CDC (MPI) floppy drive

g-wright at g-wright at
Thu Feb 28 01:34:17 CST 2008

Hi Tony

Since my 7771 1501 dive had problems and I did not find
any Info. I did find a NIB dive. It has  the same weight 
that seems to be there to stablize the movement of the
head. The weight on the new drive (but old stock) has 
no grease on the frame of the drive but was stuck on the
shaft. It does have the thick grease or ?? on the ends of
the weight where the shaft enters and exits. After warming
it a little it started to slide on the shaft. I can slide 
it the whole distance. I looked at the old drive and it does
the same. It looks like it dampens some of the quick motions
of the head carriage?? But the grease keeps it from moving 
very much. 
I would guess it has real thick grease in it ??? So it can
only slide a little on the shaft. It may have some kind of 
"o" ring to help seal one end, but I did not take it apart.

If needed, I could take apart the dead one.

- Jerry

Jerry Wright
JLC inc
g-wright at

-------------- Original message ----------------------
From: ard at (Tony Duell)
> Does anybody haev a CDC/MPI full height 5.25" floppy drive? No, I am not 
> looking to buy one, I need some information on how it goes together.
> I have one in an HP9826, it's fucntionally the same as a TM100-2A, but 
> intenrally quite different. The area I am baving prolems understanding is 
> the head positioner.
> The head carriage runs conventionally on a pair of metal rails fixed ot 
> the base casting. At the rear right of the drive is a stepper motor with 
> the spindle axis vertical. On that spindle is the metal drum of a taut 
> band mechanism, there's alos the conventional taut band. That fits over a 
> pin on the drum. The ends of the band have holes that fit over pins on 
> the head carriage, the rear p[in being fixed to the carriage, the front 
> one is spring-loaded to tension the band. 
> So far, so good. 
> Mouleded into the head carriage are 2 arms that extend to the right of 
> the drive, past the taut band assemly. They seem to carry some kind of 
> damper. And that's the real prolkem
> In my drive, the damer had oozed grease all over the chassis. I've 
> stripped it all down and cleaned it up. What I can't work out is how it 
> should go back together.
> The 'damper' consists of a weight made af a soft metal, probably lead. 
> And a metal shaft, about 1mm diameter, that runs through a hole in the 
> middle of this weight, the ends of which locate in the arms I mentioned. 
> And that's all I have. There's no obvious place to put grease inside the 
> weight (I've looked down the hole as best I an). If you put grease on the 
> shaft, it's just going to ooze out again.
> Also, what keeps the weight in the right position on the shaft? It's 
> considerale shorter than the space between the arms. Surely it shouldn't 
> just flop backwards and forwards?
> Another odditiy. When I removed the tauth band, I notixed what appeared 
> to be a plastic clip on one of the pins. More careful inspection showed 
> it was an O-ring that had split. OK, I can get replacements. But why put 
> an O-ring there in the first place? It's not going to keep the band on 
> the pin, or anything like that.
> My thought is that this has been dismantled before, that the O-ring 
> actually came from the shaft that carries the weight, and that there may 
> be parts missing (Springs, washers, etc).
> Does anyone ahve such a drive and could at least tell me what the damper 
> appears to consist of (No, I am not asking you to take it to bits, just 
> indicate if there's anything on that shaft other than the weight, if 
> there are any ruber seals. etc?
> -tony

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