Old car transmission flush-- effect on seals?

I have a '93 Jeep Cherokee with about 175,000 miles on it. Not having any problems but it’s time for a transmission flush I think. Last one was at 120,000 miles. My AAA-certified mechanic said that changing the tranny fluid may affect the varnishes and stuff holding the seals together and so the transmission might leak after the flush. Is this a real concern?

With a flush, especially on your old trans, there is a concern that pieces of varnish or sediment will get stirred up and find their way into the valve body. Then you’ll have bigger problems.

The safe and recommended method is to drop and clean the pan, change the filter, then refill with fresh fluid. You are overdue for doing this.

Do not do a flush unless you want the transmission to stop working. Just change fluid and filter.


Yes I was hollering

3 responses, all saying do not flush. Appears we have a consensus. I won’t flush but will have the pan dropped and the filter and fluid replaced.

Thanks to all.

Very different vehicle, but a related anecdote. My wife’s BMW was leaking transmission oil around the shifter shaft when I replaced her tranny oil and filter for the first time at 100k miles. The seal is on the inside, so the tranny has to be dismantled to replace the seal, so I didn’t. Interestingly, the leak stopped soon after I put in different fluid. That was 40k miles ago.