View Full Version : Proper Brake Fluid

05-21-2003, 08:30 PM
What is the proper brake fluid for a BJ8? I have used Castrol LMA fluid (DOT4?) in other British cars and have used it in my BJ8. A few months ago during the replacement and bleeding of a clutch slave cylinder my local auto parts store only had DOT3 fluid which I purchased and installed. Currently the brake system may have a mixture of DOT3 and DOT4. Has any harm been done either by this potential mixing or the use of DOT3? If so can this be rectified by the draining of the fluid and the installation of DOT4? Thanks.

05-21-2003, 09:30 PM
Aloha Greg,

DOT3 and DOT4 brake fluids can be mixed. DOT3 is a low cost brake fluid that is widely available, however it has some disadvantages, it dissolves natural rubber brake seals that may be found in older cars, it damages paint if it is spilled and it readily absorbs water (hydroscopic) which corrodes metal parts and reduces the brake fluid boiling point. DOT4 brake fluid is more costly than DOT3 but it has some advantages in that it is more resistant to water absorption and has a higher boiling point. The boiling point of a DOT 3 & 4 mixture is theoretical proportional to ratio of the mixture. I use DOT5 in my TR3 and MG TF, it has the advantage of not disolving paint if spilled and it does not absorb water. The disadvantage is that it is somewhat compressable and some feel that it causes a "spongy" pedal.

Safety Fast,

05-25-2003, 10:56 AM
I've been using silicone fluid with great success. I know there's controversy with silicone but I ignore it.

RF Thom
05-26-2003, 12:29 AM
Stretch - Try synthetic brake fluid. It's rated as Dot 4 & has all the advantages of silicome, 1/4 the cost, and avoids the rubber compatability question. I have it in all my vehicles British and daily runners.

Regards Bob

05-27-2003, 08:58 PM
Thanks, I'm not familiar with it and will check it out.

Dave Russell
05-27-2003, 11:13 PM
Castrol GT LMA brake fluid is a synthetic although not advertised as such. It is "Girling approved" to be compatible with Girling brake parts.

05-28-2003, 09:32 AM

I chose silicone for my BN4 because it has served me well, and it will not eat paint. Does anyone happen to know how synthetic brake fluid reacts with paint?