Silicone brake fluid... Or not?

Barten

Barten

Active Member
I have completely overhauled my braking system of my 3500s. I am putting it all together now. What do you recommend? Silicone brake fluid or normal Dot 4 brake fluid. There is no residues left of the old brake fluid anywhere in the system.
Regards, Barten
 
Hi Barten,

The general consensus is not to use Dot 5 (silicon brake fluid) as it can result in swelling of the rubber seals. The best option is to use Dot 4 or Super Dot 4 fluid and change it every 2 years.

Ron.
 
Personally, I would stick with DOT 4. If you have removed all the old fluid and replaced all seals, the theory is that you can switch to DOT 5 which does have some advantages. What would put me off using DOT 5 is the kind of con's listed below quoted from the site: http://www.gomog.com/allmorgan/brakefluids.html

Disadvantages:

It does NOT mix with DOT3 or DOT 4 or DOT 5.1. Most reported problems with DOT 5 are probably due to some degree of mixing with other fluid types. A residue of the former non-compatible fluid is sufficient to cause serious issues. The best way to convert to DOT 5 is to totally rebuild the hydraulic system. Additionally, the same advice applies if switching from Dot 5 to any of the other fluids.

Since DOT 5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics.

Careful bleeding is required to get all of the air out of the system. It is hard to you without introducing bubbles and thus results in soft pedal feel. These small bubbles will form large bubbles over time. It may be necessary to do a series of bleeds.

DOT 5 is less compressible (often creating a slightly softer pedal). It is not recommended for racing application.
It is hard to pour without introducing bubbles and thus results in soft pedal feel,

It is not recommended by the brake manufacturer, especially for ABS brakes.

It is about twice as expensive as DOT 4 fluid.

So silicone fluid aerates easily. Harley-Davison, one of the sole current OEM users of silicone fluid, warns buyers to let the fluid sit at least an hour before using it. If shaken on the way home, it will aerate enough to look like a freshly poured soft drink. Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content, and worst of all, neither accepts or disperses moisture, making systems using it more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occurring lubricity, making it incompatible with the mechanical valving in some anti-lock braking systems.
Click to expand...

Here is one of the best articles I have ever read on brake fluid: http://www.mossmotors.com/SiteGraphics/Pages/Brake_Fluid/brake_fluid_long.html
 
Thanks for the replies guys. Quite clear recommendations! I see from the very comprehensive article both pros and cons. With slicone i won't have to worry for the pAintwork in the engine bay, but i don't like spongy pedals. Just have to make sure to avoid leaks! I think I will go for a good quality dot 4 fluid. Regards, Barten
 
Blindingly simple answer - NOT!

I am deeply cautious about mixing rubbers deigned for old fashioned fluid with the new stuff. Also I would be cynical about the 100% accuracy of "all old fluid removed" - and it only takes the tiniest trace amount.

So I'd stick with the old style fluid.

Chris
 
I've used it in another classic after replacing all the brake components - a Triumph Vitesse - never had any problems and didn't notice any sponginess in the few years that I had it on the road. That car has now been sitting in my garage for a further number of years awaiting full restoration and I'm optimistic that the brakes parts will still be in good condition - something I definitely wouldn't say if it was full of DOT4. I'd love to find an old P6 with similarly uncorroded brake bores.
So personally I'm not worried about issues of rubber swelling, provided that rubber hasn't previously been subjected to conventional brake fluid. I suspect the spongy pedal issue is not something that many of us would even notice.
The only claims that would concern me over using silicone in a P6 relate to diminished lubrication properties alledgedly causing the rear caliper pistons to stick. I've no idea if there's any truth in it or not and probably never will.

I don't know why, but a lot of folks who've never used silicone fluid seem to enjoy telling everyone else how awful it is. I can't help thinking that if the situation was reversed and we'd been using silicone fluid from the beginning, anyone proposing mineral brake fluid with all its faults would be laughed out of town!
 
I've had silicon fluid (Automech) in mine for around 10 years now. I did change the fluid this year as it had lost it's purple colour in the reservoir and had turned transparent, so I thought best to replace it.

I haven't noticed a spongey pedal.
 
I've used it in another classic after replacing all the brake components - a Triumph Vitesse - never had any problems and didn't notice any sponginess in the few years that I had it on the road. That car has now been sitting in my garage for a further number of years awaiting full restoration and I'm optimistic that the brakes parts will still be in good condition - something I definitely wouldn't say if it was full of DOT4. I'd love to find an old P6 with similarly uncorroded brake bores.
So personally I'm not worried about issues of rubber swelling, provided that rubber hasn't previously been subjected to conventional brake fluid. I suspect the spongy pedal issue is not something that many of us would even notice.
Click to expand...

This is typical of folk who use and advocate the use of silcone brake fluid in a classic. People who are too lazy to flush the system every 2 years and wouldn't know a good brake pedal if it bit them on the arse. How people can be so complacent about the brakes on a car beggars belief.

Keep a bucket of soapy water handy when working on the brakes. If you spill any brake fluid on the paintwork wash it off immediately.
 
pat180269 said:
I've used it in another classic after replacing all the brake components - a Triumph Vitesse - never had any problems and didn't notice any sponginess in the few years that I had it on the road. That car has now been sitting in my garage for a further number of years awaiting full restoration and I'm optimistic that the brakes parts will still be in good condition - something I definitely wouldn't say if it was full of DOT4. I'd love to find an old P6 with similarly uncorroded brake bores.
So personally I'm not worried about issues of rubber swelling, provided that rubber hasn't previously been subjected to conventional brake fluid. I suspect the spongy pedal issue is not something that many of us would even notice.
Click to expand...

This is typical of folk who use and advocate the use of silcone brake fluid in a classic. People who are too lazy to flush the system every 2 years and wouldn't know a good brake pedal if it bit them on the arse. How people can be so complacent about the brakes on a car beggars belief.
Click to expand...
I hope that's an attempt at humour. :?
 
Being a large chap with very large hands it is tricky to get the hand in between the underside of the boot floor and the diff to bleed the rear nipple. You ideally need to change conventional glycol fluid every 18 months. All well and good if you have plenty of time on your hands, a Beadle sized hand or sufficiently deep pockets to pay someone else to do it.
 
When I rebuilt the entire brake system of my series 2 landrover it was then filled with silicon fluid. It really is fantastic as the old girl doesn't get used much but when she does the brakes are always brilliant. Pin sharp infact.

I would say if you rebuild the system as I did then go for it, its not laziness, its practicality.
 
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