Q. for AndyM, brake fluid

[embee 7,288]

Question aimed at AndyM but I've posted it up for general consumption, in case anyone is interested.

 

I need to get some new brake fluid for general vehicle use on my fleet, bikes and cars of various vintages (1975 -2012, ABS and non, linked and separate etc). I've used various brands in the past, always stuck to recognised stuff (Castrol etc).

Eurocarparts have various stuff listed, a couple from ATE (makers of the retarders on my airhead BMW). The difference is in the viscosity, the SL6 (DOT4) is a much lower viscosity (700cSt at -40C) than the TYP200 (DOT4) (1400cSt at -40C). I can understand the principle that lower viscosity could in theory improve response rates for ABS etc. particularly when cold, not that I often ride any bikes in -40C. The differences in wet/dry boiling are pretty academic as far as I can see.

https://www.eurocarparts.com/ecp/p/car-accessories/engine-oils-and-car-fluids/auxiliary-fluids/brake-fluid/?524770042&0&cc5_179

https://www.eurocarparts.com/ecp/p/car-accessories/engine-oils-and-car-fluids/auxiliary-fluids/brake-fluid/?524770150&0&cc5_179

 

A couple of questions.

Is lower viscosity a good thing?

Would the low viscosity stuff cause issues with the older kit with suddenly starting to leak or similar?

Should I just use something more "traditional"?

Or does it matter?

 

Ta muchly.

Edited May 3, 2019 by embee

[Andy m 23,508]

It is many years since I did hydraulics but I think you have the jist of it. 

 

DOT 4 is a standard, so anything that meets the standard is OK. It'll brake on a normal day, not swell your seals etc.

 

Then we have the car makers deciding that DOT blokes weren't strict  enough and wanting to tighten everything up. This is because either/and:

 

Lower viscosity is  easier to pump round so means the ABS pump can handle it on a smaller fuse.

Lower viscosity is easier to bleed, so that knuckle joint they didn't quite get right will clear of air a lot sooner

Their lawyers told them they couldn't insist the bottle had a logo, so went for the next best thing.

 

Braking performance isn't going to change, you are using the oil as a substitute for steel push-rods, it isn't flowing that much. The cycle rate in practice is slow enough it won't do anything. It will be slightly more prone to leaking so your older systems may not like it.

 

I would cheerfully use DOT4 meant for the newer vehicles in the older ones. They are tougher, simpler and will either leak or won't. I'd rather use fresh fluid of slightly the wrong sort than old stuff or even worse what's been in use so long it stinks.

 

 Andy

[embee 7,288]

Cheers.

After writing the above I reflected that if new brake fluid makes seals start to leak, they were probably on the point of leaking anyway.