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MG MGB Technical - Which Brake Fluid???

I need to refill my reservoir very soon, will DOT3/4 synthetic brake fluid work, or do i have to use something else. Thanks.

1974.5 MG B GT
Brian Salazar

Brian - Any of todays brake fluids will work fine in you GT. Good luck - Dave
David DuBois

Brian-
The information in the previous posting is stone wrong. In fact I suspect that somebody out there is using David Dubois' name because we all know that the real David Dubois knows that American-made DOT3 brake fluid will dissolve the seals in your hydraulic system. If you're not purging the system of old brake fluid, then I'd highly recomment Castrol LMA DOT 4 brake fluid. It won't harm the seals. You can get it at just about any auto parts chain store. Great stuff, as I'm confident that subsequent posters on this thread will confirm. If you want to use a synthetic, purge the system with alcohol and refill it with Valvolene SynPower brake fluid. It'll go the F555 before it boils. DOT 4 boils at F446 and DOT 3 boils at F284. I use Valvolene SynPower and am very happy with it. Nice firm pedal and no fade at all. If your old brake fluid has turned brown, then it's time to replace it and purge the system.
Steve S.

Thirty years of experience has lead me to use nothing but Castrol. Why risk hydraulic failure?

I've seen numerous failures with other fluids. What I was always told was that other fluids attack the natural rubber that our British Bs use.

Whatever the truth, I've seen way too much evidence of the harm caused by other fluids to use anything but Castrol.



Steve Lipofsky

Before I list the following quotes I have used Castrol in all my vehicles for over 20 years until recently
when I switched to Valvoline SynPower on the 74 MGB. My two newer vehicles have the factory
DOT 3 fluid and will be changed to DOT 4 when a fluid change is scheduled.

Now for some interesting quotes.

The following information is on the master cylinder caps of my 68 GT and 74 roadster
" AP Lockhead Warning. Clean filler cap before removing, use only DOT 3 fluid from a sealed container"

Haynes MGB 62-80 repair manual in Chapter 9 Braking System Brake fluid type/specification,
"Hydraulic fluid to SAE J1703 (Duckhams Universal Brake and Clutch Fluid)"

The Complete Official MGB 62-74 in part I drivers handbook for 62-70 GT and Tourer. Editors notes
M. Brakes Page 22 in my book.
"Standard brake fluid must not be used as they will boil under hard use in a disc brake system,
resulting in a "spongy" pedal and much reduced stopping ability. Any heavy duty fluid specified for
disc brake systems will give satisfactory results."

Chapter 2 Handbook for 71-74 GT and Tourer, Brakes on page 32.
" Use only Lockhead 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
degrees C. (500 degrees F.)."

FWIW, Clifton
Clifton Gordon

I find it interesting that Lockheed makes the components of our brake systems and yet no one seems to care to use their fluid made specifically for their products. I am not trying to promote it, but it has just always been a bit of an anomaly to me. What can I say? I use The Valvoline SynTec fluid and am happy with it.
Bob Muenchausen

I use Castrol GT LMA DOT 4 in my two MGs without
any problems.

The caps on the reservoirs do say DOT 3 -- but
they mean _British_ DOT 3, which has a different
chemical formulation from U.S. DOT 3. British
DOT 3 will not hurt the seals, U.S. DOT 3 will.

The advantage of Castrol GTLMA is that it is
available at many parts stores in the U.S., not
just via mail-order. I also noticed that both
VB and Moss have started selling Castrol alongside
Lockheed DOT 4 in the past year through their catalogs.
Ronald

Brian,
Why do you need to refill the reservoir? If you have a leak, you need to repair it. It is normal for the level to go down as the brake pads wear. Check your pads, they are probably worn out if the reservoir is that low.
Leland Bradley

Steve S and all - No, that was not someone else using my name and I didn't have a gun to my head when I wrote the last posting. First off, my area of expertise is in electronics and SU fuel pumps, I am not and do not claim to be an expert on brake fluids or brake systems. I do, however stand by what I wrote in the previous posting, based on what I have read on the subject. I looked in my MGB Workshop Manual by British Lealand (12th Edition) and found exactly the same thing that Clifford Gordon found regarding the specification of AP Lockheed Series 329 Brake fluid. I have a can of that brake fluid on my shelf (no Bob, I don't use it either, just won it as a door prize) and it states right on the side that it is DOT 3 fluid. DOT3/4/5 are American Department of Transportation specifications and if the DOT specification is going to be cited on a product, it has to meet those standards. To my knowledge, there is not a British version of DOT specifications (if there is, it goes by a different acronym). In fact, the following is a quote from article in the Octagon Car Club news letter:
"DOT 3 and DOT 4 are both based on glycolethers, in fact DOT 3 fluids are straight glycolether based and DOT 4 fluids are typically based on borate esters of glycolethers. DOT 5 are silicone based fluids. THIS IS GLOBALLY VALID" (emphasis added).

When I had a TD during my high school senior year in 1959 and as late as 1974 when we got another TD, the common wisdom of the time was that you could not use any other brake fluid than Lockheed DOT 3 in the brake system of british cars because they had special (natural rubber) seals and to use any other fluid would eat up the seals and cause the brakes to fail. It would seem that that common wisdom has been reversed today. Interestingly, I had a 1984 Audi in the late 80s and the shop manual said not to use DOT 5 in the braking system. When I asked the service manager at the dealers why this was so, he told me that "German cars uses natural rubber in their systems and Dot 5 will eat them up". When I told him that this was the same BS that everyone was told 30 years ago about British cars, he admitted that he didn't know the reason (which turned out to be due to the very small orfices in the proportioning valve and the propensity for arification of DOT 5 fluid).

I still feel, based on the information that I have read and on the fact that the seals are made of the same material as any other brake systems, that any of today's modern brake fluids can be used in the brake systems of our cars with no harm to the system. Personally, I use DOT 5 silicon and have for almost 20 years with excellent results. Bob Muenchausen used the same brand of silicon fluid as I do and had bad experiences with it. Perhaps I have been lucky, I don't know, but I use it in our TD and MGB and will probably continue to use it based on my experience. I use DOT 4 in my Mazada truck and have used DOT 3 in the past in other cars. I have never had bad experiences with any of them other than corrosion build up in the systems using DOT 3 & 4 and that was because I didn't flush the system periodically.

I have 2 articles on brake fluids that I will sent to anyone who is interseted in them. One is AP Lockheed's take on silicon fluid (not suprisingly, against it) and the other is on the development of slicon fluid and an bit on DOT 3 & 4 fluids.
Cheers - Dave
David DuBois

As I have said before here, recently, I have come to the conclusion that my luck with GE's silicone fluid in the late 80s must have been a bad batch, an anomaly, because of experiences such as Dave's and others. I don't see any reason to not use it, but I just don't, and I couldn't give anyone a rational reason why, I am just happy with what I use.
Bob Muenchausen

Bob - Your last statement, "I am just happy with what I use", is definitely reason enough to use what you do. Dave
David DuBois

Interesting debate. I have just replaced clutch & brake mc's and accidentally mixed DOT 3 & DOT 4 in the brake mc. How bad is this?
Thanks.
Paul Cruser

Thanks a million for all of your responses. I knew there was something with the seals that I should worry about. I put in some Valvoline DOT3/4 "safe for all cars" fluid in the system to top off the reservoir, and the brakes work fine now.

I had to drive the car during a hot evening rush hour. Everything was working fine when I parked the car, and when I got back in I noticed the brakes seemed a bit "light"!!! I had to drive back home very carefully since the brakes would only grab at the last 1/8" of pedal travel. I have never had any brake issues, and when i checked the reservoir it was virtually empty.

After refilling the reservoir, all is fine. I drove it yesterday to my garage in Lawrence (about 35 miles of highway driving), and checked the levels. No fluid was lost.

My suspicion is that the brake fluid boiled over somehow during that rush hour drive AFTER the car was stopped and turned off. In fact, watching the DC Gran Prix today, they mentioned some of the brake issues with cars in the race had to do with overheating after coming out of a pit stop. And the need to ventilate the brakes during a pit stop to keep them from siezing. I wonder if this is a similar diagnosis to my problem....

Brian Salazar

David-
The problem with US-formula DOT 3 brake fluid is that it's blended with petroleum distillates which are intended to act as both a lubricant and as a stabilizer. The UK-formula brake fluid doesn't have these. If the OE brake system has been rebuilt, there may be no rubber components in the system since suppliers prefer modern synthetic materials which are cheaper and more reliable, so US-formula brake fluid would be safe in such a rebuilt system.

It could be that US-formula brake fluid has been altered. To test this I would suggest dropping a dry latex condom into a glass of US-formula DOT 3 brake fluid and watching the results over a period of time. Let us know the results.

Paul-
It depends on what kind of DOT 3 fluid it is. If it's not the UK-formula DOT 3, I'd suggest that you'll need to get it out of there, and real soon, too.

Brian-
I would suspect that one is your brakes is only partially disengaging,probably due to one of the pistons binding. The resultant friction would build up enough heat to boil the fluid. Once this happens, the bubbles remain in the body of the fluid. Time to purge the system with alcohol, refill, and bleed it out.
Steve S.

Steve S., Thanks for the advice. I'll replace the fluid, but should I purge the system with alcohol, or is it ok just to replace with British compatible fluid & bleed?
Paul Cruser

Paul-
It's best to purge the system with denatured alcohol to get rid of the last of the old fluid and flush out particles and varnish. You'll be surprised at what comes out! Afterwards, refill the system with DOT 4 Castrol LMA (available almost everywhere) which has a boiling point of F446 or, better yet, Valvolene SynPower synthetic brake fluid which will go to F513 before it boils! DOT 3 boils at a lowly F284.
Steve S.

The following article," Brake Rubber and Fluids (Copied from Octagon Car Club newsletter.)"
may be of interest to anyone concerned about adding DOT 3 brake fluid to MGB brakes..
http://members.aol.com/tfrecord/page31.html
I have no comments on the article, I'm passing it along FWIW. Clifton
Clifton Gordon

DOT 3 brake fluid was quoted above as having a 284 F. boiling point, correct for the minimum wet
boiling point for DOT 3 brake fluids The minimum wet boiling point for Castrol GT LMA is 311 F.
Valvoline Synpower is 343 F. Information came from the Castrol and Valvoline Labels on brake
fluid containers. BTW, the minimum boiling point for DOT 3 brakefluids is 401 F. Just want to
compare apples to apples. Clifton
Clifton Gordon

I think that David is "on target" and that this whole brake fluid incompatibility issue is one of the popular legends associated with MG and other British cars.

Does anyone really believe that brake hoses, seals, etc. are being sold that DISOLVE in DOT3 brake fluid? This would be such a huge product liability issue that I can't even go there. Has anyone noticed big warnings on the AP/Lockheed boxes stating "CAUTION - USE ONLY BRITISH DOT 3, OR DOT 4 FLUID. USE OF NON-BRITISH BRAKE FLUID WILL CAUSE SEALS TO FAIL PREMATURELY. FAILURE TO HEED THIS WARNING CAN CAUSE INJURY AND POSSIBLY DEATH TO DRIVER, PASSENGERS, AND OTHERS"....no but I don't think they just forgot.

Also, AP/Lockheed, the guys who make the OE seal kits for our cars is OWNED BY DELPHI, a global USA based company spun-off by General Motors http://www.aplockheed.com/

Cliff
Cliff Maddox

Clifton-
So, let's sum up by putting things in perspective:

DOT3 DOT4 SynPower (meets and exceeds DOT 4)

F284 F311 F343 (Wet)
F401 F446 F513 (Dry)

Cliff-
In a previous posting I pointed out that nowadays manufacturers prefer the synthetic materials to the old natural rubber. Cheaper, more durable, etc, etc, than the old-tech natural rubber seals. So that's what they usually supply nowadays. However, the point remains that unless one knows for a fact that the car's hydraulics is not original, he should play it safe and presume that the seal are the OE natural rubber seals.
One of my female cousins was foolish enough to disregard her Audi mechanic's warning that the natural rubber seals in her old power steering system wouldn't tolerate petroleum-based power-steering fluid. Being the mechanical idiot that she is (who else would pay a crooked garage $168 for a battery?), she listened to a friend who told her that the mechanic was just trying to keep her coming back so that he could bleed her for money. Like you, her friend used the Product Liability reasoning. She poured in some power stering fluid that she got at Pep Boys. The whole system ended up leaking like a sieve. Cost to repair? Don't ask! Now, if she had just read the Owner's Handbook that specifically instructed her on what to use, but nooooooooo.......

Like Steve Lipofski, I've seen the damage that American-formula DOT 3 does to the OE natural rubber seals of LBCs. If you're not sure of what you have, play it safe.
Steve S.

Sorry folks, I cannot buy that American DOT 3 fluid contains petroleum distillates. This would be in direct violation of the federal standard that specifies the DOT specs for brake fluid. In the AFCO racing products article "Understanding brake fluids" it states "All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids). the entire article can be read at: http://www.rpmnet.com/techart/fluid.shtml
Below are excerpts from Federal Standard #116.
TITLE 49--TRANSPORTATION

CHAPTER V--NATIONAL HIGHWAY TRAFFIC
SAFETY ADMINISTRATION, DEPARTMENT
OF TRANSPORTATION

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS--Table of Contents

Subpart B--Federal Motor Vehicle Safety Standards

Sec. 571.116 Standard No. 116; Motor vehicle brake fluids.

S1. Scope. This standard specifies requirements for fluids for use in hydraulic brake systems of motor vehicles, containers for these fluids, and labeling of the containers.
S2. Purpose. The purpose of this standard is to reduce failures in the hydraulic braking systems of motor vehicles which may occur because of the manufacture or use of improper or contaminated fluid.
S3. Application. This standard applies to all fluid for use in hydraulic brake systems of motor vehicles. In addition, S5.3 applies to passenger cars, multipurpose passenger vehicles, trucks, buses,
trailers, and motorcycles.
S4. Definitions.
Blister means a cavity or sac on the surface of a brake cup.
Brake fluid means a liquid designed for use in a motor vehicle hydraulic brake system in which it will contact elastomeric components made of styrene and butadiene rubber (SBR), ethylene and propylene rubber (EPR), polychloroprene (CR) brake hose inner tube stock or natural rubber (NR).
S5. Requirements. This section specifies performance requirements for DOT 3, DOT 4 and DOT 5 brake fluids; requirements for brake fluid certification; and requirements for container sealing, labeling and
color coding for brake fluids and hydraulic system mineral oils. Where a range of tolerances is specified, the brake fluid shall meet the requirements at all points within the range.

It would seem that the last item in the definition of brake fluid would preclude the use of petroleum distillates in any of the DOT 3, 4, 5 or 5.1 fluids. It further means to me that that condum would be safe in any of the specified brake fluids.

Anyone interested in reading the entire Federal Standard #116(or has the stamina to do so) can find it at the following web site: http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=49&PART=571&SECTION=116&TYPE=TEXT

At this point, I am going to drop out of this discussion. I doubt that any of us are going to change the minds of any one else. I suggest that we just agree to disagree and go on to other topics.
Cheers - Dave
David DuBois

I feel the need to repeat once more that the only brake fluid that I can unreservedly reccommend for an MG is Castrol.

I've owned nothing but MGBs and GTs since 1972 and had an MG repair business at one time. I don't know all there is to know about MGs, which is one reason that I find this forum invaluable, but brakes can be the differance between life and death, and I find it irresponsible in the extreme to advocate the use of brake fluids that could lead to brake failure.

I've seen countless seal failures as a result of the use of improper brake fluids. Using Castrol is such a simple, inexpensive thing to do to ensure your safety. There may be other fluids that work, but why take the chance?

Silicone fluid is good stuff, but my understanding is that it can cause seals to swell to the point that they may block the brake fluid return hole (if I remember correctly) in the master cylinder.

Steve Lipofsky

Just to round off this discussion, which brake fluid will NOT eat away the paint adjacent to the master cylinders when you (inevitably) spill it during top-up.

John
John Minchin

Silicon brake fluid will not harm the paint. But as I understand it you have to remove all traces of glycol fluid from the system before changing to silicon- silicon and glycol do not mix.

Just my 2c
Growler

Empirically, silicone fluids and even, Valvoline Syn Power* fluids are the only ones I know of that have some safety factor for your paint. I "*" the Valvoline product because it is safe only within certain experiences I have had with it.

Let me explain. I have accidentally spilled Valvoline Syn Power fluid on the paint, but if carefully wiped off within a few seconds, and followed with a degreasing solvent (I used Simple Green) immediately, I suffered NO damage to the Ditzler Deltron paint on my GT. No marring, no loss of surface gloss, no lifting, no nothing.

However, a later leak with that same fluid which had several days to work on the paint did just as much damage as ordinary fluids. These comments are strictly from empiric experience, and not to foster an unwarranted confidence in the Valvoline product. Nevertheless, it tells me that this product has a different chemical composition and nature than most other glycol based fluids. It can be RELATIVELY safe to paint IF due caution and timely attention is paid to a spill. That may be worth noting along with its other characteristics for someone contemplating using it. FWIW.
Bob Muenchausen

I use dot3 fluid in my 78 midget and my 67 BGT, but then I am in the UK :-) I am in the process of setting up my BGT for racing and this means a complete new system so i will probably start to use a silicon based fluid from thaat point.
TJ

I'm blown away by some of the comments here. I have always used "whatever was available" DOT 3 brake fluid(US) in all british cars I have worked on. In my own 73B I have had for a dozen years I have never flushed the system and have replaced calipers and cylinders as they wore out or as a mater of "might as well" and have never had any of the problems discussed here. When I was younger I beat the hell out of the car and drove it till the tires were smoking and the brakes stopped working due to fade(ie there was pressure, but no slowing down) and never had the fluid boil over. I have never had a leak that was not directly related to a worn out seal. I understand flushing it out is a good general practice, but I think needing a 400+F boiling point or only using one brand is a little much in a street car.
J Arthurs

J.:
Perhaps your experiences show what even DOT 3 is capable of in spite of it all? Most of the folks here are way into maintenance and prevention and ultimate performance compared to the average owner who pretty much drives and deals with their car as you have. I am not saying your habits are wrong, they are simply typically american. And many of us here are not typically american. Nor typical. ;-)

No offense, folks, but to be as concerned with proper maintenance, development, and use of our vehicles as most of us on this BBS are is not bad, it is just our bent. We find it interesting and to our advantage to always try to do the "right thing". Most of the rest of the world, even the MG world, have experiences more like J's. That won't stop me from experimenting with things and reading up on other people's findings and recommendations, that is much a hobby as is the simple enjoyment of driving these wonderful old sportscars.
Bob Muenchausen

I believe in preventative maintanance as much as the next man, but I think that maybe it's just a little too far. I have never flushed system with alchohol as I don't want a drop left in the system. The brakes were made to be used with DOT 3 and I always endup bleeding the cluth/brakes every two years as I do a brake job/rebuild/fix leak/ect... I always just bleed 'em out and never stop short of seeing clear new fluid coming from any of the bleed nipples. This is what the factory recommended, 24,000 miles I think, and I have never had a break down in seals related to brake fluid. AS for the paint, I always take care and wrap a rap around the master cylinder in case of spills. There is always some leaking and spilling eventually and I just repaint every several years. The brake cover comes off relatively easliy and a quick strip/paint doesn't take but an hour. I just think flushing with alcohol and changing fluids is too much maintanance, nust like synthetic/addatives in the gearbox. They were not available when it was being designed and through trial and error, I assume, people realized they did more harm than good.
I have seen seals fail in cars before. I used to maintain british cars for a few years, and all the seal problems I have seen were people mixing fluids or converting to DOT 5, or just plain old and tired. I mean if the 20 year old rubber on the outside of the car is old and deteriorated you have to expect some of the seals inside the system to deteriorate too.
My point is, if you have an original car, use DOT 3, preferably what you have been using, if your car is somewhat original and does not leak. I would only convert to DOT 5 only if I was doing a rebuild of the whole system and knew all the parts were tested with it.
J Arthurs

"I believe in preventative maintanance as much as the next man, but I think that maybe it's just a little too far. . . .The brakes were made to be used with DOT 3 and I always endup bleeding the clutch/brakes every two years as I do a brake job/rebuild/fix leak/ect... . . . I always take care and wrap a rag around the master cylinder in case of spills. There is always some leaking and spilling eventually and I just repaint every several years."

To me, it sounds like you are doing more maintenance than most when it comes to brake related work.
.

My MGB British Leyland handbook for Tourer GHN 5UD and GT GHN 5UD for U.S.A. cars has the
following note about brake and clutch fluid on page 33.
"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. (500^F.)"

Can anyone supply a British Leyland technical reference stating I should disregard the statement in my
owners handbook?
It does refer to US DOT 3 specifacation as it is a USA market handbook.

I don't think Lockheed Series 329 brake fluid is available and I believe the Castrol Girling fluid was a green
fluid, thats what is specified for my Jensen. I don't think DOT 4 existed when the MGB first appeared on the market.

Most brake problems I have seen were caused by seal failure, but how do I tell if the seals failed due to
normal wear, lack of proper maintenance or by using the incorrect brake fluid? A laboratory analysis of
the suspect fluid?

BTW, Castrol is no longer stocked by any store in my area, I bought from Advance for years, I may have
been the only one buying it.

I noted the Castrol I put in my 68 GT after replacing the silicone fluid turned a light purple. I didn't think
silicone would mix with conventional brake fluid. I bought some Motocraft, heavy duty DOT 3 fluid and replaced the Castrol. Motocraft has a dry boiling point of 550 degrees F. So if you see a sandy beige Gt headed toward you give me lots of room as my brakes may about to fail. I'm sure, as David said no one
is going to change their opinion, so this is my last post on this subject, if I have a brake problem
due to the use of Motocraft I'll post that. Best regards, Clifton

Clifton Gordon

J-
You said that you've "never had the fluid boil over". I should hope not! When brake fluid boils, small bubbles form within the fluid. These bubbles compress just like a spring and absorb some of the pressure exerted at the pedal, thus creating what we all call "brake fade". A higher boiling point simply forestalls this event, thus giving the driver a healthier safety factor when driving hard. This is why Federal regulations now require all new cars to use at least DOT 4. As previously mentioned, Castrol LMA DOT 4 is widely available and works well in out cars regardless of seal material. Another contributing factor to Brake Fade is the heat-induced formation of a boundry layer of gas between the brake rotor/drum and the friction material. Friction material with a higher heat tolerance, such as Carbon Kellate or Carbon Kevlar will also give a healthier saftey factor here as well.
Steve S.

Hi Steve,
I have boiled Castrol LMA ... once. A very hot day at Westwood race track in British Columbia, Canada. Westwood was built on the side of mountain with a hair-pin turn at the end of the main straight at the lowest point of the track. The brake fluid boiled and overflowed the reservoir, out from under the bonnet, over the windscreen and onto my helmet face shield. Drove the last laps looking through the brake fluid. I didn't know what would happen if I tried to wipe it off. Turned out it wiped clean. The other fast 'B' in that race boiled his fluid same lap, same place. This was in the mid-70s. Steve and I were both using LMA and DS-11 pads.
Leland Bradley

My point was that if your running a B so hard on the street your suffering boilover or fade, your really not going to live long anyway. As for the over/under maintance issue, I was just stating that on average I usualy end up bleeding the system ever couple of years for one reason or another as you have to open the brake lines for a multitiude of different reasons.
J Arthurs

Clifton,

If you can't get Castrol where you live, call Bob at Brit-Tek ((800) 255-5883). His prices are reasonable and he's knowledgeable.
Steve Lipofsky

Interseting discussion. By Federal regulations requiring all new cars must use DOT 4, does Steve mean section S5.3 of Federal Standard 116 that Dave D. gave us a web site for? I didn't see any reference to requiring all new cars to use any specific DOT, just that it be one of the fluids that conforms with the requirements of this
standard. If he is quoting from another Federal standard, Steve should give us a web site where we can read that one. Regards, Russ
Russ

Leland-
Wow! Egad! Now, that's really hot! I'll bet the grease in your wheel bearings melted and was all over the place! Of course, when I was describing the formation of small bubbles in the brake fluid I was refering to what happens in common street usage, not disasters on the racetrack. I'll bet that you can downshift faster than anybody around!
Steve S.

J Arthurs- you claim you've never changed your brake fluid, but have changed your cylinders and seals when they 'wore out'.

Have you considered that your seals and cylinders may have 'worn out' because of the damage caused by 'wet' brake fluid and the rust created by it? I'm just thinking aloud here, but I've never had to change hydraulic seals because they just plumb wore out- I always find them shredded by rust particles, or the cylinder pitted. As a matter of interest, my grandad's A35 has done more than 250,000 miles, still on its original brake cylinders/seals, but has a fluid change every 6 months. (I think the flexible hoses perished around 120,000 miles though)

Just my 2c
G

Growler

Ok I apologize for dragging this out with one more post, but I can’t help myself. I pulled the following specs today and did some reading and dug-up more about brake fluids than I really need to know.

Required reading - FMVSS No. 116—Motor Vehicle Brake Fluids
SAE J1703—Motor Vehicle Brake Fluid
SAE J1704—Borate Ester Based Brake Fluid
SAE J1706—Low Water Tolerant Brake Fluids
ISO 4925—Road vehicle-Non petroleum based brake fluids

The requirements for brake fluids are described within the Federal Motor Vehicle Safety Standard 116, prepared by the National Highway Traffic Safety Administration. Within this Standard, motor vehicle brake fluids are classified as DOT 3, DOT 4, DOT 5, or DOT 5.1 based upon minimum wet and dry boiling points, viscosity characteristics, and in the DOT 5/5.1 case, base fluid chemistry. Further information is contained within SAE J1703 (Motor Vehicle Brake Fluid), SAE J1704 (Borate Ester Based Brake Fluid), and SAE J1705 (Low Water Tolerant Brake Fluids).

All Brake fluids that meet these criteria are non-mineral oil based (non-petroleum) by specification. Common compositions may include synthetic glycol ethers, borate esters, or silicone.

BFL….DOT3, DOT4, SUPER DOT 4, DOT5, DOT5.1 ALL of these fluids are tested for compatibility with all common automotive seal types, including natural rubber.

ALL common available brake fluids are covered by one or more of these standards including CASTROL GT LMA Brake Fluid.

THERE IS NO SPECIAL BRITISH DOT 3 VERSUS US DOT 3, ETC. DOT 3 is DOT 3 is DOT 3. Any of these fluids should be GOOD TO GO for by SPECIFICATION AND DESIGN not cliché stories, or condom tests (could not find that one in the SAE test methods, Steve).

Also for what it’s worth there is also a common fluid compatibility for the DOT3 and DOT4 fluids where they are tested with a mixed brew of six common industry brake fluids and they must all mix and not separate out.

If you read the SAE standards (J1703, J1704, and J1705) all conforming brake fluids must pass compatibility testing with NATURAL RUBBER, and synthetic material (styrene-butadiene rubber, and ethylene-propylene elastomer). These compatibility tests are mandatory to the extent that the chemical make-up recipes for the test brake components are all fully defined in the standards.

ISO 4925 is the equivalent European standard for SAE J1703 and includes very similar requirements.

Another interesting document is SAE J1709, which is a Service Information Vehicle Report entitled “European Brake Fluid Technology” and includes the following information which explains some the “oddball” products.

Super DOT 4 Fluids—Super DOT 4 brake fluids are commonly based upon mixtures of glycol ether and borate ester chemistry. Although an official specification has not been established to date (and is not planned), it is commonly accepted that such fluids should attain a minimum dry boiling point of 260 °C and a minimum wet boiling point of 180 °C as required by the DOT 5 (silicone brake fluid) or DOT 5.1 (non-silicone brake fluid) category.

Borate Ester DOT 5.1 Fluids—Revisions to FMVSS 116 have been published to accommodate non-silicone based DOT 5 fluids. The fluids are categorized as DOT 5.1 and, unlike DOT 5 fluids which are dyed purple, can vary from colorless to amber in color. DOT 5.1 brake fluids are based predominantly on borate ester chemistry. Borate ester chemistry allows for SAE J1703 DOT 3 and DOT 4 fluid miscibility.

5.3 Silicon Ester Fluids—Silicon ester based brake fluids typically achieve boiling point characteristics above the requirements of the DOT 5 specification. Silicon esters do not have the same chemical structure as silicones and differ in physical properties. Silicon esters are similar in structure to borate esters.

Cliff

Cliff Maddox

Ahhhhh.....The imfamous, recurring brake fluid thread! I don't think there has ever been a topic so widely debated (unless you've seen the Vintage Racing list discussions on car originality!).

I happily choose to believe Cliff M's research above. It actually gives me some relief as I have been running DOT 3 racing brake fluid in my MGB race car for 5 years now (with terrific results). I too remember, from the time of my first exposure to Brit cars, being told that anything but Castrol LMA will ruin the system rubber. I finally chose to assume this was a myth. (But always wondered none-the-less.) My car has Girling master cylinders, normal Lockheed calipers and typical rear cyliders.

When choosing the brake fluid I would race with (and entrust my life to) I wanted a high boiling point to reduce the chances of brake fade and low cost since the stuff gets purged and replaced so routinely in a race car. I found a DOT3 racing fluid by "Stainless Steel Brakes Corp." advertised to have a very high boiling point and that was described as "a glycol based fluid suitable for all brake systems". Compared to other exotic racing fluids it is quite resonably priced too. See:
http://racerpartswholesale.com/bkfld.htm

I just found it impossible to believe that somebody selling specially formulated brake fluid to racers would suggest universal suitability but really mean (without printing it) "except for all those British cars which this stuff will promptly ruin".

My results with this stuff have been flawless.

I'll also admit that until today I never told anybody that I had been using DOT3 fluid in the car for fear of being branded a careless, ignorant idiot.

Thanks Cliff for assuring my peace of mind.

By the way, I've sucessfully run DOT5 Silicone fluid in my MGC street car for years which totally fixed the caliper seizing problems it had for a long time on "good old" Castrol.
Kelvin Palmer

This thread was discussed between 20/07/2002 and 26/07/2002

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