Actually, the 535is springs are different than regular 535i springs, at
least part number wise. Don't know about M535i (which is a slightly
different car than the 535is). Ironically, it's the M5 that shares springs
with the 535i (though the _rear_ part numbers are different, the rates are the same).

>From a Pete Read post I archived:

E28 Front Springs
- -----------------
coil spring, all 535i and M5 31 33 1 126 024
533i from 3/83
coil spring, 528e 9/82-9/86, 31 33 1 125 726
528e bilstein from 9/86,
533i bilstein from 9/84
coil spring, 528e from 9/86, 31 33 1 126 904
533i to 3/83, 533i bilstein
coil spring, 528e bilstein up to 9/84 31 33 1 127 503
533i bilstein from 9/84
only applies to sports suspension:
coil spring, short red (535is Mtechnik) 31 33 2 225 645
coil spring, short (535is Mtechnik) 31 33 2 225 646
(Note: M535 springs have 1 coil less than 535i springs
according to the microfiche. In reality they
actually have 1/2 to 3/4 less coils. However,
the coils are stretched further apart giving a
firmer ride. The car will sit approx 1/2cm lower.
Uninstalled, when stood side by side, the two
springs are the same height. The rod diameter
used to make the spring appears to be the same.
The part no. stamped on mine is: 31 33 1 126 024 Ed.)
spring pad upper (3mm, all but short red) 31 33 1 128 523
spring pad upper (9mm, for short red) 31 33 1 128 522
spring pad lower (3mm, all) 31 33 1 124 322

E28 Front Shocks (535i/s, M5)
- ---------------------------
shock absorber-insert Boge (535i) 31 32 1 124 448
shock absorber-insert Bilstein (535i) 31 32 1 127 525
shock absorber-insert M Technik (535is) 31 32 2 225 662
shock absorber-insert Boge (M5 ) 31 31 1 133 517
absorber (not bilstein) 31 33 1 126 024
protection tube (not bilstein) 31 33 1 134 314

E28 Front Strut Housing (all)
- -----------------------------
spring strut front left 31 31 2 226 166
spring strut front right 31 31 2 226 167

E28 Rear Springs
- ----------------
coil spring, 535i up to 9/86 and bilstein 33 53 1 127 836
524td, 533i, 528e from 9/86
coil spring, 535i from 9/86 33 53 1 131 799
coil spring, short red, 535is M Technik 33 53 2 225 654
coil spring 528e bilstein 33 53 1 125 326
coil spring 528e bilstein 33 53 1 125 328
coil spring 528e 9/82 to 9/83, 33 53 1 127 849
524td and 533i bilstein
coil spring 528e 9/83 to 9/86, 33 53 1 128 708
524td and 533i bilstein
spring pad upper 33 52 1 124 507
spring pad upper (for short spring, red) 33 52 1 124 591

E28 Rear Shocks (535i/s)
- -------------------------
shock absorber rear (all but M5) 33 52 1 125 802
shock absorber rear, Bilstein (all but M5) 33 52 1 127 527
shock absorber rear, M Technik 535is 33 52 2 225 666
absorber 33 52 1 124 573
protection tube 33 52 1 124 575

E28 Rear self-leveling shocks (M5)
- ----------------------------------
shock absorber rear left (up to 2/87) 37 12 2 225 774
shock absorber rear right (up to 2/87) 37 12 2 225 775
coil spring (up to 2/87) 37 12 1 121 418
absorber (up to 2/87) 33 52 1 117 661
shock absorber rear left (from 2/87) 37 12 1 126 753
shock absorber rear right (from 2/87) 37 12 1 126 754
coil spring (from 2/87) 33 53 1 130 723
absorber (from 2/87) 33 52 2 225 023

rubber boot (combo spring pads and boot) 33 52 1 109 689
(same for booth self leveling shocks)
Hope this helps (and isn't too much info),

im a newbie here! happy to know you!nice forum!
its looks so good!wedding gown amamzing!
wa, it looks so interesting! i like it ~