1) Torque truncation works by taking the crank speed sensor reading and the road speed reading and by doing a comparison in the ECU it calculates when it is in first gear. This does not require all gear ratios to be programmed in. It is simply a comparison table. You may not like the sound of it, but that's how it works
2)As a history, the IB5 started off as the B-4 in 1978 for the 1.0/1.1/1.3 litre Fiestas (max 60HP). The IB-5 program started in 1996, with closed bearings, bearing D with innering, 1st/2nd and 3rd gear double synchronisation, retuning of 4th/5th gear synchronisation, neutral selection springs in the transmission and hydraulic clutch actuation.
3) Failures. When the 1.7 Sigma SE161 project began (Puma to non-Fordies), durability testing discovered three main flaws with the gearbox.
a ) Final drive gear tooth failure
b ) Reverse gear tooth failure
c ) Bearing D failure (I have no idea what this is)
Other failures experienced were 4th gear crashing, and 1st gear jumping out.
At this time there were two final drive ratios under test - 4.27 and 3.82. At 4.27 the teeth broke off the pinion gear. This was then shotpeened to improve the failure rate. This improved it by 20%, but it still failed. Torque truncation was introduced to limit the torque from 157Nm to 135Nm, and 110Nm in reverse gear (as reverse is lower and hence has a higher loading). Someone made a bloody stupid comment on this list about "how does torque limiting protect the car in 2/3/4/5/ gears". Well, if you have ever ridden a bike with more than one gear, you will know that the torque multiplication goes down as the gear ratio goes up, and hence torque truncation only needs to be on 1st/reverse gears.
The production final gear ratio was chosen as 3.82. This could not be shotpeened for manufacturing reasons (gear size). Without torque truncation on the super accelerated life test, there was a 62% failure rate. With torque truncation this became 100% pass rate.
4) In answer to the question about "how does this protect your gearbox if you rev the engine and dump the clutch?" - it does not. There is no protection on the Puma for this. I asked this question and was told "we expect our customers to have a bit of common sense". The bigger engined Foci do have this problem as they kept breaking driveshafts during development. The solution was to put a peak torque limiter on the car. Basically this is a delay valve in the hydraulic clutch line which limits the speed of engagement. During normal driving conditions this is not noticed, but during stupid driving will allow slip to protect the drivetrain.
5) To a member - whoever told you that the IB5 can take 300 bhp is probably not well informed. If you drive sensibly than your gear box may well last. The testing carried out during car development is deliberately harsh and represents 100,000 miles + of motoring, so I am not going to say to anyone that there gearbox will break without a torque limiter because it is not necessary true.It depends on how you drive it.
However, the IB5 gearbox design torque limit is 135Nm.
