1965 Buick Wildcat power top hydraulic fluid

[Norm R]

My 1965 full size Buick body manual indicates the use of "Delco #11 Hydraulic Fluid (GM Hydraulic Brake Fluid Super #11 or its equivalent)" for the power top reservoir.  What current fluids can I use?

[NTX5467]

The fluid used in the convertible top cylinders MUST be compatible with the seals in the power cylinders and pump.  UNLESS it's been converted OR a newer-spec fluid has been flushed through and into the system, that original GM specification brake fluid (now DOT3, I believe, is the equivalent of the Delco Supreme fluid, which is "normal brake fluid, anyway) should be used.  Used CAREFULLY due to its negative affect upon painted surfaces!

 

Convertible top fluid probably should have been a particular viscosity of either hydraulic fluid (as power steering fluid) or motor oil, but brake fluid was of ONE viscosity and it was "everywhere", so that was the fluid of choice.  As generic as hydraulic fluid and motor oil might have been, there were many different formulations and additive packages, other than just normal viscosity . . . all of which could affect the pump's ultimate performance AND would need costly and time-consuming flushes to get things right again.  So, "common old brake fluid" was the fluid of choice for many years.

 

You CAN get the hydraulic system converted to a (now) better fluid.  Some of the convertible mechanism supply shops have it.  Possibly it is compatible with the existing brake fluid, too?  But for now, I'd recommend you use the normal brake fluid (DOT3 or DOT4) non-synthetic brake fluid from a closed container.  Brake fluid still absorbs moisture, as in the past.  There is also a recommendation that when the hydraulic rams are extended, to wipe the exposed surfaces with a rag moistened with brake fluid to keep them clean.  Again, be very careful to protect any painted surfaces from brake fluid drops!

 

NTX5467

[Norm R]

Thanks NTX5467 for your very detailed explanation.  Now I guess my next problem is to find non-synthetic brake fluid as it seems all the brake fluids I see today ARE synthetic.

[NTX5467]

The DOT3 fluid is still around almost everywhere.  DOT4 has a higher temp rating, but that's not needed for a convertible top application.  The DOT5 fluid is silicone and the other version of DOT5 (DOT5.1?) is synthetic.  Last time I looked.  DOT4 appeared, in GM, with the Aussie Pontiac GTO cars, as I recall.  All other GM cars still used DOT3 at that time.

 

NTX5467

[Norm R]

Hi again,

 

I can find DOT 3 and 4 readily but they are all synthetic.  I checked with some of the larger auto parts stores and none have non-synthetic  in any DOT rating.

 

 

[old-tank]

5 hours ago, Norm R said:

Hi again,

 

I can find DOT 3 and 4 readily but they are all synthetic.  I checked with some of the larger auto parts stores and none have non-synthetic  in any DOT rating.

 

 

And they all say they are compatible with any other DOT 3-4 fluid.  Synthetic in this case may just be a marketing buzz-word.  DOT 5 is synthetic, but silicone based and will not mix with other fluids.

[Norm R]

Thanks old-tank.

[kgreen]

I was curious as well and consulted the HAMB pages and kept getting speculation and "what oughta' be" answers.  Here's what Prestone, a manufacturer of brake fluid says:

 

Good Afternoon Ken,

 

In the context of brake fluid, the word ‘synthetic’ is entirely meaningless.  All DOT 3/4 brake fluids are synthetic by definition, the glycols they are made from are not naturally ocurring so it is not possible to make a ‘conventional’ brake fluid. 

 

All DOT 3/4 brake fluids are compatible with all other DOT 3/4 brake fluids, as a requirment of the specifications that define DOT 3/4 brake fluids.  The reason DOT 3/4 fluids cannot be mixed with DOT 5 is that DOT 5 is silicone based, which is chemically incompatible with the glycol based DOT 3/4 fluids. 

 

We do not have any white papers on this subject, however a more brake fluid specific company, such as Castrol, might be able to help you with that.  Please let me know if you require anything further.

 

Sincerely,

 

Aaron Jones

Prestone Consumer Relations Representative

[Norm R]

Thanks to you also kgreen!  I think the answer to my question is to simply use any good quality current DOT 3 or DOT 4 brake fluid.