Replacing 1N4001 for higher current diodes
The 1N4001 diode is considered a general purpose rectifier. It's in a family along which includes the 1N4001 through 1N4007 diodes.

I have never heard of (and cannot find) a 1N4008.

You should look at the datasheet for these diodes to determine if you can substitute them safely.

The main difference is in the maximum ratings:



You will have to make the determination of what constitutes an acceptable replacement because we do not know the characteristics of your device.