Paul writes:

I have a Sears front wheel drive lawn mower, 21 inch 6.75HP, model #
917376551, that is about 6 years old. Today while mowing, when I
engaged the front wheels by squeezing the lever on the handle, I
heard
something €œPOP€� and then the wheels froze up. The drive wheels had
been making a €œslipping- as if a gear inside wheels was slipping and
then re-engaging€� noise periodically for the past few months. I took
the plastic cover off the drive assembly area and the cable from the
handle lever is not broke, it stills seems to move the lever that is
attached to what appears to be a gear box. Both wheels are frozen and
will not turn by hand. I read some of the previous posts in the
forum,
but still getting educated on mower repair. Any ideas on further
troubleshooting to see 1) what problem might be 2) is it something I
could repair(reasonably handy) 3) not cost effective to repair 4) or
any other things I failed to think of ? thanks in advance for your
help.

No experience with gear drive, but I'd suspect ground up gears.
Can you detach the gear box or open it?

--
Dan Espen