Brake Fluid Replacement

[Lost Boy]

Is there a brand or type that would be better than the standard Halfords stuff??

I do a mixture of road and track miles, but do notice a softer pedal after some hard driving on track. Running standard disks and brakes btw.

Thoughts appreciated

[Jonathan Kay]

When was it last changed?

Jonathan

[Lost Boy]

3-5 years ago, so I know it needs doing, just wondered if there was an upgraded option better for track use??

[ChrisC]

I use Castrol React Performance Dot 4, its a high temprature alternative to dot 5.1 (apparently).  Seems ok for my track days.  

[Mankee]

I used to use cheapo Halfords DOT 4 with no issues. What is your budget for brake fluid? You could try anything from Comma DOT 5.1 (which is what I use in both my cars) all the way up to the likes of Motul RBF660 and Castrol SRF. Bleeding technique is just as important, as it is very easy to leave air stuck in the rear calipers, due to the way they are fitted.

[Jonathan Kay]

I use Comma DOT 5.1. I have no idea if it's better or worse than anything else. I'd like a harder feel.

There's a vast amount on this in the archives, including "DOT 4 v DOT 5.1" and specific comments on Castrol products. I can't draw any conclusions.

Jonathan

[Mankee]

I use Comma DOT 5.1. I have no idea if it's better or worse than anything else. I'd like a harder feel.

Try different pads and/or master cylinder?

[revilla]

I would have thought all brake fluids should be pretty much incompressible when cold. As I understand it, you would change fluid in an attempt to find better high temperature characteristics, i.e.resistance to boiling when the brakes get hot. If the feel is not how you would like it to be even when the brakes are not particularly hot then I would say it's nothing to do with the fluid choice. As Mankee suggests above, you've either got some air in there or you need to look at different components like the pads or master cylinder.

[Lost Boy]

Thanks guys, have gone for the Comma DOT 5.1, gotta be better than the old stuff that's in it!!

Ian

[ben7]

How much do you need to replace the lot?  I currently have SRF in mine but it needs replacing (not with SRF I hasten to add!).  That Comma looks good, just need to know how much to buy.

Ben

[CharlesElliott]

Just over 1l usually.

[oldbutnotslow]

This is interesting and the question of DOT performance tends to resurface every few years.

So these are the "standard" specs for the various DOT(Department Of Transport) specs.

              dry boiling point      wet boiling point

DOT 3    205 °C (401 °F)    140 °C (284 °F)
DOT 4    230 °C (446 °F)    155 °C (311 °F)
DOT 5    260 °C (500 °F)    180 °C (356 °F)
DOT 5.1    260 °C (500 °F)    180 °C (356 °F)

DOT 3, 4 and 5.1 are all polyglycol ether based fluids cannot be mixed with DOT 5.0, which is silicone based.

Interestingly some dot 3 fluid have a dry boiling point of 275 degrees! (AP 551 Racing Brake Fluid which is what I use)

So whilst DOT 5.1 looks (is) better in terms of its dry boiling point I would suggest that unless your car is only ever used on track (as mine is) and you have very agressive friction material (which I do) you will never need to go beyond DOT4! That is because the frictional rotational retardation is turned into heat at higher levels. (jumping on the brakes at the last moment)

Castrol SFR is similar to DOT3/4 but with a dry boiling point of 300 c 

SFR typically costs £60 for 1 litre wheras the AP 551 costs about £17.50 per litre

You makes yer choice and pays yer money in the end. 

[OliW]

Comma Dot 4 is perfectly good for most applications, as OBNS suggests.

[Lost Boy]

Is ot as easy as open the bleed valves and pump until its drained, close, refill and then bleed from the longest pipe first??

Anyone know the correct order or any ideas for ensuring I have all the air out of the rear calipers?

[dikko]

If, as it seems, you need to spend money on expensive brake fluid, you'd best get someone to put it in properly!!!!!!!!!!!

 

    try buying a pressure bleeding kit and mind you don't dribble too much out the nipples or it  'll cost you another fortune.

 

You might find your rear pipes go to one wheel then continue to the next and onlu have to bleed one nipple. Fronts equal length maybe?

[SM25T]

Don't drain it. Do furthest one first and look at plastic tube you will fit to each bleed nipple in turn ... for change in colour as new fluid arrives. Old is like treacle. New is clearer.

[Terry Field]

I think I am right in saying that Dot 5 never (?) needs replacing because it does not absorb water from the air, although I am ready to be corrected by my more knowledgeable Blatchatters.

If you don't have one, buy an Eezibleed kit - it saves gallons of fluid and does a really good job - wish I had bought one 20 years ago.

Cheers

Terry

[SM25T]

And from my experience .... don't put any brake fluid in the Ezibleed bottle .... just keep topping up the master cylinder reservoir. A leak in the cap under pressure is just a nuisance with air. It can be a catastrophe when spraying brake fluid under pressure ... trust me.

[Lost Boy]

Thanks all, will have a go later this week when I have some support on the brake pedal 

Also currently have a slight squeak i think from the fromt brakes when doing about 40mph, it sounds like a canary so not consistent, will check pads but think they are OK, wondered if I had warped front discs? Also brakes squeal but only intermitently, so is the trick copper grease on the back of the pads?

Thanks in advance

 

[Jonathan Kay]

I now do it the same way as SM25T: top pressure bottle with no fluid, valved bottle at the bottom. One person job with no drama.

Jonathan

[SM25T]

Yes to copper grease on the back of the pad backplates. Also file a small 45 degree chamfer on the leading edge of the pad friction material.

[TomB]

This the most recent thread on the subject, so one I chose this one to resurrect.  

Im planning on doing the Oulton Park track day in a month or so, so I want to change my brake fluid.  Currenly Ive got Halford DOT4 in, and last night bought a litre of Comma DOT4 to replace the fluid.  Afterwards I thought about DOT 5.1 and whether I should have bought the higher temperature one instead.  The car is on standard brakes with Mintex 1144 on the front, has the big race master cylinder, 150bhp and will be running Yoko 48s on the day (assuming its dry!).  Apart from the odd track day, its road use only.  So should I go back to Halfords tonight and exchange it for Comma DOT5.1?

[Roger Ford]

I'd have paid the extra £1 for 5.1, but the DOT4 should be fine. Not much chance you'll boil that in a Caterham with standard brakes.

[martyn]

If you're interested then check the dry boiling point of each.  You might find there isn't anything in it.  A lot of DOT 4 fluids will have a higher dry boiling point than many lesser priced DOT 5.1.

Of course the wet boiling point is of interest too.  If you don’t change your fluid all that often then a DOT 5.1 may be better because they have other things in the spec that relate to longevity.

[TomB]

Comma DOT 4 Dry BPt = 270c, Wet BPt = 160c

Comma DOT 5.1 Dry BPt = 275c, Wet BPt = 183c

Does 'dry' in this context mean fresh from the bottle with no dissolved water, and 'wet' with a certain amount of dissolved water?