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Sega Magnetic Particle Clutch Rebuild Info

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lilshawn:
Alright boys and girls,

You are all probably familiar with the OPC 20D-01 magnetic particle clutch used in many Sega games. (Daytona USA, Sega rally, etc)

Probably familiar with how much they can cost if you can find one.

Luckily I came into possession of a cabinet that someone had disassembled the clutch and had taken it upon themselves to clean and lube it.  :banghead:
so I'm going to outline what you need to rebuild one of these bad boys. I've seen some people say they are going to attempt it.... but seems like they never do. so, here I am.

if you don't know how these work, you basically have a disk on a shaft that spins independently of an outer housing. you spin the outer housing and the center shaft will freewheel... apply a voltage to a coil on the outside. this causes the particles of iron to stick together... locking the shaft and the housing together making the whole assembly turn as one.

now if you are like me, and cannot obtain a new one, and wish to rebuild your clutch...and you feel so inclined, grab yourself:

2x AG0369E rubber seals
2x 6001-2NSE bearings (original ones where labeled 6001NSE but this part number results in a bearing that is open on one side, and sealed on the other.)

if your bearings and seals are still good... then all you need is:

A scale. (you want a precision scale... not your mom's kitchen scale. going to want something with a 0.01 gram resolution because we aren't going to weigh out much.) talk to your drug dealer friends or hit up a head shop and get one.

a small square of paper that fits on your scale.

a quantity of "reduced iron powder" (99% pure, ultra fine)

you don't want "iron oxide" or the like. this is essentially rust.... we want IRON because it's magnetic. this "reduced iron powder" is produced by taking molten iron and spray it out of a very small nozzle and at really high pressure. this results in iron powder that is the consistency of cornstarch and a shape that is irregular granules... about 30 microns in size. your quantity of iron powder is going to vary according to who you are getting it from. I had to order a 1kg pack, despite only needing an extremely small quantity. I ordered mine off of amazon and it shipped from china. I found similar products available from 100 gram container sizes to industrial barrels of it.

Sorry, no pictures... this is already a pain to do, let alone document it... but if you are at this point of rebuilding the clutch... you likely already know this thing.

you are going to want to remove the clutch and the pulleys off it... and remove the largest snap ring from the back side to remove the clutch center assembly from the magnetic coil carrier and it's large bearings. There may be a thin shim behind the clip, so be cautious removing it so you don't crunch it.

Be careful not to nick or gouge the surfaces of the clutch and it's shafts, or it's going to be REALLY hard to take apart and put back together with jacked up metal being put into a precision ground bearing!

the clutch is held together at both ends by smaller snap rings with more shims. remove the clips and keep track of your shims and where they go. the tolerances inside the center section are VERY tight and any shaft endplay will result in it crashing into the housing and locking up. the space between the end housings and the rotator plate is only about 0.0095" (0.22mm)

inside of the center portion of the clutch is where the magic happens. pull all this stuff apart, being cautious again to not bang or nick things.

I decided to lightly sand the surfaces of the housing halves and the disk on the rotor shaft with some 600 grit sandpaper. My surfaces where a little glazed and had some gouges from something. (likely when or possibly... why... someone took it apart)

clean everything up nice and neat and replace your bearings and seals if you wish. be sure the felt seals also go back. I decided to leave the bearing out of the rear housing for now, as it makes getting things put back together easier.

i found it easiest to assemble the front half with the center section applied to the front end housing and install the shaft. install the shims and clips. all you should have left are your back housing, the rear housing bearing, the other shims if you have any, and the other snap ring.

Stand your partially assembled clutch upright and get ready to refill it with the iron powder. place your paper square on your scale and zero it out. measure out *1.55* grams of your iron powder. I know this doesn't look like much... but the free space inside the clutch is not a whole heck of a lot. Too much, literally 1.8 grams... is too much and the rotor will just be locked up once assembled.

Install the powder on top of the plate and slowly rotate the shaft back and forth to distribute the powder around. The holes in the plate will help move material to the other side. try to distribute the powder in the chamber as evenly as you can... if there is a bunch near the edges, it could be difficult to push the housing on and lock up the rotor as the powder gets mashed at the edges... shake the clutch back and forth gently to evenly distribute it.

install the rear housing, being sure to keep the shaft from messing up the seal as you slide it on.

Rotating the shaft back and forth as you push the housing on. the rotor should still spin freely... even with a little resistance... at least until we get things properly distributed. install the rear bearing and shims and install the clip. ensure the rotor shaft rotates when you hold the housing still. If it does, from now on when we rotate the shaft or housing, it must be done in a horizontal position. if the housing is allowed to be on it's end, the powder will build up on one end of the housing and lock the rotor shaft up.

you are going to want to spin the clutch housing while holding the output shaft for a few minutes to make sure it remains free spinning. there will be some drag... but if it feels like it's firming up...something is wrong.

once your clutch is all put back together it can be installed in the coil housing and you can proceed with electrical testing.

have fun!

buttersoft:
Wow, that all sounds intense. I do have a tough - where is the clutch you speak of, is it part of the ffb system?

lilshawn:
yes, the force feedback system on the steering wheel controls.

what essentially happens is there is a high voltage DC motor (like 100 volts) that can be powered so it spins left or right (clockwise or counterclockwise).... it drives the outside casing of the particle clutch through a toothed belt and pulleys... then the output of the particle clutch is tied to the steering wheel, also through a toothed belt and pulleys.

when we want a particular direction of feedback, we spin the motor in that direction and then feed voltage (from 0vdc to 24vdc) through the coil of the particle clutch. this either locks the motor and the steering wheel together so the motor drives the wheel hard (if you put full 24 volts into it)... or will slip and provide a small amount of feedback ( from 0 volts and up to the maximum) the more voltage we stuff into the coil of the particle clutch, the harder it grabs and the more feedback response you get out of it.

Joanm123:
Hello
I do not understand really how to diassemblly and add the new iron into the clutch
May do you have any picture to see it better ?
Thanks in advance!!

lilshawn:

--- Quote from: Joanm123 on June 24, 2025, 10:50:18 pm ---Hello
I do not understand really how to diassemblly and add the new iron into the clutch
May do you have any picture to see it better ?
Thanks in advance!!

--- End quote ---


--- Quote from: lilshawn on May 21, 2025, 07:10:59 pm ---Sorry, no pictures... this is already a pain to do, let alone document it... but if you are at this point of rebuilding the clutch... you likely already know this thing.

--- End quote ---

again, if you are at the point of needing to disassemble and rebuild this clutch... you already know how to disassemble it. This isn't a casual maintenance instruction set. This is the last-ditch repair instruction. This instruction includes information other threads on the subject lack... concrete information. None of the other threads about this contain any concrete information.

The pure number of threads I discovered out there where someone posts about trying to find or fix the MPC's and there has been replies like "oh yeah, i got ALL the stuff and i'm gonna rebuild it... i just don't have the time" is ridiculous and tantamount to school aged children saying "I can _______ , I just don't want to"

gettin real tired of feeding bots and algorithms. Utilize the concrete information and your concrete will work fabulously.

also, my current favorite interest is throwing broken tools into the algorithm and seeing how the information is indiscriminately absorbed and inserted without any rational thoughts.

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