Silicone brake fluid debate
228A
Silicone or mineral brake fluid for V8s
?
Georg Muller has contacted the V8 Webmaster with a workshop note saying "last weekend I changed my brake fluid. I'm now using silicone based brake fluid, which might be interesting for other owners as well. Therefore I wrote the attached note". Before we publish this note I feel it is worth seeking fellow members' views because the case for silicone fluid is not universally accepted and some believe it is not the best choice, particularly for a classic car. The following contributions are set out in the order received by the V8 Webmaster. (15.3.05)

Comments from Dave Wellings (15.3.05 @ 0829)
Dave, one of our longstanding members, has commented following reviewing the draft note that "if a change to silicone fluid is undertaken, the complete braking system should be stripped and ALL seals replaced. When I did my rebuild, I was in a position of having a completely new and dry system. I considered the evidence very carefully. The anecdotal evidence of problems far outweighed those who were satisfied with silicone fluid, so I stuck with mineral fluid. The issues are a softer pedal and a tendency for seals to stick, making the brakes slow to come off. If it was that good it would be a standard fit on new cars. The main areas for corrosion when using mineral fluid are around the wheel cylinders and caliper pistons. Both easy to deal with, which is why I stayed with mineral fluid. I have no regrets. My rebuilt servo recently failed after 15 years by the way, so it lasted 32 years using mineral fluid".


Comment from Gordon Hesketh-Jones (15.3.05 @ 1539)
Gordon comments whilst I agree with Georg that silicone fluid has some benefits, I also totally agree with Dave Wellings that a change to silicone should only be made at the time of a 100% brake system rebuild. I went through the 100% brake rebuild process in 1998 but stayed with standard fluid.
Frankly I think that Georg might have some problems in the future as all he seems to have done is to just to clean the system then put in the new fluid.

Comments from Steve Bowley (Harvest Gold 0255) (15.3.05 @ 2130)
I finished my 1973 GTV8 rebuild last July. I thought long and hard about silicone fluid and followed various discussions. In the end I went for DOT 5 silicone for brakes and clutch BUT I must stress that ALL the brake and clutch components were brand new all the way down to washers and servo clips. Only trouble I had was bleeding the brakes. Car was trailered to Brown & Gammons to give it a thorough going over, especially the brakes, prior to its MOT. So far 1,200 miles and no leaks or long pedals. Using drilled discs and greenstuff pads with uprated shoes at the rear. It is down to choice but so far I have not had a downside.

Response from Georg Muller (16.3.05 @ 0900)
Georg responded "are you aware what a huge market is behind yearly replacement of brake fluid. In addition all the repairs and replacement of brake equipment based on failure caused by glycol brake fluid. There are millions of cars, so there are millions of litres of glycol brake fluid sold every year, not talking about spare parts. Do you think vendors like AP Lockheed will give up this attractive market only because people are getting maintenance free hydraulic systems based on silicon fluid? This is a billion Dollar market and the aftermarket sales are much more attractive than dealing with the car industries. As everybody knows with the car industries there is nearly no margin left".


Georg notes that only one comment [on points in the warning note from AP Lockheed reproduced in V8NOTE228 and set out in the box below] will show already that we are not talking about serious feedback:
Sudden loss of brakes
o Air absorption - gasification of absorbed air at relatively low temperature produces vapour lock effect.
o Immiscibility (failure to mix) with water - whilst the presence of dissolved water will reduce the boiling point of glycol based fluids, any free water entrapped in silicone filled systems will boil and produce vapour lock at much lower temperatures (100C or thereabouts).

Air absorption
: It might be more difficult to bleed silicone fluid based hydraulic systems. This is beyond all doubt. This takes time and you need to redo the bleeding a minimum of another time. But once the system is air free, there will be no issue at all. It's even less of an issue than with glycol based systems. This is because of boiling water, which is always available in glycol based systems. This boiling water will free up air! Result: Fading

Immiscibility with water: Boiling water is "the problem" with glycol based hydraulic systems we are all afraid of. Once loosing the total brake system based on fading will stay in your mind forever. Glycol brake fluid is hydroscopic. Therefore the seals will become hydroscopic as well. This way water comes into the systems. That is the reason why we have to change glycol fluid all the time. Conclusion:
o There is no glycol based hydraulic system without water, and
o This causes fading which is a high risk.
Looking to a silicone based hydraulic system we will identify that it will not have this "type of leaks". It's a real closed system and so water hasn't any chance to come in.

My conclusion is that we must be very carefully about statements from market effected industries. I think it's not the best idea to announce their statements on the register webside without comment. You should talk to US Army mechanics or Harley Davidson owners. None of them could state to me serious problems with their silicone based hydraulic systems. I am not talking about thousands of happy oldtimer owners singing "Thanks God we got rid of this damn glycol brake fluid".

V8 Register - MG Car Club

Comment from V8 Webmaster - this note from Georg Muller is not only critical of the information available on the V8 Website but also critical that the V8 Register published it without comment. That is not the case as you can see from V8NOTE228 - the AP Lockheed warning note was under a comment from Ron Gammons, a leading MG specialist in the UK and someone who has raced MGs and other cars for over 40 years, who expressed the view based on his experience that "silicone fluid attacks rubber seals and causes swelling. Girling, a leading brake component manufacturer does not recommend silicone brake fluid".

Reply from the V8 Webmaster
(16.3.05 @ 0918)
What is clear is the case for mineral and the case for silicone fluid is not clear. There are defects and benefits with both fluids and quite rightly you have to make a judgement, as informed as it is possible to be, on what will be best for your V8. I am not unaware of the boiling and fading problem with moisture build up in mineral fluid as I used to race an MGB in the mid 1970s when I formed and ran the BCV8 Championship. I found it was necessary to change the fluid regularly to ensure the brakes would not fade as they got red hot!! I agree that losing braking efficiency through fade when you are pressing a car to its limits ona track is not a comfortable feeling at all!

I can also accept your natural concern that manufacturers of equipment and braking systems using mineral fluid might have a tendency to skew their advice but so far as a number of members with technical expertise in the UK are concerned this does not appear to be the case with the Lockheed cautionary note which we included in V8NOTE228 as long ago as 2001.

I think the debate of the issues is both healthy and desirable and your views are very valuable based on your personal experience and on the evidence you cite of other enthusiast bodies. On a point of detail, did you in fact remove all mineral fluid so you had a completely dry system before recharging your system with silicone fluid?

Georg Muller response (16.3.05 @ 1201)
There are basically two ways to proceed.

1. Rebuild and refill: open the brake system and replace all seals, refill a complete dry and rebuilt system. This needs to be done, if the seals are more or less gone already. If the seal are already hardly attacked by glycol fluid they will not recover using silicon fluid.

2. Rinse the system and refill: drain off the old brake fluid, rinse the system with silicon fluid, refill the system with new silicon fluid, and then the system must be rebleeded after 1 to 2 weeks (the seals will release glycol fluid and water).

Remark: There may be a third way of doing this - that is getting the system dry without seal replacement. This will only help if you keep the system dry for at least 2 weeks. So the seals will release glycol fluid and water and become dry as well. Otherwise this will not help and you can go for the second way of doing. I decided to go for the second and I took about 1 1/2 litre of silicone fluid rinsing the system. This takes some time and also it will be better to dismount the calipers and hold them upside down so the old fluid runs out. The glycol and silicone fluid stay completely separated. You can't get them mixed. During rinsing, the silicone fluid will blow out the glycol fluid like bubbles. Once the system is "clean", refill with new silicone fluid and start bleeding. As the two fluids stay completely separated - silicone above because it's lighter, I have been told that you could drain the silicone fluid and reuse it. But I did not and would as well not recommend this. In two weeks time I will bleed the system again to get the get contamination out which was released by the seals.

Comments from Allan Doyle (16.3.05 @ 1128)
Allan says that "I work for an automotive supplier and several of our customers demand that we guarantee silicone-free products. I'm enclosing two examples".

o Hella (Lights etc)
They even specify the method to be used to determine the silicone content in indirect materials.

o SiemensVDO
Point 20 on the initial sample checklist is confirmation of silicone free supplies

"I've been told that the reason for this requirement is the "creep" of silicone which can play havoc with electronics. This may not be a problem with our electronic-free "old bangers" but I think those two companies know what they are talking about. I've stayed with normal brake fluid and plan to change it after 5 years".

Response from Georg Muller (16.3.05 @ 1223)
Hello Allan, I can understand that people for whatever reason stay with glycol based brake fluid. But five years!!! Are you aware about the risk you are taking. It's not only the corrosion, it's the risk that the brake system is going to fail at high speed and on longer downhill roads. Recommend changing at a maximum of 2 years. Better would be to replace the fluid every year. In addition - as the brake system becomes older (seals) then the more often the change should be made.
Take care.

Posting from Paul Wiley (17.3.05 @ 1305)
I noticed the silicone debate and my understanding of this fluid is that the large molecules allows air to reside in the fluid. This air cannot be bleed out and gives the slightly spongy feel. However, if this is the case what are the effects at high temperature and altitude? Also Castrol SRF is a silicon ester but still attracts water?

Comprehensive review of brake fluids. More
What do other members feel about the mineral-silicone brake fluid debate? More contributions will be very welcome on the V8 Bulletin Board.

V8NOTE228 - servo failure & brake fluid.

V8NOTE228A - additional notes on the debate - silicone or mineral brake fluid for V8s?

V8NOTE228B - extra note with the views of Georg Muller on silicone fluid.

V8NOTE398 - comprehensive review of brake fluids by Bob Owen
V8 Register - MG Car Club with support and services for MGV8 enthusiasts