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· layabout
Over-complicated pile of bits that oneday will be fitted to my '91 SilverShItBoX
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Is the 6 speed version of mk2.5 less reliable…heard that they are more prone to fail/explode. True or nah
🤷‍♂️

the car or gearbox?

to be fair, a 20 year old car (or gearbox) probably needs a little tlc (or maybe a rebuild:p)

the 6 speed gearbox in the mk2.5 was slightly uprated but I have little idea as to what (apart from the selector-mec. having an extra 'indent-plunger' to hold in gear / make the gearchange slightly more positive:unsure:)

Rich.
 

· Registered
VVT swapped NA & TD04 turbo NB
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633 Posts
Is the 6 speed version of mk2.5 less reliable…heard that they are more prone to fail/explode. True or nah
There was some anecdotal evidence on the Nutz facebook page where some guy kept blowing them up with a 300bhp ish car - completely isolated and no scientific tests that I could find.

I would take DIY tunes with a pinch of salt personally. Gearboxes die mostly from torque and standing launches.
 

· Banish a little rust a day people
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The mk2.5 6 speed is basically identical internally. The made the shifter stronger/thicker, and adjusted the throw to be slightly longer. They moved to a larger nylon bush on it as well to account for the larger selector ball. Other than that they are the same and both take about 280ftlbs of torque before exploding. Your mileage may vary.

There are 3 main reasons for failures, the first is as above, DIY tunes which hit high torque early on and stress the box. People thinking they can clutch kick and do burnouts all day with sticky tyres will also quickly kill boxes. The final reason for failures is heat, they get too hot under sustained hard track use and the clearances between 3rd and 4th go a bit wonky and cause a failure.

As a rule of thumb show some mechanical sympathy, have a smooth torque curve that doesnt spike hard early, and if you're at a power level where you've had to put forged rods in it (or should have but are risking it) then keep controlling heat in mind on track.
 

· Banish a little rust a day people
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I must have been living under a rock because I thought the opposite was true, the 6 speed is more capable of taking torque than the 5 speed...
yeh, it's the other way around
 

· Banish a little rust a day people
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It's not a bad diff tbf, the problem is just the tabs breaking which I hear is largely due to incorrect brake testing in MOTs. Everyone loves the stock torsens but the bias ratio on them is pretty trash, if you drive in a way that actually makes use of an LSD then given there are some mental fuckers out there trying to monopolise pricing at £500+ you are far better off buying a new Blackline one. Yeh you need to swap the cores, seals, set lash etc, but most used torsens have over 100k miles now and really ought to have those things done anyway (especially for the money you're spending now).
 
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· Happily expanding the To Do list since 1997
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Granted, an unbroken Fuji is an excellent diff. Seen a bit of chat recently around the refurb that McNeill engineering do and Crapengineering suggesting they might offer a similar service.
 

· Banish a little rust a day people
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5,454 Posts
The co owner of TheMX5Restorer has turbo'd his car and has had a 6 speed gearbox failure or two on his
Means very little. Age, previous use, tyres, how it was driven, what power he's actually making, heat the box was at the time, what torque is at what rpm etc all can cause failures.

No gearbox is built proof, they'll all fail given enough abuse or power, it's just the 6 speed typically fails later.
 
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