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MG MGB Technical - Brake fluid?

I have to bleed the brake and clutch system on my '71 B GT...someone told me that I have to buy the Lockheed fluid because if I go with any other fluid (even if it's DOT3), I risk to damage the rubber seals..
true or false?
I just did a rebuilt of the master cylinder (clutch and brake)..and I bought the original seals from Lockheed for that..

thanks
J-F
JF

JF-
The seals in your hydraulic system are made of natural rubber, hence they will be ruined by American DOT3 brake fluid. I'd recommend either Castrol LMA DOT4 brake fluid or, better yet, Valvolene SynPower synthetic brake fluid.

Now folks, let's not start the old Silicone vs everything else arguement, OK?
Steve S.

so it's true..
thanks for the answer..
J-F
JF

After receiving rebuild kits for my brakes it can be said that natural rubber seals are a thing of the past. Several long time MGB owners and mechanics told me the same thing. Rumors still persist and while natural rubber may still be used on pre-war MGs, all later rebuild kits are synthetics. I know several people who use silicone, as do I but in another type of car for over 20 years w/o any problems.
MaGee

MaGee,

But is it safe to assume that all the rubber in a given car has been changed out? Unless I had personally rebuilt all the hydraulics, I think I would assume that there WAS natural rubber in the system and use LMA to be safe. No, wait -- I'd use LMA either way! ;-)
Rob Edwards

All brake fluids are "synthetic." The use of the word is just a marketing ploy by valvoline. That said, my dad is a chemist. Though he hasn't worked in the brake fluid industry in many years, through his studies, he concluded Castrol LMA was the best brake fluid on the market. Nonetheless, when he can't find Castrol, he uses the Valvoline Synpower.
Greg Bowman

A note on silicone:

I switched to it for its kindness on paint.

However, all cylinders were rebuilt with all new lines and hoses.

The two, i believe, are not compatable.
glg gimbut

On page 11 in the MGB Haynes manual the recommended brake fluid is Hydraulic fluid to SAE J1703. The same information is on Page 146. Look at any DOT 3 brake fluid container and it will state the fluid meets or exceeds SAE J1703.

In the General data section of the MGB shop manual the specified brake fluid is Lockheed Disc Brake Fluid Series II).

My 68 owners handbook reads, "Use only Lockheed Disc Brake Fluid (Series 329) or Castrol Girling Brake Fluid amber for topping up."

My 74 owners handbook reads, "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.).

Page 22 of the 62-70 driver handbook of my Bentley, The Official MGB is an editors note M Brakes. "Standard brake fluids 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.".

I understand the reason for the editors note. In the 60's and early 70's it was difficult to find fluid for disc brakes because most US cars had drum brakes.

None of the above publications have a caution or warning about not using USA made brake fluids because they are harmful to the rubber components. I wonder why they wouldn't warn the reader about something that can cause brake failure?

Almost a year ago when the brake fluid question came up in a BBS thread I was in the process of rebuilding my 68 GT calipers. I went to the Ford parts place and purchased some Motorcraft DOT 3 brake fluid and installed it in the GT brake system. It's still there and the brakes are as good as the brakes on my 74 roadster with Valvoline Synpower fluid. The Motorcraft fluid has a boiling point in excess of 500'.

I'm not trying to convince anyone to use DOT 3 brake fluid, but if in an emergency you happen to fill your master cylinder with DOT 3 fluid there is no reason to panic and start purging the system of that evil stuff that is used in most new cars. BTW you will not go wrong using Castrol LMA, I've used it in most of may cars over 20 years.

I'll probably regret this posting but I'm clicking on submit now. Clifton
Clifton Gordon

Finaly I bought DOT 3 Lockheed brake fluid at my local MG parts supplier..I don't know if it's good, but it's what I will use to bleed the system...

J-F
JF

Gentlemen,

The most important thing when changing MG brake fluid, it is absolutely crucial to flush the system thoroughly with a least a quart of Gordon’s Dry Gin. Failure to do so may have dire and grave consequences...........Cliff
Cliff Maddox

Gentelmen - I like Cliff's recomendation, I think I will follow it religiously from now on. By the way, ther is no difference in the minimum requirements met by British or American fluids that are labled DOT 3. There is only one DOT and that is the Department of Transportation in America. Lockheed's DOT 3 for disk brakes exceeds the minimum boiling point for DOT 3, but in order to be sold in America as DOT 3, all fluids have to meet the same requirements as specified in the Federal Motor Transportation Safety Standard #116. In that standard it states that all DOT 3, 4 & 5 must be compatiable with all seal materials natural rubber or neoprene. Cheers - Dave
David DuBois

Cliff,

How do you get the bubbles out of the Tonic?
AJ Munro

AJ, That is classified information.
Clifton Gordon

This thread was discussed between 16/03/2003 and 21/03/2003

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