Which brake fluid to use?

[andyjshaw]

How can you tell which brake fluid your car has inside it? Do you assume that it has DOT4 as specified in the Haynes Manual? Also, does anyone know how much brake fluid you need to do a complete change of fluid?

I am planning to change my front discs and pads tomorrow but I am also considering changing the fluid at the same time. I am assuming that I should use DOT4 (as recommended in the Haynes Manual) but I am concerned that if it has ever been changed before it might have DOT5 in it. As it is advised generally that you do not "mix" fluids as it can cause corrosion, am I safe replacing the whole system with one fluid (whatever it is) or might replacing it with a different type than it is used to also cause problems?

[Kandyman]

Hi Andy,

you go for the EBC ones in the end ? i would try and replace the fluid with DOT 5 but not sure the best way to do that :shrug: But do let us know how you get on .

Good Luck

[MartinW]

Do NOT, under any circumstances, use DOT5. This is silicon based and whilst it won't absorb moisture, or lift the paint, it is incompatable with DOT3/4/5.1 fluids which are also synthetic but are glycol ester based.

DOT5 is purple, so you'll know it is DOT 5 if it is in there, and it should not be, but it is really only in the classic car side of things (pre-fancy ABS brakes etc) that DOT5 makes sense being suitable for longer service life, but in ABS systems with pumps, DOT5 will aerate and is totally unsuitable.

DOT5.1 is ok, but has a higher boiling point and consequently a shorter service life, so stick with DOT4. As to how much, doesn't Haynes state the volume required? Also, you'll notice your new bottle of brake fluid that you buy will have a foil seal on the top, ensure that when you fill the system, you keep sufficient to top it up immediately after or within a few days, but then dispose of the rest.

Keep a small sealed bottle in the boot for later top-ups. In this damp Winter weather, without the foil, the fluid will be useless within the month. Normal brake fluid will absorb moisture and this reduces the boiling point, causes bubbling/vapour bubbles at higher temperatures near the hot discs under hard braking and induces rust in your piping, and wheel cylinders leading to seal failure.

[JohnDotCom]

Some very Useful Information there Martin, Thanks a lot will bare all that in mind as due a Brake fluid change.

[andyjshaw]

Thanks guys. Yes I did go for the EBC brakes and I am looking forward to fitting them - they look mean - and what a great service I got from them too.

Thanks for the details regarding the fluids, I will make sure that I put DOT4 in as the current fluid is not coloured. I was confused by info on the internet so your help is greatly appreciated!

I will post a picture of my new wheels once the discs are fitted!

[MartinW]

I'm about to fit Galfer pads and discs and handbrake shoes. Be interesting to see how they work as they are a similar price to OEM.

[Kandyman]

Do NOT, under any circumstances, use DOT5. This is silicon based and whilst it won't absorb moisture, or lift the paint, it is incompatable with DOT3/4/5.1 fluids which are also synthetic but are glycol ester based.

DOT5 is purple, so you'll know it is DOT 5 if it is in there, and it should not be, but it is really only in the classic car side of things (pre-fancy ABS brakes etc) that DOT5 makes sense being suitable for longer service life, but in ABS systems with pumps, DOT5 will aerate and is totally unsuitable.

DOT5.1 is ok, but has a higher boiling point and consequently a shorter service life, so stick with DOT4. As to how much, doesn't Haynes state the volume required? Also, you'll notice your new bottle of brake fluid that you buy will have a foil seal on the top, ensure that when you fill the system, you keep sufficient to top it up immediately after or within a few days, but then dispose of the rest.

Keep a small sealed bottle in the boot for later top-ups. In this damp Winter weather, without the foil, the fluid will be useless within the month. Normal brake fluid will absorb moisture and this reduces the boiling point, causes bubbling/vapour bubbles at higher temperatures near the hot discs under hard braking and induces rust in your piping, and wheel cylinders leading to seal failure.


Very Helpful Martin thanks :)

[Kandyman]

Thanks guys. Yes I did go for the EBC brakes and I am looking forward to fitting them - they look mean - and what a great service I got from them too.

Thanks for the details regarding the fluids, I will make sure that I put DOT4 in as the current fluid is not coloured. I was confused by info on the internet so your help is greatly appreciated!

I will post a picture of my new wheels once the discs are fitted!

I have got new front and back discs and pads to get fitted when i find the time :) had them about 3 weeks now

[andyjshaw]

What a day! Didn't change the fluid in the end as I had problems with both sides of the brakes. Firstly the pad sensor had seized into the offside pad and the housing had already broken, and then the nearside torx screw that hold the disc in place had no "whatever you call it" to get a tool in to undo it - I finished up having to drill it and hammer a bit into it to get some leverage to undo it. Anyway, got there in the end but the fluid will have to wait! Hopefully I can get a new sensor (part no. anyone?) as I can't put up with the dash warning light being on all the time.

[GreyGhost]

You can get sensors from ECP for about £15.00 the pair, (1 front, 1 rear)

[David3807]

What a day! Didn't change the fluid in the end as I had problems with both sides of the brakes. Firstly the pad sensor had seized into the offside pad and the housing had already broken, and then the nearside torx screw that hold the disc in place had no "whatever you call it" to get a tool in to undo it - I finished up having to drill it and hammer a bit into it to get some leverage to undo it. Anyway, got there in the end but the fluid will have to wait! Hopefully I can get a new sensor (part no. anyone?) as I can't put up with the dash warning light being on all the time.


I believe part no is SOM100030

Thats for a 75. Dont think its any different for a 190.

[andyjshaw]

Thanks - They are in stock at Betts in Hemel so I can pick one up tomorrow.

[Kandyman]

Glad you got it sorted in the end andy, just remember the picturs if you can :pic:

[andyjshaw]

Yes, all sorted and they do look good.
Pictures as promised...