Dot 5.1

pepsilol

pepsilol

pepsilol

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I'm going to get some braided hoses onto the E39 when I get it and will get the fluid flushed aswell.

Is there any difference between 4 and 5.1 ? How much is required for the change?

The car isn't being tracked or anything like that. Just think that if they're both the same price and one is slightly better day to day then I might aswell get the better one.

If not then I will just stick to the usual 4 but any particular brand to get or is it all the same stuff?
 
Dot 5.1 will have a higher boiling point so your brakes are going to be able to take more abuse before they fade, no reason not to use 5.1 really. A litre will probably be enough.
 
I'm convinced that since swapping to dot 5.1 my brakes lost a little bit of feel. That initial bite just doesn't seem quite as urgent as before. That said it is marginal enough to just be a figment of my imagination.

I don't really drive my car that hard for long periods of time to notice whether or not the fluid overheats less or not.
 
Plenty of reason not to use 5.1.

5.1 is more hygroscopic so needs changing more often, DOT 4 is plenty good enough for road use where you dont need the higher boiling point of DOT 5.1.
 
A brake system is not perfectly sealed and moisture can get into the system and be absorbed by the fluid. The effect is to reduce the boiling point of the fluid, which reduces the efficiency of the braking system, as described above.

The DOT specifies two reference tests for brake fluids.

* Dry boiling point - the boiling point of fresh fluid

* Wet boiling point –the boiling point once the fluid has absorbed moisture (representing brake fluid after time spent in a real situation).

There are two main types of brake fluids:

* DOT 3, DOT 4, Super DOT4* and DOT 5.1 which are based on poly glycol compounds.

* DOT 5, which are based on Silicone.

Note the two types of fluid are not compatible and must not be mixed in a braking system.

SILICONE BRAKE FLUID (DOT 5)

Silicone based DOT 5 was originally introduced to give higher temperature performance over glycol DOT 4. Silicone fluid also has other advantages, it does not damage paintwork and it does not absorb water.

However, silicone fluid is a poor lubricant and does not lubricate ABS pumps as well as PAG fluids. It is also more compressible than PAG fluids, which can result in a sluggish or spongy pedal. It therefore requires special design considerations in braking systems. Further, because it does not absorb water, any water remains as globules, which can pool in low spots in the system and cause corrosion. This water can vaporise when heated under heavy braking giving a disastrous effect on braking efficiency.

DOT5 fluids are not recommended for motor sport applications.

POLY GLYCOL BRAKE FLUIDS (DOT 3, 4 AND 5.1)

Glycol based DOT 4 fluid is the current mainstream brake fluid, and you will see that the specification is considerably better than DOT 3 which it replaces.

DOT 5.1 has higher specification still and is for fast road and occasional track day use. It has a similar spec to DOT4 for the boiling point (>260) but is a lot lower viscosity @-40C typically 900 centistokes (compared to 1500 - 1800 centistokes for DOT 4 and super DOT 4).

Listed in the table below, are the minimum dry/wet boiling point specifications for each DOT level.

BOILING POINTS:
DOT 3 - 205°C (dry) / 140°C (wet)
DOT 4 - 230°C (dry) / 155°C (wet)
DOT 5 (silicone) - 260°C (dry) / 185°C (wet)
DOT 5.1 (PAG) - 260°C (dry) / 185°C (wet)
Super Dot4 * - 300°C (dry) / 195°C (wet)
(racing brake fluid)

* Super DOT4: The main difference between DOT 4 and Super DOT 4 is the dry boiling point. Normal Dot4 is >260C whilst Super DOT 4 is more like >310C

:D
 
Waste of time buying DOT 5 unless your car specifies it.

If you want decent fluid, spend money on Super ATE or similar.
 
Is it worth it unless you require new hoses anyway or are tracking it?

I just get new fluid changed by BMW for 50 quid every 2 years, doesnt seem worth faffing about to do anything other than that.
 
I just really liked the firm pedal feel it gave on the E46, was such a nice reassuring feel. Also pedal travel is cut down so much aswell. They only cost £50 so why not!

I know it is something I will eventually do, or I may do it as soon as I need some discs and pads doing and it can all be done in one go.

Trust me fox, it's such a nice upgrade for little money.
 
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If you want a firm pedal then braided brake lines will help massively, but as brake fluid seems to be quite often overlooked, you may just find a flush and bleed would leave it to your satisfaction.
 
Next time you need a pads and discs change, find out how much extra he would want to fit the hoses. They're made by Goodridge.

I bet everytime you brake now, you will think your pedal feels a bit spongy :p
 
pepsilol said:
I just really liked the firm pedal feel it gave on the E46, was such a nice reassuring feel. Also pedal travel is cut down so much aswell. They only cost £50 so why not!

I know it is something I will eventually do, or I may do it as soon as I need some discs and pads doing and it can all be done in one go.

Trust me fox, it's such a nice upgrade for little money.
Click to expand...

On your E46 did it change the way the car behaves while braking too? As you can imagine I'm exploring various things on my own one at present and I'm due a brake fluid service soon too so was considering braided hoses. What I don't want is to decrease brake pedal travel and want to keep the braking progression the same because it's very predictable and because of that it's easy to give it a bit of extra footing when required and know exactly how much it's going to stop.

I considered it because I've read braided hoses increase braking strength but if it means less pedal travel and loss of gradual progression then I'll stick with OEM.
 
It cut the pedal travel, firmed it up, and it made it so much more controllable and predictable with the braking.

It was the extra control over the braking that did it for me.

I'll be honest and say I don't really know what you're getting at with the whole footing thing but I can say that the braking is a lot more controllable.
 
As in, when you apply the brake, say 2 inches of travel, the braking is light, apply another 2 inch and braking increases and so on and so on. I've driven cars with firmer brake pedals where if you give the pedal 2 inches of travel then the brakes kick in strongly, any more travel and it would be an emergency stop kind of manoeuvre, I found this to be the case on many newer cars like Audi (A3), Lexus (ct200) etc - That I do not like.

I like light pedals that have a gradual progression whether it's the clutch or the brake so if braided hoses change that then I'll stick with OEM.
 
IMO it wasn't like that.

It was a simple case of more pressure = more braking power.

It wasn't where it was gradual braking and then a little bit more push and suddenly you hit your face on the wheel.

It's not pedal travel, it's more resistance against your foot hence the control.
 
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