No life (a.k.a. DattoMaster)
Joined: 2008/10/10 22:02
From Melbourne Australia (and likely under the car)
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Relatively speaking, there's not going to be a huge difference in cost between rebuiding the 4 or 5 speed. the only way there's going to be a difference is if you only change the bearings that are completely past it, but left in a few that were showing some wear but would still last a good few years. Any box I've personally rebuilt, of any type, i've tended to go the other way - unles the bearing (or whatever item) is in absolutely tip top condition, I'd replace it, and I ended up getting longer life out of them vs just doing the 'bare minimum'
SO on that basis the rebuild costs won't be astronomically different - you then have to look at what is a better gearbox all things considered. And on that basis, even if the strength difference is negligible, that extra gear is a MASSIVE advantage. You can run 4.11 gears and in 5th it'd be like having approx 3.3:1 diff with a 4sp. Huge drop in freeway rpms. Alternately if you find em, you could run 4.375 diff gears and it'd be the equivalent of around 3.6:1 gears in 5th. Those 4.3s would be good with a 'bigger' cam spec. I suspect that 4.88s would be a litte lower than ideal for a mild cam (more suited to competition stuff) - but just for the hell of it - 4.88s in 5th gear would be similar to approx 4.00:1 gears. so they'd see very very very slightly lower freeway rpm than with a 4sp and 4.11 gears (which you almost certainly have now)
So basically you can tailor diff ratios to suit the fact you have an overdrive 5th gear and get the best of both worlds, improved acceleration with the lower geared (higher numerical ratio) diff but a bit lower freeway rpms, or alternately simmilar acceleration (keeping your current 4.11:1 diff gears) and a much low freeway rpm, or alternatively a BIG improvement in accelration, but little change in freeway rpms.
So that's the first 'big advantage' of the 5speed and why it would be of benefit to rebuild it rather than a 4 speed.
The other reason won't affect you straight away, but down the track - it costs similar amounts to reco either the 4 or 5 speed, BUT if you ever wanted to sell the box, you'll get a decent price for the 5 speed (still won't likely recover all costs of course) but you'd likely have real trouble selling a reco 4 speed for much money at all.
Posted on: 2012/9/30 8:33
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