* Age and Condition: A 30-year-old transmission likely has seals and gaskets that are hardened and brittle. The flushing process, especially a power flush, can dislodge debris and put pressure on these weakened seals, leading to leaks.
* Type of Transmission: Without knowing the specific transmission type (automatic or manual), it's hard to say for certain, but older automatic transmissions are particularly vulnerable to damage from a harsh flush. They rely on the old fluid's properties to help maintain seal integrity. A complete flush removes that beneficial "gunk."
* Fluid Degradation: While a fluid change is beneficial, a complete flush might remove the small amount of naturally occurring friction modifier that helps protect the transmission.
Better Alternatives:
Instead of a full flush, consider a drain and fill method. This involves draining the old fluid, replacing the filter (if applicable), and then refilling with the correct type and amount of new transmission fluid. You can repeat this process a few times over several days/weeks to gradually replace most of the old fluid. This is much gentler on an older transmission.
In summary: Unless your 1993 Isuzu pickup has a very specific transmission problem requiring a flush, it's generally recommended to avoid a full flush. The risk of causing more damage often outweighs the potential benefits. A drain and fill is the safer and more appropriate method for maintaining an older transmission. Consult your owner's manual for the recommended fluid type and capacity.
