I'm stuck with an old 40MB HDD. It spins up, it talks to the IDE controller on my Rectron RT-4S3 late 486 motherboard - but I can't find any C/H/S settings that will do anything.

Here is IBM's own information on it:
http://ps-2.kev009.com/ohlandl/IBM_HD/WDA-L4x.pdf

That suggests I should use 1067 Cylinders, 2 Heads and 39 Sectors. That gives a nice plausible 42MB size. Fdisk (MSDOS 6.22) detects the drive and lists no partitions, and when I try to make some, after a reboot they are gone. I have the distinct feeling I'm hitting a 1024 cylinder BIOS limit, which I should be able to work around via geometry translation - but I can't for the life of me find anything.

I tried halving/doubling the cylinders/heads, so 533 / 4 / 39, but same result.

The only other resource I could find was this:
http://computermuseum.informatik.uni-stuttgar … /ASCII/1720.TXT

1                                                       Native³  Translation 
2                                                        ÄÄÄÄÄÄÅÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄ
3Form                 3.5"/HH               Cylinders    1067³     ³     ³     
4Capacity form/unform    40/      MB        Heads           2³     ³     ³     
5Seek time í / track      /     ms          Sector/track   39³     ³     ³     
6Controller           IDE / AT              Precompensation      
7Cache/Buffer               KB              Landing Zone         
8Data transfer rate          MB/S int       Bytes/Sector      512
9                            MB/S ext      

So no translation, but >1024 cylinders...

For what it's worth I also tried IDE autodetection. It clearly doesn't detect correctly, but the fact I get anything back at all tells me the drive should be alive. Here's what 'auto' gave:
C 15277 H 5 S 17 (=664MB) in Normal mode
C 7638 H 10 S 17 (=664MB) in Large mode

Anyone have any suggestions?