is dot 5 safe to use in a dot 4 system?

[Thom]

ive done this before but today ive been told that it is not adviseable.

Now im not entirely sure of the difference but in my mind dot 5 feels firmer on the lever, im not really sure but i like it more than dot 4 which feels crap (could actually just be rubber brakes hoses)
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Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

[G]

Dot 4 absorbs water, Dot 5 doesn't; if I remember. However this means that water can 'pool' and start to corrode stuff with Dot 5.
I believe Dot 5 has a higher boiling point; but this shouldn't be an issue, even for decent club-level racing and beyond.
Dot 4 and dot 5 shouldn't be mixed, as your bike will melt, or something.
Fresh fluid and decent lines will make a lot more difference than Dot 4/or 5. You can also get Dot 5.1 which is 'compatible' with Dot 4, but claims to be better.

[MattEMulsion]

Why do you want to use something that is better than DOT4 anyway? DOT4 is fine for everyday use.
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Yamaha YZF-R6

[MarJay]

Dot 5 is not road legal, whereas dot 5.1 is IIRC.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Cigaro]

I'd put Dot4 in it if I were you.

Using the wrong brake fluid can be very expensive, as I once found out.

[map]

As said, use DOT 4 if that's what it says on for the bike as that's what it was designed with. However, you can use DOT 5.1 (the .1 is important) if you've made any mods to the brake system or just want to try it.

DO NOT use DOT 5 on a road bike in everyday use.

I hope that's clear.


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...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Kickstart]

Hi

Dot 3, 4, 5 and 5.1 are road legal. From memory a load of Harleys use DOT 5 fluid.

DOT 5 is silicone based and cannot be mixed with the others (which are Polyalkylene Glycol Ether based). Also there is the possibility of seals in the system not being compatible with DOT 5.

Main difference is the boiling points.

DOT 3 = 205° C dry boiling point (140° C wet boiling point )
DOT 4 = 230° C dry boiling point (155° C wet boiling point )
DOT 5 = 260° C dry boiling point (180° C wet boiling point )
DOT 5.1 = 270° C dry boiling point (190.6° C wet boiling point )

A fluid might well only just meet one of these specs and massively exceed one of the others. For example fluids intended for race use might be rated DOT 3 as they have a poor wet boiling point despite a very good dry boiling point. For race use where they are expecting the fluid to be changed often the wet boiling point is pretty irrelevant.

The silicone based DOT 5 fluid is often said to give more level / pedal travel than the normal fluids (it is alleged the fluid itself is slightly compressible). Its massive advantage is that it doesn't absorb water and so should last pretty close to indefinatly (people lob it into rarely used classic cars so that they can ignore it, rather than DOT 3, 4 or 5.1 which would still need regular changing). The down side of it not absorbing water is that should any water get into the system it is very difficult to flush it out.

For a regularly used bike just put in a decent normal fluid (DOT 5.1) and change it occasionally. And unless you want to be changing the fluid every few weeks then ignore the specialised fluids for race use.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Thom]

cheers lads maybe its more in my head than anything then!

I think i could be investing in some 'budget' brake lines soon!
____________________
Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

[Kickstart]