Kohler K91 Owner's Manual page 206

0
Part-way through the 1979 model year, the charge pressure relief valve
on hydraulic lift models was changed from ball-type to conetype. Both
constructions are illustrated below, with part 'numbers given for the
cone-type valve system.
SERVICE NOTES
Oil The recommended transmission oil is
SAE 1 OW-30 or SAE 1OW40
engine oil. IMPORTANT: All 1972 and prior, and some 1973 models
use automatic transmission fluid (Dexron 1 1 ) . Determine type of oil in
these units Do Not Mix engine oil and automatic transmission fluid.
Units may have been changed to engine oil ,during prior overhauls. To
convert to engine oil, the entire system transmission, transaxle, hoses,
hydraulic lift valve must be totally cleaned O f transmission fluid.
Pressure Checks Keep in mind an "unsealed" condition anywhere in
the transmission will cause a low-or-no charge pressure condition.
Troubleshooting charts and the lack of charge pressure seem to point to
the pump section as the source of the problem. Experience shows
most
"loss
of pressure" conditions to be due to: sticking-acceleration or
forward/reverse check valves, charge pressure relief valves, o r a
problem
in
the motor section. Motor section problems are most
commonly snap ring, special retaining ring,
or
spiraloc retaining ring
failure, causing the motor cylinder block to lose i t s spring preload
against the valve plate.
Contamination Where dirt or failed parts have circulated through the
system, it is essential the entire system be disassembled and flushed
clean both transmission sections, the transaxle, hydraulic valve, and
hoses
o r
hydraulic manifold. Residual contamination will quickly destroy
the repaired unit.
Supplement 2