I have a 93 civic 2 door coupe with a b20 in it, I'm not sure what transmission I have it is a 5speed.
I was driving the other day and discovered it will no longer go into 3rd gear it just grinds and pops back out.
I've never worked on transmissions before so I'm not sure how to go about fixing this problem.
Do i take it to a transmission shop and have them fix the gear or do I need to buy a whole new transmission?

 

It can be repaired. The cost will be steep if a transmission shop does the repair for you... even the parts won't be cheap to purchase if you attempt to fix it on your own... but at least you will know what you have then.

 

What is your budget and where are you located? If west coast, I'd call Synchrotech and if east coast, I'd call Tall Pines Racing. Both are manual Honda transmission specialists and are capable of repairing your transmission.

Another option is buying parts from Synchrotech and doing the repair yourself. It's not that hard, but does require some specific tools most folks don't just have, and acquiring them may be more costly than paying the pros to repair it. If you do decide to repair it yourself, follow the instructions in the Helm manual.

Your third option would be to buy a used transmission. This is probably the cheapest, but could be risky. There are some places like Hush Performance that pull transmissions from junkyards and open/inspect them before selling.