Depends on what has gunked them up... Disassemble the unit and wipe down with some good 99% isopropyl alcohol as a first step. Generally this will get rid of typical EM dust/grime.

After the general cleaning make sure to clean the contacts to a nice shine. Really fine grit sandpaper works or even some polish. You want to have good metal-metal contact for reliable operation.

For me, the most effective way is to just take them all apart, clean with various degreasers/cleaners, then reassemble. Stepper units can really build up a lot of gunk over the years, and work best by giving them a good rebuild. It's also a good way to examine the parts and check for broken or fatigued ones and address issues early.

(yeah, it takes a lot more time, and they can be tricky to disassemble/reassemble, but for an EM, the steppers are like the little engines of the machine; they need to be snappy.)

Depending on the gunk that's on them, I use anything from Goop, to Mean Green, to various liquid degreasers. Just depends what's caked on it.

Here are a couple pics of a Gottlieb 100K unit from a woodrail. These usually aren't so dirty (not like the continuous stepping 10K units!), but are often frozen/stuck.

100K_before.jpg 100K_after1.jpg 100K_after2.jpg

I agree that alcohol makes a good solvent. I don't know of the percentage, but I use denatured alcohol from the home improvement/hardware store. Find it in the paint section.

For especially grimy parts that are 100% metal, I'll use a spray can of carburetor cleaner. The pressure in the can is good at blasting stuff away. But there can be NO plastic involved, as it will dissolve some plastics. And it's not too kind to your skin, either.

If the part was assembled dry, put it back together dry. If there was lubrication before, lubricate it. I use Dow Corning Molycote 33 low temperature grease, simply because I have it already and know it is safe on plastics. Maybe somebody here can point out a lube that is more readily available. But leave the damned WD-40 in the can! I can think of NO place it belongs in a pinball machine.

I know that most people here use needle files and sandpaper to clean contacts, but I prefer the tool that was intended for the job, and that is a contact burnisher. It cleans the contact without removing metal and reshaping the contact like files and sandpaper do. Then I finish up with a light spray of De-Oxit. If you're not familiar with De-Oxit, my first thought is to call it a contact cleaner. But it is so much more than that. It has cleaners, lubricants, anti-oxidizers. Really good stuff.

HTH's

Bill

Superlube synthetic grease works well ,just a thin coat only!on the rivet heads.
Specs ,part #s > http://www.super-lube.com/synthetic-multipurpose-grease-ezp-49.html
Find a retailer here > http://www.super-lube.com/authorized-distributors-ezp-10.html

For those I use a nylon scuffpad ( fine scotchbrite)on them which is perfect for it.

Purchase TOP dvds 1 and 2. They do a VERY good job of showing how to do this work.

The only things I have to add here are the things I personally do when rebuilding a stepper:

1. When everything is apart and removed from the steel frame, and the frame is de-gunked and clean, I'll remove the oxidation from the parts with #0000 steel wool. It will also remove polish over rusty spots and make it shines real good. Below is before-after pics of a Gottlieb score motor and Williams steppers cleaned this way.
2. I find it important to apply a layer or two of Miniwax furniture paste wax on the steel parts I cleaned with steel wool to retard future oxidization.
3. I'll cut a small square of green scrubby pad soaked in alcohol and scrub the bakelite plate and contacts in the direction of travel. I do the same with the rotor shoes or contacts.
4. I make sure the Gottlieb style spring loaded rotor contacts move smoothly and freely within their brass cylinders. If not I'll drip some alcohol in them and work the shoes in/out until they work smoothly. If any still bind or are sluggish I'll remove the offending shoes and spring, clean the cylinder with a more substantial de-greaser and polish the friction sides of the shoes with #0000 steel wool, fix the spring if its bent and see if it works properly.
5. I use a tiny dab of Brasso brass cleaner on all rivets and contacts, working it into them with my fingertip. I wait a few minutes and polish them brilliantly with a clean cotton towel rag. *I don't use Brasso on printed circuit contacts*
6. I put *a drop* of oil on the stepper shaft on reassembly. Some use Teflon oil.
7. I put a *thin* application of Teflon grease over the contact rivets and on the Bakelite board where the rivets skate across. So thin you can't see it unless light reflects off of it. I also put a tiny amount on the end of each contact or shoe. Below is a pic of a cleaned and greased stepper ready for the rotor.
8. I do steps 3-7 every 12 months. Takes 10-15 minutes to do for each stepper.

1-Score_Motor.jpg 20130602_215622.jpg Wlms_Steppr.jpg Miniwax.jpg