E30 front strut "shock absorber top nut" won't come off

I'm changing springs and shocks on my 1991 318i. Rear is done: no problems. I've got the front strut off, spring is compressed, but I cannot get the top (center) "shock absorber top nut" off to remove the spring and shock absorber. It turns out my sad little 75 ft-lb electric impact wrench can't get it off.

Are there other ways to get this nut off?

(I'm thinking of filing flats onto the polished strut piston with my Dremel tool to give me a place to clamp it with vicegrips and use my breaker bar on the nut.)

I've also got the nut soaking with PB Blaster overnight.

It actually helps to have a little load on it when trying to remove it, but an air impact is the way to go. If you can bring it to a friendly shop with some donuts, someone will knock it off for you in the morning.

what he said thats what I did. BUT I think to do it without that you need a speical tool, it looks like a deepwell with a cut out for a allen head. At least thats how it was done on the minis.

Yes, Impact is best and easiest. Once I was removing a crankshaft pulley from my alfa and my impact wasn't cutting it so I went to the local Ace hardware and rented a beat up old impact which surprisingly took it right off, although it sounds like you may not have an air compressor?

Done! Thanks!

Got it off. Strut is now rebuilt and installed.

Since no one balked at the idea, I decided to go with Plan A, which was grind a couple of flat spots on the polished strut piston. After that, it came off easily with a breaker bar. Total time was 10 minutes.

Plan B was to use donuts to remove it per MooseheadM5. It would have just taken more time.

You managed to grind flats in 10 minutes!? Frankly, if the insert is trash anyway, I just use one of these on it:

That nice shiny metal is remarkably soft. I have a cool little grind stone for my Dremel which worked great. I would say that I had the flats ground within 5 minutes. "Flats" being a relative term: I ground two spots for my vice grips to grip; not flats to put an open end style wrench.

Initally I tried my vice grips on the shaft and even they wouldn't bite.

Yeah, I need a big pipe wrench. (I got a big Channel Lock pliers for most stuff though.)

Hard to get a pipe wrench in between a compressed spring unless it is a small one. Glad it worked.

I use that only to get it broken loose, so the spring is either not compressed at all or very little.