About 3 weeks ago, many know I put down about 525 rwhp on the dyno (dynojet corrected) when my clutch slipped and let go. This launched me into drivetrain upgrades that I felt should be made. This is the second in a series of reviews on the items I upgraded.
Driving a 400 - 500 rwhp car with "one tire spinning" has provided some challenges particularly in hard straight line acceleration and accelerating out of corners. From a dig, the rear of the car has been really unpredictable and shifts caused the rear out to the slide toward the driver's side quite often. In the corner, I always felt very concerned about how much throttle to apply because they rear just slid out so easily. I always intended on getting an LSD, but I felt this would be the perfect time for the project since my transmission/driveshaft was lowered for the clutch & flywheel upgrade.
What does an LSD do? It is detects when you have wheel spin and instaneously transfers torque to the tire with better grip. This in fact is exactly the opposite of what the stock open differential does. We want power to both tires and many of us are very disappointed BMW did not make this option available to us.
I think a lot of people know there are a couple of options for LSDs on the 135/335. Like everyone else, I labored for a while on what LSD to choose. In 99% of situations these differentials are similar in the targeted performance. The things that were tremendously important to me from my LSD were:
1. Durable enough to handle the power.
2. Not prone to seizure.
3. Quiet operation.
After spending a lot of time on the phone and researching, I decided to go with the Quaife LSD. Simply put this differential is the most proven LSD in the world from circuit racing, drag racing, rally racing, and infinite road testing. Quaife has been doing LSDs right for many, many years with lifetime warranties on their products. All Quaife LSDs are CNC built and tested to very fine tolerances.
One thing that must be noted is BMW uses an inner scrolled output shaft bore on a standard final drive. Why? BMW uses this to prevent seizure on the output shaft. Here is a picture of what I am referring to:
Notice the groves in the output shaft. Quaife replicates these scrolls on the differential because they felt it is essential to preventing the seizure. To be honest, this was a major selling point because of the high power I plan on putting through it. I know that not all LSDs replicate this inner scroll on the output shaft and that was a serious concern for me.
Finally, the Quaife is a notoriously quiet differential. This sealed the deal for me and it was off the figure out who to get the LSD from. I do have a welded rear differential, so that did pose some problems. I felt the easiest way to plan my approach was by contacting Bird's Auto. A lot of people in the US may not know about Bird's Auto. To say they are a strong Euro shop would be an enormous understatement. Just talk with them for 2 minutes and you realize these guys are the real deal. I spoke in depth with Kevin Bird and was blown away with his knowledge on BMWs. He has been a truly enormous source for information through this process and I couldn't be more appreciative of him. Kevin Bird suggested I contact VAC Motorsports for the machine work and spoke very highly of their work. Armed with this information. I ordered the following from VAC Motorsports.
- Quaife LSD pre-installed in a stock rear differential with a refundable core deposit.
Experience with VAC Motorsports
To say the least VAC Motorsports is a serious BMW shop. They have built more BMW race cars than I could imagine. They are a 14,000 foot full machine and remanufacturing shop. I think they put it best:
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Our machine shop curently features the latest and greatest in equipment, just a few include a RMC Boring Mill, Serdi Valve Machine, HAAS & Hurco CNC Mills, Automated grinding equipment, Romi and Doosan CNC Lathes, Crankshaft Balancer, a Flow Bench along with Solid Works and Mastercam CAD/CAM Software. This is where we design and build Engines and Drivetrain Components and also design and manufacture our own line of VAC BMW Performance Parts that are used in High Performance and Racing applications around the world.
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I was very confident they could do the work for me and do it well, so this was a very easy decision for me.
The ordering process was tremendously easy. The differential with Quaife LSD was installed and shipped within a week. I had tracking information the same day it shipped and I was able to plan the install process very well.
I asked if I could get a few pictures of the install process from VAC Motorsports / Bird's Auto and they were very kind to provide quite a few.
Here is an image of the welded crownwheel exposed.
Pulling the output shaft.
Pulling off bearing inner races.
Removing the crownwheel and differential assembly.
Crownwheel parted from differential.
Old differential next to the Quaife LSD.
Preparing the Quaife LSD.
Pressing on inner races.
Assembly placed in differential casing.
Checking for backlash.
Outout shaft installed.
Buttoning things up and torquing to spec.
That at least should give you an idea of what goes into this assembly process.
After the above process was completed, VAC Motorsports packaged things up and sent out the differential with Quaife LSD installed. The differential with Quaife was sent to me in a shipping tub.
The differential was protected well in the tub using carboard and newspaper to insure it came to me in prisine condition.
Here is the differential as it arrived to me with Quaife LSD installed.
If you go this route, you will simply send your differential back to VAC Motorsports upon completion of the project to get your core deposit back. VAC Motorsports was very easy to work with and I suspect I will doing more with them in the future.
Installation
You take all responsibility for the install and this is just a look at how I did the install. I strongly suggest you get a Bentley Service Manual to assist in the process.
I am sure the first thing that will be asked is "Can I DIY this project". I think the answer is definitively yes, but a lift will help in tight spots and a transmission jack is a must for the 101 lb differential. In some areas you can rent a lift, and that might not be a bad idea. You will also need a large and thin 52 mm wrench to remove the driveshaft from the differential. This wrench is used to loose the insert nut that locks the driveshaft onto the rear differential. Fortunately, AR Design makes this wrench and sells it for about $50. It is a very good looking item too! I order this from AR design and it was shipped same day, tracking info was sent immediately, and arrived a few days later. As always, AR Design did a fantastic job on the build quality.
This is an important item to release the rear section of the driveshaft from the differential. Here is ultimately where it will be used.
This is the actual insert nut.
One thing should be noted, when you buy the differential with LSD already installed from VAC Motorsports, the insert nut is already replaced, so this is ready to bolt up.
So let's dive into the install process. This really is a two man job, so have a friend with you to help.
Obviously you are going to need to raise the car whether it be a lift or some jack stands. The lift will give you greater clearance to meet torque specs later in the install. The first thing to do is remove underbody panels, exhaust, and heat shields covering the driveshaft.
This will expose the driveshaft. Here is the front of the driveshaft
Here is the rear of the driveshaft noting the blue arrow point to the insert nut securing the rear section of the driveshaft to the differential.
The project begins really when you start to remove the driveshaft. Make sure you suspend it by wire to protect the universal joint. You can see how I did that in this picture.
Make sure to mark the driveshaft/flex disk or flex disk/output shaft of tranny with paint to insure correct orientation upon reassembly. Remove the bolts. I chose to remove the flex disk from the output shaft on the transmission.
Next, brace the rear section of the driveshaft with a wire. Grab your AR Design 52 mm wrench to remove the insert nut by turning the bolt clockwise direction.
Do not use the bihexagonal nut for bracing!
Now the driveshaft should be loose from the differential at the rear and the front. At this point, remove the bolts for the center universal joint while the second person holds it on place. Make sure you are clear on both sides and remove it out of the car taking care not to bend the driveshaft at the universal joint. The universal joint is highlighted below.
Now it is time to get the half shafts removed. Before removing the half shafts, you will want to secure them with wire to protect them from hanging after you remove the bolts. They are connected to the differential with torx bolts that will need to be replaced. Here they are connected.
Half shafts removed.
It is time to swap out the differential. You will need a transmission jack to brace, lower, and raise the differential because it is 101 lbs. This is actually a very easy process because only 3 bolts mount the differential. Two bolts are on the front and one bolt/nut is on the rear. Remove them while the differential is held in place with the tranny jack. Once they are off, lower the differential out. In the picture below you can see the two front and 1 rear bolt locations.
Now it is time to prepare your new differential to be installed. It does not come with fluid, so I added Redline Synthetic 75W90NS.
If you choose Redline, make sure you use the NS version! It is suggested by Bird's Auto to fill while the differential is level until it overflows.
Using two people, place the new differential on the tranny jack and raise it into place. Using new bolts, secure the two front and one rear nuts/bolts and torque to spec. Now, orient the half shafts correctly and using the metal brackets you removed from the stock differential and new torx head bolts, bolt up each half shaft. Once you have all bolts in place, torque to everything to spec.
Finally re-install the drive shaft. Remember the insert nut that connects the rear driveshaft to the differential is new from VAC Motorsports, so you are ready to go. Always support the center universal joint! Install the rear section of the driveshaft to the differential and tighten the insert nut, install the front of the driveshaft to the flex disk or output on the tranny noting the proper orientation and torque to spec. Finally, bolt up the center universal joint and torque to spec. Then get all the heat shields and belly pans back on and the process is complete.
Some notes, I would replace all nuts and bolts along the way as BMW suggests. Always torque to spec and in correct order when required.
This was really not a difficult job at all to be honest. It is hard for me to estimate time because I had the driveshaft off for the clutch install and adding Quaife LSD swap to the job was 90 minutes at most.
Results
Testing the Quaife LSD had to wait a few hundred miles while I was breaking in my new clutch and I have to say it was a painful wait! With that said, the wait was worth it. All my testing was done with traction control completely turned off. There are three aspects of the Quaife LSD performance that I want to cover… noise, straight line hard acceleration, cornering performance.
Noise
The Quaife LSD is absolutely silent with no clicking whatsoever in all the testing I performed. I honestly wasn’t overly concerned, but I know some might be and I wanted to put your mind at rest if that was a major concern.
Straight Line Hard Acceleration
I have to admit this was going to be a make or break area for my happiness on the Quaife LSD. I have had serious problems at my power level avoiding out of control wheel spin and the rear end sliding erratically to the driver’s side of the car. First gear has been basically useless to me for quite some time. With the Quaife LSD, I am definitely seeing better traction from a launch but where I am really noticing the difference is in the shifts. The 1st to 2nd shift has been a traction loss exercise on my car. I have been wasting a lot of power for a while. With the Quaife LSD, now I am immediately hooking once the car hits second and rocketing forward. I am not going to give the illusion that I am not at the limits of street tires still, but the Quaife vastly improved the straight line acceleration from 2nd forward. It should be particularly helpful as well when I spend some time at the track.
The second and more concerning problem was when the rear kicked and totally slid toward the driver’s side when I lost traction. The difference here is night and day with the Quaife. Now, the rear will slip slightly toward the driver’s side with a lot of predictability in the behavior. Before it was spin, spin, spin... With the Quaife LSD, after the initial tire spin you can feel the car fighting for traction. Now I feel I can stay in much better control of the car under hard straight line acceleration. It is a car that fights for traction rather than giving up on traction all together.
Cornering Performance
I felt this was probably going to be the area where the Quaife LSD shined and I was definitely right. During hard cornering, the weight is always transferred toward the outside of the vehicle and that inevitably means you are always low on traction on one tire. This has been particularly troubling for me because I always felt scared to get into the throttle during and especially exiting corners because of how easily I could lose control of the rear of the car. I was very excited to test this area. The results here simply blew me away. The rear of the car no longer feels loose when I am accelerating during cornering and exiting the corners. It is almost difficult to describe how different the car reacts now in the entire corner. I can really push the car through the corner and
snap out of the exit so much faster, almost like how my coilovers created stability from a suspension standpoint. While the front is hugging the road, you can accelerate to the limits of the suspension so much easier. It is simply exhilarating to drive the car like this. The spirited windy road experience is so much better now. Straight line acceleration is all about that feeling you are being pressed back in the seat. Now, I can get that feeling more dynamically through cornering and I absolutely love it. I am now looking for twisties to hit, so I can feel that snap as I accelerate out of the corners.
Conclusions
Bird's Auto was an enormous help through this entire process. To say they are valuable to our community is a gigantic understatement. VAC Motorsports was a pleasure to deal with from start to end. VAC did the machine work and installed the Quaife into a stock differential housing shipping me the final drive unit. This streamlined the install process for me making the swap a very easy and painless process. Their communication was excellent, their shipping superb, and the return process for the core is painless.
The Quaife LSD has improved my hard straight line acceleration, particularly in the shift from 1st to 2nd. The car now grabs hard for traction rather than simply letting go in the lower gears. The predictability of the rear end is night and day better. The Quaife operates completely silent from all the testing I have done. The Quaife absolutely shines in corner acceleration. You will have more confidence in your traction during and exiting corners with the power the N54 can produce. The spirited driving experience went from an uneasy feeling to excitement fwhen I encounter windy roads. I never thought I could enjoy the cornering experience as much as I do.
Finally, the Quaife LSD has a lifetime warranty with an unmatched reputation in the LSD world. I know the Quaife can handle the power I throw at it and that is exactly what I was looking for. In addition, Quaife keeps the scrolled output shaft on their unit just like BMW to protect from seizure. The tolerances on the Quaife are very tight ensuring a high performance experience for us.
As the N54 continues to push into higher and higher horsepower territories, traction will become a bigger and bigger problem. The Quaife LSD is absolutely necessary if you want to enjoy that power and not become the highway queen many high horsepower cars inevitably become.
For pricing and more info, you can check out VAC here.
http://store.nexternal.com/vacmotors/vac---335i--135i--performance-built-rear-differentials-p2324.aspx