EXPERTEC TSB (41-1)

EXPERTEC TSB

TECHNICAL SERVICE BULLETIN

AUTOMATIC TRANSMISSION - SUPPLEMENTAL ADDITIVES

Model(s):

Bulletin No.: Oldsmobile 41-1

Date: 09/30/1990

SERVICE INFORMATION

UNDER NO CIRCUMSTANCES DOES GM RECOMMEND THE REGULAR AND CONTINUED USE OF ANY SUPPLEMENTARY ADDITIVES IN GENERAL MOTORS AUTOMATIC TRANSMISSIONS!

Dexron-II approved Automatic Transmission Fluids (ATF's) are a delicate blend of approximately 90% refined petroleum oils and 10% of an additive package. These additive packages are used to enhance the chemical and physical properties of refined petroleum oils, and are comprised of friction modifiers, viscosity index improvers, dispersants, anti-oxidants, corrosion inhibitors, anti-wear agents, anti-foam chemicals, seal swell compounds, dye, etc. The amount and type of additive package used is dependent on the chemical and physical properties of the original refined petroleum oils used. This is done in order to match the chemical and physical properties of the refined petroleum oil used with those of the additive package used. Too much of an additive can upset this balance and be as bad as too little.

In an understandable effort to maximize customer satisfaction and to improve the "smoothness" of transmission shifts, some service areas are adding supplemental additives on a regular basis to the automatic transmission fluid. In light of this, the Hydra-matic Division of General Motors ran performance evaluation tests on a number of commercially available supplemental additives. The results of these tests indicate that the effects of adding these products to Hydra-matic automatic transmissions can range from having no beneficial effect to causing premature faiture of the transmission.

Many of these supplemental additives contain chemicals called friction modifiers. The purpose of these chemicals is to allow intentional "slipping" or "sliding" between band and clutch friction materials and the metal surfaces they contact. The duration of this slipping is often referred to as "lock-up time". When too much friction modifier is present in an ATF, excessive slipping occurs. This results in longer lock-up times and thus smoother short term shifts. This excessive slippage between the frictional material and the mating steel surfaces results in greater heat being generated at these surfaces in the transmission. Temperatures as high as 900 degrees F have been reported under sever conditions. These excessive temperatures not only break down the ATF, but also glaze and burn the frictional materials as well as cause seals to become brittle, resulting in premature failure of the transmission.

In addition, too much friction modifier can greatly decrease the "static capacity" of a transmission band or clutch (decreases of up to 50% have been reported). The static capacity is a measurement of how resistant a clutch pack or a band is to slipping once it is already locked-up (its load holding capacity). This decreased static capacity can result in the clutch or band slipping when put under heavy loads that occur when towing or passing, resulting in burned or glazed frictional materials.

Due to the previous information listed, the use of General Motors Limited Slip Differential Lubricant Additive, a strong friction modifier, in an automatic transmission has been reported to cause the silicone seals to dissolve, clutch plates to glaze/burn, and negatively affect the ATF's original properties.

Furthermore, adding a supplemental additive to an automatic transmission CANNOT "rejuvenate" the petroleum oil once it has deteriorated. The search for an additive that can rejuvenate used oil is much like Ponce de Leon's search for the Fountain of Youth.

The exception to this rule is the use of a supplemental additive that contains only seal swell compounds. This type of additive may help stop a small leak in an older transmission. Larger leaks are indicative of worn, cracked or partially deteriorated seals and should be addressed by replacing those seals.

If a customer feels that their automatic transmission fluid has seen better days, help it out by changing the fluid. DEXRON-II approved Automatic Transmission Fluids contain the proper additives in the proper quantities and are blended with newly refined petroleum oils.