Converting to Silicone Brake Fluid

[Paul J.]

Re: Converting to Silicone Brake Fluid

I wonder if i should go for silicone brake fluid since the calipers, brake lines and hoses are brand new for my car and not yet installed
Then i should not have any worries that other than silicone brake fluid is in the system

Yes. This is the best time.

[Paul J.]

Re: Converting to Silicone Brake Fluid

In 1986, I rebuilt the wheel cylinders on my 64. It had DOT3 fluid in it which was probably original to the car. The cylinders where not pitted and were easily resurfaced with a hone. As far as I could see, the inside of the lines looked fine also. After installation, I allowed the fluid to drain and replaced it with silicone fluid. The system was simply flushed and I wasted a large can of silicone fluid during the flushing process. 11 years ago I rebuilt the master cylinder. There was some very slight waving but no pitting. However, I did notice a very small amount of dark sludge. I only bled the brakes this time and was able to get a little bit of sludge out. When I disassembled the system 2 years ago for my restoration, everything looks fine. I have since read the SAE paper regarding the military vehicles in a damp environment and I have found what they stated to be correct. Remnants of DOT 3 in a system filled with DOT 5 have no noticeable effect, both in the short and long terms. My example was over a 27 year period in a system in good shape despite not being properly maintained. Despite this, I still always try to remove all of the DOT 3 when converting over to silicone fluid. I do this because it's the correct way to do it, but I don't sweat it if I don't get all of the DOT 3 out.

[Jim L.]

Re: Converting to Silicone Brake Fluid

Remnants of DOT 3 in a system filled with DOT 5 have no noticeable effect, both in the short and long terms. My example was over a 27 year period in a system in good shape despite not being properly maintained. Despite this, I still always try to remove all of the DOT 3 when converting over to silicone fluid. I do this because it's the correct way to do it, but I don't sweat it if I don't get all of the DOT 3 out.

I tend to agree with you, Paul. In fact I once did a "worst case" test of this approach and mostly got away with it.

I converted my bride's track car (seen in my avatar) to DOT 5 by just draining the DOT 3 and then flushing with DOT 5 as I bled the brakes. I readily admit that I would have preferred to have started with components which had seen only DOT 5. But since I planned to install bigger brakes eventually, and being basically a lazy person, I opted to postpone the larger project of purging the system of every last globule of DOT 3.

At Laguna Seca, I was driving the car in an open track event. 10 lap session. Approaching turn 11 (last turn before Start/Finish) on the last lap, brake pedal felt funny (but not funny "HA HA"). At turn 1 on the cool down lap, the pedal went to the floor.

So, for 9.97 hot laps, the hodge-podge of DOT 3 and DOT 5 worked fine. My guess is that whatever moisture had been absorbed by the DOT 3 lowered its boiling point and turned some of it to a vapor..... hence the loss of pedal. In a street driven vehicle these conditions would never happen and one could "get away" with an imperfectly converted system for a long time.

That's my story and I'm stickin' to it.

Jim

[Claus S.]

Re: Converting to Silicone Brake Fluid

Jim for racing i have heard that you should not use silicone brake fluid because the fluid gets hot and once the fluid have been hot you will have to change it

If this is correct i do not know but that is what i have heard

[Jim L.]

Re: Converting to Silicone Brake Fluid

Jim for racing i have heard that you should not use silicone brake fluid because the fluid gets hot and once the fluid have been hot you will have to change it

If this is correct i do not know but that is what i have heard

A lot of people believe this but it doesn't match my experience.

We have two track cars, the one in my avatar which my bride drives, and mine, a tube-frame '63 coupe which I vintage road race. Both have DOT5 fluid in their brake systems and, with the single exception I cited previously, the brakes have been absolutely flawless. In fact, with my own racer, I can out brake anyone, waiting half a beat later to get on the brakes, and then really standing on the pedal.

Conventional wisdom says that you have to bleed the brakes before every race to keep the brake fluid boiling point as high as possible.

I run DOT5 out of sheer laziness. I hate bleeding brakes.

Those who bleed their brakes before every race do so because they are running either DOT3 or DOT4 which absorb moisture that lowers the boiling temperature. DOT5 doesn't absorb much moisture (if any) so its "wet" boiling point is nearly as high as its dry boiling point. That has given me the freedom to bleed brakes only when the systems have been opened for other reasons.

Our cars have gone for years and thousands of track miles between brake bleeding sessions.

Jim

[Brian K.]

Re: Converting to Silicone Brake Fluid

Well, finally got it all together, bled out and I must say, the pedal isn't quite as firm (there is no air) but that may be due to new everything (pas, rotors, pistons, etc) and not seated in. One possible problem is I reassembled the new master with dot 5 and lubed the rubber boot. I am seeing some fluid weep down under the master and maybe its the dot 5 fluid used in assembly just weeping out but appears to be a little more than expected. There isn't much to these non power masters and I doubt I messed up reassembling. We will see but for now the roads are a disaster here and road test will have to wait.

[Duke W.]

Re: Converting to Silicone Brake Fluid

New pads, especially if the rotors aren't turned, may have a somewhat soft pedal until the pads break-in/seat, which usually takes 200-300 miles of normal road driving.

That's why brake shops always turn rotors when installing new pads. The pads will bed very quickly, but turning shortens rotor life. As long as the rotors aren't warped the pads will seat, but it takes time.

The rotors on all my cars are severely scored from race track hot lapping. Most brake shops guys would say they are junk, but they are not warped. It just takes a little time to bed in new pads, and once done the brakes are superb.

The vented Monza rotors on my Cosworth Vega are on their sixth set of OE Delco semimetallic pads, severely scored, but well over the minimum thickness. I could outbrake Porsches at Riverside and Willow Springs back in the eighties/nineties when I ran four track events per year.

Duke

[Brian K.]

Re: Converting to Silicone Brake Fluid

Rotors up front are new & shimmed for .001 run out & rears were done by Bair's so I'm sure they true them as well.

[Ken A.]

Re: Converting to Silicone Brake Fluid

Did you pressure bleed? Silicone fluid needs a pressure bleeder to get out all the air.

[Brian K.]

Re: Converting to Silicone Brake Fluid

nope.....gravity bleed. the pedal is high & doesn't come higher on the second pump which is the tell tale for air

[Ken A.]

Re: Converting to Silicone Brake Fluid

Pumping the pedal puts air into the fluid, if you want a rock solid pedal, then pressure bleed. Otherwise you will have to "pump bleed" about 50 times.

[Jim L.]

Re: Converting to Silicone Brake Fluid

nope.....gravity bleed. the pedal is high & doesn't come higher on the second pump which is the tell tale for air

Gravity bleeding works fine. I've used this technique with DOT 5 fluid and had no problems. Generally, as long as the bleeding process proceeds at a glacial pace (and gravity bleeding certainly qualifies), you'll get all the air out of the system and have a firm pedal.

Jim

[Marco H.]

Re: Converting to Silicone Brake Fluid

Another great side effect of DOT5 is, that it does not harm painted or plated surfaces.

[Brian K.]

Re: Converting to Silicone Brake Fluid

Pumping the pedal puts air into the fluid, if you want a rock solid pedal, then pressure bleed. Otherwise you will have to "pump bleed" about 50 times.

Ken, You misunderstand, I am not "pump bleeding"; I am refering to post gravity bleed (which is a glacial pace as Jim states) with all bleeders shut, to test for air, pump twice...if the second pump improves the pedal, you have air. I have none.

I'm sure it's just as Duke states, everything needs to "seat".

[Timothy B.]

Re: Converting to Silicone Brake Fluid

Ken, I gravity bleed my 67 and 63 using silicone without issues, never had a problem with the air that others report.