model 6216 Simplicity unable to put into 2 & 3 gear

Goes smoothly into reverse and 1st gear. Only excessive force will put it into 2 & 3. Any hint what may be happening?
Also, what is the procedure to remove the rear axles? Want to remove the shroud (which includes the batter platform, etc) that is captivated by the design of the right side of the shroud around the axle, i.e. the shroud has a hole on that side. Left side uses a modified 'U' bolt. Manual shows only a design with modified 'U' bolts on both sides.
Model 6216Simplicity (Mfg Nr.1690688 - 1671), 1671 is the serial number. Purchased in 1982.
Thank you, Vern
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Vern wrote:

Shifter fork worn or perhaps clutch? Don't know anything about specific model so just the generic manual transmission stuff that would be the normal suspects would, I think, be the same suspects here.

Probably requires disassembling drive case that would presumably include integral differential.
No exploded parts diagrams available online? Looking for that would be where I'd start, but I've no experience w/ Simplicity so don't have a clue what they have available.
If online fails, what's their service network? Maybe local dealer has repair manuals would let look at? JD green is good that way; no idea again about Simplicity.
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