Change to ATF in Conv.pump.

[Leif Holmberg]

Is it possible to remove the Brake Fluid in my 1956 Conv,Top pump system ,and fill it with ATF oil.

Thanks Leif in Sweden.

[Guest simplyconnected]

Keep ALL petroleum based oils & water, far away from your brake system.

The rubber seals are made for DOT-3 (alcohol base) fluid. They will swell and fail quickly if you use any oil. Because DOT-3 brake fluid is alcohol based, it should be changed every three years. Alcohol easily dilutes water. When it gets saturated, rust starts from the inside of your steel brake lines.

When you change old brake fluid you will see a red-ish color from rust. Keep flushing until the discharged fluid shows clear. New brake fluid will stop any further rust (until it gets saturated again).

I will NOT open my brake system on a rainy day. Make sure your unused DOT-3 container is sealed very well from the atmosphere.

Hope this helps. - Dave

[Leif Holmberg]

I have heard other people change their Brake Fluid to ATF oil in the converible pump system without problem,just wonder,how could they do that without change the rubber seals.I know it´s impossible to do that in the Brake system.

Leif in Sweden.

[JohnD1956]

There was a change along the way. Our 69 has ATF in the convertible top system. Are you putting new seals into the system when you make the change? All I can think of is that the ATF would have more resistance and thereby increased pressure when pumped, so seals treated to brake fluid for all these years may not hold as well.

[Guest simplyconnected]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Leif Holmberg</div><div class="ubbcode-body">...I know it´s impossible to do that in the Brake system.</div></div>

I guess, when you think about it, glycol makes sense. Convertible tops certainly aren't life-threatening like brakes are.

Back in '56, our seals weren't as versatile as they are today, meaning they were specifically made for certain fluids. We all know that ATF comes in Dextron and Mercron, so even THEY are different. Now, we have orange and green antifreeze that aren't compatable, either.

If your system came a certain way I would stay with it, rather than spending a lot of repair money just to find out it's not compatable.

Are you having troubles with leaks? I am interrested in why you want to change. - Dave Dare

[Guest 70 Electra]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Leif Holmberg</div><div class="ubbcode-body">I have heard other people change their Brake Fluid to ATF oil in the converible pump system without problem,just wonder,how could they do that without change the rubber seals.I know it´s impossible to do that in the Brake system.

Leif in Sweden.

</div></div>

I do not know what materials were used for the "rubber" seals in different convertible top systems, but I would agree with Dave about being VERY cautious. Some rubbers (like EPDM, for example) will swell and fail when exposed to petroleum products (including ANY ATF).

My 1960 Buick manual specifies brake fluid for the hydraulic top system, but my 1970 manual says ATF should be used if components are replaced.

If you are replacing all the hydraulics with new or rebuilt parts, I would ask the parts vendor if it is OK to use ATF. It is plausible that new/rebuilt components may be constructed to operate with ATF. However, I would strongly recommend that you not use ATF in an original system that specifies brake fluid.

[NTX5467]

Not JUST the seals might be sensitive to the type of fluid being used, but ALSO the rubber lines.

I think the service manual for my '68 5467 mentions wiping the "rams" on the hydraulic cylinders (when extended) down with brake fluid every so often (to keep them clean before use?), but I think the fluid for the hydraulics is not brake fluid. Seems like some of the convertible parts vendors sell a gallon jug of fluid with related tubing to purge (the system of air) and refill it?

Might be that the earlier systems were spec'd for brake fluid as that was thin and plentiful and easy to find, unlike ATF might have been back then? As more cars had automatic transmissions in later years, then using ATF in the system was not that hard to do (or find) rather than use hydrualic oil from construction equipment and such?

Just some thoughts,

NTX5467

[Leif Holmberg]

Thanks to all of you who answerd my question,it seems that I have to wait with ATF until I changed all the seals.

Thanks Leif in Sweden.