Convertible Pump Fluid - What kind?

[Guest Infinity Performance]

I'm seeing everything from lite weight motor oil to transmission fluid, compressor oil, brake fluid, etc.

Application is for a pair of 50's Cadillac's and I don't have a service manual.

Thanks in advance!

Jason

[Bhigdog]

50's Buicks call for brake fluid. Most folks use ATF to eliminate the brake fluid problems. If you are just adding fluid to what's already there you might have a problem unless you purge and flush before adding ATF.................Bob

[NTX5467]

From what I've observed with many automotive fluids, other than engine fluids, is that the particular systems were generally configured to work with "readily-available" fluids rather than otherwise. I feel this is why the convertible top mechanisms back then were typically spec'd to use brake fluid . . . it was in every gas station and auto supply, as a matter of course. Just as the per-1960 era power steering units were spec'd for Type A automatic transmission fluid, rather than a particular power steering fluid, as in 1961 and later.

One KEY thing is that whatever rubber items (hoses, seals, etc.) were spec'd to work with the factory-specified fluids. Putting something else in the systems could easily lead to leaks or other issues later on. For example, the few times I've purchased a used vehicle which had "red" power steering fluid (middle-1960s and newer, in my case), there has been an existing power steering "seep"/leak. Conventional wisdom would indicate that new hoses might be in order, but (after I'd found some NOS hoses that would work) I purged the system of the "red" fluid and installed factory part number power steering fluid . . . seeps/leaks stopped soon thereafter.

I would suspect similar would be the case with convertible top fluid systems. It's MORE than just the viscosity of the fluid, but the chemistry of the fluid and how everything else in the system is designed to work with that particular chemistry. Of course, some people tend to have better luck with such "cross-breeds" than others -- mine usually don't work -- be that as it may.

I tend to concur with Bob's idea that brake fluid would be the "spec fluid" for your model year of Cadillac, considering that Buicks spec'd brake fluid . . . and some of the hard parts are probably the same between Buicks and other GM cars of that era.

Just some thoughts,

NTX5467

[Curti]

I use low viscosity hydraulic fluid. It is a hydraulic pump.

[Guest Infinity Performance]

Thanks for the replies!

After cleaning out the lines it does appear to be brake fluid. It is consistant with what you see of older brake fluid in color, smell, and viscocity. After cleaning out the existing system I filled with new brake fluid just to see if it would work (the car hasn't been on the road since 1967....this is for a 1954 Eldorado). The top will only open about half way before things seem to fizzle out. Manually assisting it doesn't help. Although quite a bit more fluid was required to fill the system than what came out, the system does not appear to have an significant leaks in the pump, hoses, or cyclinders. I guess im attributing the initial lack of fluid to 45 years of no maintenance.

This is the first convertible I've relley messed with, and although I'm a pretty quick learner I really don't know much about them. Im guessing the pump is losing it's ability to keep adequite pressure to moive the top all the way through its cycle, but I could be off base with that assumption.

Everything on this car is original, and I know its history since the late 1950's as it was my grandpa's car. I'm not interested in replacing parts as I would prefer to rebuild as much as possible.

Any insite into this situation? Rebuild kits, pump rebuilders, similar experiences and fixes? At the moment, my goal is to clean it up and get in good mechanical condition to enjoy. I'm not sure a full resotoration is in it's future since all the chrome, paint, and interior are original and in decent shape.

[Bhigdog]

Your pump is probably just gummy and clogged. Possibly so are the lines. There is not much to the pump. It is easily disassembled for cleaning and the necessary O rings and/or seals easily available. New pumps, hoses, and cylinders are also available. Do check the cylinder's rods to see if they are rusty. If so don't fool with them just get new ones. BTW, one good reason to use ATF is it will not remove the car's paint like brake fluid will. Be VERY carefull with brake fluid around your car's finish...............Bob

Edited March 11, 2013 by Bhigdog (see edit history)

[impala]

BTW, one good reason to use ATF is it will not remove the car's paint like brake fluid will. Be VERY careful with brake fluid around your car's finish...............Bob

Exactly, I wouldn't use brake fluid because any little leak or seepage is going to ruin the paint or trunk spatter paint, etc. As mentioned earlier it's a hydraulic pump so use hydraulic fluid or ATF.

You can't assume the pump is bad without some diagnosis. I would disconnect the cylinders at the top and operate the top by hand (this might require a helper). I bet you're going to find binding linkage which requires freeing up and lubricating every joint from front to back.

impala