I have a standard 3.4 diff in my Cooper S 3 synchro box.
I also have a 4 synchro box with a 2.95 diff under the bench.
Is it possible to swap the two, put the 2.95 diff in the S box?
Will the 4 synchro pinion fit on the 3 synchro mainshaft?
The S has Hardy Spicers and the other box had rubber doughnuts. Is it easier to exchange the whole diff after changing the output shafts, or swap crown wheels?
Also your views on 3.44 v 2.95 diff ratios?
Swap A+ Crown wheel and pinion with Pre A+
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Kiwi Craig
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Spider
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Re: Swap A+ Crown wheel and pinion with Pre A+
Hi Craig !
Yes, you can fit the taller gears, pretty much no problem, you will though need to remove the C Bearing Retaining Plate and open it up a little as the 2.95 Pinion is bigger in diameter. You do do that on a Lathe, Mill or a Die Grinder.
All the S Parts will swap in to the 2.95 Crown Wheel OK. You can use the later Centre that takes the Planet Gear Thrusts that have the Tang on them, that stops them spinning and wearing the Centre.
As for which ratios, my own view is I'll have the 3.44 over anything taller (like a 2.95 or even a 3.2) for any road use, including motorways, any day. I find the taller ratios just suck the life (and fun) from them. If you are running a Close Ratio Gear Set, like an S set, adding a 2.95 FD Ratio on top of that puts 1st at being quite tall. If you do a bit of stop / start driving in your Mini, you'll find it will wear the clutch prematurely. The other thing I've noticed from the Injected cars that run these tall drives is that because they rev so much slower, the cams wear out much faster, as they are only splash fed from oil flung off the Big Ends. With a lower reving engine, not only is the crank speed slower, but the volume of oil being pumped is less.
Yes, you can fit the taller gears, pretty much no problem, you will though need to remove the C Bearing Retaining Plate and open it up a little as the 2.95 Pinion is bigger in diameter. You do do that on a Lathe, Mill or a Die Grinder.
All the S Parts will swap in to the 2.95 Crown Wheel OK. You can use the later Centre that takes the Planet Gear Thrusts that have the Tang on them, that stops them spinning and wearing the Centre.
As for which ratios, my own view is I'll have the 3.44 over anything taller (like a 2.95 or even a 3.2) for any road use, including motorways, any day. I find the taller ratios just suck the life (and fun) from them. If you are running a Close Ratio Gear Set, like an S set, adding a 2.95 FD Ratio on top of that puts 1st at being quite tall. If you do a bit of stop / start driving in your Mini, you'll find it will wear the clutch prematurely. The other thing I've noticed from the Injected cars that run these tall drives is that because they rev so much slower, the cams wear out much faster, as they are only splash fed from oil flung off the Big Ends. With a lower reving engine, not only is the crank speed slower, but the volume of oil being pumped is less.
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Kiwi Craig
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CooperTune
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Re: Swap A+ Crown wheel and pinion with Pre A+
As with most things there can be more than one opinion. I agree the A and A+ gears interchange without issue other than
the mentioned clearance of the third motion bearing retainer. The later diff cage with the spider thrust tabs will accept
your Hardy Spicer bits.
Where I differ is in regards ratios. 18 years ago I built 85 1000 E from a new shell. With a heavy coat of pick up bed liner
undercoat and lots of sound deadening she ended up heavy. Around 1700 lbs heavy. My funds ran short and I bought a rusty
998 donor. The speedo indicated 76,000 (who knows if it was correct) and freshened it up. Diff seals, timing kit and seal,
tappet cover gaskets, V C gasket water pump, by pass hose. As it turned out the tranny was a rod change DAM 5626 with
a 2.95 CWP. I drove that combo for about 100,000 miles and found it a very nice trade off. Due to a failed by pass hose on
a 20 degree day that power unit had to be replaced.
Replacement unit another a 1360 cc Cooper S with a Hi Torque cam on top of a rod DAM 5626 with the wide ratio gear set
resulting in roughly 4 to 1 , 3 to 1 , 2 to 1 and of course 1 to 1. Using a 2.76 CWP along with two O/D drop gears I come up
with roughly 2.56 to 1 over all ratio. Someone said gears take the fun out of driving. I like running my car on 10s but have
so many 12s I mounted a set of Rover 12s with 145s. Tire spin in all four gears was a problem in the wet. Care had to be
used in first to avoid wheel spin. Going to 165/12 helped with the wheel spin. We tend to live a little further apart than you
guys. I have to merge with trucks and cars at 70 plus mph going to work each day. I did a 500 mile one way to attend a mini
race and rolling along at 70 mph at 3000rpm is nice. On the way home a fell in with three hot hatches running just under 100
mph. We covered about 30 miles at that speed and honestly the wind noise is uncomfortable and best to pay attention at that
speed. Yes as a kid I had an 850 with 4.10 and turned it to 8000 rpm all the time, my autocross car was 1330 Cooper S with a
4.35 red lined at 9300. And we held the Vintage racer 3.7 to 8700. I love rpm as much as anyone. Time and place for everything.
Steve (CTR)
the mentioned clearance of the third motion bearing retainer. The later diff cage with the spider thrust tabs will accept
your Hardy Spicer bits.
Where I differ is in regards ratios. 18 years ago I built 85 1000 E from a new shell. With a heavy coat of pick up bed liner
undercoat and lots of sound deadening she ended up heavy. Around 1700 lbs heavy. My funds ran short and I bought a rusty
998 donor. The speedo indicated 76,000 (who knows if it was correct) and freshened it up. Diff seals, timing kit and seal,
tappet cover gaskets, V C gasket water pump, by pass hose. As it turned out the tranny was a rod change DAM 5626 with
a 2.95 CWP. I drove that combo for about 100,000 miles and found it a very nice trade off. Due to a failed by pass hose on
a 20 degree day that power unit had to be replaced.
Replacement unit another a 1360 cc Cooper S with a Hi Torque cam on top of a rod DAM 5626 with the wide ratio gear set
resulting in roughly 4 to 1 , 3 to 1 , 2 to 1 and of course 1 to 1. Using a 2.76 CWP along with two O/D drop gears I come up
with roughly 2.56 to 1 over all ratio. Someone said gears take the fun out of driving. I like running my car on 10s but have
so many 12s I mounted a set of Rover 12s with 145s. Tire spin in all four gears was a problem in the wet. Care had to be
used in first to avoid wheel spin. Going to 165/12 helped with the wheel spin. We tend to live a little further apart than you
guys. I have to merge with trucks and cars at 70 plus mph going to work each day. I did a 500 mile one way to attend a mini
race and rolling along at 70 mph at 3000rpm is nice. On the way home a fell in with three hot hatches running just under 100
mph. We covered about 30 miles at that speed and honestly the wind noise is uncomfortable and best to pay attention at that
speed. Yes as a kid I had an 850 with 4.10 and turned it to 8000 rpm all the time, my autocross car was 1330 Cooper S with a
4.35 red lined at 9300. And we held the Vintage racer 3.7 to 8700. I love rpm as much as anyone. Time and place for everything.
Steve (CTR)
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Spider
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Re: Swap A+ Crown wheel and pinion with Pre A+
Oh, forgot to mention that Cam Choice too will probably have a bigger bearing on choice of ratio, ie, if you have a Cam that doesn't 'come on' until you are doing say 2700 RPM, you really wouldn't want a 2.9 FD, it would be a real pig to drive in any traffic.
Any time mate