Overdrive blown up - Help please

[AcecaRacer]

I have just finished rebuilding my race motor and it has speced out at 144BHP.  I have a standard gearbox and overdrive.  In my first race last weekend, I found my gearbox starting to slip when under load, eventually becoming completely useless halfway through the race.
   
   I do not believe it is the clutch as the clutch is new and there was no smell at all.  My mechanic believes it is the OD.  I did not hear any sound, bang or anything when I eventually lost the ability to move forward.
   
   Prior to the rebuild, the OD was working fine with no sign of slipping.  However, I was running about 85 BHP at that time.
   
   So, my questions are these:...
   
   Has anyone else experienced this?  Do you think it is the OD?
   
   If it is the OD, can I just pull the OD off and put on the non-OD tail shaft with a shorter drive shaft and be done with it?
   
   Is there an OD designed to handle higher HP?  I don't need it for track racing, but I do need it for rally's and road racing.
   
   Any help would be appreciated!
   
   Cheers,
   Rob

[AC Ace Bristol]

Rob.
   
   What clutch are you running ..[?]
   
   Most of us in the  UK especially for competition use upgrade to a 8.5 inch Heavy Duty Diaphram Clutch and use a 8.5 inch Competition friction plate.  ( MGB GT )
   The throw on the clutch release has to be measured and adjusted/ shimmed accoringly.
   
   If the O/D unit burns out and ceases to function  I would have thought you would still have drive, same as if O/D was not engaged [?]
   I could be wrong.. []
   
   What sort of noise and gearchange problem did you experience prior to loss of drive ..[?]
   
   
   Keith ..[]

[AcecaRacer]

I actually received no real noise at all.  The gearbox just started to slip.  Acted a bit like wheel spin. I would press the accelerator and the car would move forward then the revs would jump up and then it would catch and then the car would move forward.  A bit like if I were to rest my foot on the clutch a bit causing a slight slip.
   
   Again, I did not smell anything like a burning clutch. I did not hear anything like grinding gears.  It just started slipping to the point where it acted as if the engine and gearbox were no longer connected.

[AC Ace Bristol]

Rob
   
   Four questions for starters:-
   
   Could you change gear or engage gear from nuetral .[?]
   
   What free play have you on the clutch pedal and the clutch slave cylinder.[?].
   
   Level of clutch fluid in the reservoir..[?]
   
   Looking through inspection cover on top of bellhousing has the clutch gone over centre..[?]
   
   Just trying to establish cause of problem without being hands on.
   
   Have you constant pressure on the clutch pedal, does it fade or improve by pumping...  sorry thats question  5 and 6
   
   Keith..[]

[AcecaRacer]

It looks like we have found the problem...broken stub axle.
   
   The Woodruff key has shorn.
   
   So...a couple of questions arise from this:
   
   Where can I get replacement parts?
   Are the stock stub axles strong enough?
   Has anyone upgraded to cobra stub axles?
   
   Thoughts?