The service manual for my Softail calls for 26 oz. of oil in the primary which is an amount to just get to the bottom of the diaphragm spring. So, what harm is caused or what performance is degraded if the primary is overfilled, say to 1 qt.? One quart is only part way up on the bottom of the spring, so not far. Thanks.

(btw - I use Red Line MTL and change it every 5000 miles)

 

I was told that it could cause it to become more difficult to shift, and possibly cause the clutch to slip........

 

Just ride it......one quart is not going to make any difference compared to one quart. A little overfilled is ok and your bike will never know the difference.

 

You could ride it to see if there is a difference or just drain 6oz.

 

As far as I can tell, an excessive amount of oil in the primary will effect clutch operation only. When a clutch is engaged oil is squeezed out from the plates in order to grip. If the level is excessive the extra fluid in the basket will slow this function down. You willfeel it immediately asslip.Doubtfull a slight variation in oil amount would have any effect that you would notice.
Ron

 

Were talking about 3/4 cup of oil.
In that big ole primary, I don't think it's
anymore than a few drops in the ocean.
Even thoughthe book calls for 26 Oz -
6 Oz = 3/4 cup spread overxxx square inches
will not make a very big splash.