Thoughts about diff mountings and floorpan failure

[matchy]

There have been several posts concerning stuctual failure of the diff mounting metalwork (ZM forum ) ; does this affect cars across the Z range ? Could it be only a matter of time before cars with less power suffer from this . My friend who is a skilled jaguar mechanic says he has seen the higher powered versions of the Z4 with floorpan fractures , ( the BMW dealer is near to where he works and he is friendly with their mechanics ) ... Is computer aided design these days not able to work out the REAL stresses involved in a sportscar chassis ? Perhaps we will never know . It does seem a real shame though , Cars need to be much tougher than this. Cheers , Matchy.

[garyw]

Matchy, can you clarify that was definitely Z4

garyw

[SpunkyM]

Failures would appear to be more common on the coupe rather than the roadster - it's possible that the less stiff chassis of the roadster actually absorbs more energy and takes some of the stress away from the subframe, but it's juts a theory.

More scary pics here... http://www.z3mcoupe.com/forum2/viewtopi ... highlight=

[c_w]

Failures would appear to be more common on the coupe rather than the roadster - it's possible that the less stiff chassis of the roadster actually absorbs more energy and takes some of the stress away from the subframe, but it's juts a theory.

More scary pics here... http://www.z3mcoupe.com/forum2/viewtopi ... highlight=

There seems to be 3 people in a thread on here with roadster having the problem so I would say it doesn't make any difference. One link has pictures to all kinds of variatns, from 1.9s to ///Ms.

[Deano1712]

[/quote]

There seems to be 3 people in a thread on here with roadster having the problem so I would say it doesn't make any difference. One link has pictures to all kinds of variatns, from 1.9s to ///Ms.[/quote]

All variants of Z3's are capable of transmitting similar maximum loads through the diff and into the crossmember above it. You cant put any more torque through the diff than the tyres can take before they spin. 1.9's can spin the tyres if the clutch is dropped. Bigger engined cars behave just the same but are capable of transmitting high loads more often, depending on how they are driven. Its no surprise to me that smaller engined cars can have this problem too. There are very few spots welds on my car holding the crossmember to the boot floor - that seems to be the weakness in the design. When one spot weld pops the rest will eventually go and everything is going to get very flexible as the cross member looses its support from the boot floor.

[Guest]

Perhaps it is better to prevent this problem rather than experience it. The answer of course, is to avoid 'dumping the clutch at 5000 rpm' as we have seen several owners advise, or to use full throttle in first gear.

OK - the car should be strong enough to avoid such problems, no matter how the driver treats it, but it would be interesting to know if anyone who has had this problem can honestly claim to have treated the car with sympathy in the lower gears.

[c_w]

Perhaps it is better to prevent this problem rather than experience it. The answer of course, is to avoid 'dumping the clutch at 5000 rpm' as we have seen several owners advise, or to use full throttle in first gear.

OK - the car should be strong enough to avoid such problems, no matter how the driver treats it, but it would be interesting to know if anyone who has had this problem can honestly claim to have treated the car with sympathy in the lower gears.

It could be, but as you say the car should be capable of coping with this. I wonder if the road conditions affect anything, as the diff is bolted to the very moveable suspension subframe? so it could be tugging it about on bumpy roads.