Dot3

[Hans]

Hi. I need to soft the surrounds on a pair of LE14. Cant find DOT3. Can I use DOT4 or...?

[Woofer]

Hi. I need to soft the surrounds on a pair of LE14. Cant find DOT3. Can I use DOT4 or...?

I've used Dot 4, with OK results, BUT, they were with the old grey surrounds and I'm not sure if they are quite the same as the 'yellowed' surrounds. Someone here may know more.

I actually chased this up with a local Brake Fluid manufacturer some time ago, and this was their response (which I quote....)

The non silicone oil based brake fluids are the type that you are
describing. They are predominantly based around the class of substances
called polyethylene glycol ethers and polypropylene glycols and
polypropylene glycol ethers.


These substances are included in brake fluid formulations and when chosen
properly, their solubility in rubbers is very low and so they do not cause
swelling in these master cylinder rubbers, seals and gaskets. It is not
true that additives are included to prevent rubber swelling. The lack of
rubber swell is inherent in the properties of the chosen ingredients in the
brake fluid itself.


Your problem of restoring old HI Fi "rubbers" is an interesting one. All of
these "rubbers" are no doubt types of flexible polymer foams. All polymers
are usually formed from compounded masterbatch mixtures which also comprise
what are called plasticizing agents. These plasticizer substances are
included in the base polymer to confer flexibility on the polymer.
Plasticizers are usually low molecular weight esters. These plasticizer
esters are not included in brake fluid compositions.


I am guessing that a certain amount ( perhaps not all) of embrittlement of
some synthetic rubber foams is as a result of loss of plasticizer over
time. Loss of flexibility is also no doubt due to the effects of aerial
oxidation of the polymer and cross linking through the effects of UV light.
Your Hi Fi rubbers may well be benefiting from some sort of plasticising
effect that brake fluids can confer, in a similar way to the action of
normal plasticizers in plastics production. However, this is not an expert
view of the subject from the perspective of a polymer chemist.


I don't really think that there is any way that you can buy small amounts
of brake fluid components other than by purchasing brake fluid itself. The
purchase of plasticizer chemicals is also problematic in a normal retail
market.


I am sorry that I cannot be of any more help in this regard.


Gary Holliday,
Technical Manager (Consumer),
Huntsman Corporation Australia,
Surfactants Technical Centre,
61 Market Road, Brooklyn, Vic, 3012, Australia.


Cheers all,
Woofer.

[BMWCCA]

DOT 3 and DOT 4 are basically the same with a higher resistance to temperature on the 4. DOT 5 is silicone based and not the same.

IMHO, if DOT 3 works on Lansaloy surrounds, then so will DOT 4. Keep either away from any painted surface.