I saw a thread on here earlier about fork oil weight and how it effects suspension resistance.  Lighter = softer, heavier = harder.  So I'm looking for lighter, as a 6'3" 240lbs guy.  None of the auto stores around me sell anything lighter than 20wt oil.  So my question is: would it be okay to use automatic transmission fluid as a very light oil instead?

yep sure is but it is as heavy as you would want to go.

ATF is as heavy as I'd want to go?  Just due to my size?

Hi there, If I remember well, BMW recommended fork oil from 3 to 10. I've used ATF and after a couple of rim bendings, discovered that it is more than 10. So I bite de bullet and paid for an overpriced motul 5 fork oil. No more problems. Then I understood why them recomend 10 only for competition.
Hope this helps.
Best regards
JAP

In a previous life I did a lot of off-road enduro/reliability trial riding. (305 Ossa, 430 Husqvarna etc) ATF was the fork oil of choice for me in those days.

Tried it in the K100LT...MUCH too firm. Had some Castrol 10 Wt in the shed, put the required amount in and the front is now a shade better than perfect. I'm 115 Kg with the riding gear on. Tried 5 Wt, but much too "wallowly/insipid/soft"
Didn't try the 15 Wt. My understanding is that ATF is equivalent to about 20Wt.

Rickmeister.

G'day Rabidchiwawa007 , maybe a dumb question so don't flame me , you mentioned "auto store" , every bike shop ( store ) that I go into has shelves of fork oil in every weight , go get the right stuff for the job , could save you a lot of quessing & wasted time , I use a multigrade ( 0-20w ) fork oil , no drama's end of problem

not trying to be a smart arse , just suggesting

JR

Melbourne Australia

I agree.  I was referring to car auto shops, as there are no open moto shops near me today.  I ended up just using the ATF and all seems well.

 I'll put the right stuff in if I start getting problems or with the next change I do on them.

I also replaced all the Allen bolts for the brake discs with hex bolts of the same size and thread.  All my Allen bolts heads were stripped.  Pain in the arse to have to take the discs off just to get the front wheel off.  Anyways, I bought hex bolts and ground down the heads so they don't hit the forks.  I'm much more confident in the discs now, as I was able to torque them to spec better.

If you openthe pads right out in the calipers then they should lift of the disc and clear the wheel.  Only just but they do come off.  If you put a normal hex head bolt on the disc the clearance to the fork leg is very minimal to say the least. The button head cap screws only just clear.
I remove the two bolts that attach the caliper to the slider and then twist the caliper so the pistons and pads retract away from the disc and it will come over the edge and just clear the wheel.
You may want to put some gaffer tape over the caliper or wheel to stop scratching the paint on the wheels.

Ill give that a try next time, but I can say this much.  The calipers sit farther in under the wheel on this model than they did on my other (1985) model.

I made sure clearance of the bolt heads was more than acceptable via grinding the heads down.  It's about the same as the Allen heads were.  (No paint on the wheels, just cast metal)

I also manage to remove the wheel without having to take off the discs. Even with new discs and new pads the caliper does come off with a bit of wiggling. As Rick says some gaffer tape on the rim saves the scratches.

I always liked 7.5.  5 always felt underdamped.  10 was fine on the road, but we used to ride a lot of dirt and 10 was too harsh for that riding.  Also used to run a shade more oil than standard to reduce the airgap and reduce the fork dive, Tom Byrnes used to do that for the cop bikes apparently.

Al