MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Purging Brakes... revisited

Hi.

I am in the process of changing out the brake and clutch master cylinders (may have been leaking when I got the car..old clutch master had pitted bore)in my 1971 mgb. Unfortunately after I got the car last summer I put the dreaded dot 3 fluid into the systems. Now I want to purge the system so as not to destroy the new masters. There are no leaks yet at the clutch slave (new last year) or wheel cylinders so hopefully it's not too late for them.

I searched the archives and found denatured alcohol is best to use, but I can't find any where I live.

Methyl Hydrate (99.9% pure methyl alcohol) is readily available.
Can I use the methyl hydrate as a substitute or will it destroy the rubbers too?

If it shouldn't be used I will resort to purging using dot 4 fluid unless there are other alternatives.

Thanks. Tim

Tim Mayor

Any hardware store in your area should have denatured alcohol, sold in either a gallon can or quart size - sorry - liter or 2 pint. If not at a hardware (home improvement) store, try a paint store. It is very common and inexpensive.
Jeff Schlemmer

Not sure about the effect on the seals but methanol is very toxic and can be absorbed through the skin. It also has a very low flash point, so I'd not contemplate using it as a cleaning solvent in a garage.

Don't know how they sell denatured alcohol in Canada. In UK it's commonly available as methylated spirits. It used to be ethyl alcohol plus methyl alcohol and a purple dye. Several years ago to cut down on health risks suppliers took out the methyl alcohol and put in a small amount of Bitrex which is claimed to be one of the most bitter tasting chemicals there is. I wonder who they get to do the taste ranking on things like this.
Good Luck
Vic
V Todman

It seems that this stuff is not as readily available in Canada. I have tried many hardware stores (including Home Depot), Autoparts Stores (NAPA and Canadian Tire), paint stores, and pharmacies. The only positive I got was from a company that manufactures shellac, but it only comes in 20 litre pails and they are unsure if they can sell it to the public! I will find out tomorrow. Perhaps it is not allowed for sale in Canada.

Are there any Canadians out there that have seen it being sold in Canada? If so please let me know where to get it! Thanks. Tim
Tim Mayor

Tim, The Haynes MGB repair manual recommends using hydraulic fluid to SAE J1703 in the brakes.

SAE J1703 is DOT 3 fluid. DOT 4 is fine but I'm wondering why you are concerned about running a little DOT 3 fluid through the system. The cap on the Lockheed master cylinder on my 74 MGB specifies DOT 3.
BTW, DOT 4 SAE J1704 brake fluid didn't exist when most MGB's were built.

Clifton


Clifton Gordon

Hi Clifton.
From what I understand there is a difference between British spec Dot 3 fluid and North American spec Dot 3. The North American stuff is not compatable with the natural rubber used in the original brake parts, and will rot them.

There seems to be some debate as to whether the recently manufactured Lockheed cylinders, and the rebuild kits that are available, use natural rubber or a more compatable material (neoprene?).

In support of the latter material theory the brakes in my TD were rebuilt in 1996 and filled with NA spec dot 3. The master just started to leak this year..not bad 9 years!

Doesn't really matter for the mgb because I bought an old NOS brake master...sure to have natural rubber.

So the search continues. I found one, half liter bottle of denatured alcohol at a pharmacy in Winnipeg. Not enough. I also got a hint that "Fondue Fuel" was denatured alcohol with blue dye. I dug through the cupboard to find my wife's bottle of fondue fuel. On it it reads "contains methyl alcohol"...but does not say how much of it is methyl. I also asked for "methylated spirits" but nobody seemed to know what that was.

Thanks to everyone for the suggestions.

So back to my original question. Is methyl hydrate safe to use with rubber? Tim
Tim Mayor

Tim - Have you tried your paint stores, yet? Denatured Alcohol (Ethyl Alcohol) is the solvent of choice for most all shellacs, and I can't believe they wouldn't have it.

Another alternative might be Isopropyl Alcohol (the active ingredient in "rubbing alcohol"). It's totally compatible with natural rubber, and is miscible with water and brake fluid. It's also sold in paint stores.

And, finally, Methyl Alcohol is available in auto parts stores as "Brake Line Antifreeze", though they're referring to the air-brake lines of large trucks.

IMO, most any of these solvents would be in contact with your rubber bits for such a short time, that any swelling should be inconsequential.

Best of Luck - - Alec
Alec Darnall

This thread was discussed between 07/06/2005 and 09/06/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.