New fork oil, suspension still soft, 81 xs400

[xs400newbie]

Hey guys,

I recently changed out the fork oil in my 81 xs400 and the suspension is still very soft. The springs look fine. They stick out the top considerably and took quite a bit of force to compress them. I used 20w synthetic fork oil, as recommended, and filled the forks with 142cc's, as I've read here. Should I use more oil?

 

[Old Mose]

I had the same problem with my 80. I particularly didn't like the diving when I applied the front brake. I ordered a bottle of Bel-Ray high performance 30w and changed it using the recommended amount and to my surprise it worked. I must admit it is pretty stiff but I can deal with that to stop the diving.

 

[xs400newbie]

We've had this bike for 25 years and I can say that the suspension has always been like this. Since it's spent most of it's life in the garage, I never looked into it. Now I'd like to get this thing on the road. Should I try adding a bit more oil before I go to 30w? I measured precisely 142cc's in each fork.

 

[16VGTIDave]

The oil viscosity will only change the damping rate. Thin oil = less damping. Thick oil = more damping. The springs control ride height and stiffness. Oil volume will change the compression / bottoming characteristics of the forks. If the forks are bottoming often or harshly, increasing the oil volume slightly (reducing the air volume in the fork) will help a bit. But don't over do it or you can blow out the fork seals or even hydraulically lock the forks.

Get the springs right first, before you try to fine tune with the oil.

 

[xs400newbie]

I haven't had the forks bottom out, but a touch of the front brake and you get significant diving. Maybe the stock setup is just crap? How much more oil should I try first? I hear some sloshing around when I push down on the suspension. Not sure if that means anything.When you say get the springs right, do you mean replacing them? Is there a set of springs you would recommend?

 

[xschris]

You may be just grabbing the front brake too hard. I have five of these bikes and never had any problems with diving, only if I pull hard on the front brake at a sudden stop. Make sure the brakes are adjusted, clean and moving as they should.

 

[xs400newbie]

The front brake is quite sensitive, so perhaps adjusting it some will limit the nose diving. I will take a video of what I'm experiencing. I don't have much experience riding, but I still believe the suspension should be stiffer.

 

[16VGTIDave]

It sounds like you have been reading the crap written by moto journalists, or getting advice from those who do. Most of those twit journalists think every bike should handle like a race prepped, track use only bike. In the real world, on real roads with potholes and other fun obstacles, suspensions are supposed to actually work. That includes the forks compressing under load, and using their entire travel when required. You should keep in mind that the forks on our bikes are the cheapest possible to manufacture, 30+ years ago. If you are wanting significantly better, you will have to spend money to replace the forks.

If you are willing to accept the stock forks with all their design compromises and just want to improve them slightly, as I said before, the springs are where you need to be looking. Take the time to calculate the correct spring rate for you, measure static and dynamic sag, and have springs custom wound for your needs. No springs currently available are worth their cost, unless they miraculously happen to be the correct rate for you, which is highly unlikely. Once you have replaced the springs, then you can spend weeks playing with oil viscosity and volume. That process will be trial and error. Take good notes!

 

[xs400newbie]

I You should keep in mind that the forks on our bikes are the cheapest possible to manufacture, 30+ years ago.

Yes, that's partly what I figured, and thanks for the detailed write up. In truth, I wasn't so much interested in track performance, but wanted to be sure there wasn't a safety issue. I don't want to spend a ton of money on this bike, and just want to have some fun cruising some country roads. I just thought I would feel something more with the new 20W oil, but I'm willing to accept it for what it is.

 

[xschris]

Remember that these bikes use a 33mm fork tube which is not very big. If you are a heavier rider you can only expect so much. I have ridden bigger and smaller bikes from the same time when these where made and they work for the size of the bike.