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MG MGB Technical - Brake Fluid

Castrol LMA brake fluid is getting hard to find in my area. Of course, I can order from Moss but local is so much more convenient. I seem to remember a fairly recent posting here about a synthetic brake fluid from Valvoline but I can't find it in the archives. I have been to the Valvoline website but I can't determine whether or not it is suitable for British cars. Can any of you provide information on this product?


A Sneed

Mack, I have used Valvoline Synpower about three years and it works as well as Castrol LMA for me. I switched for the same reason you mentioned, I couldn't find it in this area. It will still ruin paint and has a higher dry boiling temp than LMA (500F). I think Bob Muenchausen started using Valvoline several years earlier.

Clifton Gordon

Thanks Clifton. It looks like I will be making the switch also.

A Sneed

I have been using the Valvoline Syntec as Clifton has said since it first appeared back in the late 90's. It has served me very well, and falls somewhere between silicone and standard fluids (amongst which is LMA) in terms of picking up water and longevity of the seals.

It also is quite capable of a good hard pedal. And, you can use it directly to replace the fluid in a regular fluid system without having to flush or redo the system as for silicone. If cleaned away immediately, it is not nearly as damaging as ordinary brake fluids to paint, almost as good as silicone in this respect. FWIW.
Bob Muenchausen

Amongst the brake fluids presently available there are three possible candidates. The first, DOT 3, is a poor choice for high performance driving due to its low wet boiling point of F284 (dry boiling point F401) and is now generally considered to be obsolete. Be advised the American DOT 3 brake fluid is formulated differently than British DOT 3 and is incompatible with the Original Equipment natural rubber seals used throughout the brake system. It will slowly but surely dissolve them! The second candidate, DOT 4, is much better with a wet boiling point of (dry boiling point F446). Of the different Brands of DOT 4 brake fluid on the market today, Castrol LMA appears to be the best. The third choice is a synthetic fluid, Valvolene SynPower, which wins with a wet boiling point of F343 (dry boiling point of F513). DOT 5 Silicone-based brake fluid is a poor choice for any automobile as it has problems with air retention, making bleeding of the brake system a real bear, and poor lubrication, sometimes allowing the pistons of calipers and/or slave cylinders to bind in their bores and lock up the wheels. With a boiling point of F500, its performance is inferior to that of Valvolene SynPower. While it is true that silicone-based brake fluid does not absorb water, water still gets into the system through condensation. Because water is heavier than silicone fluid, it will ultimately sink and gather in the lowest point in the system. Should it freeze, line blockage and brake failure becomes possible. It is also possible that should the temperature of the brake fluid rise above 212F, the water will vaporize, increasing pressure within the system and locking a brake. Brake systems with small orifices or rapid action of the system, such as automatic proportioning valves and antilock braking systems should definitely not use silicon fluid since the small orifices and rapid operation of the system will cause airification as a result of cavitation of the fluid, which will certainly cause a spongy pedal. Should you decide to use silicone-based brake fluid, be sure that all of the seals are in excellent condition as it will easily find its way past a leaky seal and air will get into the system. Be sure to flush the system with denatured alcohol prior to refilling it with the silicone fluid. Failure to do so will result in the residual glycol-based fluid interacting with the silicone fluid to form a sludge which will destroy the seals in the system, resulting in catastrophic brake failure. Perhaps the only argument in favor of silicone brake fluid is that it is slow to damage paint. However, if the brake system is leaking, it should be promptly repaired in the interests of safety, regardless of the type of brake fluid used in it.
Steve S.

Thanks, Steve, for clarifying the differences.

I have been using it for so long, I have forgotten even the correct name, but I know it on the shelf in the store. And I know, that having used all the various fluids mentioned at one time or another, I will not go back to any other than the Valvoline SynPower fluid. My experiences with GE Silicone fluid in the late 80s was very much proof of that fluid's weakness for air retention. Bad enough that GE doesn't deal in it anymore.

Anyone interested can dig through the archives for our discussions about this product years ago, but I don't really think that is necessary since you have nailed it all pretty well in far fewer words.
Bob Muenchausen

Std Brake fluid is synthetic. Silicone fluid has a high proportion of dissolved air and is not an option with ABS, however in reality I have not heard of a water issue as most std fluid absorbs water via brake hoses.
Paul Wiley

To follow up what Steve said, US D.O.T. 3 fluid may (or may not -- I've heard it both ways) attack original British rubber seals, but I'd not be too concerned about it. If you have original seals in your brake system, they're long past due for replacement. You don't want them in the car with any type of fluid. Modern seals are 100% compatible with US D.O.T. 3 fluid (this is mandated by Federal law). While you still probably won't want to use D.O.T. 3, you could in a pinch if you had to (say, at 2 a.m. and it's all the Quicky-Mart has on the shelf....)

With all due respect to Steve, I disagree that "DOT 5 Silicone-based brake fluid is a poor choice for any automobile." I'm on 12 years with it now in my '69 B, with no problems and having experienced none of the horror stories that are told about it. He's correct that it does not absorb water, but neither does it attract water like D.O.T. 3/4/5.1. It repels water, whereas the others will literally pull moisture into the system through the pores in the hoses. I flush my brakes every year(ish), and have never seen any evidence of water contamination in the fluid. I should also point out that this is in a car driven year-round in all weather and which is not garaged. If you were to consider converting to D.O.T. 5, you'd have to follow Steve's advice and completely purge all the previous fluid.

D.O.T. 5 is *not* for cars with ABS, though, and Lockheed recommend against it in their remote boosters (such as those on the MGC).

The discussions over brake fluids tend to turn into Holy Wars, with neither side convincing the other that theirs is the One True Fluid. My observation has been that in this sort of situation, neither side can convince the other because there is no one clear, correct answer. Both sides are (somewhat) correct! ;-)

Rob Edwards

The Lockheed master cylinder fill cap on my 74 MGB has the following. "Use only DOT 3 fluid from a sealed container.". The owner handbook has the following information about brake fluid. "Use only Lockheed Disc Brake Fluid(Series 329S) or Castrol Girling Brake Fluid; alternatively, use a brake fluid conforming to F.M.V. S.S. D.O.T.3 specification with a minimum boiling point of 260'C."
The brake fluid requirements for vehicles sold in the USA since January 1, 1968 is contained within the FMVSS

It appears the factory recommended brake fluid for USA MGB's sold since 1/1/68 is USA DOT 3 or a fluid that complys with FMVSS Standard No. 116 - Motor Vehicle Brake Fluids.

As mentioned I use Valvoline SynPower fluid which is backward compatible. I did try Motorcraft DOT 3 in my MGB for a year and everything was OK with it.

I tried to find a time line on brake fluid but didn't come up with a lot of information. I believe DOT 3 fluid was first available in the mid to late 60's. When the first MGB rolled off the assembly line I believe SAE 70R1 brake was a premium brake fluid in the USA, it was good for drum brakes but not so good with disc brakes, most all American cars had drum brakes at the time. DOT 3 came about the time that American cars started using disc brakes. I don't remember seeing DOT 4 fluid until somewhere around 1979 or 1980. I started using Castrol DOT 4 in my cars about that time. That would be about the same time the last MGB was built.

If you are still reading this you may find this link by the late Carroll Smith interesting. It will tell you that DOT 4 fluid should be changed more frequently than DOT 3 fluid because the wet boiling point of DOT 4 falls more rapidly that of DOT 4.

FWIW, I just looked at the brake fluid choices in two local stores and I find no indication DOT 3 fluid is about to go away. I only found two brands of DOT 4 fluid. My 2002 Mazda Protege 5 and 2004 Toyota Tacoma with ABS specify DOT 3 only fluid.

Clifton Gordon

Should read "DOT 4 falls more rapidly that of DOT 3".

Clifton Gordon

First. I do not race or do what would be considered driving that requires "hard" braking. But I have had the same silicon fluid in my TD for over 20 years. I have also had it in my B for the last 3 years (clutch and brakes). I did fully rebuild the entire braking system prior to using the silicon, but I have no problem with leaking, and my brake pedal is hard enought that I can lock all 4 tires with a good push.

My cars are exposed to the temperatures of wisconsin winters in an unheated shop and I have never had one brake problem. I also have not had any problems with oxidation on the aluminum cylinders or the steel pistons in the TD. Prior to using the silicon, I had to take my brakes apart every year after storage as the steel piston had stuck to the aluminum cylinder in the TD.

I know there are a number of members on this site and on the T series site that have very similar stories and have no issues with silicon.

Oh, yes, I also have not had to repaint any wheels pr backing plates due to brake fluid eating the paint.

Only downside - It is very hard to clean it off of painted surfaces and you have to use orange peel preventer if you have to repaint anything that has gotten the silicon on it.
BEC Cunha

I won't spend much time on this, but I did have an issue with the GE Silicone fluid I used in the late 80s-early 90s. That particular brand held air bubbles in it from the time I installed it until I flushed the system (as per Steve's procedure). My guess is that GE's material was simply bad from the get go, and that other brands probably had a different formula, hence the difference in experience of other silicone fluid users.

Also, as with most other things, time marches on, and over the years all fluids have changed significantly in their composition, altho it appears that the basic operational parameters have generally remained as specified. ie: boiling points. As for other aspects, I would also guess that experience in designing any of these products over time reflects changing materials used in the brake systems themselves. So, if seal materials have changed, the lubricating and reactive properties have also changed to reflect the new environments and materials in use. I never have seen much evidence of water or water corrosion in any system I have worked on in the last 10-15 yrs, altho I have encountered plenty of it in the years preceding.

Different metals, fluids, and seal compounds are probably as responsible as anything and I have sometimes wonder if some of our concerns are based more in past experiences than in present ones. Sometimes the knowledge base and our assumptions take a while to catch up with the realities out in the field. It would be interesting to hear what folks like John Twist and Carl Heideman encounter today vs. what they saw years ago.
Bob Muenchausen

Thanks Folks. I really didn't intend to start a lengthy discussion but it has been interesting. Like some of you, I wonder about the materials used in new seals for our cars. Maybe the type of fluid we use is now a moot point as far as seals are concerned. I have been driving, mostly Detroit iron, for more than 50 years and moisture and paint damage has never been a problem for me. I have never changed brake fluid except for major brake failures and I haven't had a major brake failure in 30 years. Castrol LMA is now almost impossible to get in my area and I was looking for a suitable substitute. From the forgoing, it looks like Valvoline SynPower may be what I am looking for.


A Sneed

This thread was discussed between 09/04/2007 and 12/04/2007

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