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SHIFT_Leverage: Part I - Chassis-Mount vs. Extended Short Shifter

Updated: Feb 1


Enter: The Chassis-Mounted Shifter

My first introduction to a chassis-mounted shifter was a while back when I sat in an E46 BMW M3 with a CAE unit installed. Seeing the beefy looking metal components, 'Sequential Transmission' was the first thought that came to mind. I was surprised when the owner of the car mentioned that the original transmission was still installed. I rowed through the gears in the parked car and was simply blown away by the precision with which the gears engaged. I was reminded of the AP2's direct gear throws and positive engagement. A short while later, I hopped into a 370Z with a Coolerworx unit installed. A similar feeling. Direct gear throws, positive engagement, and a substantially raised gear lever position, bringing the shifter closer to the steering wheel. Granted, I have yet to drive a car with this shifter installed, this is my perspective having sat in a couple of cars and having felt the shifter at a standstill.





My first thought was: this is incredible, I want this. What an awesome way to improve the shifter feel on any existing transmission. Why doesn't every car have one of these?


So I started digging deeper and learning more about this upgrade, and how it works.


Pros & Cons

The coolest thing about this shifter is without a doubt the direct and positive engagement. In both the Z34 and E46 where I tested this out (w/ engine off) I was seriously impressed by the engagement of gears. The shift effort was reasonable, not too high or low, the gear engagement felt notchy in a good way, and the shift path from one gear to the next was short especially for the length of the shifter arm. I was reminded of the S2000's shifter which is a phenomenal setup from the factory, although the chassis mounted setups were a step up in crispness and just an all out 'race' feel.


What are the drawbacks then? Let's consider the mechanics. Anyone who's driven a car with a manual transmission will know very well that the gear lever can vibrate and generally move around quite a bit whilst driving the vehicle. Why is this? The gear lever is directly connected to the transmission, which of course is connected to the engine on one side, and eventually to the wheels on the other. This movement is a direct result of the 'transmitting' of torque and power, from the engine to the ground, via the transmission (eyy), as well as any feedback brought back into this system from the point of power delivery, e.g. bumps, wheelspin, wheel hop, etc. The important thing to note here is that although the gear lever vibrates with the drivetrain, the entire chassis and cabin do not.


Most cars that are meant for public roads will have the driveline components like the engine, transmission, subframe, diff, mounted with soft rubber bushings. These bushings are meant to absorb the vibrations and harshness that is a result of the drivetrain and road. Having soft bushings here means that the vibration doesn't enter the passenger cabin for a teeth-rattling and jarring drive.


Well, what happens when you rigidly mount the shifter to the chassis itself (while changing no other parts)? Yes, you get very direct shifting feel, however, you also constrain the motion of a component which would be free to move otherwise. Now, imagine you are riding the curb just over the crest of the corkscrew at Laguna, with the vehicle pitching downward, while applying throttle input as the differential is debating which wheel to send it to with all the weight transfer going on. With a standard shifter setup, your gear lever might be wobbling all over the place, but imagine that movement is constrained because the shift mechanism is mounted to the chassis. It's quite likely that you will lose your gear engagement and drop into neutral, at best, or grind against another gear or otherwise damage the transmission, at worse. The Laguna example is meant to be illustrative, but a similar condition could occur whilst winding down a canyon road with some bumps mid-turn.


This is why anytime you install a chassis-mounted shifter, it's a required upgrade to also switch over to stiffer engine and transmission mounts. This ensures that there is decreased relative movement between the drivetrain and the chassis. What does that mean for your teeth and them rattling, however? Anyone who's dailied a car with poly engine mounts will tell you that you can forget about taking a phone call while idling or cruising down the highway.


I've had someone claim that stiffer mounts are not needed because their Mini uses a cable linkage instead of a solid linkage. While the cable will allow a bit more flex than a solid linkage, I really doubt the transmission will be happy during heavy loads and g's. It's your car, do what you want! My point in writing this article is so that people who choose to upgrade to a 'cool chassis shifter' will understand the implications in doing so.


Having run Nismo motor and transmission mounts on a daily driven 240SX, I know that this is not the setup I want on a weekend warrior, as cool as a chassis mounted shifter sounds. I also don't want to risk damaging my transmission just for the upgrade, so unfortunately this option is out!


What, then?

The previous owner of the Z installed a B&M Short Shifter kit on the vehicle. He tried a TWM (now out of business) short-shifter kit and didn't like it, so he switched over to this one and said it was way better. I took his word for it and hey, it was already there. It feels solid, the throws are short, there's no vibration or rattling that some folks out there have complained about. The shift effort is higher than I'd prefer, although it's a natural result of shortening the shifter and decreasing the moment arm above the shift fulcrum.


A brief recap on the mechanics of short shifters (explained very well here https://www.risingxedge.com/bmw-chassis-mount-shifter-buyers-guide/), is that they generally increase the length of the shifter below the fulcrum (closer to the transmission), while decreasing the length of the shifter above the fulcrum (closer to the gripping point). The increased length below the fulcrum is what actually 'shortens the throw', while the decreased length above the fulcrum is what gives the shifter a lower position in the cabin.


By decreasing the length of above the fulcrum, you will of course, lose leverage while shifting and this explains why short shifters typically require more effort to shift. This effect is often countered by running a heavily weighted shift knob and is a likely reason why knobs like the 1/2 kg Tommykaira 'Hebi Bebi' (heavy baby) are popular. Adding some mass on the top of a shortened shift lever will effectively increase the length of the moment arm to perform the shift.


This is great and all, but why not simply use a longer moment arm to achieve a smoother(easier) shift? While a short throw is something I can appreciate, in practice of performance driving scenarios, I don't see the point of having a very low lever position in the cabin, at least with the Z34's cabin layout. I'd rather have a lever that is closer to the steering wheel to decrease the distance traveled by my hand when needing to shift while cornering, for example. In addition, adding some more leverage to the installed short shifter should make for smoother, easier shifts, something I value on the daily commute.


Enter: the Shift Extender

Here it is folks. A simple shaft made of machined steel, that is threaded on both ends. What does it do? It extends the length of the shift lever in the cabin. Mated to a short-shifter kit (with an increased length below the fulcrum), this ought to cancel out the 'shorter throw' of a short-shifter by bringing it up to near OEM levels, while increasing the cabin position of the shift knob, making it easier to reach and easier to move while driving.


Side note: Installing a shift extender on a stock non-short-shifter setup is probably not the best idea. While it will increase the in cabin height of the shifter, the shift-throws might grow excessively long to the point where it's awkward while driving. While you will find many non-performance-oriented cars out there with a long shift lever, in a performance driving scenario the optimum setup is a balance between the height of the shift lever, the length of the shift throw, and of course the level of effort required to perform the shift.


Cons of the shift extender: There is also the risk of the increased leverage allowing you to put enough force on the shifting mechanism to damage some components. Something to be mindful of as well.


Overall, I don't expect the direct-shift precision of a chassis-mounted shifter from installing a shift extender. However, it should offer the best of both worlds, with a shift grip that is closer to the wheel, reduced shift effort, potentially smoother shifts, while retaining the NVH characteristics of OEM drivetrain mounts!


Stay tuned for updates once this is installed and tested out!

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FYI: The title of this article is a spin off of an old Nissan marketing campaign! "SHIFT_Obsession"

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