Is it OK to mix power steering fluid with transmission fluid in 70s and earlier GM power steering pumps without any issues?

 

NEVER use power steering fluid in these vintage cars. ATF only. The steering gearbox rebuilders will void the warranty if you use power steering fluid. They can tell as soon as they take them apart what fluid was used.

 

Could you elaborate on this?. I figured power steering fluid is just a version of hydraulic oil and the power steering pump is just a hydraulic pump. The ATF fluid is similar right, but perhaps with an additive package? Curious on what damage either could be causing the pump.

 

I've always used ps fluid in my '72 Supreme since I bought it 4 years ago with no issues. I never knew to use ATF

 

I've used both PS fluid and ATF, never saw a difference in 40+ years. I doubt mixing will cause any harm either.

 

I'd like more information about steering box rebuilders voiding the warranty when PS fluid is used. I've never heard this before. What damage does it do?

 

I used both for many years, no issues!

Pat

 

I do not know what the difference is but if you get a gear box rebuilt, the paperwork you get with it will tell you this. I asked the power steering services guy about it in 2013 when I have one rebuilt and he said something about a waxy film all over the parts that is left with PS fluid. He said he can tell instantly just by touching the parts what fluid was used.

 

OK, The same place that had that note with the gear box I had rebuilt now says this..... So I guess now it is ok?? When I get home I will dig out the old paperwork I got that said to never use ir.

http://www.powersteering.com/blog/20...teering-system

 

I just had A PUMP, not the box, rebuilt by Cardone through Rockauto, the information they put in the box said to use power steering fluid.

 

CSMs for years specified use of PS fluid in the systems and that ATF _could_ be used to top off the system if less than a pint was needed.

I suspect that caveat was similar to Jasper's transmission warranty that required bypassing the radiator oil cooler and using an external air-to-air cooler.

I've never had any issues using either ATF or a designated PS fluid. Eric, you sure they weren't talking about a stop-leak type of fluid?

 

Rocketraider, I recall pretty much the same thing from an Olds dealership mechanic. He told me ATF was half the price of PS Fluid.

 

So, the consensus is that it is OK to mix them?

 

yes, I believe the concern in using transmission fluid was the transmission fluid has additives like detergents etc that may harm seals over a period of time. If you are using a rebuilt pump check with manufacturer .

we always used tranny fluid in the pump , I worked at a Sunoco station many many years ago ( we still sold 260 for less than half a buck a gallon lol) and we’re required to wash your windows check air and fluids. There was always a half can of tranny fluid to top up the pump .

 

We could just read the owner's manual...

 

party pooper ……lol


case closed I guess :-)

 

When I added ATF to mine for the first time It stopped leaking on the floor in the garage when parked....so far

 

Problem here is a whole lotta these cars no longer have their owner's manual, and those that still do, provided the owners even read them they don't know what kind of neat information is in them.

 

Add to that the fact that owners' manuals were written some fifty-odd years ago and fluid and ATF formulations have doubtless changed since then.

 

The same information is in Section 0 of the CSM.

 

Joe- if people haven't tried to get a year correct owner's manual, do you think they've tried to acquire the service publications? Or even know those exist? Just sayin'...

That's why the first thing a lot of us recommend to a newbie is buying the shop books. I don't mind using mine to help or answer questions, but there's just something about having your own print copy, complete with decades of grease smears and garage smell embedded in the pages!😎

Maybe even some PS and ATF smears!

 

I avoid PS and ATF smears by having an 'in the garage' copy and an 'in the house' clean copy.

 

So. The steering system is a hydraulic system in a basic form. The transmission is also a hydraulic system in a away. The difference between the 2 is . Transmission fluid has detergents which are not bad considering transmission fluid is pretty dirty in nature but it also has friction modifiers which help with some of the " rough " aspects of a shift which is why hard core race guys use type F or straight hydraulic fluid for transmissions. Power steering fluid is more basic . No clutch materials to deal with no slip factors or major wear to really warrant fancy fluid.

So with that in consideration take a look at how a power steering system works. It has no clutches. It uses rubber seals like a transmission will on drum assemblies. It's a fluid that never really gets changed so " dirty " . Its turned by a pump like a transmission does.

The only thing that is different is the operating temps and application pressures . Transmission fluid expands a hair . But not enough to hurt the power steering pump imo. If anything the transmission fluid is better than typical power steering fluid by design. But I can be wrong on that. That's just my thoughts tho. Both system kind of do the same thing. The power steering is less prone to be affected by viscosity . I have ran 15w40 in leaky gear boxes. The only time it was affected was on below zero days in the Midwest.

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