Silicone brake and clutch fluid

[BritCarFan]

I've been hearing a lot about silicone brake fluids lately and I wanted to find out if they are suitable on the Mini. I was thinking to replace the brake fluid and the clutch fluid with this. Any thoughts?

 

[Steve]

I believe that you would have to replace all the seals in the entire system if you did so....more hassle than switching would be worth.

 

[RonMacPherson]

Depends,

Have you done any repairs recently? Replaced any hydraulic components?

The BEST way is when you are putting new cylinders, or rebuilding the cylinders(calipers, masters, slaves, etc. That way you can do a new fluid install and do not have to worry.

If you've got early original rubbers watch out.

My Triumphs I just flushed the system, making sure that I would rotate the calipers and slave to get all the previous fluid out.

I recommend a good silicone Dot 5 fluid.

 

[dklawson]

The silicone fluid will not attack the original seals if they are in good shape but the system will need to be flushed. Drain all the old fluid out then bleed the system using isopropyl alcohol. Give the alcohol a little time to sit, then drain it out and blow the system dry (reservoir to each open bleed nipple) using low pressure compressed air.

There is one component that will surely die when/if you switch to silicone fluid. No one seems to know why, but there are an enormous number of us who found that after switching to silicone fluid the hydraulic brake pressure switch dies. The easy way around this is to mount a mechanical switch to the pedal box (like later cars) and wire it in parallel to the original brake switch.

Now for a side comment. If you're considering going to the trouble of switching to silicone fluid, it's a more prudent use of your resources to go ahead and replace all the old rubber bits, right down to the flex lines. Start over with completely new brakes for less cleaning fuss/muss and no lingering worries about whether you flushed out every bit of trapped old fluid.

 

[Patrick67BJ8]

I've been hearing a lot about silicone brake fluids lately and I wanted to find out if they are suitable on the Mini. I was thinking to replace the brake fluid and the clutch fluid with this. Any thoughts?

I did my Healey with silicone about 20 years ago. I'm still replacing/rebuilding the hydraulic components. I don't like the pedal feel on the brakes and the very high cost of the fluid(when you can find it). I've replaced two brake light switches before finally installing a mechanical switch. The silicone will give you slightly slower pedal response. It is also more time consuming to bleed all the air out of the system.

I will be changing back to the original stuff when the car is restored.
Patrick

 

[Kuz]

So what is best to use? I'm in the middle of replacing /rebuilding all the hydraulics right now.I have heard arguments against everything from dot 3 to dot 5. If I'm using all new replacements parts ,and all my lines have been flushed or replaced does it really matter?

 

[dklawson]

The longer you cruise message boards the more of these threads you see. Brake fluid selection is forever a topic of debate. The final decision is always yours.

I have my preference and my choice may not be right for you. Nonetheless, I'll give you my succinct take on pros & cons. Only you can make the final choice.

DOT-5
Racers hate DOT-5. Their reasons range from difficulty bleeding to poor pedal feel.
Weekend drivers with restored cars love DOT-5 because it lasts longer than anything else and won't attack paint. Its ability to collect and pool water in the system is documented, but most collector cars are so frequently maintained that this is not an issue.
Daily drivers don't often use DOT-5 because it is expensive and more difficult to find (as mentioned above).

DOT-3
IF your car has all new brake rubber (not old and not NOS) then you probably can run readily available DOT-3. It's fine. The only caveats are you need to flush and bleed the system every couple of years and you need to keep it off the paint.

DOT-4 (Castrol LMA)
This was probably used in your car when new. When you can find it, it's great. The same caveats apply as for DOT-3... regular maintenance and keep it off the paint. It is (was) also harder to find.

DOT-5.1
This appears to be the current favorite among my acquaintances who race. I have no experience with it. However, do not confuse it with DOT-5. They aren't similar chemically.

What's right for you is largely a function of how you plan to use your car. In my case, both my LBCs are weekend restorations. I run DOT-5. I did not have the difficulty bleeding the system that others complain about. I don't think my cars' brake pedals feel bad either. I did experience the hydraulic brake switch failure that was mentioned above.

The strongest warning I will give you about your selection regards the age of your car's brake rubber. If your car was made before the mid-1970s, you REALLY need to be 100% certain that the rubber in the car has been replaced with the later compound before you consider running DOT-3. DOT-3 will attack the "natural rubber" used in the brake seals of early cars. However, this is not limited to the caliper/cylinder seals. The fluid can also attack brake hoses, proportioning valves, and brake servos. You need all the rubber to be new (later formulation) before you consider DOT-3.

 

[LarryK]

Seconds to dklawson, best way to put it!!