Fluid VS Hydraulic oil

[Darrell]

There is a chap on difflock with a vitara that has put hydraulic oil (excavator type) in the brake system. This to me sounds a really stupid thing to do. Am I right in thinking all the rubber seals and hoses are now knackered as the rubbers will swell. I've not heard of anybody doing this before but I have seen how much the brake caliper slide pin seals can swell by using ordinary petroleum based grease instead of rubber grease. One chap has already expressed his opinion and I expect more to follow. Anyone know for sure ??

http://forum.difflock.com/viewtopic.php?t=71289

[lazy rambler]

Not sure, but from my experiance with mtb's is a very bad idea. I've got one bike running mineral oil and one running DOT 4, there's big warnings in the instructions and bleed kit (I have 2, 1 for each fluid) not to cross contaminate.

[ScottieJ]

All i can say to that is

What a silly thing to do

[Tramp]

In fairness I imagine that its virtually the same thing, what is brake fluid made out of? I think oil. After all it does the same job in either role, if its safe to use with hydraulic system seals I'd have thought it would be the same with brake system seals

[ROBBIE]

Would seem its not a good idea after reading it all

[Christoff]

It's not the same stuff at all. Both are used in very different applications. Take Powersteering fluid and brake fluid, both hydraulic systems, however powersteering oil is much thicker and if spilt on rubber hoses like coolant it needs to be cleaned off because it will attack it.

Brake fluid needs to withstand very high temperatures without thinning or shearing or boiling.

[Tramp]

I can't say I'm an expert when it comes to hydraulic systems & I don't know how hot brake calipers can get but what I do know is when I worked at the steel works we had a lot of hydraulic systems to roll the steel it all got pretty hot especially in the caster where it was in close proximity to 1000 degree plus steel. I don't think heat is an issue really. I'd not really considered viscosity, after all the system is all small bore pipework so thinner would be better.

however powersteering oil is much thicker and if spilt on rubber hoses like coolant it needs to be cleaned off because it will attack it.

This is the same for all hydraulic fluids including brake fluid isn't it? They all have the same coshh assesments & ppe requirements don't they?

I mean I certainly wouldn't use the stuff myself but I can understand why he thought it would be suitable, it is the same theory & type of system after all!

[Christoff]

Well yeah I'm sure I'm missing a decisive point of argument somewhere really. It wouldn't ever occur to me to try any other fluid than brake fluid. You would just hold the job back until you got the proper stuff.

[Tramp]

I agree! If it specifies brake fluid, use brake fluid - end of!

[Christoff]

It's just designed specially for that particular system. Suppose someone's got to try it we should thank him for taking the trouble to do it so we don't have to.