Is a line lock a one way check valve or a soleniod
that stops the fluid my car was set up with the line lock on the rear wheels it works great but my buddy says it is wrong should be on the front?

A line lock is a solinoid that stops the fluid from being relesed. It's location depends on what you want to use it for. Placing it in the rear brake line you use it as a staging control and luanch when you release it. I have mine in the front line and use it for doing burn outs. Then there are people the run dual linelocks.

I think it's illegal to have them on the rear per NHRA rules.

It is leagal to use a line lock on the brake line going to the back (you install it backwards). If you want you can put it in the line going to the back brakes to BLOCK line pressure and in that case you activate it, then press the brake pedal and then do your burnout. That way to can release the brake pedal and roll out of the water.

In this case it wold be a good idea to use a "dead man" switch for the line lock to insure that it is not left on reducing your braking at the end of a run.

I know of several cars set up this way.

I sorta like the idea of being able to control your rollout during your burnout. It also gives you the ability to use it to run your brakes at the start line, as holding the rear brakes will normally hold the car, whareas holding the front brakes only, most cars will push through the lights. some may find this more consistant than a regular foot-brake starting procedure.

Thoughts?

Yes that is how mine works I use it to roll out of the box it works good for me that way but was not sure about the check valve coment my friend made still not clear cause half the responese say it is the other half say it isnt?

not sure about the check valve coment my friend made still not clear cause half the responese say it is the other half say it isnt?

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You would need to test it or look at the design to
see if its a check valve design. If it has a spring
between the soliniod and the valve its a check valve
design which most are. Also the manufactuer would
say it holds X pressure(about 2500 lbs). Also in
the design, if it has a slooping edge on the supply
side it will allow pressure to be applied while its
engaged.... its all in the designs for what you have
EDIT
You wont be abile to see the differences in the outer
looks

If you want to use a Valve to BLOCK rear line pressure they do make valves (line lock type) specifically for this purpose. They are used on circle track cars to get them to turn into corners. They block brake pressure to a specific wheel in certain circumstancs.