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MG MGB Technical - Brake fluid
|About a month ago I flushed the brake lines and put in new Dot3 fluid. Now, based upon what I've been reading here, I want to flush them again putting in Dot4 this time.|
My question is how to go about this.
1. Should I do one brake at at time (standard proceedure: furthest first, then working my way closer to the master cylinder), putting new fluid in the reservoir as needed (not mixing the old and new of course)?
2. Should I try and get all fluid out of the whole system before adding any of the new fluid?
3. Should I do any kind of intermediate flushing process to completely clear the Dot3?
|Drain all you can first. Then you will need to perform several flushings with DOT4. The two fluids will blend together making it very hard to get all the DOT 3 out of the system. If you have the time and want to get it all I would dissassemble the wheel cylinders and calipers. clean them in DOT 4 and reassemble. While they are disconnected flush the master cylinder and lines using DOT 4. It is hard to say how much DOT 3 can remain mixed in the system without causing you problems.|
Is there some sort of flushing agent I can use before putting the Dot4 in? The thought being it would clean out the Dot3 before it had a chance to mix with the Dot4.
|You could leave all the D.O.T. 3 in if you wanted. D.O.T. 4 is better, but D.O.T. 3 won't hurt anything. It used to be said that D.O.T. 3 would destroy the seals in British brake systems, but if that was ever true it hasn't been true in decades, and if you have decades-old rubber in your brake system then you have bigger worries! ;-)|
Suck all the D.O.T. 3 from the reservior, fill it with D.O.T. 4, and bleed as normal. Any D.O.T. 3 left will not hurt anything.
|I agree with Rob. The master cylinder cap for 68 and later cars specify DOT 3 brake fluid. The cars must have been delivered with DOT 3 fluid. I don't think DOT 4 was avaliable until the late 70's. I made the switch from DOT 4 to DOT 3 and back to DOT 4 several years ago. I left the DOT 3 in about a year. Nothing unusual happened and I couldn't detect any difference in braking. I just changed the fluid and didn't do any flushing. For more information on brake fluid see.|
|Thanks everyone. I think I will first check my resevoir cover and see if it says "Dot3". Just curious.|
I'll change out the Dot3 for Dot4 though simply because I just used Dot4 in my rebuilt clutch system and would like to be consistent. Aging brain cells ya know.....keep it simple for memory sake!
|DOT 3 and DOT 4 fluids are completely compatible, so you don't have to be very careful about flushing one to install the other. Their properties are similar enough that you might as well wait a couple of years and then just bleed and refill with DOT 4. Unless you are racing, DOT 3 will work fine. -G.|
This thread was discussed between 12/06/2007 and 15/06/2007
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