if possible. I think the fork springs on my XJ are past their best. Any advice for improving damping on the front forks. Is it feasible to fit shims below the fork nuts at the top of the forks?

 

buy a new set of springs would be best.
change fork seals
going a higher wt oil will help but is just a short term fix
atf is used and so is motor oil

fork oil wt and motor oil wt are not the same thing.
is used in xj 750s

 

Cheers XJ550H Yes I am going to change the springs, as the bike is twenty seven years old and that should make a big difference. I may try 10wt fork oil too. Thanks for your post regarding the oils too.

 

ATF is roughly the equivalent of 10W fork oil. Both fork oil and ATF have anti-foaming agents, while motor oil does not. You do not want the oil inthe forks to foam. The bike was sprung and dampened for a lighter rider than is common today. I find that 10W is a bit too mushy, but 15W is about right.

 

Fork oil in the forks! Keep it clean. Most of the old bikes don't have anodized sliders. They wear and the aluminum get suspended in the oil. It gets gritty and wears much faster. It's probably a good idea to change fork oil at every third engine oil change.

Before you spend real money, change the fork oil. Ignore the oil quantity specified in the service manual. Collapse the fork and remove the spring. Add your favorite oil until it is 130 mm from the top. Reassemble. The smaller air space will stiffen the forks in their last 30% of travel. You might even be happy with it.

If not, I prefer straight rate springs chosen for my weight. Switching to heavier viscosity oil will slow high speed damping. High speed is hitting a pothole and has nothing to do with motorcycle speed.

 

Cheers k-moe and JetmechMarty,