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MG MGB Technical - synthetic brake fluid or not

I have a friend, a BMW aficionado, who was aghast that I would use synthetic brake fluid in my brake system. Having already put it my A model without complaint I’m wondering if it was a good idea after all? He tells me it may cause the rubber to breakdown and get squishy & fail under pressure? My B has a lot of rust in the area of the master cylinder due to spillage and leaking… so really hoping synthetic brake fluid is all it’s cracked up to be. good idea or not?
danny jacob

This is a real can of worms and it may be advisable to have a good look through the archives first otherwise we risk going to a very long thread !!
Iain MacKintosh

She rises from the grave again! Love these insane debates. Please hold on to the bar as we go round and round.

Paul Hanley

Very true...Iain. I use it without problem. Danny, if it was clear as your friend says do you think it would be sold widely with the liability standards we set in the U.S.? Pejorative, no argument statements like that are rarely true, in my opinion. As Iain says there are arguments both ways. You are supposed to clean the system thoroughly before using DOT 5 if not a brand new system. Little softer pedal. Lasts a long time. No moisture absorption. You still need to get car up to op temp frequently..there is moisture in the system...just not in the fluid. There is also LMA Castrol (low moisture absorption) DOT 4, etc. etc. etc. etc. etc. Do check the archives. You will find very lengthy threads.
J.T. Bamford

It makes good bed time reading. Take your laptop with you !!
Iain MacKintosh

Oh Yeah!

A chat about which is a better baseball team, the yanks or the red sox, would be concluded before this brake fluid talk.

Flip a coin for the best closing argument.

(I use silicone)
glg

Unless the system is new, silicone will not be effective. By that I mean a restored car. It is not possible to completely clean out an old system. I like silicone as it keeps the rubbers in good condition,and there is no moisture, especially with a car that is stored.

Kim Rutherford.
K Rutherford

Downsides of Silicone purple DOT 5
Does not mix with other brake fluids including DOT 5.1
Contains air so not a performance fluid spongy pedal and may cause problems at altitude and with high fluid temps (racing).
IF water enters system it will end up in callipers and the boiling point will be 212f. However the only way I can see this happening is condensation in M/C but if in doubt a regular bleed off of some fluid could be added insurance.
Cannot be used with ABS.
Expensive

Upsides
Kind to paintwork
Changed on a less regular basis

The choice depends on what type of brake fluid meets your needs.

Paul
Paul

I've been using it in various cars I restored since 81 and I never had a problem and the fluids available today are better than they were then. Takes a lot of bleeding to get a firm pedal but I think it's worth it.

BTW, I hope you installed new brake lines as stell ones rust from the inside out too.
Mike MaGee

Note that air is dissolved in Silicone Fluid and cannot be bleed out unlike entrapped air, and is reason why it cannot be used in abs systems.

Paul
Paul

Just my last thought on this:

I would not recomend changing fluid types without installing a completley new brake system. That is all new pipes, cylinders and calipers, master cylinder etc.

I would not take the chance of cross contamination by trying to bleed the old system to take the silicone.

And as my really last thought -- I would suggest changing the clutch hydralics also -- just so there is only one hydralic fluid in use --. It'd be too easy to forget which is which and inadvertantly putting the wrong fluid in either of the systems.

I say all this only because I did a complete restoration of a '64 and had all new or refurbished hydralic parts to work with.

If you're not willing to re-new all the brake system stuff, bleed out and replace with the old type fluid.

(cardinals in six games)
glg

glg,

<<cardinals in six.>> Hope your neighbors aren't on this board. Sox in four!!

ps sage advise.
Paul Hanley

Paul in Surrey - I don't believe that air is dissolved in silicon fluid, but it can become entrained in it due to cavitations when it is forced through small orifices, such as found in ABS systems and proportional valves and for that reason it is not supposed to be used in systems like that. Also if the fluid is agitated in the can it can entrap air bubbles which don't work out as easily as they do in DOT 4 fluid. Silicon fluid does require special handling, but the results are well worth it. I have had it in our TD for better than twenty years. In that time I have never flushed the system or had to add fluid and it is as clear today as when I put it in the system twenty years ago, which tells me that there is no corrosion anywhere in the system. As to condensation in the M/C, Since the M/C on the TD is mounted under the floorboards and we drive it year around in cold wet weather in the winter, and I don't see any signs of corrosion in the system, I would have to say that no condensation exists. By the way, about the only place I have seen the issue of water in the system collecting in the low spots brought up, is by other brake fluid manufactures who don't make a silicon fluid. This leads me to believe that, while in the strictest sense this is true, it is used as a red hearing by the other companies.

Now that we have had all this discussion about silicon brake fluid, did anyone else besides me Danny's original question was about synthetic brake fluid? Synthetic brake fluid is DOT 5.1 and not silicon, so I have to ask Danny if he was really talking about synthetic brake fluid (DOT 5.1) or silicon brake fluid (DOT 5). If you were really interested in DOT 5.1 fluid, we all have to start all over with our discussions;). Cheers - Dave
David DuBois

David,

DOT 5.0 has large molecules and air is finely dispersed in these microscopic gaps between these molecules.

Can condensation form in an open brake system?

Castrol SRF is a Silicon ester rated DOT 4+ absorbs water and used in F1, probably the best and most expensive brake fuild.

Paul
Paul

Why not add more input?
I've used Silicone DOT5 in my BGT since 1985 and in my MGA since 1990. No problems. Bleeds as easily as DOT3; pedal seems as hard as other cars using DOT3; no missing paint work; no rusty bits. Initially, it didn't even go into a totally new system. The MGA is still running on rear wheels cylinders which were used for DOT3 (they're being re0built this winter).
Fraser
Fraser Cooper

This thread was discussed between 22/10/2004 and 24/10/2004

MG MGB Technical index

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