Discussion
I had a similar issue with my 94 Chimaera and a GKN diff. The previous owner had apparently had the diff rebuilt around 2012 and it had gone again which did not fill me with much hope for another rebuild, although I do not know the extent of the previous rebuild. The car is modified 500, megasquirt ECU, coil packs, decatted, smooth bore induction, 72mm throttle/plenum. Although the garages may well have been trying to flatter my engine or push me down the BTR route, there was a suggestion that TVR stopped using the GKN diff as it was not coping well with the extra power of the 450 and 500 engines (I have no idea if this is true and it could simply have been that the BTR was cheaper or easier to get)
I spoke to a few people about the GKN diff, and gather there were concerns about the availability of parts to repair it. Prices to rebuild were looking around £400 to £600, plus the cost of getting it removed, sent off and refitted. Although I could have removed the diff on the drive, it felt like one for a garage to tackle given the limited access and the fact I already have a bad back, which just pushed up the cost. Turnaround times were around 2 to 3 weeks for the diff rebuild once I could find a garage with availability to do the work. I doubt I would have much change out of £800 or £900 by the time the car was back on the road.
I opted for a new BTR diff from Central TVR, along with their BTR / GKN conversion bracket and a new speed sensor. All in it was approx £1800 (inc labour, VAT). They did the job in a day, the week after I initially contacted them, although they had my car for about 5 days as I could not get over to collect it. With a bit of planning you could drop your car off in the morning, spend day at one of the local tourist attractions and collect the car in the evening. I am sure Adrian said they had a courtesy car available.
The BTR has a slightly different ratio to the GKN, which I feel has made the car easier to drive in slow moving traffic and 30mph zones.
Yes, it was a more expensive option, but I got the car back on the road in much quicker and I am really happy with the results.
I took my old diff home and sold it on ebay for £100, clearly described as noisy and in need of a rebuild. That, is another option for you. Used GKN diffs do come up for sale occasionally, buy one and get it rebuilt and do a straight swap on your car, then sell the old diff.
N7GTX said:
^^ lol. After the turbo fitting, I asked Powers if I should buy a BTR for its reputed strength as my GKN had done 50,000 miles. An emphatic 'NO' and I am still on it with 481 lbs/ft torque. For now anyways......
Let’s see how good it is after a run up the strip 
a new one is nice though 
I’ve had gearbox oil changed before and the gear stick still got fairly hot on somedays.
How a diff change effects the gearbox I’m not sure but the gearknob has been stone cold ever since. Straight up.
Sardonicus said:
Nothing wrong with the GKN apart from the scarce parts e.g crown-wheel and pinion 
seen no proof of the BTR being stronger or more reliable
Agreed. seen no proof of the BTR being stronger or more reliable In November 1995 GKN sold their axles group that made the differentials to Dana Corporation in the US. Dana was already making BTR diffs as a competitor to the GKN so they stopped making them and TVR had no choice but to stop using them.
Edited by Jon100p on Friday 29th December 10:51
N7GTX said:
You just like spending my money 
but only because I’ve ran out of the stuff Nobody said the BTR is better or stronger than the GKN.
Maybe my BTR pre load had legged it but the new diff is much better allround. Accelerating feels safer and less likely to develop one wheel spin up.
I was not expecting to replace or even repair my diff and the cost was a pita when your not budgeting for it and so fairly pissed off I was doing it at all,, by the time I’d got to the M25 from Dorkings premier Tvr Service Centre
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