I recently bought a D6 9U VIN 9U6706. It has already been converted to electric start. The problem i am having is the started will work fine for awhile then for no reason it sounds like it is just free spinning and not engaging. I am assuming the solenoid is bad. Am i thinking correctly. Batteries are fully charged. If it is the solenoid what size solenoid should i get or where should i get one. Please help me out if yall can. Thank yall in advance.

If it spins it is not the solenoid, as that is what gives it juice to make it spin. Maybe a weak spring or just dirt holding the bendix gear from moving out to engage the ring gear. Or worst case the starter is weak and not spinning with enough speed to spin the bendix gear out. Thy pulling starter out and clean and lube the bendix.

Exactly as Ray said. It is a bendix issue.

May be a dumb question but can you explain what the bendix gear is. Is that a brand or what the exact part.

The bendix is the gear that engages the ring gear to rotate the engine for starting. It is engaged due to centrifugal force from the rotation of the starter motor.

Thank you sir

if i have to get a new bendix, do you guys have any recommendations on what brand or where to get one?

I would take it out, clean it and lube it with a dry graphite lube. Sounds like it is sticky is all. If a new one is needed, I would go to a good parts house and get one matched up. Brand a non-issue with them.

yes sir thank you

Good luck trying to find one of those old inertia type starter drives.
Generally winds up having to upgrade to one of the 40MT, 42MT or 50MT conversion starters.