Problems in Connection with Flushing of Gear Cases

 Different problems may arise in connection with flushing gear cases. First the used oil should be removed from the case as  completely as  possible so that  contaminants  are also  removed  and none  of the Oxidized  oil  remains to act  as a catalyst  for the  fresh oil. In so doing, if a volatile solvent is used, this should also be removed completely. Very little of a solvent is required to reduce the viscosity of gear oil, and naturally this is undesirable. Further the  gears should not  be left  without  a coating  of oil  for even a short  period because  rusting  will take place  under  such  conditions. Also  the gears should  not  be  operated  without  a coating  of oil,  even though there  is no load. Troubles have been encountered when gear cases were washed out with chlorinated solvents. 

                                                                 

After fresh oil was added, corrosion developed because some of the solvent was trapped in the case. The best correction for this problem is not to use such a solvent. In fact the safest course in flushing gear cases is to use prepared flushing oil. 

Power Steering Gear Fluids

As a base for such a fluids, a solvent refined oil of about 250 viscosity SUS at 100 degree F may be used. While , as Johnson and Mortensen state, the major requirements are shear  stability  and high  V.I., the oil should  also  be  resistant  to oxidation and  have no  adverse effects on both metals  and  seal and  hose  materials. Likewise the blended oil should have a low pour point. All of the above point to a solvent refined oil which will have the desired high V.I. and aniline number.

Chrysler MS 3590 “Hydraulic Steering Fluid with Rust Preventive”, summarizes the composition requirements as follows:

“Well refined oil with admixture of proper rust preventive additives. Small amounts of oxidation inhibitor and pour depressant may also be used to meet the details requirements. The use of   detergents and V.I. improvers is prohibited. The additives small be selected to have a minimum effect on the seal and hose materials”.

Therefore, additives may  include up to 0.5 per cent  of an  oxidation inhibitor, such as  can be  recommended  by  an  additive supplier, or  may  be  phenyl  alpha napththylamine , 2,6-ditertbutyl – 4- methyl  phenol, mixtures  of these  two  types, or  an oil-soluble  organic thiophosphate salt of certain  metals, such  as zinc  methylphenyl  dithiophosphate.

If the pour point of the oil is above -20 degree F, from 0.2 to 1 per cent of a pour depressant, such as “Acryloid  150”, “Paraflow”, or “ Santopour C”, can be added.

Suitable rust inhibitors, used in concentrations of 0.5 to 2 per cent, include petroleum or synthetic sulfonates, such as “Petronate” or barium dinonyl naphthalene sulfonate. A combination oxidation and rust inhibitor, which is usually used in a concentration of 1 per cent or less, is “Vanlube 76”.