brake fluid confusion

[pharriso]

There's an interesting write up here - http://www.mossmotors.com/SiteGraphics/Pages/Brake_Fluid/brake_fluid_long.html

Most relevant section reproduced below:

"What About the Stories of Silicone Brake Fluid Causing Seals to swell?

These stories abound on the internet, but I have not actually spoken to the person it happened to, so I cannot comment on the actual incident that started the story. We do know that it is very, very unlikely that a brake fluid meeting FMVS 116 would do that. The testing is designed to make that sort of thing impossible. I can tell you that the literature is full of reference to the grotesquely swollen and gooey seals that you get if the brake system is contaminated with petroleum based oils or solvents. It does not take much of this kind of contamination to ruin all of the seals in a system. The contamination can usually be traced to the use of improper cleaners, rags contaminated with motor oil or grease, or handling the seal with hands that have petroleum based contaminants on them. We have tried to duplicate these reported problems by soaking brake cups in DOT 5 fluid, but we have never found a problem. However, these stories have a life of their own and it is doubtful that they will ever go away. It is perhaps a modern version of the traditional British natural rubber brake seal warning about using ?the wrong fluid?.

Maybe it's just urban legend? Moss Motors would know, they'd be getting parts return claims ...

[elanner]

Last October I fitted a new brake master cylinder purchased from R.D. Enterprises. I used standard DOT 4 fluid, which is what the installation instructions called for.

So, for the past 14 months (2000 miles or so), every time I check the brake fluid I find it to be getting blacker and blacker. It's now to the point that I'm going to flush it and start over, either before the Winter shutdown or next Spring.

So what's going on? Are the seals simply deteriorating, dissolving into the fluid? Shouldn't clean brake fluid (where you can clearly see the bottom of the reservoir) stay clear? Do I need to fit new seals?

Heck, you wouldn't think hydraulic fluid and seals would be rocket science these days.

Nick

Edit: Opps, I didn't mean to ding R.D. Enterprises, only to make it clear that I got the master cylinder from a reputable supplier!

[Lyn7]

Hi Nick, in my experience when the fluid goes black the seals are perishing! If you are going to the trouble of "flushing" through you might as well change the seals at the same time.
Cheers Lyn..

[Chancer]

Great article!

Nick, this part is relevant to you:

We have all seen old discolored brake fluid and I used to think that was a pretty good indicator of ?old? brake fluid. ?A number of independent sources pointed out that the color of brake fluid cannot be used as an indicator of its condition. One brake fluid manufacturer went on to explain that some new brake fluids have additives that will cause the brake fluid to change color when exposed to the rubber seals. Another source provided data showing that brake fluid appearing almost pitch black can pass all available tests while other fluid samples appearing to be "good" could fail those same tests.?

Worth reading the whole article though.

[elanner]

Hmm. Well, that's all about as clear as my brake fluid!

You're right, it's a good article, now that I've read through it a bit more and found the part you mention.

But from all of this I realize that by Spring the fluid will be 18 months old - not that far off 2 years - so coming up for a flush anyway, regardless of its colour. As Lyn mentioned, while I'm at it it would be prudent to check the seals and see what they look like. And once they're out I may as well fit new ones.

I forgot to mention that the fluid in the new clutch master cylinder, which I fitted at the same time, remains as clear as the day I filled it.

Nick

[rgh0]

Nick

i have the reverse with the fluid in my brake master cylinder reservoirs stayingclear like new but the clutch fluid goes black soon after changing.

My brake master cylinder in the Elan is a Nissan / Datsun sourced unit and the clutch the original Girling unit. The rubbers in the Girling unit clearly wear or dissolves faster than the Datsun brake master cylinder rubbers in the same fluids.

There are so many variables in terms of brake fluid, seal rubber components, cylinder designs and use patters that it is not surprising you get so many different comments on what works and what does not.

cheers
Rohan

[elanner]

> There are so many variables in terms of brake fluid, seal rubber components,
> cylinder designs and use patters that it is not surprising you get so many
> different comments on what works and what does not.

The gentlemanly art of understatement lives!

I prefer Rohan's problem to mine - losing the clutch due to rotten seals ain't so much of a problem. Losing the brakes however.....

Nick