old syle gearbox, fill through large flat head or inspection

I have an s20 with the old gearbox. I understand it uses straight 20 weight oil. I would like to change the oil. The drain plug looks like it will move, the inspection elbow plug comes out no problem. The large flat head plug high in the box doesnt seem to be able to budge.

Do I refill slowly through inspection overflow elbow port after draining? Or must that top screw come out? I do not want to brutalize unit.

incynr8 wrote:I have an s20 with the old gearbox. I understand it uses straight 20 weight oil. I would like to change the oil. The drain plug looks like it will move, the inspection elbow plug comes out no problem. The large flat head plug high in the box doesnt seem to be able to budge.

Do I refill slowly through inspection overflow elbow port after draining? Or must that top screw come out? I do not want to brutalize unit.

Drain it refill it threw the elbow you can also use any of the new synthetic gear oil out there 75 140w 80 145w whatever you can get it will last for another life time

so I can use syth 75 multi weight IN gearbox and FOR worm drive gear in the 'oil pan'?
if so, awesome!
thanks
Al

Yup,indeed you can,like coal berner said

I like to mix a few ounces of STP in with the oil

Glenn