I believe that the reason your suspension parts move back to their origins in game is because the bones in 3d program have a scale position set.
Try selecting all the bones and resetting their transforms in the new positions.
Depending on your program… Maya was always z up, 3dsMax was y up and I spent years struggling with that. I’m now working in Modo and you can set zup (y up is default). If you set it THEN import the rig it works.
The AnimBP only tells them how to react to each other (ie: pyhs wheel moves up, the visual wheel looks at that and matches it)
I’ve started a rerig from scratch. It just takes forever to align and name the bones properly. I have the back left wheel setup and when I go in game (disconnected all other bones in animBP for time being).
It’s now the correct scale, and everything is still in place. I was also able to create a pyhs model that doesn’t bug out on simulation.
However the suspension is fully compressed and doesn’t move.
–edit–
Ok, OK. I had animstance on the animBP, not vehicleanimstance so I couldn’t create a wheel handler node. Now that that is in things are working properly.
Just have to make 100 more bones now and rerig…
Do I need everything rigged? I don’t know. I was hoping to see functionality working with one wheel before I proceed. 
The main reason I am trying to rescale is I believe the standard character mesh for UE4 is the same scale as the sedan so it’s better to have it all the same.
Good luck on your project. I’ll keep pluggin away over here. Whoever gets it first wins !!! 
It’s good to have someone else working on this. If I get a proper rig working I’ll send it over.