I have been doing some research on the subject of silicone (DOT 5) brake fluid (and clutch) in older cars. I believe I have decided to convert my wedge. The impetus to do this was a story about a '71 Toyota Corolla in Hemmings Motor News recently. The guy bought the car new and it now has 610,000 miles...that's not a typo. He converted the car to silicone fluid back in the 70s or 80s. Never had a problem and when he inpected the rear wheel cylinders recently found them 'shiny like new'. That's a lot of bleeding he missed! He called it 'the best kept secret in auto repair'. Silicone fluid (DOT 5) is not good for racing really and NOT for ABS brakes, but in many weekend driven classic cars might be just the ticket.
I have another vintage car that will probably get converted first, but the wedge is on the agenda.
Here's a couple of good research links if you care to read them. A little more searching will find many others, but I will just post these two.
http://www.tr-register.co.uk/forums/ind ... topic=3423
“In it's previous life from new to 80,350 miles I used Dot 3 fluid. I had caliper pistons rust and freeze up. The rear cylinders got covered with a whitish paste.
Since 1990 when I finished my restoration, (it's 2nd life), I have driven more than 83,000 miles with silicone Dot 5 fluid for my brakes and clutch with no freeze-ups. And I only drive it in the summer months from April to October. I have heard that silicone lubricates better - or it repels water, so no rust is formed. The front caliper pistons are the original ones with 163,000 miles on them in 46 years.
Don Elliott, Original Owner, 1958 TR3A, Montreal, Canada
TR Register member since 1987
http://mysite.wanadoo-members.co.uk/tre ... 3a_big.JPG “
“Yes Silicon is OK to use.
Can need diligent bleeding to get the air out and more prone to giving a soft brake pedal after repeated hard braking.
I've experienced this a few times driving in the Alps so may not be suitable if you live in mountainous regions.
Oddly enough I've never experienced it elswhere in spite of repeated heavy braking at sea level. (This may reflect lack of hills to give the brakes more to do) “
http://www.imperialclub.com/Repair/Brak ... efluid.htm
“Silicone brake fluid has a number of strengths, and a number of drawbacks:
Strengths
1.) High boiling point - since it does not absorb water, there is no so-called wet boiling point
2.) Doesn't absorb moisture
3.) Doesn't remove paint
4.) The viscosity is more stable over the extremes of temperature
5.) With the exception of some formulations used in external boots, silicone brake fluid is compatible with all current braking components
Drawbacks
1. ) Very hard to pour without entraining air bubbles - hence an application will generally have a softer, spongier pedal feel
2.) Doesn't absorb water - any water in the system accumulates in the lowest point of the system and stays there, concentrating rust
3.) Whereas glycol fluids begin to compress near their boiling points, silicone fluids begin to compress at around 300 to 350 degrees Fahrenheit.
4.) Additives in the fluid can vaporize at comparatively moderate temperature, increasing the spongy feel.
5.) Silicone fluids expand significantly when hot.
6.) Functionally incompatible with systems which have held glycol-based fluids for any length of time, requiring flushing and seal replacement (Note that there are counter opinions on this that state that the modern silicone formulations are in fact compatible with only a flushing, rather than a complete reseal. ) The actual DOT specification requires chemical compatibility, so as far as that goes, the two fluids won't cause reactions if used in the same system, but they certainly won't mix, either.
7.) Functionally incompatible with anti-lock brakes. In the first place, the silicone fluids tend to be more viscous, which can cause problems with the timing of the pulses, which are intended to work with the thinner glycol-base fluid. This sometimes leads to damage to the ABS valving.
Secondly, the rapid pulsing necessary to anti-lock function tends to cause cavitation in the fluid, as the tiny bubbles collapse and coalesce into larger ones, and then collapse and reform into smaller ones. This tends to nullify the ABS effect, can diminish the actual effective braking to a dangerously low level, heats the fluid leading to further sponginess, and can damage the ABS controller. Thirdly, silicone brake fluid tends to foam when expressed from a small orifice under pressure. This, of course, reduces its hydraulic effectiveness to nothing in the area affected.
8.) The silicone tends to attract and bind with the fragmentary wear products of the rubber components in the brake system, creating a gelatinous sludge, which can block fine passages, particularly in ABS systems.
I have read of the experiences of a number of members of my Triumph list who have gone to silicone brake fluid - other than flushing and resealing the system, and the seemingly permanently slightly spongy pedal, most reported that they were satisfied. One very real issue with these cars is that the seals are not what the could be in the brake and clutch master cylinders, and _every_ owner has stories of leaking MC seals destroying the paint on the firewall, so this aspect represents a very real value. Also, these are usually weekend cars, for pleasure driving only, so they don't see a lot of
brake system heat.
Having torn silicone fluid down, who uses silicone fluid then? The sole major user, to my knowledge, is US Government, mainly the armed forces,
although the Post Office is a big user, too. They use it because it is stable and predictable over a wider range of temperatures, has a high boiling point, and doesn't absorb moisture. ( It does not appear whether the government cares about the paint issue. ) I can find no evidence of any other major benefits that the government expects from the silicone fluid.
In a word - do not use silicon fluid in systems with ABS - water droplets can damage the ABS pump if caught in the pump when ABS operates.
I use Castrol LMA or MB fluid (Pentosin brand) - both are DOT 4 rated . . .â€
“From Ron:
I have 25+ years experience using silicone brake fluid, over 10 years as a USPS contract repair shop serving 2 PO's with over 300 vehicles. I am a shop owner, and I use this in ALL my NON ABS cars. I have used it in just about all (wrongly advised?) ways possible; in totally renewed systems in partially renewed systems in old drained, flushed, inspected systems Mixed in over old dot 3
etc, etc, etc.
In my own work car, a Honda Accord, when I did the front brakes w/new calipers/pads only, all I did was suck out the master and put silicone in over the top (the rears are still on dot 3 but they share a common reservoir so there is some mix) Did that 3 years/80K ago NO PROBLEM
I use(d) it in ALL my Chrysler Corp cars including my last '67 Imp CC
Don't be worried about reports of a leaking tendency, those systems that leak have other problems/conditions that cause the leak.
If it doesn't leak on Dot 3 it won't leak on Silicone.
Personally, ALL ( 20+) of my non ABS cars/motorcycles have Silicone, it's near the first thing I do to a new arrival, and on ALL old cars when I do a restore brake job.â€
were rebuilt as were the rear brake cylinders. A new uprated master cylinder and uprated servo were also fitted as were both clutch master and slave cylinders. Both systems were filled with silicone fluid, they took a number of bleeds but eventually became good. Personally I do not find the pedal spongy (I do approx 5-6000 miles annually) and am very happy with the result.
