Issue #1: at low spindle speeds the DC motor "chugs" It doesn't in reverse. Increasing IR comp makes it worse also the thyratrons flash their blue glow in sync. #2: the back gear box leaks. The lathe is in as new condition otherwise.The lathe is a 1959 model. Thanks in advance John

#1: Can't help on this one.

#2: The back gear box has a number of possible leak points such as the drain plug, sightglass gaskets, the lip seal on the shift shaft, gaskets sealing the gearbox castings and the gasket on the small plate on the face of the output pulley. Make sure all the fasteners are tight and clean all traces of oil off the motor end bell, back gear box and pulley. Run it, find where the oil is coming from, repair as required is one approach.

My lathe was in generally good mechanical condition except for the back gear box. It worked but it was a mess when I took it apart. Bad countershaft bearings, incorrect lubricant, worn out sliding dog clutch, a tablespoon of metal particles in the sump, broken off taper pins, a cracked main casting. There are several versions of the back gear but they are all simple. It's not difficult to simply tear it down and do the entire thing. It's 50 years old. The lip seal on the shift shaft is probably a goner.

BTW, the spindle motor does not need to be removed from the lathe to pull the back gear box.

Check the spindle speed in both forward and reverse without changing the speed setting. If the speeds vary it's possible that the brush ring has moved and need to be returned to neutral. If there's little difference in speed check the brushes for good tension on the springs and a good fit, a brush that moves between forward and reverse can cause similar problems.

Once you've eliminated brush (and motor) problems we can look at the drive.

Make sure that it wasn't overfilled. Overfilling will have oil come out the front as there's no real sealing there. If it wasn't overfilled it'll need to have the gaskets replaced.

Order a set of gaskets from Monarch, pull the backgear and replace the gaskets. Likely you'll need EE2401, EE2402 and EE2469 but it's best to give Monarch the serial number and let them make sure that they match. While you're in there clean out the oil passages to the sight and make sure that it's working, if you're taking it apart you'll need the cork gaskets for it as well (2 of them).

My '56 used to have a problem holding oil, now it's never a problem and I have to remember to check it once a year or so.

If you order gaskets from Monarch it might be best to send them a photo of your back gear box to make sure you get the correct gaskets. The Monarch manual for my lathe shows a different back gear box than what is in the lathe.

I made all the gaskets except for the sightglass from 1/64 in. Felpro Karropak which any good auto part store can get for you. They can also supply a sheet of 1/16 in. cork to make the two sightglass gaskets. It's much cheaper and there's no waiting.

Use a quality gasket dressing. An excellent one is Hylomar.

A SKF 4996 seal (any bearing house can supply one) will take care of the shift shaft. Be careful not to nick it on the taper pin holes. Clear packing tape is a handy way to cover the holes as you slide the seal over the shaft.

Thanks all for the info.