brake fluid - can I change back from Silicone to DOT 4?

[Rubce]

Hi All

Our Stag has DOT 4 in the brakes and clutch and the GT6 has DOT 4 in the clutch. This is because I have rebuilt all those systems. However, the GT6 still has Silicone in the brakes. Currently that car has its rear drums off as I am replacing the wheel bearings and UJ's. I would like to take the opportunity to replace the brake fluid with DOT 4 so both cars are standardised on one type of fluid.

Will it cause any problems with seals etc if I simply purge/refill/bleed the system with DOT4? Or can I only change over to DOT 4 if I replace the cylinders/calipers?

Regards

Bruce

[new to this]

bruce

why change from silicone i thought it was better than dot 4

dave

[Rubce]

bruce

why change from silicone i thought it was better than dot 4

dave

Hi Dave

That is subjective and you will get many different opinions on this Forum as to which to use. I simply want to standardise on the one type of fluid to eliminate the chance of me making a mistake and putting the wrong fluid in the wrong system.

Cheers

Bruce

[73stagman]

Silicone brake fluid still meets the DOT standard. It is DOT 5. It is more suited to vehicles which stand still for some time as it is "non Hygroscopic" ie it doesnt absorb water from the atmosphere. the other more friendly user property is that it doesnt damage paint work if you spill it!
The pay back... because there always is one, it is way more expensive! The other hassle is that it is not readily available from your local garage.
The real question is why would you want to swap back unless it is a price issue then there might be no option. However look here http://www.britcycle.com/Manuals/DOT5.htm and read the article... they recommend that you DO NOT CHANGE BACK!

[Rubce]

I want to change back because at the moment that car has DOT 4 in the clutch and silicone in the brakes. This means that I have to have TWO bottles of fluid in the garage and there is always the risk that I will pick up the wrong bottle and either put DOT4 in the GT6 brakes or silicone in the GT6 clutch or the Stag clutch or brake which then causes a contamination issue.

Simple really! So what is the answer to my original question?

Bruce

[73stagman]

The article I linked suggests that changing back causes the Silicone to "gloop" up with sludge that the "hygroscopic" DOT4 brake fluid carries. They suggest that this gloop may cause problems in master cylinder passageways etc. There would be an option I guess to flush the system completely through with DOT 3 or 4 then keep doing it until the Silicone is all gone. Again the article suggests that this may take forever! Read it anyway because its quite informative!

[Rubce]

Interesting article as it basically says Silicone is crap but if you have started to use it then you are stuck with it. HMMMMMM

Bruce

[grumpy2]

I changed from silicone to mineral fluid some years ago when I needed to replace a clutch slave at very short notice. flushed about 1/2 litre of mineral through in an attempt to stop problems and still the whole system sludged up within a couple of days resulting in a breakdown. my advice would be to standardise on silicone once you've used it. I no longer use silicone in anything

[KOY 23]

Interesting article as it basically says Silicone is crap but if you have started to use it then you are stuck with it. HMMMMMM

Bruce

Can't see where they say that about silicone fluid.

Why not label the bottles GT6 brakes etc.. Simples

[dasadrew]

If silicone fluid is non-hygroscopic does that mean you don't have to change the fluid every two years or whatever?

Edit:

just been reading up on silicone brake fluid (DOT5) and I tend to agree with Bruce (Rubce). Seems the only advantage is a very slightly higher boiling point, quicker response in ABS valves and the fact that it doesn't eat paint. Disadvantages are softer pedal and collection of water pockets in the system which might be in a brake caliper which gets very hot!

It seems that leading manufacturers like Ate don't even make it.

Interesting also is that the newest development DOT5.1 is NOT silicone and is a continuation of the DOT3, DOT4 sequence. It seems to have the advantages of DOT5 (except for the paint friendliness) but without the downsides.

Drew

[mjheathcote]

I rebuilt my complete braking system, the lot, pipes, new master cylinder etc and refilled with silicon. Never had to touch the braking system since, that was 16 years ago!
Having also fitted PTFE braided pipes at the same time, no problem with a soft pedal
For me, it was a good choice.
Mike

[elvimto]

This is my first car and when I did the brakes I used silicone fluid. I went through the full system and i have no problems with the braking system. This is used by a lot of the show car guys that have really expensive paint jobs just in casethey have a leak. In my car I am happy with the braking and the pedal feels good I only needed one can did the whole job which also surprised me. Its not that expensive when you think that you do not have to change fluid again, messing about with bleed nipples which usually break or stick and laying under a car when you can be driving the thing.

Cheers Stuart

[dasadrew]

Hi Stuart,

on the different forums people mention that the fluid should still be changed and purged every so often because a) water gets trapped in 'pockets' in the system as it is not by silicone brake fluid and b) the wear on pistons and seals is still there so the brake fluid gets contaminated just like 'normal' stuff. (I'm guessing the reason why brake fluid changes colour over its life is this contamination).

I'm guessing the 'softer' pedal would probably only be noticed by Seb. Vettel even if it is measurable in the laboratory.

Still, each one to their own I say! I'm glad this thread cropped up and prompted me to peruse the different sites - I'll probably plump for DOT5.1 myself.

Drew

[Gresley]

Hmmmmm...this is interesting! I was thinking of changing over TO silicone fluid in the Stag. I have had it in my 2.5PI for the last 7 years and it has been fine...so far! The brake pedal is solid and certainly not spongy.

[MB]

I have had Silicon fluid in my braking system for nearly 20 years, changed master cylinder, brake pipes all seals/cylinders and braided flexible hoses before I installed it. Mine had problems with the rear cylinders seizing or leaking every few years previously but not touched them since using silicon fluid.

The other side of the argument I have noticed recently there are small black specks in the reservoir and the peddle sometimes pumps up a bit lately. I think the seals in master cylinder are on the way out. Would they have lasted this long with dot 4, don’t know

Looking around for replacement seals or master cylinder and notice LD parts say on their website warranty is void if silicon fluid used in their refurbed/stainless steel insert M/C.

I think I will still use silicon fluid though as Braided hoses with Silicon fluid give a more solid pedal than dot 4 with original spec flexible hoses. I still have bodywork marks from drips of dot 4 and for a classic cars over long term/lowish mileage the non Hygroscopic properties gives a more reliable and probably more efficient brake system. But not lifetime use, unless you count in dog years.

There are discussions about the compatibility of the different fluids, the manufactures claim you can mix dot 5 with 4 you just loose the benefits. Lots of discussion saying differently on the web though.