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LM IV forks

baloches

baloches

Cruisin' Guzzisti
Joined
Feb 9, 2009
Messages
136
Location
Mascouche, Quebec
I just picked up an 86 LM IV, and wonder how the air forks work. First, my crossover tube is leaking, so i'm not maintaining air pressure.
I assume the air is preload, how do I adjust damping? oil viscosity? In the manual I have they mention ATF 150cc's per leg. Can I change oil viscosity or level to have better damping?
I was under the impression these forks were stiff, is this correct? Mine sure aren't! Is this just because the lack of air pressure or should I also look at defective/inefficient damping components?

Cheers

Kai
 
On my LeMans there was no crossover: it had individual valves on each fork leg. You could do away with it & fit seperate valves so there are less joints (= potential leak points). If my memory is right I found about 20 to 25 psi was best.

I think the oil is only for lubrication & doesn't have any effect on damping.
 
Yes, the oil is only for lubrication. Baloches, if the forks aren't holding air it's probably cause the seals in the sealed damper units have blown out. Without knowing many years ago when i was very :mrgreen: i hooked mine up to the service station tyre pump and bingo, POP.

Considering the age of the bike i'd say it;s time to replace the sealed dampers with a set of FAC's, $400AUD. These like the std items are non adjustable. I have tried using thicker weight oil but could not feel any real difference.

There is room there to adjust spring preload, but you will have to take the whole thing apart. If you can take a photo of the top of the forks we will be able to tell if your dampers are still the original's.

These LM4's with the 16" wheels handle a bit different to others so don't be to concerned that it doesn't feel right, it's something you have to get used to. I have found that running high pressure, 40psi front and rear feels better and also i have found that mine does not like worn out of shape tyres. Make sure the steering damper is working properly. This is a must.

I have just replaced the dampers in mine because they were shot and the bars were shaking, and now i find that the steering head bearings are also shot so it is wise to check these as well.

Once you have taken care of all this you will have one of the best handling and stable motorcycles on the road.
 
Baloches, just realised you said the conector tube is leaking so i would be confident in saying you still have the original dampers in place :huh: . Time to spend some money and do some maintenance ;)
 
Thanks for the replies, been out of town past few days, I'll fix the tube and then see what happens. Thanks for the heads up on the damper, I just brought it home, not on the road yet. I'll be checking these items out.

Thanks
 
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