Decided to take the plunge and get a LSD fitted to my car since I was having uprated turbo's fitted and have FBO. Looked around at options and Birds UK came up with cheapest option and easiest option. So Birds took my diff and fitted a Quaife LSD which requires the original diff on the crown wheel to be machined off and then the Quaife reattached to the crown wheel. This was done and I got this back after around a week and the only thing Birds had noted was that the side bearings showed signs of wear but nothing that was considered in their eyes to need urgent attention. After getting the diff back my garage did the reinstall of the diff. I drove it away but couldn't put my foot down as was waiting on a custom map to be sent to me from Twisted Tuning in America So the car was driven extremely lightly from the garage to my home 11 miles and I did notice a vibration as you pulled away but put that down to what I thought to be the exhaust catching the bodywork where everything had been taken off and then put back on. A week later drove the car again not even 3 miles and the diff has completely failed with no drive. Had the car recovered to my garage and contacted Birds who straight away said it sounded like there was no oil in diff. I checked this and showed Birds a video of the oil dripping out and confirmed the correct fluid had been used. Then Birds said it couldn't be them as they hadn't touched anything so must be the garage, which I found strange as its a bolt off/ bolt on job nothing major! After some time Birds contacted the garage and did agree that it was nothing that the garage had done! Birds then asked for this to be sent back to them so they could see what had failed. Once they got it back they took it apart and confirmed that the pinion drive and crown wheel had been completely destroyed. James said that this must have been through me driving the car extremely hard, I again assured him this was not possible do to the fact that I couldn't push the turbos; until I had the base map which I hadn't had! He then asked Kevin at Birds to ring me. Again Kevin said that this could not have been caused by them. I tried to explain that my diff had shown no signs of problems before going in as Kevin said it must have been going prior to the work being carried out. This seemed strange as Birds said that they had checked everything prior to doing the install so surely they would have noticed something like this! Since then Kevin has been extremely unhelpful and wanted another £1,100 to put the work right. When Kevin initially run me he said that they had done thousands of these yet never had any problems, yet when I get his email report on the damage the thousands then suddenly dropped to 697! Since Birds are refusing to put right I have no choice but to take this Court. Having spoken to quite a few other people including other diff specialists they all have the same opinion that this could have only be caused by something that happened during the installation of the Quaife by Birds. They all said if I had no noise heard from my diff prior to it coming off originally then this could not have happened so soon without something that had been done when the crown wheel was put back in. Possibly the backlash wasn't measured correctly thus causing the crown wheel and pinion to fail. From the first sign of the failure Birds have constantly tried to push the blame onto other people at first saying the garage had not put oil in it, then saying I had driven in extremely hard and then that my garage had installed the diff incorrectly. Yes they have done over 4000 Quaifes but these are standard diff changes whereas this is a specialist job that requires the crown wheel to be machined. He also again in the same email insinuates that I'm lying saying that the customer states that the car was only driven 25 miles. He also states facts that are not true with regards to modifications and power output of the car, again looking for avenues to avoid the truth of the matter. Having shown the photo's to a number of other BMW specialists and garages that deal with diff's they have all come back with the same opinion that the failure must have occurred after the crown wheel had been machined and then the Quaife the installed onto the crown wheel, which has then caused the complete failure. Since the above Kevin has since seems to have lost himself all over the place, at first he emails me and says " In the meantime, we are arranging to replace/repair the damaged parts at our cost." so I email him back and say so your now saying that your going to repair it and admit responsibility. He then comes back and backtracks on this and says now they are purchasing a final drive unit and will fit my Quaife into it and will only release it if I pay the additional £1100 (which they drop to £540) I straight away go back and inform Kevin that I have not given them authority to replace any parts as the unit is mine regardless of whether it works or not. I ask him if he's using this as blackmail as clearly it seems to me this way. He then digs himself deeper into trouble saying he will not release my parts out to me regardless of whether they replace the final drive or not! I then inform him that I suggest he takes legal advice as these parts I have paid for and are mine and I will inform the Police accordingly! He finally comes back with he'll release the parts if I want to come and get them or tell him who is authorised to do so. Not wasting 6 hours of my life doing round trip to pick these up so arrange courier to pick these up. Never meet someone who's customer service is virtually non existent. Having now found out that Wavetrac actually do this in UK I wished I'd known sooner as they have seen pictures and totally agree that Birds that have not done the job correctly. Wavetrac said that if this would have been one of theirs they replace no quibble as it lifetime warranty on their diff conversions! Now have the hassle of getting my money back through the courts and spending another £2500 with Wavetrac to get another diff sorted as car sits in garage at mo. Please if anyone is thinking of using Birds think about this as I wasn't expecting to be treated like this as believed they had a good reputation but appears my trust has been misguided!