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MG MGB Technical - Castrol LMA

A search of the threads didn't show any discussion of LMA? I'm redoing all of my hydraulics (1974 MGB GT, Dual cylinder, no servo)and intend to use LMA as my new fluid. It appears to be a DOT 3/4 hybrid. What experience have others had? I'm avoiding, I hope, DOT 5 brake fluid.
Thanks, Paul
P Simeone

Paul - DOT 4 brake fluid is, by definition Low Moisture Absorption (now termed Low Moisture Activity). Any brake fluid that is DOT 4 is LMA and can be used in any system compatible with either DOT 3 or DOT 4 fluid. Cheers - Dave
David DuBois

I've used it, in my '67, for as long as it's been on the market. Nothing but good results. I would recommend it to anyone. RAY
rjm RAY

Dave and Ray;
Thanks for the informative and reassuring responses. You've just eliminated my last minute uncertanty.
Regards, Paul
P Simeone

LMA seems to be much the same as Super DOT4/DOT5.1 as far as water absorbency and boiling point goes, has been around much longer, although current availability seems pretty limited. It's non-silicone so compatible as far as mixing goes with DOTs 3 and 4, but not DOT5. The gob/smacking thing is that the powers that be decided to label the improved DOT 4 as DOT 5.1, even though it is totally incompatible with DOT 5!
PaulH Solihull

Paul, You were expecting logic to prevail? RAY
rjm RAY


Someone ought to tell the numpties in Halfrauds and the other Motor Factors in Cornwall that DOT5.1 is not the same as DOT5. When I, recently, looked for a local supplier of DOT5 Silicone brake fluid to fill my newly rebuilt braking system on my restored MGB GT, they all said that DOT5.1 was Silicone - although I knew that it certainly was not!

I, eventually, bought DOT5 from Tim Kelly mg specialists in St Agnes in Cornwall.


And, by the way, Paul, it is a Solihull car that I restored.
Robert Lynex

Okay, confession time. I rebuilt the brakes on my unmolested 77 RB Roadster. The cap on the master cyliner said, "Use only DOT 3 Brake Fluid" so that is what I did.

Was I a fool? And if so, should I swap it for DOT 4 or Castrol LMA?

C R Huff

DOT 4 has a slightly higher boiling point. I'd run the DOT 3 until it's time to replace your brake fluid in 2 years time. RAY
rjm RAY

Can't really blame them, Robert, compared to who decided on the designation of DOT5.1 in the first place. However they (Halfords and Co) would probably be liable if the wrong fluid was used and caused a problem, which could include anything up to brake failure and a resultant accident which is pretty serious.

DOT5/Silicone is harder to find as it is incompatible with ABS, which of course most modern cars have and is what Halfords cater for.

Halfords aren't all bad, I was changing pads and discs on a BMW and discovered I needed a 7mm Allen key, when mine and my neighbours sets jumped from 6 to 8. Hunted round the generic tools and couldn't find anything that included 7mm so asked at the counter - "Ah, a caliper wrench" he said and directed me to them.
PaulH Solihull

Thanks, RAY.

C R Huff

Of the different brands of DOT 4 brake fluid on the market today, Castrol LMA (Low Moisture Absorption, now termed Low Moisture Activity) synthetic brake fluid with its dry boiling point of 509 Degrees Fahrenheit (265 Degrees Celsius) and a wet boiling point of 329 Degrees Fahrenheit (165 Degrees Celsius) appears to be the best available. As David noted, it is also has the advantage of being markedly less hygroscopic than either DOT 3 or DOT 4 petroleum-based brake fluids. Since Valvolene discontinued production of its Synpower brake fuid, It's what I've been using, and it works well.
Stephen Strange

I am still looking for more specifics on the new Valvoline Synthetic Dot 3 & 4 fluid (I too used the SynPower since inception) and this is what I have found:

What I noticed in my use of the Valvoline SynPower (and perhaps the current product) is that it was the only fluid I have ever used that stayed clear for a noticably longer time (quite a long time actually) than either Castrol LMA or any other brand of Dot 3/4 fluid I've used since 1966. Even when flushing before renewal, yes, some dark and weird stuff in the fluid expelled, but nothing like the sheer blackness of many others. My thought was that it was perhaps simply better at lubricating and slower at moisture absorption? Also, noted that there was only minor evidence of corrosion inside of wheel cylinders, etc. Just my empirical observations, not exacting science.

And this which I suppose could help someone monitor their brake fluid's condition. I have no connection except through a google search on the internet:
Robert Muenchausen

Thanks Stephen.

Actually it won't be too long before the 2 years is up, though it has hardly been driven since I have been doing other work on it. So, when the time comes I think I'll go for the LMA.

C R Huff

This thread was discussed between 06/01/2011 and 10/01/2011

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