• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Silicone brake fluid conversion - existing system

Share this page

steveg

steveg

Yoda
Gold
Country flag
Offline
I'll be converting my system to DOT 5. Would be interested in hearing if anyone has done this with existing equipment - i.e. flushing the existing system and just installing the fluid.

I saw on another forum you can use methylated spirits (denatured alcohol). I'm thinking 99% isopropyl from the drug store would also work.

Experience-based comments?
 
I have DOT 5 in my system. Considering how much I spill refilling the MC, I wouldn't use anything else.

99% isopropyl works fine for cleaning, but you've go to get it all out or it will boil. I doubt you can get it all out without disassembling the cylinders. You can blow it out of the lines.
 
John Turney said:
I have DOT 5 in my system. Considering how much I spill refilling the MC, I wouldn't use anything else.

99% isopropyl works fine for cleaning, but you've go to get it all out or it will boil. I doubt you can get it all out without disassembling the cylinders. You can blow it out of the lines.
Click to expand...

John - thanks for the input - agree re the cylinders. Since the caliper entry points and bleed screws are on the tops of the cylinders, I can see where you couldn't blow them out - you'd just be diluting the fluid in the cylinders. Guess I'll dismount everything and disassemble.
 
I converted my BJ8 many years ago. IIRC, I flushed with either denatured alcohol or 'dry' IPA (not the beer) and blew the lines out thoroughly. No issues in many thousands of miles (just returned from 4,850 mile road trip).
 
Last edited:
Is there any concern regarding the rubber currently used for master cylinder and wheel cylinder seals?

I ask because some Corvette parts vendors now will not warranty parts (master cylinders) from a system that uses DOT5. Apparently certain rubber seals will swell with DOT5, whereas others will not, but they don't want to take the chance. Has anyone seen problems with the rubber type currently used for Healeys?
 
Hi Steve,

I converted my Healey to Dot 5 in 1989 during my full rebuild of restoration and used denatured alcohol to clean out the original lines and blew then clear after. Since I was in the process of rebuilding all major hydraulic components (masters and slaves), I also used the alcohol to clean out these units prior to installing the new seals and also blew them dry. This guarantied that all the alcohol was removed prior to pre-filling with the Dot 5.

The interesting thing is that there is no corrosion in any brake component since I first installed the Dot 5 as apposed to the Dot 3 I used prior. Also, I had totally flushed the Dot 3 every 4 years and have not flushed the Dot 5 since installation but did bleed once when adding the clutch bleed extension and addressing a slight leak in one of the rear original back brake slave rebuild and everything remains very clean.

Ray(64BJ8P1)
 
PHulst said:
Is there any concern regarding the rubber currently used for master cylinder and wheel cylinder seals?
Click to expand...

You have to be concerned with rubber bits but NOT brand new rubber compounds. Your concern should focus on rubber parts that have had previous exposure to DOT-3 or DOT-4.

First, no readily available NEW brake rubber has issues with exposure to DOT-5. Period. Modern brake rubber is typically EPDM which has no problem with silicone fluid. The only seals easily attacked by DOT-5 are silicone seals which are not used in brake systems. I have seen manufacturers like TRW will not warrant new MCs used with DOT-5. The explanation given to me (second hand by a vendor) was that the techs at TRW feel DOT-5 offers less lubrication for the seal which may shorten their lives.

IF the seals in the brake system have previously been exposed to DOT-3 or DOT-4, then long term exposure to DOT-5 will cause the old seal to swell and sluff off black goo. Complete failure of such seals can happen quickly or take years to occur. Replace ALL the old rubber in a system that has been using DOT-3 or DOT-4. That includes MC seals, wheel cylinder seal, rubber flex lines, PDWA seals and proportioning valve components where applicable. Most people I have discussed this with fit braided stainless brake hoses to insure a firmer pedal. If you are fitting new MCs and/or wheel cylinders, inspect them carefully. Some reproduction parts are assembled with brake fluid as a lubricant, not the traditional red rubber grease. If you see the seals are lubricated with brake fluid in a new cylinder... rebuild it with new seals even if it is new.

Isopropyl is great for flushing the old metal lines. It is also good for washing out master cylinders and wheel cylinders to remove contaminants. Since you should have the flex hoses, and all the cylinders disconnected... you can easily blow through the lines with low pressure air. Leave the air running for a few hours to evaporate all the isopropyl.

There is lots of online information about filling reservoirs and bleeding the system. Make the process easy on yourself to the extent possible. Take a long, very clean screwdriver and place its tip against the bottom of the reservoir through the open top. Slowly, gently pour the DOT-5 fluid against the top of the screwdriver shank so it runs slowly down. This prevents a lot of bubbles from becoming trapped in the fluid. You may also find it is easier to get good results if you vacuum bleed the system. Pressure bleeding can trap bubbles in the system while vacuum bleeding will draw them out.
 
Last edited:
Like Ray, I found no corrosion of my brake system after ~15 years with DOT 5 fluid. I decided to rebuild it because other rubber parts were going bad, but upon inspection, the brake rubber parts were fine.
 
Perhaps Doug Lawson answered my question. I have a completely new brake hydraulic system and I want to use Dot 5 silicone fluid. New lines, new caliper seals (4 wheel disc brakes), new hoses and etc. HOWEVER, my brake servo is my original, but rebuilt. I suspect that it MAY have been reassembled with DOT 3/4. I don't know. Since this is a bit different than blowing out lines, what do you think? I am not going to rebuild my servo again so am I stuck with continuing to use DOT 3/4? After experiencing the paint removal characteristics of DOT 3/4, I was hoping to switch to silicone.
Lin
 
The SS braided brake lines typically have a Teflon tube for the interior wetted surface. Therefore, you will be OK cleaning and flushing them just like they were metal lines.

I don't know what to say about the brake servo. There are seals inside that may be compromised. All I can do is share one bit of personal experience. Twenty-five years ago when I rebuilt the brakes on our GT6 I addressed the clutch hydraulics at the same time. I used an aftermarket clutch slave cylinder which had been assembled using brake fluid for the lube. Fast forward 20 years and that one seal failed. As a safety precaution I replaced all the seals in the brake system and clutch system just in case they too were damaged. Only the one seal in the clutch slave was damaged. All the others were in near perfect shape. It took 20+ years for the aftermarket clutch slave seal to fail. However, that was a new part which had only seen DOT-3/-4 for a short while.
 
Lin,

Thinking back when I installed the Dot 5, I had an issue with my original servo (keep in mind that my Healey is a phase 1 and the phase 2 servos are a little different). Although during the 6 years of my rebuild, the servo had been sitting dry and I think (but am not sure) I had flushed it with alcohol prior to installing. After installing the Dot 5, I kept loosing fluid without any indication where. It turned out that the fluid was being collected within the vacuum canister of the servo. When dismantling, I broke an air valve and could not locate one at the time. Additionally, the unit needed a full rebuild and I actually attributed this to age (28 years) and not to the change to Dot 5, however, Dot 3 was previously used and I can't say was not a factor but the seals were not swollen.

Ray(64BJ8P1)
 
Beware if using the modern brake booster conversion, lockheed will not warrentee if DOT 5 silicone is used. I know there is much debate on this subject, pros and cons , I will only use DOT 3/4 and change fluids in the time interval 2-3 years. Just did an XKE that had sat for at least 5-6 years with silicone, everything was ruined, all new M/Cs clutch and brake,booster replaced all caliper pistons gunked up . Silicone just carries moisture and it sits at your rubber seals and corrodes the liners. At least use SS lined calipers and still change out your DOT 5 . Sorry I'll stick with DOT 3/4 for my customers, all doing well.
Carroll Phillips
Top Down Restorations
 
Hi Carroll,

Silicone just carries moisture and it sits at your rubber seals and corrodes the liners.
Click to expand...

Silicone doesn't absorb moisture and I am confused by your statement. Again, my experiences have not mirrored yours and seem to be opposite. When rebuilding my original booster, I broke one of the air valves and because I could not find one at the time, installed a Lockheed replacement. I do not remember seeing any document that indicated warranty claims would not be honored if installed using silicone brake fluid.

I appreciate and respect your selection of Dot 3/4 as the only fluid you will use, however, how secure are you that the XKE was properly prepared before changing over to silicone fluid? The natural result of improperly cleaning of the Dot 3/4 from the system before filling with silicone is as you have described.

This brings up a "Warning" for those who have switched over to Silicone Brake Fluid. How many have Labeled their system reservoir "DOT 5 ONLY". Without this labeling, the system is open to an add of the wrong fluid (most likely by a new car owner who is following the manuals). I know I have not but intend to do so immediately.

Ray(64BJ8P1)
 
Thanks for the information. The previous owner of my 100-6 used DOT5, and then in an attempt to improve his brake feel switched to DOT4. I suspect he did not clean the system, and my intent is to replace all of the wheel cylinders.
I'll likely rebuild the relatively new master cylinder with new seals, and all flex hoses will be changed to Cobalt stainless steel lines.
 
Top Down Resto said:
Beware if using the modern brake booster conversion, lockheed will not warrentee if DOT 5 silicone is used. I know there is much debate on this subject, pros and cons , I will only use DOT 3/4 and change fluids in the time interval 2-3 years. Just did an XKE that had sat for at least 5-6 years with silicone, everything was ruined, all new M/Cs clutch and brake,booster replaced all caliper pistons gunked up . Silicone just carries moisture and it sits at your rubber seals and corrodes the liners. At least use SS lined calipers and still change out your DOT 5 . Sorry I'll stick with DOT 3/4 for my customers, all doing well.
Carroll Phillips
Top Down Restorations
Click to expand...

During the restoration of our BN2/100M my dad fell ill and was indisposed for a while. The rolling chassis--with all-new brake system filled with Castrol LMA--had to sit for a couple years. When we restarted the restoration the brake fluid had completely gelled throughout the system. We flushed the system and used Pentosin--the brand BMW recommends, I believe--and, although the car still sits for long periods have had no problems since. Maybe the storage environment has something to do with it?
 
Converted to DOT 5 since restoration 25 years ago with no issues. Installed SS brake lines (wilwood) about 10 years ago which improved brake pedal feel. Flush fluid every 3 to 5 years as preventive maintenance. Agreed with dklawson about introducing bubbles when adding DOT 5 into the system. Go slow. Or, alternatively, wait a day for the tiny bubbles to dissipate before bleeding. Gonzo
 
Apologies if it's a thread hijack, but what would be the interval for fluid renewal on dot 5? My BJ8 had it installed during the rebuild but that was some years ago now. Ought it to be changed?
 
SteveT3000 said:
Apologies if it's a thread hijack, but what would be the interval for fluid renewal on dot 5? My BJ8 had it installed during the rebuild but that was some years ago now. Ought it to be changed?
Click to expand...
I went about 15 years on my renewal, but that's probably too long. No problems, though.
 
Hi all,

Just did a Jag XKE dot 5 complete flush last Thursday. Its been 5 years since the last flush the owner told me . Fluid was blackish, has S/S lines throughout and Low Pressure lines renewed last flush. Another disadvantage to DOT 5 is it does not have the lubricating capabilities as a Glycol base DOT 3/4 and seals will wear out faster in your M/C and slave units. In my earlier post what I mean in the sentence about silicone just carrying water is true, it is not hygroscopic meaning water absorbing so any moisture that enters the system ( however it can get in ) will just travel and go to the lowest point or get stuck seals and over time if the car is not used will cause rusting to the ferrous cylinders. What I am trying to promote here is flush your systems regularly DOT 3/4 and DOT 5 ! Yes storage has a lot to do with how moisture can get into a system, climates the car is living in ect. , all systems are vented to the atmosphere , thus allowing a certain amount of moisture in . The Jag I replaced all the components in was professionally restored and fluid bottles well marked DOT 5 only. I cannot answer why the entire system was pretty much trashed.
As for the servos it is still a big no to use DOT 5, see pic posted on instructions, Harley Davidson is now not recommending use of DOT 5 as well as Wagner Lockheed. 006.jpg

Again this is from my experience ( my day job) yes it can be used and has been for many years but these are problems that keep popping up and now manufacturing companies are backing down from its use. Im not here to start a pros and cons thread, just google the info yourself.

Carroll
Top Down Restorations Inc.
 
Back
Top