1978 f250 plow truck
Ive got a 1978 f250 with a snow plow on
the front. A few plows ago I started hearing
a rotational knock coming from underneath
only in 4wd moving forward or backwards.
It doesn't do it in 2wd. After hearing this I
had the front outer cv joints replaced but
plowing this afternoon I could still hear the
knocking/clunking. Are there inner cv's that
should also be replaced or should I be
looking for other issues. The truck has the
1ton axial with the lockout hubs.
Check U joints, and check rear seal.
Check to make sure your going into and out of four wheel drive properly. Make sure you got some weight in the bed across axles not to much but enough so the rear can have some grab. To much and you will find it's hard to steer with your wheels off the ground.
The last time I heard a rotational clunk from a differential it was a badly chipped tooth on the ring gear, replaced the ring and pinion and all of the bearings and the noise was gone. Note: if it is the ring and pinion it will get worse just before it fails completely due to all of the metal shavings being created at every clunk noise. HTH
Agree with TS,a clunk usually is in the gear,s.