The fork tubes need to be removed from the bike. 

• Put the bike on the centerstand with a scissor jack under the front of the engine

• Drop the front wheel and remove the fender and brake caliper(s)

• Remove the fork nut from the crown

• Loosen the triple tree clamping bolts

• Apply WD40 or other thin lubricant to the stanchion tubes (and possibly a wedge to the triple tree)

• Pull the tubes out and replace the boots

This is an excellent time to re-pack the headpost bearings.

Thanks Ricard - this is exactly what I was looking for - appreciate it.

Got it disassembled and when I took the fork nut from the crown I didn't hold the allen screw so when I removed the fork the spring is exposed from the top. I wanted to change my fork oil anyway so I poured it out from the top of the fork into my oil pan ....is this cool? When I put it back together going to take off the handle bars so I have more room to work with.  Should I pour the proper amount of fork oil in prior to assembly or put it back together and do it then?

That's how it usually goes. Spring pops up, gets in the way, ruins your day ! 

The fork is a complete hydraulic system. So the oil is not simply going to 'pour out' easily or fully. With each stanchion, you'll be there pumping the fork leg back and forth, fully extending and collapsing, up-side-down over a bucket. Two minutes per side should get it done. You'll never get it all.

Repack the headpost bearings.

Buy some honest-to-goodness "fork oil" to go back in. Oil goes in before the springs, once the tubes are re-installed. More pumping is required to get oil back into the system or insertion of the springs may make it overflow. Lower the springs in slowly; don't drop.

Don't tighten the triple tree pinch bolt until the top fork cap is fully tightened. These may need to be somewhat snug to hold the stanchions, but not tight.

The axel needs to be greased each time before insertion.

Be extremely careful with the brake fluid master cylinder and reservoir. DOT3 / DOT4 brake fluid will eat the paint off any surface it touches or remains on. Wipe up spills immediately with a soapy rag soaked in hot water. Just in case you missed some... Wash the entire front end, tank, and frame with LOTS of warm/hot soapy water as the finishing step to complete the repair.

Hope this helps.

Helps a ton - thanks -- I thought not very much oil came out when I just tipped them over into pan. The oil is purple is that normal? I have Liqui Moly fork oil to replace & I use this brand for almost everything except I use Bel Ray brake fluid. I hear you about brake fluid I took tank off already and will cover frame, etc with rags. Won't have new gators until tomorrow so I have plenty of time to pump the fork legs prior to reinstalling them. Glad I have you in my corner.

@gpopovichcastlerockwinery-com

If you want to keep your new fork covers nice for a long time, keep them away from detergents. Those seem to leach out compounds that keep the "rubber" soft and pliable. It also never hurts to spritz them once a year with spray silicone or Armor-All as a way of keeping them soft and protecting from UV. 

Thanks, I'm actually glad they ripped the previous owner tried a jury rig paint job on the front fender (I improved that already) and they had paint splatter on them. Also, can change out fork oil, etc.  I have gators on my 75/5 and I do wipe them down with rubber protection spray (I like 303). Is there anyway visibly to tell if the springs are in good shape? The PO had the rear Ohlin shock rebuilt 3k miles ago so I kind of assume he'd keep up the front end as well? It does dive about 4 inches under hard braking but from what I read that's about normal for a 80G/S?  

I just pumped one fork a lot more and the purple oil that came out at first looked pretty clean now the more I pump them the dirtier the oil looks - with brown splotches. Glad I'm changing it. 

Purple fluid sounds like some fancy synthetic oil. Sounds like a couple of things were being done.

As for the springs, make sure they are the same length. Sometimes one will collapse and be 1/4" shorter. Stock BMW springs will usually have a progressive rate (a different coil wind) at both ends, whereas the industry std is to only have that at one end. On a GS, I think your travel is good. The springs control the total travel distance; fork oil controls the rate of travel. 

Hope this helps.

I'm with 303. armor all is for pretty, 303 has real uv shielding in it. use often.

purple fork oil is common. royal purple and belray are purple as well as others. aeroshell is red.