View Full Version : Convertible hydraulics...what fluid & how to bleed
07-11-2010, 09:56 PM
Looking for some advice on what fluid to use when replacing all the original hydraulics on my '57. New pump, cylinders, lines...all of it. The replacement pump I got came with ATF in it, would that be the best bet on a fresh system? Seems it would be less hazardous that brake fluid, especially if a leak developed on down the road. Also interested in what the procedure is to bleed the system...anyone have links to a good detailed article? Thanks!!
07-13-2010, 09:33 PM
We have a convertible '55 and when we bought it, the pump reservoir was pretty empty. What was in there looked really dirty. I used a thin tube and hand-pump to pump out as much as I could, and did not bleed it to get it out of the pistons or the hoses. I filled it back up with silicone brake fluid, that I was told was used in motorcycles, and was not caustic. After filling up the pump, it works fine, even with what I'm assuming is a combination of old dirty brake fluid, and clean fresh silicone fluid. If I would have had the time, I would have disconnected the pistons, blown air through the lines, and pumped the pistons to pump out the old fluid...but I didn't. Anyhow, I would recommend just disconnecting the lines to blow them out, drain out the pump, and then try to actuate the pistons to see if you can force out any fluid. I suspect that if you push the piston rod down into the cylinder, sucah is when the top is down, that should force out the fluid, but that's just a guess. Let me know if you come up with anything concrete. The good news is, mine has had not problems for 3 years like that, although I rarely activate the pump. I keep the top down all the time, but I did just put it up last week, and it workd fine.
07-13-2010, 10:20 PM
The first thing you should do is get a shop manual. The convertible top and hydraulic system is covered fairly well in there.
The system does run on brake fluid. The shop manual says to use "Super #11" fluid. I didn't know what that was until I found in the shop manual that that's what GM called brake fluid in 1955. ATF is totally incompatible with brake fluid!!!! And the seals in a system that uses brake fluid. :eek: I can't stress this enough.
The system is self bleeding. All you have to do is operate it, and top off the fluid until the level becomes stable.
07-20-2010, 09:55 AM
Rick, why do you suppose the new pump came with ATF in it? I bought all new stuff from Classic Chevy...pump, lines, cylinders. Seems if ATF is harmful to the system they wouldn't have sent the new pump already full of it. Even has a tag on it that says "contains ATF". Any further thoughts? Thanks!
07-20-2010, 07:50 PM
If you're starting all from scratch, you shouldn't have any issues. I think the point Rick was making is you can't mix the two if you had Brake Fluid in the cylinders and ATF in the new pump for example.
I'm going with ATF in mine as well.
07-20-2010, 08:04 PM
Seals and rubber hoses that are compatible with brake fluid are usually not compatible with ATF, and vice versa. But if all the parts that contain hydraulic fluid were purchased together, I'd think you're OK.
Personally I'd rather have an ATF based system than a brake fluid based system, just because of what brake fluid does to things when it leaks. The only downside is that your top mechanism may not work well in really cold temperatures, but who cares?
What I would suggest you do is go over to chevytalk.com and post your question in the stock 55-57 forum. Hopefully a guy that goes by "67SS427" will respond to your question. Or go there and send him a PM. He's one person who's on these forums that I feel sure can give you an expert answer, as he's done several 55-57 convertible restorations, and he's quite a helpful and knowledgeable guy.
07-21-2010, 11:47 AM
Thanks for all the help guys. I'll see if I can track down the guy at chevytalk as well for confirmation.
07-21-2010, 06:00 PM
Hey gang, for future reference, tow members at Chevytalk.com were able to confirm that a clean hydraulic system works totally fine with ATF and has the added benefit of being a much safer (less destructive) fluid. I'm going with it on my car, and hopefully this sting will be of help for others!
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