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Discussion Starter #1 (Edited)
First, this is only my view and take on things, nothing more.

If you only want to drive your car down to cars n’ coffee and back, don’t bother yourself and stop reading here.

Secondly, I actually like the 4wd behavior of the car too, it gives the car a certain character that can be used to its advantage in certain situations, like coming out of medium or tight turns on an alp road, getting on the throttle right at the apex. I have driven the car with the simple 2wd mod, and it drives ok-ish, but as soon as you start to push the car, the compromises are showing. Especially the steering feel and understeer is less than perfect.
Goal is to make a perfect handling 2wd Superleggera, a complete Superleggera-Balboni if you will. I was not willing to making ANY permanent changes to the car, all is 100% bolt on.

So, here is what it takes to make a 2wd Gallardo drive well, heavily inspired by Lamborghinis own R&D for the Balboni, off cause. A complete part to part diagram review has been made, including the WSMs for details on technical deviations.
This is based on a pre-LP SL, which is going to be slightly more complex to convert than an LP model. The pre-LP uses its own Lamborghini suspension setup unlike the LP that shares components with the actual Balboni and Audi R8
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Also, a quick note on the ESP effects going from 4wd to 2wd. It is important to understand that the 4wd system is a 100% mechanical system, using a viscous coupling to distribute torque to the front axle. The ESP system uses ABS sensor/wheel speed, accelerator meters and steering angle as input and reacts with throttle and individual brakes only. The system is unaffected going 2wd.
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Below is what needs to be changed, besides the normal 2wd conversion, which have been covered in multiple threads already. Use the Balboni stubs or machine the FEBI Audi A8 ones to the same dimension, does not matter, does the same job.

btw, On the SL the 2wd conversion removes exactly 47.6kg. Slightly more on the std car, as the SL use a lightweight front diff case and lighter axles.


Sway bar setup front and rear.
The Balboni uses a re-configured sway bar setup, with a 22mm bar at the rear and a 31mm bar at the front. Stock the car runs 24mm in the rear and 29mm in front.
Remember that torsional stiffness of the bar is ^4, so this is a significant change with 70% rear stiffness and 130% front stiffness going to the 2wd setup.
The Balboni sway bars needs a bit of machining to fit the pre-LP. For the front the threaded bungs needs to be moved inwards to maintain the sway bar link angle. The Balboni chassis mounts and bushings can be reused with a modified bushing. The lateral stops are removed and new adjustable ones added.

On the rear bar the angle of the of the bars mounting point needs to be adjusted/twisted and a spacer machined to fit the stock sway bar link. This can be done with no effect on torsional stiffness, locally at the flat mounting end of the bar.
With the spacer in place a new equally longer bolt is then needed. This is where the AUDI family is a big positive. An identical stock bolt with the new length was sourced.
The stock lateral stops were machined to the correct pre-LP mounting position and an exact stock type bushing for a ø22mm bar was found. (yes, a lot of catalogue digging needed…)

New stock type bushing, fitting the 22mm Balboni bar.
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19mm spacer made and new stock type longer bolts to match
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Difference in LP and Pre-LP rear sway bar mounting… which look cooler….. ;)
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New bars ready for mounting
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Lateral stops for the front bar. Doubt they are really needed, as the chassis mounting points hold the bar right where it turn 90 degree.

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Suspension + ride height
This is a topic on its own. The pre-LP has adjustable coil over suspension from factory, where the LPs do not.
As the static load distribution of the car has now changed, the springs rates are adjusted accordingly. The 2wd mod changes the weight distribution by around 10%, which is also tweaked out with new spring rates.
On a pre-LP equipped car with the front axle lift, you can only lower the car around 5mm before you run out of spring pre-load. And even if you run with no pre-load (don’t!) you can only lower it 8mm or so. Does not look completely right, imo.

Note: The SL uses the same Bilstein sport suspension that can be optioned on a std. Gallardo, but the SL being 106kgs lighter, will simply sit even higher than the already too high std Gallardo. 3mm to be exact. A lowered SL looks good….like really good…

The LP uses a non-adjustable coil over, and more important a progressive spring setup, vs. the pre-LPs linear spring rate f/r.
Talking with some of the people who offers Gallardo lowering springs, I got some rather bad or non-educated advice on both spring rates, springs types and one guy even suggesting to just run the springs loose…. Not exactly the type of solution I am going for here…

The challenge is the front setup, since there is no off-the-shelf springs that fit the available free length and dimensions.
Goal is; tweak the spring rates for a 2wd setup, level the rake back to stock spec, 6 mm. Achieve a 20mm overall drop, with pre-load, and travel to bump stop. A working front lift. Ride and performance as stock SL setup.

These cars have around 20mm travel to bump stop, stock, so any significant lowering need to be followed by changing the bump stops to get the right performance and ride quality. Otherwise you are simply riding around on the bump stops.

Some vendors solve this by adding a lot of spring rate to compensate, not a good solution.
In the case of the Bilstein sport dampers, there is OK damper travel to allow a 20mm drop.

I started by measuring the stock spring rates, to determine the needed new rates and dimension, matching the available free length on the dampers.
The optimal spring + helper spring setup was selected f/r. There is not a lot of options in ø70mm springs, so the front helpers are custom made, along with all the spacer and retainer hardware. This is needed to ensure that the retainers are fixing the compressed helper spring, without resting on spacer at full compression, allowing the help to slide around.

The Bilstein bump stops are progressive and can be bought separately, luck has it that the stock bump stops have a large enough linear section that can be modified 20mm to maintain the stock bump stop characteristic. This is defined by the narrow/tapered parts on the Bilstein PUR bump stops

Stock springs rates, as measured in the test bench.
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New suspension setup, only waiting for the last adapters to be machined
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Front setup at load.
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Rear setup without load
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Discussion Starter #2 (Edited)
Rear differential LSD
Locking behavior, the actual ramp angles, are much different across pre-LP, LP and 2WD models. The Pre- LP uses a 2way LSD setup (identical 45 degree ramps on both acceleration and coast side) with minimal preload. LP and Balboni both use a 1.5way, but the 2wd version with significant change to the ramp angles on both acc. and coast side. This is a fundamental change that determines the cars behavior, removing understeer and adding stability on high speed braking etc.
I got a brand new complete Graziano L140 “Balboni” LSD internal parts set. As the ramps are changed, new spider gear axle, the spider gears and side gears are needed, with new clutches as well.
While you are in there, its cheap to change the diff bearings as well. Reusing the LSD housing, you can reassemble without resetting the pinion and bearing spacers/clearance.

2wd internals
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New OEM gaskets and hardware ready for assembly
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New diff bearings
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Internals soaked in transmission oil before assembly, shims distributed for the right pre-load.
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2wd configured LSD ready to install, cover with new bearings.
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Finally, the car needs to be realigned following the lowering but also the 2wd setup, it’s can be a lot personal preference in these setups, but the Balboni stock setup can be used as a start. I prefer the Hunter laser alignment racks to play with this.

Finally, the important part! The driving dynamics of the car is amazing. The steering turn-in especially is a huge change and the chassis load transfer is much more predictable running this setup.
The SL sitting at the height and with driving characteristic it always should have had…Damn this car is a blast!
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Congratulations if you made it this far 🤓
 

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This is amazing, I always suspected there was a lot more to it thank just removing the front diff, thank you for writing this up.
Its interesting about the Pre LP 2way vs 1.5way diff. that would make a big difference in handling.
Its great that you measured the stock spring rates, I recently tried to find the information for running shorter springs and could not find stock rates anywhere.
 

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Can you drift the car well with that setup? How does it feel in cornering? Just curious. Most drifters I know change to LSD but didn’t preserve stock feel. Very good details thank you for sharing the info (y)
 

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The gallardo awd does not help in corners. Before I converted mine to 2wd I tracked it a few times and some people even asked me why the back end would come out being awd, because the front doesn't get power until the rear slips if the rear slips you have already blown the corner. To be honest when the rear was slipping and the front kicked in I never really like the feel. I haven't tracked my car in a while since I now race in WRL and Champcar but the car was way better on a track as 2wd than awd.
 

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Wow... impressive work has gone into this. It shows the love and dedication we all share for those cars.
Well done and thank for sharing.
 

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Discussion Starter #8
This is amazing, I always suspected there was a lot more to it thank just removing the front diff, thank you for writing this up.
Its interesting about the Pre LP 2way vs 1.5way diff. that would make a big difference in handling.
Its great that you measured the stock spring rates, I recently tried to find the information for running shorter springs and could not find stock rates anywhere.
Thanks.
Tbh, there was quite alot more than above to it, and quite some research as no detailed information was available. Asking 550-2 owners did not help much unfortunately.
 
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