It is not always justifiable to spend the money on a specialty tool, however in the case of rear axles a little investment goes a long way.
The problem with many german cars and particularly E30’s is that the tolerance between the hub splines and the axles splines is VERY small causing a VERY tight fit. Even the smallest amount of grease, dirt, and even oil will not allow the splines to go back in. What most people will do is clean the splines until they are very clean, inspect and remove any burs (especially in aftermarket re-manufactured axles) and then hope that they can re-install the axle without damaging anything; many people attempt to get leverage by putting a crowbar between the differential and the axle, DO NOT DO THIS, you risk damaging the diff output shaft and you will most likely bend the axle dust cover causing your newly installed axle to loose its grease and pre-maturely fail.
As far as tools go, there is two pieces of good news. The first is that there is a tool that was specifically designed to pull the hub in. This OE tool is fairly expensive at about $400. The better news for cars that have M22 x 1.5mm (such as the E30) / M20mm x 1.5mm axle shafts is that the exact same problem and tool exists for early to mid 90’s fords and has the same thread size and pitch as the OE tool, however this latter tool is $16 to $50 depending on brand.
The concept of the tool is rather simple. Traditionally once you have the axle most of the way in you would use the axle nut to pull the axle the rest of the way; essentially the purpose of the below tool is to extend the threads of the axle. This is achieved by a bolt which on one end that has female internal threads to screw onto he axle shaft, then a forcing cylinder goes from the hub end, this forcing cylinder rests on the hub lip that the factory nut would seat against. As you tighten the nut on the tool, the bolt which is threaded onto the axle pulls into the forcing cylinder, taking the axle with it.
First lets look at the OE tool which costs about $400-$450:
Made by Gedore (KLANN) the model is KL-0415-4 for the master set and KL-0415-2 for the BMW set
Adapter M16x1.5 (eg BMW F20)
Adapter M20x1.5 (eg Porsche Cayenne, VW Touareg)
Adapter M24x1.5 (eg, BMW E36, E87, E90, Mercedes W203, E46 (325i))
Adapter M30x1.5 (eg, BMW E32, E34, E36)
Adapter M22x1.5 (eg, BMW E30)
Adapter M27x1.5 (eg, BMW E32, E34, E38, E39, X5, E46 (330i))
For cars that use M22 x 1.5 and M20 x 1.5 the following MUCH less expensive options are available.
KD Tools 3532 (M22 x 1.5) also available on ebay as a no name “Ford Front Hub Installer #3532” for $16.95 shipped:
KD Tools 3020 (M20 x 1.5)
Mac Tools FHI7135M includes both M20 and M22 can be found used on ebay for cheap $25-50 since no one works on old fords anymore:
OTC sells either individually or as a set:
OTC 6298 Front Hub Installer and Puller Set ($100):
OTC 7924A M22 x 1.5 only ($40)
OTC 7135A M20 x 1.5 only ($40)
Great Neck OEM 27192 Front Hub Puller/Installer Set includes both ($70)