GM8 RA Motor Control Problem

[Ramsay11 (Stephen)]

Recently I put out a thread on adjusting Worm to Worm Gear mesh on my GM8 with Digital Drives and received many helpful tips - Thank you. My GM8 still exhibits problems and won't move its RA axis under load, via motorized operation using the Hand Controller. Removing the RA worm cover, I have verified the RA Motor is operating, the RA Worm engages the RA Worm Gear and it is slowly moving in both directions. Yet look through the scope, the DEC motorized operation is fine but RA control doesn't move along this axis.
The mount is properly balanced, not overloaded (18-19lb load) with a substantial 12V supply, having good current.
Regardless of RA clutch tension, RA axis won't turn under motor control.
This is a "new" mount, direct from the manufacturer, but internally the clutch must be slipping as I have noticed, without load (scope and accessories) the RA axis will move via the hand controller.
I have heard of owners disassembling Losmandy mounts to clean and degrease, then re-lubricate and erroneously applying grease to Teflon clutch pads - causing clutch slippage?
This mount was acquired new from Losmandy but something internally is amiss. I have put out a message to Losmandy and my previous experience has proven, they are not the most obliging with helpful information.
Does anyone have any suggestions?

[[1ponders] (Paul)]

Have a listen to the motor, try different speeds and check that the motor is changing pace as you change speeds.

It sounds like there is be grease on the clutch pads. Not a difficult fix. Remove the four hex nuts at the front of the RA Axis and remove the Dec assembly. Then remove the clutch knob and wavey springwasher and spacer. Note their order to put them back the same way. As you slide the RA axis out the thrust washers and bearings will slide off the axis.

Slide the axis right out, wipe down the shaft to remove all traces of grease. Wipe down with a turps/degrease moistened rag. Remove the nylon clutch pad. If it catches on something make sure there is no 'grease' hardened on the shaft. Once the disk is off wipe it clean really well to make sure there is no grease on it at all. I wash mine in soapy water then rinse well and towel dry. The same goes for the inside of the RA plate that is still attached to the shaft. Make sure it is grease free and dry. Also make sure that the top surface of the main gear is free from grease.

The nylon clutch pad can't have any grease on it at all. Neither can the two other contact surfaces. Grease eventually wicks its way to the pad but careful regreasing when servicing can go a long way to preventing/reducing this.

After replacing the nylon clutch, slide the RA shaft back inside the axis. You may want to put just the tiniest smear of a suitable grease (see other threads ) on the two rollerbearings but it shouldn't really be necessary. Oh it goes without saying that you'll check the condition of the grease in your roller bearings.

Replace the thrust bearings and washers, spacers and spring washer and tighten your clutches. The clutch should work well without having to strain yourself tightening. I've rarely used more than a single hand firm tightening. Over tightening won't damage anything, assuming of course you don't use tools like a wrench.

btw once you learn how to do this its barely a fifteen minute job. You aren't doing a full pull down.
See how it works then.

[Ramsay11 (Stephen)]

Thanks for that information. I unscrewed the RA clutch and pulled out the RA shaft - there was a fair amount of grease on both contact surfaces of the Teflon clutch pad. I used a mild de-greaser and cleaned the Teflon clutch pad plus both metal surfaces where it contacts. The lubricant used in the GM8 head, is a clear, low viscosity grease and likely to migrate, if stored upside down in a warm environment. Why wouldn't Losmandy include this in a FAQ section or Troubleshooting Guide?

I also own a manual AltAz mount with two teflon clutch pads and had a difficult time getting the scope to stay stationary, especially when viewing close to zenith. The scope would always drift down with gravity regardless of the pressure applied to the tension adjustment. I disassembled the mount, cleaned the teflon clutch pads and their metal surface contact areas and it resolved the problem. Too bad I didn't apply this logic to the GM8 earlier.

I am going to take the GM8 out this evening to see if this has resolved the problem.


Stephen