Brake Fluid - what DOT # do I use for 1981 300SD?
 

My owners manual does not tell me. Is it DOT3, DOT4 or what? Need to replace the master cylinder.
Thx.

dot 4

Thanks VSTECH.

both DOT 3 and 4 work well.

replace every year (most important bit)

yup.

dry fluid with clean hoses is the most important part.

even the best dot 5.1 fluid is worthless with water in there...

I would look for the synthetic ones. Valvoline used to or does make one. I think Prestone does to. A bit better at no corroding. The local import part store carries Castrol or some other brands for Euro cars. Suppose to be synthetic. If DOT 5 is the silicon stuff, I would not use it. Good hi temp performance, but I have heard some problems with very low temps. So for a summer car it might be good. Although, I do have it in my Bricklin, and can not remember any problems.

all brake fluid is synthetic.

Edit - I was wrong - it is DOT 4 - disregard this post.

Dot5 is silicone fluid. Completely incompatible with dot3 fluid. If it has it in there it was installed after market. Not stock.

DOT 5.1 is not the same as DOT 5. DOT 5.1 - Wikipedia, the free encyclopedia

QFT!

I always tell customers when buying brake fluid that "synthetic" means nothing in regard to brake fluid. It's all synthetic. 3, 4, 5.1 are all glycol and 5 is Silicone not mixable with the others.