QOTW #26 – Gear chatter on my V8 Vantage?

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Welcome to BamfordRose and another question of the week. Today we’re going to talk about gear chatter. What it is and if you upgrade to the lightweight fly one twin plate clutch do you affect it?

So, standard production cars right from 05 V8 Vantage suffered to a greater or lesser extent depending on manufacturing tolerances of each car with what is called gear chatter. This is starting from the engine and its uneven fire impulses. The engine fires seven eight, the last two cylinders in a firing sequence, giving that American muscle car sort of sound. And together with that firing order and that V8 engine is a little bit unstable in terms of combustion compared to modern engines which are very stable to pass emissions. That gives an unstable engine bank-to-bank and combustion stability which gets transmitted out of the torque tube which acts as a megaphone making the gearbox if it has loose tolerances chatter.

So, at idle, not pressing the clutch, especially if you load the engine up with a little bit of vacuum, electrical load with a little bit of light, you can start hearing this sort of chattering sound and it is gears chattering. If you press the clutch, therefore separate an engine from the gearbox, you can get this sound to go. When you’re driving, if you come into a roundabout or you’re laboring the engine typically below 1500 rpm, you can just hear this gravelly sound in the back like… And then about 1500 rpm, 1750 rpm, it disappears completely. So, that’s gear chatter.

Now some cars are standard chatter, some don’t. The factory knew this and it was a problem that needed to be fixed. They didn’t want to fix it in hardware, so it got fixed in software. So, this was engine management system calibration our idle and low speed drive, which had a massively retarded ignition figure, which damped down each cylinder’s combustion peak pressure to flatted off combustion pressure, that equalized all cylinders, made the engine a lot smoother, therefore eliminated gear chatter.

On build tolerances in the gearbox, they’re worse for this condition. Some car standards will chatter. If you then upgrade to a lightweight flywheel and a twin plate clutch, the different inertia of that and the design of the clutch tends to make gear chatter worse. So, on a car that exhibits no gear chatter standard more than likely when we upgrade to lightweight flywheel and twin plate clutch that can’t continue to make no chatter at all. So, the customer is none the wiser to the problem because they didn’t know it existed to start with anyway.

Cars that exhibit chatter badly standard, it’s only going to get worse but the lightweight flywheel and twin plate clutch. But it must be remembered, this isn’t a ware state. It’s not an error state. This noise is just poor noise vibration harshness. Some people are sensitive to it and can’t tolerate that noise becoming any worse with upgraded components. So, in these cases, what we do is we understand with the customer what their car is before we upgrade it. So, we listen to the gear chatter, is it present to start with it? If it’s not present to start with gear chatter, doesn’t form any part of the conversation during the discussion about upgrading the car.

If gear chatter is present then we have this conversation about what it is and it’s probably going to sound a little bit worse. And there are those people that realize that it’s not wear or error state, and not idle if you press the clutch, separate an engine from the gearbox, then you don’t get sound anyway and they can live with this. There are those people that poor noise quality is an issue, so what we have done since going through this cycle of understanding the noise, it can get worse, some customers don’t like that, we have a slightly heavier weight flywheel to go with a twin plate clutch which will not worsen gear chatter. So, if the car was exhibiting gear chatter standard, when upgraded with the flywheel and clutch, it’s going to be exactly the same sound, so it’s transparent like for like.

So, that’s gear chatter and its interaction with a lightweight flywheel and twin plate clutch. Hope that’s clear.

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