Brake Fluid

**The Stranger:Me** · 2nd November 2006, 09:44

So they say brake fluid should be replaced every 12 months. I didn't know if this had been done in the last 12 months and the handle was getting a little more travel lately so I took the opportunity to replace the brake fluid.
But what with?
Well it needs to be dot 4. I know dot 5 has a higher boiling point, but is silicone based and I understand should not be used in a system not designed for dot 5.
So I went into repco and got a fresh bottle of dot 4 and use the vacuum bleeder to get rid of the old and replace the fluid.
All good, feel has returned to the lever.

But wait, there's more. Just sorting out my sons' boy racer and as it has had an engine transplant to a significantly more powerful engine I wanted to ensure the brakes were up to scratch. One thing recommended to us was racing fluid.

It goes like this (or so they say) dot 4 fluid should boil at no less than 230c, dot 5 at no less than 250c. Now we already know you shouldn't use dot 5 in a dot 4 system, but they have dot 4 race fluid which boils at over 300c. As well as that it is supposedly less compressible.

So I replaced the repco dot 4 fluid on the bike (only 2 weeks old now) with dot 4 race fluid. Well bugger me. the lever is now tight as a... well lets just say it is significantly tighter and has less travel and more feel to it.

So, maybe there is a difference between the cheap shit and the expensive stuff.

**placidfemme** · 2nd November 2006, 10:09

Well... I don't know anything about brake fluids... but I guess the old saying rings true...

you get what you pay for

**ZeroIndex** · 2nd November 2006, 10:23

also to do with brake fluid, maybe someone has an answer or some help for me:

Tried to top up the front brake fluid on the GPX, it's one of those boxes with the 2 screws, the 1st screw came out ok, but the 2nd one just went to pieces (all mashed up, can't remember the correct word, where the screw section gets all buckled).. how do i remove the screw without braking the brake fluid box?

**vifferman** · 2nd November 2006, 10:25

Originally Posted by CaN

I know dot 5 has a higher boiling point, but is silicone based and I understand should not be used in a system not designed for dot 5..

No, that's Dot5.1; Dot5 is the same as Dot3 and 4, just higher boiling point. You can interchage them without any major drama.

**vifferman** · 2nd November 2006, 10:31

Originally Posted by ZeroIndex

Tried to top up the front brake fluid on the GPX, it's one of those boxes with the 2 screws, the 1st screw came out ok, but the 2nd one just went to pieces (all mashed up, can't remember the correct word, where the screw section gets all buckled).. how do i remove the screw without braking the brake fluid box?

You're just going to have to do the best you can do persuade it to come out. first put some WD40 or whatever on it to (hopefully) lube it up. Then try to use a small straight-bladed screwdriver at an angle to get it to turn a bit, tapping the screwdriver with a spanner or snall hammer (no more than 3 or 4 kg head....) If all else fails, centrepunch the screw and drill it out carefully to remove the head. Once the head's off and the cap can be removed, apply more lube to the threads, leave a while then grab the shaft firmly with some pliers or vicegrips and undo it.
Buy some new screws! Put a tiny smear of grease on their threads for next time.

Worst case scenario: replacement brake cylinder and reservoir from a wrecker.

**Postie** · 2nd November 2006, 10:36

CaN, there was heaps about brake fluid in this post

**The Stranger:Me** · 2nd November 2006, 10:40

Originally Posted by vifferman

No, that's Dot5.1; Dot5 is the same as Dot3 and 4, just higher boiling point. You can interchage them without any major drama.

Are you absolutely sure on that one?
A quick look on the web finds lots of references to dot 5 being silicone based.

**vifferman** · 2nd November 2006, 10:41

Originally Posted by CaN

Are you absolutely sure on that one?
A quick look on the web finds lots of references to dot 5 being silicone based.

Right you are - I've got it arse (bottom) about face (arse).

My bad.

I'll

now.

**The Stranger:Me** · 2nd November 2006, 10:49

Originally Posted by Postie

CaN, there was heaps about brake fluid in this post

One thing not covered there is that the silicone based fluids don't absorb water. The water instead spearates out and travels to the lowest point (the bottom of the caliper) and stays there. Water boils at 100c. As the water boils it releases gas. The gas is compressible.
Thus silicone fluids, although they generally have a higher boiling point can introduce problems at much lower temperatures.

I would be very wary of using a dot 5 fluid unless the system specifies it.

**KLOWN** · 2nd November 2006, 11:38

Originally Posted by ZeroIndex

also to do with brake fluid, maybe someone has an answer or some help for me:

Tried to top up the front brake fluid on the GPX, it's one of those boxes with the 2 screws, the 1st screw came out ok, but the 2nd one just went to pieces (all mashed up, can't remember the correct word, where the screw section gets all buckled).. how do i remove the screw without braking the brake fluid box?

do you have an impact driver? that is always helpfull for removing such screws.

**Ixion** · 2nd November 2006, 11:43

Be careful with impact drivers on such a place. The reservoir is basically just a little box to hold the fluid, nothing clever about it. And the lids just a lid. But the box (and lid) are often not strong, made of muck metal. Bashing them with an impact driver and BLOODY BIG HAMMER risks the reservoir or lid cracking or breaking. I'd drill the head off the screw myself

**Colapop** · 2nd November 2006, 12:18

Back to fluids... I have two reservoirs (1 each side of the handlebars) and both have "use dot 4" on them I haven't checked the manual yet but I suspect 1 is the brake reservoir and the other the clutch. I assume they both take the same fluid? If so then I think I should change one or both out because the left reservoir fluid is a dark milky green colour and the other is clear gold (al though slightly low) Is this right?

**vifferman** · 2nd November 2006, 12:23

Originally Posted by Colapop

Back to fluids... the left reservoir fluid is a dark milky green colour and the other is clear gold (al though slightly low) Is this right?

The clutch fluid (left) is 'ted. It's not super important from a performance point of view, as it doesn't get hot, but you could end up with the master and slave cylinders full of crud, and the water in the fluid will corrode the metal parts in the system.
Change it.

The fluid is very slightly goldish to clear when new, although some are deliberately coloured to make 'em pretty. Brake fluid is hygroscopic (absorbs moisture) and colours as it gets more moisture in it.
Dark = Bad; Light = Good.

**emaN** · 2nd November 2006, 13:05

another thing Col,
on mine it looks low, but that's just 'cos of the angle i've tilted the lever, for better riding/braking position. once you level it up, it might be ok