DOT 3 or DOT 4? for my 73 280CE

[alabbasi]

I'm planning on flushing the brake and clutch system on my 73 280CE. Do I use DOT 3 or DOT 4 brake fluid?

[cadurning]

Use DOT3. It is my understanding that DOT4 is not compatable with older brake systems.

[Graham]

Originally Posted by cadurning

Use DOT3. It is my understanding that DOT4 is not compatable with older brake systems.

DOT 3 and 4 are quite similar glycol based fluids. I think you can use either on our older cars.

But you should not use DOT5.

Please correct me if this is wrong - just going from memory.

[Bill Adkins]

DOT 3 is appropriate.
Bill

[mak]

[I][/DOT 4 is similar to DOT3 but has a higher boiling point ,Both are equally hygroscopic.
i use Dot4 in all cars.
mak

[alabbasi]

I hear that! DOT 3 is not recommended on my MGB because it eats seals. That's a 73 also.
I'm wondering if this applies to MB's as well. I do use DOT 4 in my later cars (77 and on).

[GGR]

I'm running DOT4 in my W111 Coupe. I thought the only difference was a higher boiling point for DOT4. Do I risk damaging something?

[pch2021]

dot-4, non synthetic.

[alabbasi]

Cool, i'll get some of that fancy blue stuff

[Wodnek]

Originally Posted by alabbasi

Cool, i'll get some of that fancy blue stuff

That is what I would do.

[Mark DiSilvestro]

Originally Posted by alabbasi

I hear that! DOT 3 is not recommended on my MGB because it eats seals. That's a 73 also.
I'm wondering if this applies to MB's as well. I do use DOT 4 in my later cars (77 and on).

I believe the main difference is the boiling point and one can use DOT 4 in place of DOT 3, but normally not the other way around.
I've used DOT 4 in most of my vintage vehicles without problems - at least problems that could be blamed on the type of fluid. As for MGs, on a friend's '70 MGB, it plainly says on the cover of his Lockheed brake master cylinder "DOT 3 brake fluid".

Happy Motoring, Mark

[Chas H]

DOT 3 is less hygroscopic than DOT 4. It is also compounded slightly differently, so seals made for DOT 3 may not be completely compatible with DOT 4.
There's no reason to assume that DOT 4 will give any perfomance gain over DOT 3 and in systems that have not had a fluid change in over 1 year, DOT 4 may be degraded by moisture to less than DOT 3 specs.