Brake fluid - is APL Racing Formula Dot 5.1 suitable?

[RichardS]

Well - my quick question generated a lively response! Perhaps my next post should be whether to grease or oil the trunnions!!

I've just ordered some Castrol Response Dot 4 Brake Fluid - its advertised on the Holden website which seems a fair recommendation http://www.holden.co.uk/displayproduct. ... de=090.930

I've actually bought mine off Ebay at a good price - the seller has more http://cgi.ebay.co.uk/2x-1litre-Castrol ... 1|294%3A50

Richard

[GrUmPyBoDgEr]

Thanks for attaching that interesting bit of information; a good read.
I was at first worried about the mention of varying compresibility of fluids but with further reading the statement was substantiated by the mention of air & water inclusion.
The article does put most of the already asked questions, including the original one to bed.
Cheers
John

[CBUEB1771]

Hygroscopic hydraulic fluids originated in aircraft practice. The issue in aircraft is not having water in the hydraulics boil but freeze. Pilots are not amused when control surfaces don't move due to a plug of ice in the system. This is prevented if the hydraulic fluid can absorb reasonable amounts of water into solution. A dilute solution of water in a hygroscopic hydraulic fluid will not freeze until much lower than 0 C. Frozen water is not much of a problem for racing car brakes but a very real concern for road vehicles in European and North American markets.

[patrics]

My 2 pence / cents worth to an over debated topic

No brake manufacture or vehicle manufacture would say it?s okay to put silicone fluid in their systems ? that should give you a clue.
It has so many issues
1. Becomes compressible with temperature which rises rapidly above 100?C
2. Lubrication problems with aluminium alloys
3. Effects the paint ability of metal surfaces
4. Bleed problems
5. Not suitable for use with certain rubbers in brake systems which I have in mine so sure most or all of you will have in yours.
6. Non hygroscopic could cause problems ? water enters the system through condensation / and through standard type rubber hoses

Personally don?t think that being non hygroscopic is a problem, as Rolls and Citroen have used mineral fluid in brake systems in older models without problem.

Traditional brake fluid is vegetable not mineral ? never confuse the two

If racing fluids are not suitable for road use then that will probably because of extreme low temperature performance ? just doesn?t matter to us.

Dot 5 used in racing cars?

I wouldn?t worry too much about which branded brake fluid I used in my car as long as it wasn?t silicone - I am trying to improve the performance not go the other way.
In the industry Dot 5.1 is known as super Dot 4 because it has the high temperature properties of the dot 5 fluid but not the low temperature properties ? but Dot 5.1 is used in most production cars today. Unfortunately compressibility isn?t in the spec so they can make these high temperature performance claims.

Having said that if you have silicone fluid in your system, don?t change it unless you are actually having problems ? track days etc or you are rebuilding the entire system. The problems arise with certain rubbers when silicone and traditional fluids mix ? turn your seals into chewing gum

Any way the question was is dot 5.1 suitable? ? Yes it is. In Europe standard Ford fluid is super Dot 4 (5.1)

Steveww mentioned SRF fluid which is very good but expensive. This is a silicon ester fluid which is compatible with all rubbers and fluid.

Regards
Steve

[GrUmPyBoDgEr]

Well - my quick question generated a lively response! Perhaps my next post should be whether to grease or oil the trunnions!!

I've just ordered some Castrol Response Dot 4 Brake Fluid - its advertised on the Holden website which seems a fair recommendation http://www.holden.co.uk/displayproduct. ... de=090.930

I've actually bought mine off Ebay at a good price - the seller has more http://cgi.ebay.co.uk/2x-1litre-Castrol ... 1|294%3A50

Richard

Ah yes the trunnion question, that one's really be done to death. Happy reading
Cheers
John