Quaife ATB differential    

http://www.quaifeamerica.com/                                                                                           Original differential

 In choosing the Quaife ATB differential I felt confident that this unit would be ideal for handling in autocross racing.  The Quaife differential appears to have a good reputation  for durability.  However, I must say that their quality control and documentation are suspect.  Case in point:  After receiving my unit I found no installation instructions,  recommendations or diagrams.  Only by sending and receiving a furry of emails on the Spitfire email list (spitfires@autox.team.net ) from four others who bought the same units did I realize there was a potential problem.  The stock holes in the GT6 differential flange that mounts to the ring gear are 0.381" using 3/8" (.375") bolts.  Of the five of us who bought Quaife units together, at least two of us had holes in the Quaife flange much larger than the stock GT6 differential flange holes.  Mine were .392" and the other guy's were .395".  

Quaife's response was that "we've never had a problem with these units....the bolts should be placed with locktite.  Our drawings state that the correct size for the flange holes is .395" +/- .005".  This is the standard clearance for a 3/8" bolt". If the standard clearance is .395", why did Triumph use .381.   I was not impressed with this reply.                                                                                         

 The mechanic installing my unit has been rebuilding differentials for british and other sports cars for 25 years.  His opinion was that the flange holes were too large and would eventually cause the  differential to fail.  His recommendation was to enlarge the holes in the Quaife flange and insert hardened steel sleeves to the original GT6 specs of .381".  That is what I did.  The other guy with this problem took 10 mm bolts and cut them down to 3/8" threads.  That way his bolt fit his .395" flange holes in the Quaife differential yet still had the 3/8" threads to engage the ring gear holes. His remedy cost him a little over $100.  Mine was a little over $50 to sleeve the Quaife flange holes.

The standard GT6 ring & pinion ratio is 3.27:1.  I used a 3.89:1 ratio ring and pinion for better autocross acceleration.    

 Rear end overhauled                                                                                         prior to overhaul                                                                                                                                              

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