gs450 front fork problems/questions

[sicnarf442]

I have been restoring a 1980 GS450S for the past year. Last month I got around to redoing front end so I changed a whole bunch of things at once: had new bearings installed, put in progressive springs, went to 15 weight fork oil (because ride was so spongy before that, figured it was a smart thing to do), new front tire, new brake pads. Front end is very stiff now and a little too high. Probably too stiff. I'm attributing that to the fact that I'm 160 lbs, and PVC spacer provided by Progressive assumes slightly heavier rider. Easy enough to change. Biggest problem, however, is that from the first time rode the bike I noticed a strong tendency to pull to the left, so I'm always countering that by pushing on the left bar. Problem goes away at high speeds, probably due to centrifugal stabilization, but if I am doing, for example, figures eights in a parking lot a slow speeds, the asymmetry in handling is quite pronounced.

Bike also tends to dive to right when braking hard. Not clear if that is a separate problem or a consequence of compensating for this bias by pressing to right.

Anywho, I took the bike to the local mechanic who installed the bearings for me. A very good and wise mechanic who refuses to work on old bikes like mine. He said could be any number of problems, best if I tore bike apart and redid the work. That is one option. Before I do that I was going to try loosening up the pinch bolts and rotate the forks by 180 degrees to see if handling changed, that is try to see if forks might be bent.

Another thought I had was to take the forks off a parts bike that I have, a 1983 GS450L, and see if the problem goes away. Last night I took those off the parts bike and learned to my surprise that those have the valves for adding compressed air to the shocks.

So here are some questions:
-Are the air shocks more desirable than the original shocks or something to stay away from? I would have to rebuild those.
-any thoughts on what could be causing the bike to be pulling so hard to left besides a bent fork?

Thanks,

Francis
Austin, Texas
_____________
1980 GS450, which I love more every time I ride!

 

[koolaid_kid]

Possible answers:
Tire is mounted improperly (possible but not probable)
Bearings installed incorrectly (possible but not probable)
Forks are misaligned (my best guess)
Do you know if the forks were removed when all the work was done?

There are several documents on BassCliff's website that discuss fork work, and the two I read discussed fork alignment to some degree.

AFA the stiffness, you first need to set the preload. This is done by adjusting the spacer length. If it is still too stiff, go to 10W fork oil.

 

[Bookmon]

If I may add... Don't fall for the "take your bike apart" line. I did that and got back boxes of parts.
When we rebuilt my forks, new seal, fork oil..... they performed better than they have in years. The air valve is an added comfort feature. I do not have my shop book here but, I think it is about 7lbs per fork PSI. However, we did not add any extra air pressure after the rebuild. The ambiant sea level PSI seems most fine.
As to the pull, maybe diffo in fork oil or pressure. But, I'd start with Koolaid Kid's ideas first.

 

[sicnarf442]

Possible answers:
Tire is mounted improperly (possible but not probable)
Bearings installed incorrectly (possible but not probable)
Forks are misaligned (my best guess)
Do you know if the forks were removed when all the work was done?

I took the forks off and rebuilt the left one myself: disassembled everything, cleaned it out with mineral oil, decided seals were still good and reassembled with new progressive springs. Since left fork was in good shape, I drained the oil on the right fork without rebuilding it, put in the progressive spring, added the 15 Wt oil per progressive's fill level and closed it up. Then rebuilt the front end as follows: installed forks, tightened pinch bolts (in no particular order, but following the torques set forth in Clymer manual), then installed the wheel and rebuilt the brake.

 

[sicnarf442]

Mystery Solved: bent fork. Doh!

Mystery Solved: bent fork. Doh!

After two months of riding with the bike pulling to the left I finally made the time and mental space to trouble shoot the problem. Bottom line: right fork was really bent. I missed it because I made the classic mistake of taking a short cut. When I redid the front end, I disassembled the left fork entirely, cleaned, inspected etc. Since it was clean and seals were good I merely flushed the right one with mineral oil. What I missed what how badly bent the fork was. The quy who had it before me must have compensated for this somehow by mounting the fork in such a way that it was not as noticeable.

Anyhow, this is the second time the parts bike I have has paid for itself.

Lessons if any: 1) If you haven't rebuilt it yourself, you can't assume it's o.k. and 2) in the end, there is always a logical explanation.

Francis
Austin Texas
1980 GS450S