dot 4 brake fluid

[jeffreys]

I have an MGC with dual brake boosters. I am wondering if it would be better to use the dot 4 which is partially synthetic and parcially brake fluid...or stick with the Castrol which I am having trouble finding. If I do change over to dot 4, is it just a drop-in fluid or do I need to flush the system? Thanks

 

[jeffreys]

I swapped over to dot 4 and have not had any problems.I would at least suck out the master cylinder res.You may or may not have to bleed the brakes I did'nt and the brakes work great.I also unhooked my rear booster when it went bad an can hardly tell any difference.take care,Jeff ps you will always need the front booster to operate

 

[Steve_S]

All brake fluid is synthetic including Castrol GTX. You may be confusing synthetic with silicon, which are different fluids and are not compatible.

 

[JPSmit]

I believe that they are all compatible with each other except DOT5 which is silicone based as already mentioned. You should be fine

 

[Banjo]

Castrol GTLMA is DOT 4. DOT 3 and 4 are both mineral based fluids, the main difference being the boiling points and moisture absorbtion charecteristics. they are basically interchangable by just bleeding the system out while refilling with the new kind. DOT 4 is rated higher than 3 so usually if there is a swap its from 3 to 4
On LBCs it's generally reccomended to use Castrol GTLMA DOT4 as it has the closest charecteristics to the original Gerling fluid used in our cars. But that really only holds any meaning if you have original, natural rubber parts still in your brake system. Most, if not all, new/ replacement parts have switched to synthetic rubber seals and are fine with any standard brake fluid.
I would reccomend sticking with a DOT 4 ,weather it be Castrol GTLMA or not. if you are changing fluid, a flush is a good idea anyway. it gets any pooled moisture out of the components, and removes any contaminated fluid.
DOT 5 is the silicone stuff, and is not campatible with DOT 3 or 4 It is reccomended to replace any component with seals or rubber parts if doing a swap to DOT 5
One more question. Are you constantly adding fluid to this car? If so there's a leak somewhere and it should be found. Brakes fluid leaks aren't something to ignore.
I believe Moss sells Castrol GTLMA if you really can't find any.