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MG MGB GT V8 Factory Originals Technical - dot 5 brake fluid

Hello can any one out there in mg land tell me if dot 5 brake fluid is ok to use on my 1972 mgb-gt that i am in the proceess of rebuilding the brake and clutch hydralic systems with new kits and blowing the lines out of the old nasty dot 3 fluid. Car sat for 13 years and as you can imagine my tasks have only begun. thanks from texas usa
RP Padilla

Yes, but see here http://www.american-auto-club.co.uk/aac_articles/index.php?task=show&id=70 for some interesting comments on dot 5 (silicone), like:

"The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way (as) leaded gas."

People talk about flushing the system before changing to dot 5 but "Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4."

"If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system."

My local parts place doesn't stock dot 5/silicone anymore, but it does stock super dot 4 "Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry)."

I'd stick with dot 4, vanilla or super.

Paul Hunt

When I built my system up I used Dot 5.1 Brake fluid. It's synthetic but NOT silicone.
Allan Reeling

That's it, compatible with DOT3 and 4, not DOT5. You do have to check carefully though, why they specced it as DOT5.1 when it is very different to it and not compatible with it I don't know, especially when the containers can be labelled DOT4 Super.
Paul Hunt

It is interesting to note that a well known servo rebuilder puts a label on his servos, saying the warrenty is invalid if Silicone is used.

I have seen some of the seals he has taken out when it has been used!!

CP
Colin Parkinson

This thread was discussed between 15/10/2009 and 08/11/2009

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