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Gearbox, Diff or both?
https://www.ausmini.com/forums/viewtopic.php?f=2&t=14345		 Page 1 of 1
Author:  Fat Boy Dave [ Wed Dec 28, 2005 1:10 pm ]
Post subject:  Gearbox, Diff or both?
So...
Does anyone know if anyone other than Minispares that might be doing 5 or 6 speed boxes?? http://www.minispares.com/Product.aspx?pid=36391

I don't want a S/C though, looking for helical.

I've got a 94 Rover and am currently driving to work everyday on the freeway (60km round trip) and every 2nd weekend doing 120km's. So at 110kph it's working a bit hard, ~ 3,450rpm. So based on this, I think I've got a 3.444 diff ratio. I'm thinking I can change the diff ratio, but then everything else is out, speedo, ratios on other gears or I can change gearbox and get a different final ratio as per Minispares 5 speed "This is the straight cut gear version 5 speed gearbox which has a 5th gear ratio of 0.865 which with a 3.44 diff gives the equivalent of 2.98" (I assume has the same ratio on a HC gearbox) although this would make f-all difference, so probably change diff at this stage anyway to a 2.76:1 (if I could find one).:roll:

My car is essentially stock on 12" wheels.

Is this the right way to go or should I be looking at drop gear ratios (not 100% sure on what these are anyway, I assume the gears from the flywheel to the gearbox or gearbox to the diff).

Thanks guys.
Author:  benjamin [ Wed Dec 28, 2005 2:11 pm ]
Post subject: 
if i had the money id go the 5 speed helical box :)
Author:  Harley [ Wed Dec 28, 2005 2:14 pm ]
Post subject: 
If the reason for not wanting a minispares 'box is the cost, then I'd stop looking.
They are all rediculousl expensive.
The much, much cheaper option is to change the diff ratio (pinion and crown wheel),
this will make al the gears longer, and acceleration will be affected.
EG, like starting from second every time.
The additional cost is in the rebuild of the 'box.
But it does depend on your budget, if you have another car you can use in the meantime, etc.
If noise is the problem, perhaps consider:
a) doing the speed limit (100) or lower, or
b) fitting new sound deadening/ proofing so the car is quieter inside.
:D
Author:  Fat80y [ Wed Dec 28, 2005 2:26 pm ]
Post subject: 
I suggest that at those revs, you have a 3.1 diff already, possibly 2.9.

For comparison, I know I have a 3.44 diff, on 10" wheels, my car revs ~4200rpm at 110kph.

If you really want 5 speeds, an engine conversion is the only cost effective way IMO.

Swift GTI motor, all alloy, light weight, 100hp out of the box, 5 speeds, 8000rpm reliability etc etc etc

With the prefab sub frames around, you could do it easy for $5000, the equivalent of A series 5 speed.

My 2 cents.
Author:  Fat Boy Dave [ Wed Dec 28, 2005 2:34 pm ]
Post subject: 
Cost not currently the issue. Just availability of HC 5 speed box as opposed to SC box and wear & tear constantly running the motor at higher revs than req'd.

Mind you at $5k, an engine swap does start to make more sense.
Author:  Morris 1100 [ Wed Dec 28, 2005 3:25 pm ]
Post subject: 
I would change the muffler! 8)
A bad exhaust will drone at certain revs on the freeway, it may sound nice when you rev it to 6000 and change up a gear but when you hold a constant speed they make the motor sound like it is killing itself.

The 3.44:1 diff should be OK and 3,450rpm is not really that much. A taller diff would help.
My car has a 4.26:1 with 12' wheels. :wink:

I would not go down the 5 speed route. They are rubbish.
Author:  drmini in aust [ Wed Dec 28, 2005 3:27 pm ]
Post subject: 
It is already geared pretty high, eg I'm doing 4800 at 115KMH with a 3.64 diff & 10" wheels.

Rover had lots of trouble with the 5 speed sportspacks.
All those non- racing 5 speeds (ie the ones with 5th added into LH side of box) wear things out quicker than a 4 speed due to the way 5th is driven. Bearings on layshaft were not designed for continuous power transmission, which is what happens when in 5th gear.

Also, if you gear it much higher, it will be gutless in 5th anyway. A 1275 doesn't have unlimited torque...
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