Clever ideas for shock assembly?

Trying to marry the OEM tophat to this new shock. The new nut hit significant resistance right when it's over the flat part at the top + the shaft spins if you look at it weird.

Youtubes suggests putting the flat tappet in a vice, but the nut location prevents that and I don't have a vice. I attempted it with vice grips, but just ended up marring the top of the other shock pretty badly.

Any clever ideas I'm not thinking of?

You're sure its the right thread? Probably paint in the threads. chase it with a die, or probably easier, hit it with a wire wheel and paint the tip again after the nut is on. Just get it far enough you can use the square end to hold it.

It came with a replacement nut, both stop right around the same point. Already hit it with a die

Thread file?, And double check the thread pitch for sure.

edit: Posted same time. OK. Are the new nuts the kind that are pinched at the top to act as a lock nut?

If you're confident it's the right size and you can get it on far enough on to be sure it's not cross-threaded... May I suggest this point to treat yourself to some manner of impact wrench/driver if you don't already have one?

Pneumatic, cordless... My Milwaukee M18 Fuel impact driver with the little 1/4" hex drive will do everything up to a lower-torque lug nut.

 Definitely one of an an impact's party tricks is working fasteners against the inertia of a part you can't hold.

 Alternatively and with a bit more risk, line your vice with cardboard and grab the shaft to do an initial run on/off with the nut.

Probably a lock nut. Short bursts with an impact are usually the way to go if you can't get in there to the flats on the square part. Another option is instead of using the lock nut, use two conventional nuts as jam nuts if there's enough thread available. 

New nuts have a nylon insert, old ones don't.

Already tried my pneumatic impact, which is how the first shock got mangled. 

Current thought: Small triple square bit on a breaker bar to keep the shaft from rotating? 

In reply to calteg :

I'm back to thinking they carefully packaged two of the wrong nut.

Do you have a tap or thread checker so you can verify the nuts have the same thread as the die you used on the shaft?

 If that all checks out, yes to the triple square socket, though if you need a breaker bar something's wrong...

calteg said:

New nuts have a nylon insert, old ones don't.

Already tried my pneumatic impact, which is how the first shock got mangled. 

Current thought: Small triple square bit on a breaker bar to keep the shaft from rotating? 

Maybe run a tap through the nut? You could form threads in the nylon if its a bit too stiff now.

In reply to theruleslawyer :

There we go, great idea

If the nut is damaging the shock it's the wrong nut.

In reply to calteg :

I've grabbed the shaft with vise-grips before. I wrapped one of those jar lid rubber grips around the shaft first and it was enough to hold it while I turned the nut with a wrench. No marks on the shaft afterwards.

DeadSkunk (Warren) said:

In reply to calteg :

I've grabbed the shaft with vise-grips before. I wrapped one of those jar lid rubber grips around the shaft first and it was enough to hold it while I turned the nut with a wrench. No marks on the shaft afterwards.

Just do that at the very top of the shaft just in case so any score marks don't go into the seal when the damper is compressed.

Also, I would not use an impact.  It can (rarely) loosen the nut holding the piston and valving to the rod.  

The real solution is to get the right socket ( D type IIRC looking at the picture) with a pass thru ratchet. A lot of OEMs use that style  but makes it difficult for DIYers.

Throw away the supplied nuts and use normal ones.

theruleslawyer said:

calteg said:

New nuts have a nylon insert, old ones don't.

Already tried my pneumatic impact, which is how the first shock got mangled. 

Current thought: Small triple square bit on a breaker bar to keep the shaft from rotating? 

Maybe run a tap through the nut? You could form threads in the nylon if its a bit too stiff now.

Sounds like a good way to have your lock-nut be unlocked.

I wouldn't follow this suggestion. 

DeadSkunk (Warren) said:

In reply to calteg :

I've grabbed the shaft with vise-grips before. I wrapped one of those jar lid rubber grips around the shaft first and it was enough to hold it while I turned the nut with a wrench. No marks on the shaft afterwards.

This is what I was going to suggest. 

Mr_Asa said:

theruleslawyer said:

calteg said:

New nuts have a nylon insert, old ones don't.

Already tried my pneumatic impact, which is how the first shock got mangled. 

Current thought: Small triple square bit on a breaker bar to keep the shaft from rotating? 

Maybe run a tap through the nut? You could form threads in the nylon if its a bit too stiff now.

Sounds like a good way to have your lock-nut be unlocked.

I wouldn't follow this suggestion. 

Meh. There are a lot of ways to secure a nut if the nylon is too loose after.

DeadSkunk (Warren) said:

In reply to calteg :

I've grabbed the shaft with vise-grips before. I wrapped one of those jar lid rubber grips around the shaft first and it was enough to hold it while I turned the nut with a wrench. No marks on the shaft afterwards.

Mission accomplished. Ended up using DeadSkunk's suggestion + impact gun to get the nut over the flat part. Then a tiny 1/4" open ended wrench braced against the floor kept the shaft from rotating. Thanks gang!