Brake Fluid

[Terry M.]

Re: Brake Fluid

I have DOT 5 in the 1970, and it has been there for around 30 to 40 years with no issues. That said all the lip seals and the fluid in there is that old also. If the fluid or the seal composition has changed, I can provide no testimony to that.

I think one will find that the proponents of DOT5 (count me among them) are very passionate about. The detractors are equally passionate against it. Sound like a familiar story?

[Marco H.]

Re: Brake Fluid

As many here, I have been using DOT5 exclusively for many years. Lately, many professional Corvette brake component rebuilders refuse any warranty claims if their parts are exposed to DOT5 fluid. I have talked to my supplier and he told me to submerge a seal in my fluid for 3 days and report back. Needless to say, the seal has not changed size nor has it deteriorated. The supplier informed me that they had trouble with various brake fluid brands, often found at the typical street corner discount parts suppliers.

I've been using NAPA DOT5 Silicone fluid exclusively, without any issues ever. As others stated, use good quality O-Ring seals with specific pistons machined for them, along with stainless sleeved bores (most calipers should be done by now).

Hope this helps, Marco

[Jim L.]

Re: Brake Fluid

once I have the cylinder filled, I get a neighbor who smokes cigarettes to come by and blow the smoke directly on the exposed DOT 5.

OK, I gotta ask the obvious question....... why?

Because expiring minds want to know.....

[Mark S.]

Re: Brake Fluid

DOT 5 in my 56 and 65 for many years and no problems. Had DOT 5 in a 69 that I sold; and I had no problems there also. I suspect that the new seals that some of the rebuilders are using with the calipers are not the same as the seals in the past. Might they be non-US made seals? Also, there is an outfit in Florida that sells a replacement "hockey puck" and seal for rebuilding calipers that I have had good luck with.

[Ed D.]

Re: Brake Fluid

I have DOT 5 in my 72 corvette for 30 years, with the original non rebuilt master cylinder. I dont know of any other DOT fluid that would go this long without any flush and replacement. The fluid is still clear, with no signs of rust or debris. I also found out that every government mail truck, on the road, has been using DOT 5 for years, without any problems. Their caliber manufactures are using a rubber compound that works with DOT 5. Why? The conclusion that I have come to is; the corvette caliber re-builders have changed their rubber compound, for what ever reason, to something not compatible with DOT 5. This change happened over the last 30 or so years, which I believe is a total miss service to our hobby, considering the type of driving our cars get.
Ed

[Duke W.]

Re: Brake Fluid

Silicone and conventional polyglycol fluids are not miscible. I only recommend switching to DOT 5 if every trace of glycol fluid is removed. This requires disassembling all hydraulic components, cleaning them thoroughly with denatured alcohol including brake pipes and hoses, and then thoroughly drying everything and reassembling with silicone fluid.

This means you will have to disassemble any rebuilt components you purchase and clean as above.

There have been recent discussions of silicone fluid not being compatible with some current rubber components that I don't understand. Silicone is very non-reactive and all brake fluids and elastomers have to meet DOT compatibility requirements. You'll have to use your own judgment. The big advantage of silicone is that it doesn't absorb moisture that can cause internal corrosion. Glycol fluid should be flushed out and replaced with new fluid every few years to prevent internal corrosion.

Duke

[Patrick H.]

Re: Brake Fluid

The conclusion that I have come to is; the corvette caliber re-builders have changed their rubber compound, for what ever reason, to something not compatible with DOT 5. This change happened over the last 30 or so years, which I believe is a total miss service to our hobby, considering the type of driving our cars get.
Ed

I purchased Raybestos seals as they were purported to be able to tolerate DOT5, and still got leaks.

I think that without anyone doing testing on the rubber and the fluid, we just get to guess and postulate.

[Ed D.]

Re: Brake Fluid

I purchased Raybestos seals as they were purported to be able to tolerate DOT5, and still got leaks.

I think that without anyone doing testing on the rubber and the fluid, we just get to guess and postulate.

There are other reasons beside, fluid and rubber, for leaks. Have you checked the pistons and bores, as some minor imperfections can cause leaks.
I know form all the above posts, that there is not enough information to come to a scientific, conclusion, but how come the Post Office can run thousands of trucks with DOT 5 everyday and still specify and demand it be used? How come we cant use it in our covette's, which get less abuse than a Mail Truck, without leaking.

[Patrick H.]

Re: Brake Fluid

I know form all the above posts, that there is not enough information to come to a scientific, conclusion, but how come the Post Office can run thousands of trucks with DOT 5 everyday and still specify and demand it be used? How come we cant use it in our covette's, which get less abuse than a Mail Truck, without leaking.

If I knew that, they wouldn't be leaking.

Latest time around I honed them, cleaned them again, sealed the internal edge per the service manual and the owner reports them eventually leaking. It comes back here soon, so I'll have to again see what looks out of place or what might be leaking. There was nothing obvious the first time I had it or with the re-do, which happened before it left here.

I've re-sealed DOT3 cars previously, so it is a mystery...

[Ed D.]

Re: Brake Fluid

If I knew that, they wouldn't be leaking.

Latest time around I honed them, cleaned them again, sealed the internal edge per the service manual and the owner reports them eventually leaking. It comes back here soon, so I'll have to again see what looks out of place or what might be leaking. There was nothing obvious the first time I had it or with the re-do, which happened before it left here.

I've re-sealed DOT3 cars previously, so it is a mystery...

Pat, I am sure you are aware of the sensitive clearances involved in the seal, but some may not. The reason I mentioned it, was due to the issue I had on my 74. I replaced all four calipers, replaced some of the brake lines, flushed the system, and replace DOT 3 with DOT 5. One caliper would not stop leaking. I call the re-manufacturer of the calipers and he replaced it, no more leaks. This is about 15 years ago and before DOT 5 became taboo. I had the 74 for about 10 years after the change,with the DOT 5 and no leaks.

[Terry M.]

Re: Brake Fluid

Silicone and conventional polyglycol fluids are not miscible. I only recommend switching to DOT 5 if every trace of glycol fluid is removed. This requires disassembling all hydraulic components, cleaning them thoroughly with denatured alcohol including brake pipes and hoses, and then thoroughly drying everything and reassembling with silicone fluid.

This means you will have to disassemble any rebuilt components you purchase and clean as above.

There have been recent discussions of silicone fluid not being compatible with some current rubber components that I don't understand. Silicone is very non-reactive and all brake fluids and elastomers have to meet DOT compatibility requirements. You'll have to use your own judgment. The big advantage of silicone is that it doesn't absorb moisture that can cause internal corrosion. Glycol fluid should be flushed out and replaced with new fluid every few years to prevent internal corrosion.

Duke

Duke
Another large advantage of DOT 5 fluid is that it will not damage painted surfaces. The other brake fluids are the finest paint removers known to man. However, if you ever plan to refinish a surface do not ever allow DOT 5 to get on it. There is no way to clean the DOT 5 residue from the surface and paint will not adhere to that surface.

[Len M.]

Re: Brake Fluid

I'm having the calipers rebuilt.

[Edward B.]

Re: Brake Fluid

DOT 5 fluid should work fine is most older cars providing you are starting with a completely clean (or new) system. DOT 5 fluid does entrain more air than DOT 3 or DOT 4 fluids which can make brake bleeding more troublesome. Air entrainment also makes DOT fluid unsuitable for use in cars with ABS. DOT 5 fluid provides less lubrication to moving parts than does 3 or 4 and may therefore cause some brake light switches to malfunction.
Balance these considerations against the fact that DOT 5 is non hygroscopic and that it will not harm most automotive finishes; then make your choice.

[Terry M.]

Re: Brake Fluid

DOT 5 fluid should work fine is most older cars providing you are starting with a completely clean (or new) system. DOT 5 fluid does entrain more air than DOT 3 or DOT 4 fluids which can make brake bleeding more troublesome. Air entrainment also makes DOT fluid unsuitable for use in cars with ABS. DOT 5 fluid provides less lubrication to moving parts than does 3 or 4 and may therefore cause some brake light switches to malfunction.
Balance these considerations against the fact that DOT 5 is non hygroscopic and that it will not harm most automotive finishes; then make your choice.

That is hard for me to believe since silicone, the primary ingredient in DOT 5, is very slippery.

[Michael L.]

Re: Brake Fluid

Silicone and conventional polyglycol fluids are not miscible. I only recommend switching to DOT 5 if every trace of glycol fluid is removed. This requires disassembling all hydraulic components, cleaning them thoroughly with denatured alcohol including brake pipes and hoses, and then thoroughly drying everything and reassembling with silicone fluid.

This means you will have to disassemble any rebuilt components you purchase and clean as above.

There have been recent discussions of silicone fluid not being compatible with some current rubber components that I don't understand. Silicone is very non-reactive and all brake fluids and elastomers have to meet DOT compatibility requirements. You'll have to use your own judgment. The big advantage of silicone is that it doesn't absorb moisture that can cause internal corrosion. Glycol fluid should be flushed out and replaced with new fluid every few years to prevent internal corrosion.

Duke

Duke,

I'm close to putting brake fluids into my 69 after restoration. All the hoses and lines are new, as is the MC (which BTW came with a DOT 5 recommendation) but the calipers are lonestar rebuilds with SS sleeves and O-rings. Do I really have to disassemble the calipers and clean them prior to installing the DOT 5? Why??? It would mean the removal of all calipers from the car. Please advise.

Mike