Ok I got a 90 f150 with an 87 300 inline 6 engine I was wondering how do I check to see if my clutch fluid is low the reservoir has no markings and is it ok to add dot 4 brake fluid or should I stick with the dot 3?

 

Dot 3 only. It should be just filled enough that when you put the diaphragm back in it dosen't overflow and spill all over.

 

Yes you can use DOT 4. It's DOT 3 or better.

 

You're right, I was thinking DOT 5 which is non compatible.

 

So is a hard clutch pedal good or bad?

 

You'll have to explain that one to me, since I don't buy DOT 5 so I haven't read the bottle.

 

DOT 4-5 are both synthetic brake fluids, which is why I prefer to stick with whats in the system but DOT 4 can be mixed with other brake fluids if the bottle says so.

DOT 5 on the other hand is a silicone based brake fluid designed for racing applications and repels water instead of absorbing it like DOT 3 and 4.