'86 K100 RS front shocks bad

[Glacier_g_rt]

Am wondering what is involved to replace the front shock cartridges? on my K bike. They went soft over the summer and now is the best time for me to work on it. Any clues anyone? Thanks. Dave

[Bruce C]

As far as I know the front forks on an '86 are either Fichtel and Sachs('85-'92 K75&K100) or Showa forks('93- on K75). Both of which are damper rod forks, no cartridge involved.

If the fork tubes have a ridge cast into the front of the tube, they are most likely Fichtel and Sachs forks. These forks have a capacity of 360cc. +- 10cc on a K100RT,RS,LT.

I used to run #15wt. Spectro fork oil.

 

I suggest you pick up a manual for the bike . It is available at any BMW dealer.

 

Bruce C

[tallman]

Good shock for reasonable prices.

http://www.hagon-shocks.co.uk/HagApps1.htm

Scroll down to your bike.

[ShovelStrokeEd]

Those are damper rod forks, no cartridge involved.

Likely the springs have sagged and will need replacement. Check a manual for free length and OD specs and you can find a spring from any one of the aftermarket folks that will work. If the spring is a little (less than 2") shorter, you can make up the free lenght with a spacer on top of the spring.

Do change the oil in the forks. Something a bit heavier might be a good idea.

You are going to have to determine spring rate and sag for yourself.

You could always go with OEM but, IMHO, they were never very good to start with (too soft). So much depends on rider weight and style of riding that an entire book could be written about this very subject. In fact, many have.

Take a look a the web sites from people like Progressive Suspension, Race Tech and the like for some ideas.

[Glacier_g_rt]

thank you all. dave

[RFW]

Am wondering what is involved to replace the front shock cartridges? on my K bike. They went soft over the summer and now is the best time for me to work on it. Any clues anyone? Thanks. Dave

You need to look at a Haynes manual. There are no front shock cartridges.

 

The shocks are fully disassemblable and all parts are available.

 

But your problem is probably only too thin of an oil. BMW specifies 5-weight oil, resulting in these shocks legendary reputation for being too soft. Try replacing with 10-weight shock oil before you start disassembling them. Full. complete rebuild info is in the Haynes manual. If you are unable to get the manual (and I strongly suggest y ou de, because it is excellent), then I can scan the pages and email them to you. PM me if you need to go this route.

 

IMPORTANT: Do NOT go filling the shocks with any old amount of oil! The exact amount is important. Too much and you will end up with extremely stiff front end as a result of the air inside compressing. Too little and you will end up with a lot of foamy oil. BMW specifies an exact amount per fork leg. My recollection is 360cc per leg, but I am at work and do not have access to the manual at the moment.

[DewNMoon]

The original springs will sag over the years. I replaced my 85 with springs from Progressive Suspension and I think 7.5 wt fork oil. Adjusting preload for my riding style.