I've got an 09 Fatbob. When starting out cold for the first few miles the transmission shifts relatively smoothly and quiet. After 10-20 miles, when everything warms up completely, shifting from 1-2 and 2-3 starts to get clunky. Upper gears are still butter smooth. Transmission has Syn3. Do I need a heavier gearbox oil to keep it smooth? Why would a 20w50 sythetic thin out enough to change shifting ease?

 

If your using HD syn3 I have news for you, that is a synth/fossil blend and not worth more than reg. HD oil, which is also over priced! However I can't explain why you feel your gears are clunky,can you elaborate>?

 

Lots of expansion goes on during warm up.

Might be your primary chain getting too tight as things expand.
The auto adjuster might be a click or two too tight. (one possible cause).

 

Actually, Syn3 is a (legally) full synthetic Group III oil. It is NOT a blend.

To the OP, as far as the clunk, check your fluid level and if okay, move on and fuhgetaboutit.

Gear oils that read 75W-90 are NOT the same as a 75W engine oil. No way, no how. A 75W-90 gear oil is around like a 10W-40 engine oil. Maybe a tad more, but not much.

The viscosity of a 20W-50 engine is just fine for a transmission.

 

Make sure you clutch adjustment is spot-on at the clutch basket, and the cable.

 

First adjust your clutch. Then get some Redline Shockproof Heavy gear oil for your trans. It is the bomb. 75w250.

www.redlineoil.com

BTW, my dealer stopped using Syn3 in transmissions 3-4 years ago after several came back for warranty work. They now use BelRay 85w140 gear saver which is also excellent.

 

I just had my 1000 mile service with all things adjusted and fluid changed and dealer verified everything is OK, the bike shifted just as you explained. It's probably nature of the beast. I might try the Bel Ray or Red Line Shock Proof gear oil to see if it makes a difference.

 

Primary oil effects that too.

Low fluid level in the primary will indeed give you stiff shifts.
My buddy had to shut off his bike at toll booths because neautral was so difficult to find. Shifting was stiff. Upon adding 8oz to his primary, all is fine now. The indy that worked on it last only threw a quart in there after having the primary cover off. His bike called for 38 dry and 45 wet.

Take off the derby cover and check for yourself. Trust no one.

 

Shifts to 4th, 5th & 6th are quiet and smooth, no noise at all. Clunky only from 1st to 2nd & 2nd to 3rd when transmission heats up. When transmission is cool, all shifts are pretty smooth and quiet. I'll check clutch adjustment. Transmission fluid level is good. Haven't checked primary yet. I'll be doing 5000 mile service in a few weeks, I'll check it then.
thanks,to everyone for their input and ideas. I've got plenty to think about now. I'm probably just not used to the Harley yet.