fent

iTrader: (1)

I'm having my new brake upgrade fitted next week and I notcied the brake fluid reservoir cap states "DOT 3 fluid only"... Seriously, DOT 3? I thought DOT 4 was standard and then DOT 5 as an upgrade.

When I checked the bottle on my mountain bike brake fluid it states that DOT 5.1 is compatible with lower grades but cannot be mixed with mineral oil so does the same apply to car brakes?

Is there any reason why my scooby says DOT 3 only?

car is 2003 WRX

AS Performance

iTrader: (4)

minimum requirement..............dot3, dot4 & dot5.1 will all mix if needs be but best to use one specific type IMO

just make sure you do NOT use dot5..........

fent

iTrader: (1)

Ah, I see, I read it the other way as DOT 3 only and no higher as I wasn't aware of DOT 3 or any lower, all cars I have had including my old kit car all had DOT 4.

The fluid is going to get a full change so it will not be mixed.

Out of interest what is the difference between DOT 5 and 5.1? my bike brakes I mentioned earlier are acutually 5.1

Cheers for confirming

Bob99

Don't use DOT5 as it is a silicone-based brake fluid (contains at least 70% by weight of a diorgano polysiloxane.

Unlike polyethylene glycol based fluids, it is hydrophobic. An advantage over other forms of brake fluid is that silicone has a more stable viscosity index over a wider temperature range. Another property is that it does not damage paint.

Using DOT 5 in a DOT 3 or DOT 4 system without proper flushing will cause damage to the seals and cause brake failure.
DOT 5 brake fluid is not compatible with anti-lock brake systems.
DOT 5 brake fluid absorbs a small amount of air requiring care when bleeding the system of air

However DOT 5.1 is the non-silicone version of DOT 5 and can be used with DOT 3 and DOT 4 fluids.

fent

iTrader: (1)

Cheers Bob, very helpful.
My mechanic mentioned the silicone fluid and also that it is much more expensive so I was planning on speccing DOT 4, it's a daily commute which gets spirited driving at weekends only, no track use etc so I assume this will be fine.
I'm having the Godspeed 335mm disc upgrade fitted with the larger Aston pads and two piece grooved discs so I'm hoping this will help dissipate heat better than the standard specs I had on before

AS Performance

iTrader: (4)

dot5 has a specific Military use as its main advantage is long life.............classic car guys like it also as it wont damage paint BUT if your spilling that much fluid to cause an issue you need a bigger bib

specifically because it doesn't absorb moisture is the reason it can lead to other issues as in arduous use the water turns to vapour which is compressible and hence a distinct lack of system pressure

we do various fluids from fast road through to aggressive race use if required

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