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5th gear breaking off mainshaft

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Trying to find out if it's only the v8's that break their fifth gear at times. And if anybody has broken it with their four cylinders was that with the .82 OD ratio or the taller .76 OD ratio?


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  • 4 months later...

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 Would be interesting to know, for me too. At least it would give me more confidence when accelerating with FOT in my (better breathing and S4s chipped) S4.  But, to quote Jonathan here:

What do you want out of the gearbox ?

Are you upping power - keep in mind not many V8's have wreaked the boxes, I've NEVER heard of a 4 pot doing it.

The only thing I would go on if I had the cash is a 6 speed.

The other things you might wanna do is upgrade to the later shifter design (did I say shifter, I mean gear change lol) and slightly radius the selector shafts where the ball bearing locks in gear, this mittigates the clunkiness somewhat.

A LSD might help you if you're pulling 300hp.

1 Pieces primary shaft is nice, but the cost !!!!

Unless you're pulling V8 style + torque I would leave it be - Neal on here runs/tracks a ~385hp V8 and iirc has a standard box.

It seems to be not too bad with our 4-pots.

Edited by casewolf
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I've been in Esprit technical circles for years and never known a 4 pot to break a UN1, they simply dont have the torque.

5th is usually snapped by a V8 becuase of torque reaction (similar deal in helicopter gearboxes as it happens) basically floor the car to high speed in 5th, let fully off and then fully back, the wheels are decelerating the gear, then the engine puts it back to maximum stress and 'snap'. The 5th gear also has no rear support on the casing whcih doesn't help. Not a design fault but it just needs some mechanical sympathy when driving...that said I dont know anyone 1st hand who has broken a 5th on a V8 either !

Infact I know of 2 poeple who have broken UN1's in total.

Mike Sekinger might be worth an input I believe he ran the UN1 standard with the GT1 replica ? And if that car can handle it with correct driving style, any 4 pot will.

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  • 1 month later...

Hi All,

Just thought i maybe able to help a little here - i work for GTO Racing (Who do the single piece shaft kits, 6 speed kits, quaife diffs etc). Yes, 5th gear does still break on the 4 cylinders. Its as your replies say though, if you havent big power then it should last. We had one just a few months ago that had broken on a standard car. Im sure a lot is to do with how the car is being driven etc. Using big power with lots of torque and planting the throttle in 5th will break it off. If you want to know anymore about anything with the box please feel free to contact us at [email protected] - we will always try to help as we are enthusiasts.



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Lee, there's a lot of information about the strength of the one piece shaft. Your 6 speed c/r kit still has the two piece shaft. Is it strong enough for a high power/torque v8 or restricted to smaller engines?


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