54 brake fluid

[Guy M.]

Im getting ready to fill my brake system. Is it best to use silicone fluid at this point or is regular stuff ok. What have you folks used. Thanks for the info!

[Mike M.]

Re: 54 brake fluid

been using silicone since early 80's. no problems(including crossing the rocky mtns).mike

[Duke W.]

Re: 54 brake fluid

Unless you have thoroughly flushed (with denatured alcohol) all brake pipes and hoses and have assembled all hydraulic components with DOT 5 silicone fluid, stay with DOT 3 or 4 polyether glycol-based fluid.

DOT 5 is not miscible or otherwise compatible with glycol based fluid and conversion to silicone should only be done if you start with EVERYTHING flushed of all traces of glycol fluid and thoroughly dried of alcohol solvent.

Duke

[Russ S.]

Re: 54 brake fluid

Unless you have thoroughly flushed (with denatured alcohol) all brake pipes and hoses and have assembled all hydraulic components with DOT 5 silicone fluid, stay with DOT 3 or 4 polyether glycol-based fluid.

DOT 5 is not miscible or otherwise compatible with glycol based fluid and conversion to silicone should only be done if you start with EVERYTHING flushed of all traces of glycol fluid and thoroughly dried of alcohol solvent.

Duke

Duke, I know what you said is true, but what happens if there are small traces of dot 3 left in the the systems and you put silicone in?

[Mike M.]

Re: 54 brake fluid

Unless you have thoroughly flushed (with denatured alcohol) all brake pipes and hoses and have assembled all hydraulic components with DOT 5 silicone fluid, stay with DOT 3 or 4 polyether glycol-based fluid.

DOT 5 is not miscible or otherwise compatible with glycol based fluid and conversion to silicone should only be done if you start with EVERYTHING flushed of all traces of glycol fluid and thoroughly dried of alcohol solvent.

Duke

duke is correct. i neglected to mention the lines/calipers/master cylinder need to be new or thoroughly flushed if previously exposed to DOT products. my old 65 FI roadster had all its brake pieces replaced before using silicone and that was in the late 70's or early 80's.mike

[Duke W.]

Re: 54 brake fluid

Sludge can form in the system depending on how much glycol fluid remains, but it could take some time - possibly years.

If you plan on keeping this car my recommendation is to stick with glycol and flush it periodically based on your climate and driving conditions or disassemble everything and clean as necessary to remove every last molecule of glycol fluid and then assemble the hydraulic components with silicone and fill and bleed the system as required with silicone.

Since silicone will not absorb water, the periodic change requirement is effectively eliminated unless water gets into the system through seals or the master cylinder vent (if it has one). Any water will will remain separate, and I think it will go to the top since I recall that the silicone fluid has a specfic gravity greater than water.

Duke

[Terry M.]

Re: 54 brake fluid

I put DOT 5 (silicone) in my 1970 when I had the calipers sleeved with SS. I just flushed the lines with alcohol, blew them out with shop air, and rebuilt the master cylinder, installed the SS sleeved calipers and filled with DOT 5 -- that was in the late 1970s. Some 20 years later I flushed with fresh DOT5 because I thought it would be a good thing to do. I don't think I will get a chance to flush it again on that maintenance schedule.

The lines and pistons don't have to be surgically free of polyglycol, but the cleaner the better. If you do it right one time, you may never have to do it again. And don't forget DOT5 will not hurt your paint.

[John D.]

Re: 54 brake fluid

I put DOT 5 (silicone) in my 1970 when I had the calipers sleeved with SS. I just flushed the lines with alcohol, blew them out with shop air, and rebuilt the master cylinder, installed the SS sleeved calipers and filled with DOT 5 -- that was in the late 1970s. Some 20 years later I flushed with fresh DOT5 because I thought it would be a good thing to do. I don't think I will get a chance to flush it again on that maintenance schedule.

The lines and pistons don't have to be surgically free of polyglycol, but the cleaner the better. If you do it right one time, you may never have to do it again. And don't forget DOT5 will not hurt your paint.

SAE Technical paper 810804 Compatibility of Silicone-base Brake Fluids with Automotive Vehicle Elastomers agrees with this it states:

Brake performance of systems in which silicone brake fluids and conventional brake fluid become mixed will operate normally with no fluid/elastomer related problems.

[Guy M.]

Re: 54 brake fluid

This is a brand new fill, never had anything in it as this is a brand new restoration. Sounds like its a go. I did hear that any mixing of the two products will turn the fluid to sludge. Thanks for all the input!

[Duke W.]

Re: 54 brake fluid

Unless you are absolutely postive that the master and wheel cylinders were assembled with DOT 5 instead of DOT 3 or 4 you should disassemble them, clean everything with denatured alcohol and resassemble with DOT 5. Same goes with new hoses since they are swaged using DOT 3 as a lubricant. Same with the pipes. Draining them is not sufficient. They should be thoroughly flushed with denatured alcohol and thoroughly dried.

Any DOT 3 or 4 in a DOT 5 system is a contaminent.

Duke