goo in my brake fluid. Whats going on?

[carefull]

Hi there,

Just got the Caterham back on the road and the brakes are not good. There seems to be excessive pedal pressure required to make em work. I took the cap off the fluid chamber and there’s clear goo in it and the best way I can describe it is that it looks like K.Y jelly (apparently..)

What do I need to do and what’s causing the goo in the first place?

Also, I guess I will need to replace the fluid so whats the best stuff to use?


Thanks in advance
Jason

[anonymous-user]

Somebody better informed will be along soon, but I'd investigate the effect of mixing mineral and silicon brake fluid as I believe this may have effects along these lines.

[GreenV8S]

Knackered seals can leave black goo in the fluid. Mixing DOT5 with other fluids can knacker the seals. Allegedly. Or not, depending who you believe. (Some people who sell DOT5 say it's fine but only if you buy *their* DOT5 etc.)

[sleep envy]

you might have an air leak which has let moisture into the system seeing as brake fluid is hydroscopic...

[Sam_68]

GreenV8S said:

Knackered seals can leave black goo in the fluid. Mixing DOT5 with other fluids can knacker the seals. Allegedly. Or not, depending who you believe. (Some people who sell DOT5 say it's fine but only if you buy *their* DOT5 etc.)

DOT 5 should NEVER be mixed with other fluids; it is silicone based. DOT 5.1 can be mixed with other (DOT 3 and DOT 4) fluids, though as GreenV8S says, there is some anecdotal evidence of seal problems where DOT 5.1 is mixed with lesser specifications, since I understand that the chemical composition of 5.1 is somewhat different to normal DOT 3 and 4 polyglycol fluids.

To be honest, the extra cost of DOT 5.1 is so marginal that I can't imagine why anyone would want to use anything less. Bleed you system through with lots of nice, fresh DOT 5.1, check for leaks and keep an eye on the colour!

[GreenV8S]

Sam_68 said:

though as GreenV8S says, there is some anecdotal evidence of seal problems where DOT 5.1 is mixed with lesser specifications, since I understand that the chemical composition of 5.1 is somewhat different to normal DOT 3 and 4 polyglycol fluids.

My comments were specifically about mixing other fluids with DOT5 not DOT5.1. I've always held to the view that DOT5 is fundamentally incompatible with DOT3, DOT4 and DOT5.1. However, I've seen reports from people who supply DOT5 claiming that this view is out of date and in fact you can change between them without the traditional flushing systems, replacing seals etc. I'm not at all convinced to be honest. But that is what they claim.

[Sam_68]

GreenV8S said:

My comments were specifically about mixing other fluids with DOT5 not DOT5.1.

I've never heard anyone claim that it is safe to mix DOT 5 (silicone) fluid with conventional (Polyglycol) fluid, so I'm confused why you would even want to make the suggestion that it might be, especially if you yourself are not convinced?

Bottom line is that you should not mix DOT 5.1 with any other type.

If there is any suspicion that fluids have been mixed (and the OP has not made any suggestion that this might be the case!), then the system needs thoroughly flushing through with DOT 3/4/5.1 fluid and the condition of seals checking.

[GreenV8S]

Sam_68 said:

I've never heard anyone claim that it is safe to mix DOT 5 (silicone) fluid with conventional (Polyglycol) fluid, so I'm confused why you would even want to make the suggestion that it might be, especially if you yourself are not convinced?

I have, which is why I added the caveat, but I'm not convinced, which is why I phrased it the way I did. I hope that clears up your confusion.