Diff bracket sheared off

[james.c]

My 3 day tour of Wales was cut short at the end of day 2 as a slight banging / movement from the back of the car (and a grinding when off the power in gear!) got worse and worse. 

When we got the hotel we found that the diff bracket seems to have completely sheared off. It's an18 month old 620S so hoping it should be sorted under warranty (BaT looking at pictures now). 

Anyone else experienced anything like this before? Also wondering what the chances are that I have damaged the diff over the 35 miles limping back to the hotel. It drove ok (especially under power) which is why I limped it back (also was in the middle of nowhere!)

Any thoughts / advice gratefully received!

  
Can't see much on this one other than a loose bolt!

Probably the easiest way to see that the metal seems to have failed on either side of the diff. Both bolts are just spinning round as they aren't connected to anything anymore!

This is rotated 90 counter-clockwise but you can see that the bottom bolt (right in the photo) is not just connected to the remains of the bracket which is now missing. 

[The_ASH]

The BMW diff has a carrier or subframe to adapt it to the chassis which is still engineered for a Sierra diff. Originally when these first appeared there were some failures and subsequent free re-call upgrades, as your car is a 620S I’d expect it to be after that period so have the latest version. I believe that after reading the Caterham blurb about the sub carrier it is important to visually check the whole thing regularly and also check integrity and tightness of all fixings as reading between the lines if anything works loose the carrier can fail as pictured.

Always looked a bit of a half-arsed fix to me... why have they never fully engineered the chassis to directly accept the BMW diff. That said on ultra high powered Sevens the Sierra diff used to eventually fracture its mounts and require extensive re-brazing to rectify.

[james.c]

Thanks very much! I think you're exactly right. Bookatrack spanner checked the car for me a couple of months ago and said that these were loose (one bolt was actually missing!). Since then I've done two track days and the tour of Wales. I suspect that the carrier had developed a fault from the vibrations over the previous 12 months or so and then failed. 

I'll certainly push for it to be sorted on warranty. I'm slowly learning about cars but its a long road and they don't really make it easy for you. A simple "spanner check" manual for newbies would be great. There is stuff around but you have to search hard and it's tough when you start from a zero base! Clearly I should have been checking the torque of these bolts every track day. Still learning!

[The_ASH]

Perhaps a warning for everyone in this that the carrier can still fail and is worth keeping an eye on.

I notice that if one purchases a ‘Caterham Selected’ car you get free pre-trackday inspections for the term of your ownership, depending how/where you are located could come in very handy especially if the car is more highly powered.

I hope the diff is ok, to a certain extent I don’t see why it shouldn’t be, I think the noises may well be various external parts touching (bolts etc) that normally don’t, if it’s loose and partly unsupported it will thrash about quite a bit when transitioning between loaded and unloaded.

[aerobod - near CYYC]

I’ve lost a couple of mounting bolts between the diff carrier and diff on my R400D in the past both on the old carrier and the upgraded one. I added blue thread lock and increased the torque on the M12 cap head bolts from the standard 81Nm to 110Nm (within the allowed torque for an M12 10.9 bolt, which should take st least 120Nm before stretching). I haven’t lost a bolt or had one loosen now, including track use, for the past 3 years.

Each time I lost a bolt, there were scrapping and banging noises from the diff moving around but there doesn’t seem to be any permanent damage, having run 15,000km since dropping the last bolt.

[james.c]

Thanks. I'll take a look at that once I've got this sorted!

[pgm]

Unfortunately we have seen this happen before but usually on race cars. We did have one in recently that caused significant damage to the prop-shaft, gearbox mounting and engine mountings. That is very unusual and the car was being used for a standing start at the time. Even with all that damage the differential was still ok. It is worth checking the mounting bolts regularly.

[JNC]

Out of interest was your car the ex demonstrator from Crawley CC ? Reg No LX65GVG