I’m trying to make materials like rust without using image textures for seamless results. But i cant seem to figure out how to make the rust look realistic using nodes.
Needs more quite a bit more nodes if you are going for realism. Try a color ramp between the noise textures and the mixRGB node. Look at rust and mimic. Most convincing rust materials can be made with noise and musgrave textures
Hint: Use the mixRGB and subtract a noise texture with it. The fac of the MixRGB node is the influence. Also think of things as a single shader node. Say you have metal and rust, but both are a separate shader category.
You’ll need at least two to three layers of detail in this shader/material; big, medium, and small. Even more layers if you want to get closeups. Just needs finer and finer details from at that point.
Put a rust picture right next to you and mimic the large scale color variation with noise textures etc., then move onto smaller and smaller details. Look up Sayan Mondal’s shaders before you take the plunge though. Realistic procedurally textured materials take a long time and normally turn out to be really complicated. I would really suggest sticking to image textures until you improve (http://www.textures.com/download/rust0176/49695?q=rust). Finally, you don’t want to plug a texture coordinate node right into a color mix node: send it to a mapping or texture node first 
Honestly, the biggest advice I think I can give you, is go back to image textures for now. Image texture does not mean it can’t be seamless!
Making only procedural rust takes immense skill and understanding of both blender nodes and physics.
To your nodes:
- Even rust needs some gloss.
- Use color ramps
-RodDavis already hinted that your mixRGB with generated TexCor as factor makes no sense (at least to me…) - Andrew Price did a tutorial about rust which is at least semi realistic (https://www.blenderguru.com/tutorials/how-to-make-rust/#) maybe start there and build on top of this basic setup.
Totally agree. The link I gave above is for a free seamless rust texture on Textures.com: you should definitely register there (its free to download a certain number of textures per day).