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MG MGB Technical - Brake fluid advice

The previous owner of my '72 GT put Dot 5 Silicone brake fluid in the master cylinder. Does anyone know if this is going to harm the rubber brake hoses or anything else?

Thanks for your help.

Dave
Dave Shively

Dave - I have had silicon, DOT 5 in our TD brake system for the past 20 years and in our MGB for the past 6 years. Both systems are working fine, with absolutely no problems. In fact, the fluid in the TD is the same fluid I put in 20 years ago and is still as clear as the day I put it in.

The only concern I would have is that sometimes, if the fluids are swapped and the original seals are still in the system, the seals may swell due to desorbtion/absorbtion characteristics are not the same. If you start having a problem, you will have to replace all of the seals, flush the system of all the existing fluid and start over again with which ever fluid you feel most comfortable with. This is not something I would do unless I started having a problem, such as brakes not releasing at any of the wheels.
Good luck - Dave
David DuBois

The AutoMec Silicon fluid I used advises in the literature that in an emergency, Dot 4 can be used to top off the system, but it is essential that the system is then drained as soon as possible and refilled.
HTH
Martin

Dave,
Bringing that subject up on this BBS is like discussing politics or religion. Everyone has an opinion and everyone is absolutely certain that he is righteous in his belief. There is a substantial amount of info on this subject in the archives. For what it's worth I've used DOT 5 for many years without any problems whatsoever. I didn't install new seals or hoses before I converted, either, and I've done multiple MGB's.
Regards,
David
David

Thank you all. I feel much better about the brake fluid now.

Dave
Dave Shively

Dave,

Regardless what Martin quoted above, avoid mixing silicone fluid with any other type. I did that once and the stuff turned to jelly. It was a h--- of a job to get it cleaned out. Otherwise silicone fluid is great.
Edd Weninger

Hey Dave, were you saying that you have DOT4 and DOT 5 mixed?? Edd's post is timely.
David
David

What they all said. There are a lot of very strong opinions on this subject. I use DOT 5 on the recommendation of very good long time LBC mechanic. If it's already in there and everything seems fine then just keep some in trunk for the odd time you might need it to avoid the mixing deal if at all possible. I did mix mine for a short time then bled all out and replaced with DOT 5 and had no problems. Nice thing about DOT 5 is longevity, resistance to absorbing moisture and the fact it won't ruin your paint if master cylinder leaks or you spill some.

JTB
J.T. Bamford

If you put in silicone fluid, and don't mind a little cosmetic change, you might consider a warning label along the lines of what is found here:

http://www.militarystencils.com/Decals.htm

Specifically,
http://www.militarystencils.com/images/Decals/Special/siliconecaution.jpg

That will alert anyone who would be tempted to put in D.O.T. 4 to think twice....
Rob Edwards

Automec supplies warning labels and cable ties with their bottle to secure to the master cylinders.
Martin

Here are a couple of brake fluid links I've been saving:

www.shotimes.com/SHO3brakefluid.html

www.rpmnet.com/techart/fluid.shtml

A while back I e-mailed Castrol about the shelf life of GT LMA - 2 years in an unopened sealed container. Thought I'd add that because a lot of British car guys use it.
Glenn

I've already got the new brake hoses and will be replacing the old ones shortly. Even if there is any Dot4 in the system, when I bleed the brake lines the Dot 5 should clean out the Dot 4.

Thanks again for the help.

Dave
Dave Shively

Here is a very comprehensive article on brake fluid selection. FWIW, Clifton
http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm
Clifton Gordon

Although silicone fluid doesn't absorb water readily as do the other type of brake fluids, moisture still collects. The moisture will congregate at the lowest part of the brake lines. I highly recommend that the silicone fluid be flushed every few years. Color or clarity doesn't mean that the fluid is still good. Compared to what brake parts cost it's cheap insurance.
Mike MaGee

Mike MG:
I don't doubt what you are saying about the collection of moisture in the lines with silicone fluid, but my question is one I would suspect other posters might want to ask, and that is: do you have a source for this info? I mention it as there has been so much controversy about this subject (Silicone Brake Fluid) that any good info resource would be worth reading and having in the archives to help dispel much of the bad press and urban mythology that some of us have been guilty of generating over the years. If you have a site in mind, perhaps like Gordon's, I am sure others would like to see and read it. Thanks!
Bob Muenchausen

This thread was discussed between 16/09/2003 and 17/09/2003

MG MGB Technical index

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