I have 736 Berk that has developed a problem when running in reverse. It seems like something is binding when it tries to move backward. It has gotten worse until now it barely moves. It runs fine forward and pulls fine. When I pulled the motor out, the armature/worm shaft seemed like it had a lot of axial play – 0.015 ~0.025 inches. What should I expect? The worm teeth don’t seem to be badly worn.
Maybe dress your armature plate and brushes tips. (I dont have that one) One aide of thw gaps can go low over time. Brushes can develop an angled tip, turn and hang in a gap too. Or both.
Or a thrust washer? When you reverse, it pushes the shaft the other way (up or down) as well. It can cause heavy drag and a washer helps. This can be a tiny roller bearing vs washer on some motors... bad bearing? hard bearing grease etc.. Ive added thrust washers to motors that didn't have them. It's a matter of how much thrust play is there id you can fit one.
Machine shim washers are hard, thin,and milled flat to spot on thickness vs any old washer. Brass is usually pretty good too.
Armature shaft bushings oblonged, the shaft can lean enough the armature winding body can scrape the field plates. (can be directional)
I guess axle bushings could give bind on a worm, I just haven't seen it . Normal gearing it happens. You have to watch gear posts and gear post holes, watching for leaning off plane from its mate(s) etc.
Quartering off a hair or rod issues can also be directional where you might not expect it. If taking rods off stops it, that's it.
This has come up many, many, many, many times over the last several years. It's a common problem with 726's and apparently 736's as well. Using 'Search' or 'Advanced Search' on the forum should bring up a large number of hits.
For what it's worth I have a 726 with the same challenge, except the forward direction is the sticky one. Someday I'll find the time to fix it. Until I do so I enjoy seeing this come up again and again to prep me for the task. The help on this forum, whether the earlier posts, or Adriatic's here today, will be critical when I finally get around to it.
Let us know what you find.
Here are two examples I was able to find; neither are specifically about 736's but both have good suggestions because they're of a similar vintage:
Thanks Mike, really good stuff. Does anyone have a picture(s) of new vs worn worms and worm gears? All I have are from the 0-27 vertical motors (622, 2032).
Here from a manual i bought long ago parts break down of the 681-100 motor used in 736.
Did replace a few parts in one of these but it was long ago , bottom left in green ink you can see note that TTender had them but again that was years back.
When you pulled motor did you unscrew from frame to see if it would freely run forward and reverse hooked up to transformer i ask because if it does run fine that way it may not be the play your seeing but another problem like not meshing properly with the worm gear in which case certain size shim washers are placed over the motor mounting studs.
Have heard that since these are from early 1950s after so much running one way the worm wears in that fashion so when reversed it may bind. Makes sense as the worm is softer material brass, and the armature gear is steel.