C3 Hydraulic Power Steering System - Fluid Change / Bleeding

[Ray K.]

After sitting for a period of time, I'm in the process of getting my 1971 Corvette w/power steering back on the road again this summer. In doing so, I've heard that I need or should change out my power steering fluid. Looking thru the service manual, I don't see any reference to "just" changing out or bleeding the system. Can someone help? And what is the "latest and greatest" type of power steering fluid should I replace the old with the new? Thanks. . . . .

Ray Krawczyk
NCRS Member #43777

[Jeffrey S.]

Re: C3 Hydraulic Power Steering System - Fluid Change / Bleeding

Ray,
Bleeding is addressed in the "Maintenance and Adjustments" section of the service manual (at least it is in my '69 manual). Simply raise the car off the front wheels, increase engine speed up to 1500 RPM, and turn the wheels right and left lightly contacting the stops. If the oil remains foamy, let the car sit for few minutes, and repeat the procedure Hope this helps.
Jeff

[Duke W.]

Re: C3 Hydraulic Power Steering System - Fluid Change / Bleeding

The fluid change procedure is probably the same as I've used on other cars. It takes at least two and maybe three people.

The fluid should be hot and the front wheels off the ground. Siphon the old fluid out the reservoir and replenish with fresh fluid.

Disconnect the return hose and secure it to a container under the car or have the second helper hold the hose so doesn't pop out of the container. Have helper #1 standing by with a quart of fresh fluid to replenish the reservoir.

Start the engine, let idle and slowly move the steering wheel back and forth about a quarter turn each way. The reservoir level will rapidly deplete, so the helper with the fresh fluid needs to rapidly replenish it. This all happens fast!

Once about 3/4 of the quart of fresh fluid is used, the helper should tell you to shut off the engine, then quickly reconnect the return hose, start the engine and slowly turn the steering wheel back and forth until there are no visible bubbles in the reservoir adding fluid as necessary.

Shut off the engine and fill the reservoir to capacity, and check after a short drive.

The original fluid spec was ATF, but it was an old version. I expect the latest DEXRON spec is okay and maybe generic modern "power steering fluid" is too. I don't know, but others likely have experience with current products and can report.

I used the above procedure successfully for my '88 MBZ. The reservoir has a filter at the bottom that I changed after draining the reservoir, but I don't think vintage Corvettes have a filter in the PS system.

I went through a long analysis process on what type of fluid to use in the Merc, and ended up using generic PS fluid. There are two types, one for most vehicles and one for Hondas, only. I never did figure out what is unique about the Honda-only fluid.

I also evaluated industrial hydraulic fluids. Most are relatively "light", similar to SAE 10 engine oil. They have a good dose of anti-wear and anti-foaming additives, but little or no detergent/dispersant additives like engine oil. For arctic climates, "synthetic" base stock hydraulic fluids are preferred since they flow better at extremely low temperatures, but most are mineral oil based.

Over time the fluid will oxidize and become contaminated with wear particles, so it's a good idea to change, say every 30K miles and this will likely increase the life of the system before it needs to be overhauled or resealed.

Check the service manual/AMA specs to get the fluid capacity. My rule thumb for flushing brake/PS systems is to flush through about double the system capacity to get a thorough flush when starting with fresh fluid in the reservoir. The capacity is likely about a pint or so, but check the specs and flush through about double the capacity.

Duke