Is it possible to discern which type of brake fluid I have?

[Benedict.]

Given that it seems like I'll be bleeding the brakes fairly soon is there a way of telling if fancy silicone brake (DOT 5) fluid has been used - the stuff that's not compatible with "normal" DOT 4 & 5.1 ?

 

Haven't found any receipts for brake fluid in the history, though it was upgraded to 4-pots at the front, so it's obviously been bled at some point.

 

Cheers,

Ben.

(more brake questions to follow no doubt 😬 )

[Pooh_R]

Silicone fluid is safe on paint work. 4 and 5.1 will strip paintwork so you could find some painted surface that you're prepared to have paint stripped and put some fluid on? 😳

[Jonathan Kay]

In theory you could do it by layering the unknown on the known two possibilities and seeing if it mixes. Or by seeing if it separates after being mixed with water.

 

In practice I wouldn't rely on either of those if it were my brakes.

 

Jonathan

[djg]

Silicone brake fluid tends to be purple when I have seen it.

 

It's done on purpose so it's easy to spot if you have it. AP don't recommend silicone fluids or 5.1 for the Caterham sold calipers.

 

I would just give it all a good bleed through with a DOT 4, you may be able to see the new clean stuff come through dependant on how old the old fluid is.

 

HTH

 

Doug

 

Edited by - DJG on 6 Mar 2013 22:10:05

[Roger Ford]

AP don't recommend silicone fluids or 5.1 for the Caterham sold calipers.

 

Is that "AP recommend not using 5.1"

or

"AP's recommended brake fluid is DOT 4"?

 

I'm not aware of any disadvantages of 5.1 over 4, but I'm also aware that a lot of the best brake fluids don't meet 5.1 spec for technical reasons. Would be interested to know whether there's any reason NOT to use 5.1 in general.

 

To the original poster, I think it's very unlikely that you have 5.0 in there. It's not widely used - the only reason anyone's likely to have used it is if they're paranoid about brake fluid damage to paintwork.

 

[Benedict.]

Thanks for the replies chaps (both on and off the forum). Agree is isn't massively likely that it's dot5, but for the time it takes I shall be testing its paint removing capabilities, miscibility with the dot4 I have lying around and looking for shades of purple .

 

Given its indeterminate age I'm going to take the opportunity to replace it all, and I'm contemplating replacing the master cylinder with the AP one. It already has the AP 4pots on the front, but I much preferred the pedal feel of my previous seven which had those and the AP m/c.

 

Thanks,

Ben

[elie boone]

Why would you want to mix brake fluids ? i use an air blow gun on a modifyed reservoir cap to empty the system, and i use the same system to bleed the calipers, very easy to do by yourself and no risk of air being trapped in the system.

[Benedict.]

Quoting elie boone: 

Why would you want to mix brake fluids ?

I don't, hence my original question; and if you're changing between the 2, it's not enough to flush the old stuff out you have to clean the residue from inside the calipers etc as well.

Have you a link to your air-bleed system? Does it need a compressor?

 

Ben

 

[Paul Deslandes]

unless you're sure you have incompatible fluid in there don't blow it out with air, just flush it through thoroughly with fresh fluid, bleeding each calliper (and BOTH nipples on the 4-pots) several times until it all runs clear. The last time I replaced the fluid and blew it through with air it took ages to get all the air out, especially from the rear callipers and was, in my view, an unnecessary PITA.

[elie boone]

Yes you need a compressor and a presure regulator, you need about 1bar, further you need a old reservoir cap where youdriil a 5mm hole in it.

Open 1 bleed nipple connect a tube to it to collect the old brake fluid Insert the gun in the modifyed reservoir cap and apply pressure it doesn't take long before you will see bubles, the you stop and do they rest of the bleed nipples.

 

[BBL]

Quoting elie boone: 

Yes you need a compressor and a presure regulator, you need about 1bar, further you need a old reservoir cap where youdriil a 5mm hole in it.

Open 1 bleed nipple connect a tube to it to collect the old brake fluid Insert the gun in the modifyed reservoir cap and apply pressure it doesn't take long before you will see bubles, the you stop and do they rest of the bleed nipples.

Sounds just like a Speedi-Bleed!

 

 

edit -- not "Seedi-Bleed", though I like that name as well.

 

Edited by - BBL on 7 Mar 2013 16:49:38

[djg]

Roger

 

I have read here and on AP's website that the 4 pots should have dot 4 used in them.

 

I assumed that thr seals won't like the 5.1 and have only used the 4 personally. I have had no problems.

 

Doug

[Roger Ford]

How odd. Don't suppose you know where on AP's website? Can't see anything here.

 

In case you think I'm just arguing for the sake of it, I use 5.1 in my standard brakes, and I'm trying to figure out whether there's anything specifically bad about 5.1, or whether (as I suspect) AP just want you to use their particular high-grade fluids which happen to be DOT 4.

[Grim Reaper]

Not really any difference between DOT4 and DOT5.1 apart from the viscosity and boiling points, but you can get DOT4's with the viscosities and boiling points close to those of DOT5.1's if you feel you MUST put what the manufacturer says into your reservoir.

Little FAQ thingy here

Oh, DOT 3,4 & 5.1 fluids start out as clear to amber, turning brown/black when old and having absorbed water, DOT 5 (silicone) is purple and does not change colour, it also does not absorb or dissipate water, so has similar properties to oil, ie water goes to the bottom, which in a brake system usually means the calipers where the water boils readily in the heat-rich conditions and causes poor braking feel and corrosion inside the expensive bits.

Other type is Mineral brake fluid used in citroen, rolls royce some audi and jaguar, this is green in colour.

Never mix different colours.

Mixing DOT 4 with DOT5 will result in something that looks like Italian Salad dressing and will be about as much use as this in your brakes.

 

Edited by - Grim Reaper on 7 Mar 2013 20:57:05

[keybaud]

Quoting Grim Reaper: 

Not really any difference between DOT4 and DOT5.1 apart from the viscosity and boiling points

 

I was under the impression that DOT 5.x was more corrosive than DOT 4.x.

[elie boone]

BBL, indeed speedi bleed works on the same principe, works a tread

[Grim Reaper]

The only spec that relates to 'corrosiveness' within the DOT specs for both 4 and 5.1 is the Ph, both specs show acceptable Ph as being between 7 and 11.5.

Vehicles fitted with ABS will generally (I can't think of any reason why there would be a negative) benefit from using a lower viscosity fluid.

Shell DOT4 ESL has a viscosity of 675@-40 (very thin) yet it is a DOT4 spec fluid because of its boiling point not coming within the DOT5.1 specs. (Ph7.7 according to its data sheet)

Motul DOT5.1 has a viscosity of 820@-40, (No Ph given on its data sheet)

Comma DOT5.1 claims <900 viscosity, (Ph between 7.0 and 11.5)

Castrol DOT4 1200@-40, (Ph7.3)