reverse doesn't work in 904

You might very well have toasted something running it that low on fluid. Should have had at least 7 minimum. Here are the top 3 possibilities for problems.

1. The rear band is worn/burned and now isn't adjusted correctly.

2. The seal in the servo that actuates the rear band isn't sealing (blown).

3. There's a problem in the front clutch assy. i.e. seals blown or too much clutch clearance.

The #3 problem will also cause no 3rd gear. Have you driven it to see if it goes through all the gears? If so you can rule out that one. The other 3 can be easily checked by removing the pan and valve body.

1st thing to do is test drive it to see if it has all 3 forward gears. Don't just run it through the gears on jack stands either. That don't put a load on things. Drive it down the road. If 3rd gear works fine that's good news. Means the front clutch pack is good.

Next drop the pan and check the rear band adjustment. If it's way off that could be the problem. If not drop the valve body and pressure test the rear servo with about 30 lbs. of air to see if it's applying the rear band. If you need a pix of the test ports pm me and I'll e-mail it to you.