Brake fluid tester...tested!

[Luddite]

Following Ron1000's brake problems, I thought I'd better check over mine before the season starts, as it's been just over two years since I last changed the fluid.

For the first time, I used DOT 5.1, which has a higher boiling point than DOT 4 but, on the downside, is more hygroscopic.

Although I was going to change the fluid as a matter of course, I was also curious to know whether it was strictly necessary, so I bought one of these brake fluid testers for the grand sum of £3.52



https://www.ebay.co.uk/itm/DOT3-5-Br...-/194809137201

This is what it showed with my two-year old DOT 5.1



That's between 3 and 4% water content, so definitely time for a change.

"Ah!" I hear you say. "But how accurate can something so cheap be?" Well, I wondered that too so thought I'd test it over its claimed range. (I cleaned the probes between each test to ensure an accurate reading.)

This is 10ml of fresh DOT 5.1 and, as expected, it shows a green light.



This is 9.9ml of fluid mixed with 0.1ml of water. The first yellow light illuminated confirming 1% contamination.



This is 9.8ml of fluid mixed with 0.2ml of water. The second yellow light illuminated confirming 2% contamination.



This is 9.7ml of fluid mixed with 0.3ml of water. The first red light illuminated confirming 3% contamination.



This is 9.6ml of fluid mixed with 0.4ml of water. The second red light illuminated confirming 4% contamination.



So this appears to be surprisingly accurate, especially considering the price. Note that the readings vary depending on how far the probes are in the fluid. To get a consistent and accurate result, make sure the probes are inserted up to the base of the tester, (which is what the instructions tell you).

I've never been too concerned about possible brake fade as I'm not a particularly heavy braker. But knowing that there's moisture in the system causing possible corrosion will definitely encourage me to stick to the two-year fluid change.

Also, before you throw out that opened bottle of fluid, which has been knocking about for a couple of months, you can use this gadget to tell you if it's actually still usable. (I have some fluid left and opened so I'll test it every month, just to see how it deteriorates.)

[Albie]

I will tell Alec about this. It could be useful as a safety test. Thanks for sharing.

[Mr Gazza]

Doh! I never knew there was such a thing. I threw two bottles of DOT 4 out only last weekend and bought some more.

Thanks for the heads up, I think I'll get one.

[Nasher]

That's interesting Vince.

The Laser one I have says it's suitable for DOT 3 to 5, like yours, but specifically says it's not suitable for Silicone based DOT 5.1, so is becoming less useful.

It also appears to struggle with the special, read Very Expensive, Extra Low Viscosity brake fluid in my Landy, giving varying results.

[Luddite]

Originally Posted by Nasher

The Laser one I have says it's suitable for DOT 3 to 5, like yours, but specifically says it's not suitable for Silicone based DOT 5.1, so is becoming less useful.

When I ordered this one, I noted it said "suitable for DOT 3, 4 and 5" and I assumed it meant 5.1, as it's the DOT 5 that is silicon based.

I did check out a US PRO version, (which looks the same as the cheap Chinese one), and that description was the same as your Laser's i.e.

"Suitable for DOT 3, 4, 5 (not suitable for silicone based DOT 5.1), which is incorrect.

If you look on the Laser site at their 4875 tester, the current description is

"Suitable for Dot 3, Dot 4, Dot 5.1. Not suitable for silicone based Dot 5."

So the description may have changed since you got yours, Simon.

[Nasher]

Thanks Vince, I'd better dig it out and try it.

[slob]

I worked at one shop where checking fluid with one of these was part of a standard service.
Thanks for sharing your test results Vince.

[alan s4]

Ebay seller must have hacked into our forum - price has increased to 4.22 with postage! Decided to prize open my wallet and have bought one anyway.

On the subject of 5.1, the rear brake on my monster is actually quite good. Growing up riding 70's/80's bikes you used the rear brake a lot as the front drums/discs were pretty woeful at the time. I still use the rear esp in town and 2 up riding.

The rear on my 996 (same set up as the monster) is bloody awful, got my MOT booked next week and I think it would be a fail. Wonder whether it's the fierce heat generated from the 996 and possible boiling of the fluid? Using 5.1 will presumably help?

[Darren69]

I saw that so I bought one of these instead;

https://www.ebay.co.uk/itm/185113994...hbSW6&LH_All=1

[Mr Gazza]

I found a seller based in UK for a few more sheckles and I can have it in my hand this week. In fact I bought multiple to give as prezzies and got them a bit cheaper, 14 quid for 3 posted today.

[jerry]

gotta get one of those XXXXX

[Luddite]

Originally Posted by alan s4

The rear on my 996 (same set up as the monster) is bloody awful, got my MOT booked next week and I think it would be a fail. Wonder whether it's the fierce heat generated from the 996 and possible boiling of the fluid? Using 5.1 will presumably help?

Well, it certainly doesn't hurt, Alan! I first tried DOT 5.1 when I changed the fluid two years ago and my rear brake has been perfect since. This thread shows the methods I used to get an efficient brake. Your 996 should be slightly easier to sort as it doesn't have the complication of ABS.

http://www.ukmonster.co.uk/monster/s...ad.php?t=58090

I think the 916 family are even more prone to overheating the rear brake circuit than the Monster so, once the fluid absorbs water and the boiling point lowers, it won't take much to boil that fluid.

If you look at the specs for brake fluid, they quote figures for both 'dry' and 'wet' boiling points. 'Dry' relates to fresh fluid and 'wet' is fluid with 3.7% water content, (which is about what mine showed after two years).



This graph from Shell shows the effect of water contamination on the boiling points of DOT 3 and 4 fluid.



I couldn't find a graph for DOT 5.1 but I did find a study, which showed these results:

• 0.18% = 259⁰C
• 1.15% = 229⁰C
• 3.13% = 175⁰C
• 4.01% = 157⁰C

So, with just 4% water, the boiling point drops by over 100⁰C.

I think best practice for the rear brake is to give it a thorough bleed with DOT 5.1 and then change the fluid regularly at least every two years, but maybe even annually, given the harsh environment and poor siting of the master cylinder.

[alan s4]

Luddite - a simple yes would have been good for me Thanks for the detailed explanation. 5.1 it is then.

The heat generated from the 996 is properly fierce, it actually burns your legs unless you are wearing kevlar or leather jeans. Something I've not even noticed on the 916 monster, I know the fairing makes a huge difference however I think the routing of the exhaust also plays a part.

Any excuse for a picture of the twins......

[Dukedesmo]

The 916 master cylinder is attached to the engine at the very same point where the exhaust mid-pipe bracket is also attached plus, the reservoir is very close to said exhaust. As a result the whole system gets very hot and the rear brake gets 'spongy' in short order.

It's also tricky to bleed the system due to the underslung caliper with bleed nipple at the lowest point.

The 916 is an exquisite design but the master cylinder/exhaust mounting setup is a bit of a let-down.

[Luddite]

The agony of choice!

At least the master cylinder on the Monster is out in the breeze. Isn't the 996 effectively attached to the crankcase as well as being buried in the fairing. That's got to raise it's temperature by a few degrees, I'm sure.