Popped spot welds

[Mpopaj]

Hello
I heard cracking in my trunk so I took the sound deadening out of my z3 coupe and saw that the spot welds were all popped through. How bad is the damage in the video below. It’s obviously not the worst you’ve seen but can I get away with having any shop welding it back up and putting a randy Forbes kit on while they’re in there. Would the chassis have to be straightened or anything like that or do you think it wouldn’t have had that much of an effect at this point.
https://youtube.com/shorts/SZmYkp5Hb60?feature=share
Please let me know. Thank you

 

[Mpopaj]

Also am I understanding it correctly that the subframe bushing should be solid and the diff bushings should be OE rubber or should it all be solid or all rubber for preventative maintenance. What is the consensus on that?

 

[t-tony]

Unless you track the car I would stick with OE rubber bushes, after all they’ve damaged the floor so think what solid or poly bushes could do. There is a recent thread of someone currently having a Randy Forbes kit fitted. I’ll see if I can find you a link. His floor looked to be much worse than yours is.

Tony.

 

[t-tony]

Here you go,

Hello - Z3M

Reinforcement inside and out. One more day of welding to finish putting in the kit then dressing up the welds, seam sealer and paint. It’s all good!

zroadster.org

Tony.

 

[Mpopaj]

Unless you track the car I would stick with OE rubber bushes, after all they’ve damaged the floor so think what solid or poly bushes could do. There is a recent thread of someone currently having a Randy Forbes kit fitted. I’ll see if I can find you a link. His floor looked to be much worse than yours is.

Tony.

Thanks a lot Tony. I read that subframe bushings should be solid to prevent movement and the diff bushings should be rubber to absorb the movement on the mounts. But I have also been seeing differing information. I’ll try to find what I was reading and link it.

 

[Mpopaj]

Understanding the Z3 Rear Subframe/Trunkfloor Issue

BMW Z3's are well known for having issues with their rear subframe/trunkfloor. The issue is specifically with the differential ear mount and it's attachment to the the chassis - the diff mount ear attaches to the chassis at the rear trunkfloor where it is not strong enough to handle the forces...

www.ascfabrics.com

This was it

 

[Stevo7682]

The problem with poly bushes is they have limited movement compared to the oe rubber ones so the noise vibration and harshness soaked up by the rubber has to go somewhere with poly bush.
Most zed 3 rubber bushes now need replacement due to ageing and a new set of them would make a big difference poly bushes tend to squeak a lot as well.
There is a conversion to the rear diff ( thread on here somewhere will link if can find ) Where you change the rear diff casing with I think the rear casing from an 3.0 e46 with a twin eared rear diff then you get an extra diff mount bracket welded on then this allows a lot of the torsional twist forces applied to the rear box section to be controlled.
Stephen.




Edit. twin eared diff conversion thread

Twin eared diff conversion

I had heard tales of woe about boot floor spot welds failing and subsequent cracking, so I decided pre-empt any future problems by fitting a twin eared diff cover. Of course it didn’t stop there I reckoned a complete rear end overhaul was the way to go. In the time honoured manner I stripped the...

zroadster.org

 

[Mpopaj]

The problem with poly bushes is they have limited movement compared to the oe rubber ones so the noise vibration and harshness soaked up by the rubber has to go somewhere with poly bush.
Most zed 3 rubber bushes now need replacement due to ageing and a new set of them would make a big difference poly bushes tend to squeak a lot as well.
There is a conversion to the rear diff ( thread on here somewhere will link if can find ) Where you change the rear diff casing with I think the rear casing from an 3.0 e46 with a twin eared rear diff then you get an extra diff mount bracket welded on then this allows a lot of the torsional twist forces applied to the rear box section to be controlled.
Stephen.

Yeah I think randy Forbes also offers a dual ear kit using the e36 casing if I’m not mistaken. I think that’s a bit much for my application though since I do not track it and I have not autocrossed it yet. I will probably just do a regular reinforcement and get the poly bushings. I don’t mind the noise considering how loud my gearbox is already