Deck came with 345 - I bought it new in 2002 from JD dealer.
I thought I had it figured out yesterday before my post. Everything was tight. Clearance between drive belt and adjacent pivot bolt looked like about 3/8" maybe as much as 1/2". I did not measure. I ran the tractor yesterday and cut approximately 1/4 to 1/3 of an acre. Was working fine before drive belt burned off. No vibration noticed although I suspected something might be wrong just seconds before it broke. I did not smell rubber burning - break was quick which might suggest jack sheave shifted allowing belt to jump into adjacent tension idler sheave arm pivot bolt assembly.
I believe it has something to do with the jack sheave. I am going to try to look at it again later today.
This deck was originally sold with the GX345. When I bought mine, I beleive I was inquiring about bagging attachment (thinking into the future) so they included a 54C deck with my purchase. The 345 was listed supplied with up to a 48C and only a regular 54 deck. The service manual for the GX345 lists all the schematics (very clear) of the 54C deck. The 345 manual, only the 54 (not as clear).
The machine has been great for us. Every couple of years the deck needs some service (blades, belts, minor) as we have about 3-1/2 acres to cut.
If you have a 54C, can you measure the clearances and distances around the jack sheave pulleys for me and the springs behind the jack sheave pulley.
Might help.
PS
Belt is JD - always JD parts
also can you measure clearance between drive belt and adjacent pivot bolt cap and whether belt is directly next to this cap along same horiz. plane or if the belt sits a bit higher to avoid any horizontal contact.
thanks in advance for any help.
sam