[Schurkey]

Originally Posted by geeteeohguy

I've used Dexron, then Dexron II, then Dexron III, now it's called Mercon as the Dexron ATF's are all obsolete. Anyway, I've always used GM spec ATF in mine for the past 30 years with no issues. I even have the original pump and gearbox on my '67 with 242,000 miles on the clock. The main trick is to have clean fluid and to have enough of it.

Originally Posted by David Jones

I found it fairly strange that Power Steering Services would simply state that you needed to use whatever the mfg recommended and let it go at that.

Because it doesn't make a lot of difference, and they're too lazy to provide detailed recommendations.

Do keep in mind that ATF has "evolved" over the years, it's getting thinner (lower viscosity) and it has increasing amounts of friction modifier to condition the wet clutches and bands in an automatic transmission, As it becomes more specialized for AT use, it may have become less suitable for PS use.

Given a choice, I'd happily use whatever aftermarket ps fluid happened to be "on sale" at my local parts house in every vehicle I own EXCEPT my Trailblazer--the power steering was noisy as hell in cold weather until I installed the "special" GM cold climate PS fluid (at $16 per PINT!) When I flush that one some years from now, I'm going to try ordinary aftermarket PS fluid, but if I have trouble (noise in winter)...it'll be back to the expensive GM stuff again.

[David Jones]

Originally Posted by Schurkey

As it becomes more specialized for AT use, it may have become less suitable for PS use.

As I read along, that's what I gathered. I read when GM worked with the PS fluid maker (Texaco?) to come up with it's fluid they wanted to address some of the drawbacks of A/T fluid in a power steering system. One of them being how A/T fluid was changing regularly to better work in a transmission. Also to reduce the possibility of holding air in suspension.

Thanks! for your input.

[59safaricat]

Originally Posted by Schurkey

Do keep in mind that ATF has "evolved" over the years, it's getting thinner (lower viscosity) and it has increasing amounts of friction modifier to condition the wet clutches and bands in an automatic transmission, As it becomes more specialized for AT use, it may have become less suitable for PS use.

X2. I couldn't keep Dexron in the PS reservoir very long in my '59 after I brought it back from a 25 year nap. It got low again and I had a bunch of Type FA left over from changing the trans fluid on the 4 speed hydro, so I evacuated the Dexron and substituted Type FA. It never did leak a drop after that, and top of that, low speed performance ('59 389's idle at 480 RPM's) substantially increased.