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Limited Slip Differential (LSD) Installation
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Pelican Technical Article:

Limited Slip Differential (LSD) Installation


8 hrs






Torx set, slide hammer, gear puller

Applicable Models:

Porsche 986 Boxster (1997-04)
Porsche 986 Boxster S (2000-04)
Porsche 987 Boxster (2005-12)
Porsche 987 Boxster S (2005-12)
Porsche 987 Cayman (2007-12)
Porsche 987 Cayman S (2006-12)

Parts Required:

LSD, differential carrier bearings & seals

Hot Tip:

It's best to perform this installation with the transmission out of the car, during a clutch job

Performance Gain:

Better traction and performance

Complementary Modification:

Clutch replacement
101 Performance Projects for Your Porsche Boxster

This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.

While there certainly isn't enough space in this book to cover a complete transmission rebuild, there are a few tasks that can be performed to upgrade and restore the differential portion of the transmission.

Transmission Internals: If your transmission is leaking from the driveshaft area, your differential seals are probably shot. The photo array in this project shows you how to pull your axles and replace these seals. At the same time, you can replace your differential carrier bearings. These are the bearings that support the output flanges in the transmission. Sometimes when you have a grinding noise or high-pitched whine that you cannot locate, it can be your differential carrier bearings. Often when you've replaced your wheel bearings (Pelican Technical Article: Wheel Bearing Replacement) and your CV joints (Pelican Technical Article: Replacing CV Joints and Boots / Axle Replacement) and you still have a whining noise, it's the carrier bearings that are worn.

The best time to perform this work on your transmission is when you have it out of the car for a clutch job or engine work. You can perform these tasks with the transmission still installed in the car, but it makes life much more difficult if you do so.

When you install a new differential into your transmission, you need to make sure that you have the proper shims for the differential carrier bearings. In 1999, there was a change from two 46mm inner diameter differential bearings to one 46mm and one 50mm. When you install your differential, you will need to provide a measurement to the shop that provided the differential so that they can provide you with the appropriate shim set.

Limited Slip Differentials - Gears in the differential allow the gears to rotate at different speeds, but supply torque (rotational force) to each axle equally. If one wheel is on ice, and another wheel is mounted firmly on pavement, the wheel on ice will spin at twice the speed of the ring gear, while the wheel on the ground will not spin at all. Each wheel gets the same amount of torque, and since the wheel on the ice requires very little torque to spin, the wheel on the ground also receives very little torque. Likewise, in performance driving, when turning around a corner, the weight shift due to cornering forces may increase or reduce the effective weight placed on each drive wheel. If for example during cornering the inside drive wheel comes completely off the ground (unlikely, but let's assume it for demonstration purposes), then the situation becomes very similar to the case where one wheel was on ice and the other was on the ground. The differential will supply less torque (power) to the outside wheel as the inside wheel begins to slip. This is the primary argument for using a limited slip differential. It's important to note that under normal, everyday street driving, you will almost never encounter this situation. Thus, the installation of an LSD is often overkill for street-only cars.

An LSD contains small plates inside called clutches, that limit and constrain the movement of the side gears. Springs or spring plates inside the LSD force the gears outwards against the clutch plates, which in turn forces them outwards against the differential housing. The friction between the plates causes the side gears and housing to rotate at the same speed. However, the springs and clutch plates are not strong enough to prevent normal differential rotation of the wheels on curves. When one wheel loses traction, however, the clutches will limit the "slip" and provide some additional torque to the non-spinning wheel. The amount of torque provided is determined by the clutch plates and the springs, and is called the torque bias.

Torque bias indicates the ratio of the torque that can be transmitted to the high torque (high grip or ground) axle, divided by the low torque (low grip or ice) axle. A standard open differential often has a built-in torque bias ratio of about 1 to 1.3. A limited slip differential can provide almost any torque-bias level depending upon the arrangement of the clutch discs and strength of the springs inside. Stronger springs means a higher torque bias.

A torque bias of about 1.4 (40%) is best suitable for mid-performance street cars that will inhabit the occasional autocross, or cars that will be driven on the track with stock engines and suspension. A more aggressive bias of 1.6 (60%) is best for modified street/track cars that have stiffer suspension and perhaps an upgraded or larger engine. Track only cars that are not going to see any street time often run LSDs with torque bias levels of 1.8 (80%).

Clutch-type LSDs provide excellent lock-up on both acceleration and deceleration, and the units can be customized by changing the sequence of the internal clutch plates and springs. Differential lock-up on deceleration allows for late braking and very aggressive driving into high-speed turns.

You also need to make sure that you fill your transmission with fluid that is compatible with your differential. Typically a manufacturer will have some recommendations for transmission gear oil that works well with their particular differential. If you use oil that is too slippery, you may reduce your torque bias and render the LSD less effective. If you use oil that is not slippery enough, you may increase the bias and encourage premature wear of the clutch discs inside of the LSD.

As stated previously, limited-slip differentials are not necessarily ideal for street driving. The clutch-pack limited-slip can have a nasty habit of locking up the rear differential at inopportune times, like when you are cornering a road in the rain or on slick surfaces like ice. The reason for this is that sometimes these surfaces don't provide enough friction to provide for the normal differential action that allows slip between the two wheels. Limited slip differentials also have other drawbacks. They tend to be noisier than open differentials, the clutch discs wear out because they are friction components, you need to use special transmission lubricants, tire wear is increased, and overall fuel economy is reduced. They also exhibit a slight time lag between when the clutch springs compress and when the torque is transferred. For these reasons, I primarily recommend that people avoid traditional limited slip differentials in street cars.

If you're looking for an alternative to an LSD for your street car, then I recommend looking at what is known as a Torque Biasing Differential (TSB). These are differentials that are similar to conventional open differentials, but can lock up if a torque imbalance occurs. Through a complex arrangement of gears, the TSB units provide some biasing of torque towards an unloaded axle but only if that particular axle remains planted firmly on the ground. TSB differentials are a good choice for street cars because they act mostly like an open differential, except when cornering begins to skew the traction between both wheels. TSB units, like the differentials manufactured by Quaife only provide lock-up on acceleration though, which makes these units better suited for slower-speed turns like you would find during an autocross. Using a high bias clutch-type LSD in an autocross would likely cause a significant amount of unwanted understeer.

Transmission Gear Ratios - Another thought to consider is your choice of transmission gears. A poorly matched transmission can make the most powerful engine seem sluggish. Nearly all of the Boxster and 996 engines have a somewhat high-RPM power band (like the early 911 'S'). Because of this, you will probably want a transmission with very close ratio gears. This will allow you to maintain your optimum power band, and maximize the power output to the wheels. The six-speed Boxster transmission is ideal for this purpose. It's not uncommon to find Porsche race cars specifically designed for long tracks and rolling starts that have a 'tall' first gear. This basically allows the racers to use 1st gear for actual track use, which effectively creates a true 5-speed transmission for racing. Such a car would be very difficult to drive on the street, because 'off-the-line' performance would be quite sluggish. However, on the track in the narrow power band is where the drivetrain would shine, delivering peak power in a power band closely matched to the transmission and the type of race track. For more information on choosing gear ratios, see chapter nine in the book "Gearing and Differentials in Race Car Engineering & Mechanics" by Paul Van Valkenburgh.

Another option may be the installation of the Boxster S six-speed transmission into a Boxster that normally had a five-speed. The proper gear ratios can make a world of difference - taller gears in the five-speed tend to make the car feel slower, even if the same engine is installed. If I compare the five-speed Boxster with the 3.4 engine, to my six-speed 996 with the same 3.4 engine, the Boxster seems slower, because the gear ratios are taller. If you wish to install the Boxster six speed transmission into your five-speed Boxster, the swap is pretty straightforward, but time consuming and expensive to acquire all the parts. You need the six-speed transmission, a six-speed clutch slave cylinder, the 3.2 clutch package and flywheel, the six-speed shifter and shift cables, a set of 3.2 axles, the updated transmission mounts and brackets, and a handful of other small odds and ends.

The first step is to remove the halfshafts from the transmission.
Figure 1

The first step is to remove the halfshafts from the transmission. Begin by removing the center bolt that fastens the halfshaft to the transmission. To pull out the halfshaft, I used a slide hammer, combined with an old CV joint, as shown. Place the end of the slide hammer shaft against the halfshaft flange and then fasten it down with two CV bolts. Tap the hammer along the shaft and the halfshaft should slide out of the transmission. Another method you can use involves placing two bolts into the halfshaft flange and then using them to wedge the halfshaft out of the transmission (inset photo). This is the method documented in the Porsche factory manuals.

Here's a photo of the halfshaft after it has been pulled out of the transmission.
Figure 2

Here's a photo of the halfshaft after it has been pulled out of the transmission. Although it's more difficult in the tight space, you can remove the halfshaft while the transmission is still in the car. For clarity in the photos, these tasks were performed on a transmission that was out of the car and on my bench.

After you have the halfshafts removed, you can replace the differential shaft seals.
Figure 3

After you have the halfshafts removed, you can replace the differential shaft seals. There is one on each side of the transmission, and these seal the driveshaft flanges to the transmission case. If they are old and leaking, then you will see transmission fluid leaking around your axles. Pull out the old seal, and then gently tap in the new one.

With the halfshafts removed, you can then pull off the differential cover.
Figure 4

With the halfshafts removed, you can then pull off the differential cover. Use a Torx socket tool to remove the screws on the outside of the cover (inset photo). Removing the cover will expose the differential inside the transmission. Be sure that you have emptied all of the transmission fluid out of the unit before you remove the cover: otherwise you will have a big mess on your hands. Be prepared for some residual fluid to leak out when you remove the cover. The six-speed transmission has a large o-ring on the differential cover that I recommend replacing when you reseal it.

With the cover removed, you should be able to simply pull out the differential.
Figure 5

With the cover removed, you should be able to simply pull out the differential. This is what an open differential looks like. It has planetary gears that distribute and provide equal torque to each wheel. This type of differential allows for both wheels to rotate and spin at different rates of speed, such as when the car is going around a corner or turn.

Here's the view inside the transmission case.
Figure 6

Here's the view inside the transmission case. The curved gear on the right (yellow arrow) is attached to the pinon shaft and mates with the ring gear that is attached to the differential. There is a magnet in the case that attracts debris and metallic parts that have worn in the transmission. Take a paper towel and thoroughly clean this magnet, removing any grit or grime attached to it.

If you are replacing the differential carrier bearings, then use a bearing puller to remove the old ones off of the transmission.
Figure 7

If you are replacing the differential carrier bearings, then use a bearing puller to remove the old ones off of the transmission. If they are difficult to pull off, then you might try lightly heating the bearing with a propane torch to loosen it up.

New bearings need to be pressed on in a similar manner.
Figure 8

New bearings need to be pressed on in a similar manner. If you heat them in an oven or on a hot plate beforehand, it can make their installation much easier (obviously don't pick them up with your bare hands as shown in this photo if they are hot). The open differential is shown here with new carrier bearings installed. Don't forget the spacer and any shims that you may have taken off when you disassembled the unit. If you are installing a new differential, then you will need to obtain new shims that are matched to your transmission.

Shown here is a limited slip differential from Guard Transmission.
Figure 9

Shown here is a limited slip differential from Guard Transmission. GT is one of the leading providers of LDS differentials to the Porsche market, having earned their stripes designing race transmission components for the cars that competed in the GT class of the American Le Mans series. In addition, GT is an OEM supplier to Porsche AG with components used in the factory race cars on a regular basis. The unit I chose here is a street / track version with 60/40 biasing, which is ideal for a Boxster with stiffer suspension, and higher power engines.

Here is the GT LSD installed onto the ring gear and fitted with new bearings.
Figure 10

Here is the GT LSD installed onto the ring gear and fitted with new bearings. As mentioned previously, be sure to confirm that you install the correctly sized shims with the new differential, as there have been some changes over the years (see text for details).

Here's a side shot of the GT LSD installed back into the transmission.
Figure 11

Here's a side shot of the GT LSD installed back into the transmission. The inset photo shows how the halfshafts sit inside the differential (shown without the differential cover installed).

When reinstalling your halfshafts, be sure to use a new circlip on the end as mentioned in the Porsche factory manuals.
Figure 12

When reinstalling your halfshafts, be sure to use a new circlip on the end as mentioned in the Porsche factory manuals.

Figure 13

The part number for all Boxsters (1997-08) is 012-409-413.

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Comments and Suggestions:
Hwashcraft Comments: I'm considering installing a Guard LSD into my Cayman R. OEM LSD is pretty much gone.. Including time to remove transmission, any estimate of how long the job takes? And as long as you are there, would you change the flywheel and clutch?
August 30, 2016
  Followup from the Pelican Staff: I would replace the clutch at the minimum while in there. I would imagine it will be 20 hours including removing the trans. - Nick at Pelican Parts  
Gilelvis Comments: Hi,i have 2000 boxster s tiptronic,and while i drove it yesterday my rear wheels looks and i had to tow it...
What can be the problem??
thanks gil
June 26, 2016
  Followup from the Pelican Staff: Can you explain the problem in more detail, I am not following you. - Nick at Pelican Parts  
mbgt Comments: I have a noise coming from the differential to be more exact from the drivers side I removed the half shaft and the deferential cover 2 questions 1. do you sell de differential bearings and 2. can half shaft damage bearing make a noticiable noise? porsche cayman 2008 5 speed
April 26, 2016
  Followup from the Pelican Staff: usually the damage to a bearing is cause by lubrication or heat. I am sure Pelican parts can get you a bearing. I’m not the best with part numbers.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
alex Comments: I have my 6 speed manual transmission out of my '00 986S and the left side output shaft seal is leaking. In the book, and on this online version, you show how to extract the left side output shaft but don't mention how to do the right side it doesn't seem to have the 'pads' for the tips of the screws to push against like the left side does.
Also, I don't see where you talk about putting the half shafts back in. Can I just tap them back in with a rubber hammer until the circlip snaps into place, or do they need to be pressed in?
April 15, 2016
  Followup from the Pelican Staff: Tap the flanges back in using a soft-faced hammer.

Use a chisel between the trans and the bolt when tightening to remove the axle flange. - Nick at Pelican Parts
Dave Comments: Hi
Am changing the bearings in my dif, but the Porsche dealer cannot ID those green plastic spacers on the output flanges. They're not on the parts catalog ! Where can I get them? Is there a part # ? Thanks!
November 24, 2015
  Followup from the Pelican Staff: You didn't mention what vehicle you have.
I’m not the best with part numbers.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
Patrick Comments: Forgot to mention the car has the tiptronic transmission. Also is it a good idea to replace both seals. It seams like most of the leak discussions are in relation to the right side. Any reason for this?
July 23, 2015
  Followup from the Pelican Staff: I would replace both seal, and check the vent like I suggested. - Nick at Pelican Parts  
Patrick Comments: I am a new owner of a 2001 Boxster S. I noticed a lot of oil seepage coming from the right side of the differential. After coming home from a drive I noticed the smell of gear oil in my garage. Is this smell caused from bad axle seals? From my experience gear oil has a unique smell unlike transmission fluid. Is it possible to have tranny fluid and gear oil leaking from this seal?
July 23, 2015
  Followup from the Pelican Staff: I would assume the axle seals have failed. Check the area of the seals for signs of a leak. If they are leaking, be sure the vent is not plugged. - Nick at Pelican Parts  
livvy1960 Comments: Ref my earlier post - Sorry I should clarify - I have already removed the Drive Shaft and the bearings are notchy / feel indented whilst the assembly is on the bench.
I have new needle roller bearings on order - Please can you advise assembly sequence / process for bearings to Drive Flange Shaft and then assembly to the differential
p.s. the differential is smooth in its operation
Kind Regards
May 28, 2015
  Followup from the Pelican Staff: OK, going off of the repair instructions from Porsche. Remove old bearing from differential housing with commercially available two arm pullers and special tool 40-105 (which looks like it sits in the output shaft splines of the differential housing, aka carrier, I believe just gives the two arm puller a place for the tool to push against while pulling the bearing.) To install, heat bearing to approximately 100 degrees C, then put in to position and drive in to place with special tool 40-21. I've included a pic of the tools page so you can get an idea what to get. - Casey at Pelican Parts
livvy1960 Comments: Please can you provide technical info for replacement of the Drive Flange Needle Roller Bearings mine feel notchy / almost indented including how they should feel by hand after fitment - Regards
May 27, 2015
  Followup from the Pelican Staff: I think that is normal. It is VERY hard to determine what you are feeling from the outside of the gearbox, you could be feeling the differential pinion contact pattern, or spider gears and misinterpreting it as a bearing issue. Porsche says to remove the bearings from the differential "with commercially available two arm pullers and special tool 40-105, but this operation involves using shims to set the pinion depth and carrier position. If you are serious I can ask to write up an adjustment work procedure. Again I think what you are feeling is normal. - Casey at Pelican Parts  
Endi Comments: Hi, how can I tell if my 2000 boxster s has a limited slip differential or not? thanks!
April 10, 2015
  Followup from the Pelican Staff: List and support the rear of the vehicle. Spin a rear wheel, if the opposite side spins in the same direction, it is an LSD. - Nick at Pelican Parts  
Chris White Comments: You might want to add a note that the GT LSD is only available with the earlier bearing size. You can swap in an early diff side cover if you want to use the GT LSD with a 99+ Transaxle.
May 28, 2014
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
JJ440 Comments: hi i have a similar quesiton, I have a few small drops of Diff oil which seem to be coming from the diff right hand side shaft seal, my question is can I replace my diff shaft seal on a tiptronic? thanks in advance Jim ps i have a 1999 model boxster
May 19, 2014
  Followup from the Pelican Staff: Yes, the seal can be replaced. - Nick at Pelican Parts  
Dame Comments: Hi Nick, I have a small leak of Transmission fluid coming from my right hand side drive differential shaft seal. I have a triptronic and I was wondering which differential shaft seal to buy from pelican parts, thanks again, Dame.
May 17, 2014
  Followup from the Pelican Staff: Sounds like the output shaft seal. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
Travis Comments: I didn't know my comment would below would show up on the website immediately. I thought it would be sent to your tech dept. No harm meant by it, I'm just passionate about gearboxes.
February 4, 2014
  Followup from the Pelican Staff: No problem. Thanks for the feedback. - Nick at Pelican Parts  
sandersd Comments: Perhaps you misunderstood my question or I wasn't clear: How is the half shaft pulled out if the circlip is still in place? Doesn't the circlip have to be removed before the shaft can be extracted? Isn't that the function of a circlip - to prevent the shaft from sliding out unless the circlip is first removed?
August 21, 2013
  Followup from the Pelican Staff: No, it does not have to removed. It is not that style of clip. On drive axles the circlip is made to be installed and removed in place as there is no internal access to it as there is on a RWD truck axle. - Nick at Pelican Parts  
sandersd Comments: You make no mention of when and how to remove the old circlip. In figure 2 it appears to have already been removed. How would that be possible?
August 20, 2013
  Followup from the Pelican Staff: It had yet to be removed. If you look closely at this photo: you can see the ends of the circlip on the right and left sides of the splined shaft. - Nick at Pelican Parts  
Tony1966 Comments: I have replace the CV joint couple of months ago and I did the automatic oil and filter change but after that like few weeks after the transmission started leaking at the differential shaft seals . I guess the new oil cause this ?
My question is Porsche recommend to use 2 special tools the hook VW 681 and the pressure piece 3382 this last one made me think a little more why it says that it needs to be evenly install , but in your direction you don't mention anything about it and made it very simple use of normal tools
December 11, 2012
  Followup from the Pelican Staff: new oil will not cause a seal to leak. If you disturbed the axle seals or drive flange, the seal may have been damaged, especially if it was already on the way out. Not everyone has access to special tools, we try to privde the method with or without these tools.- Nick at Pelican Parts  
Steve G Comments: I'm about to change both diff. carrier bearings as the job seems reasonably straightforward for the home mechanic. You make no mention as to the removal of the two outer bearing races. Are they just drifted out of the warmed up case and side cover or removed by some other method? I'm doing the job with the transmission still in the car 2001 Boxster S Thanks in advance for any help. Steve.
October 3, 2012
  Followup from the Pelican Staff: The races should be pressed out if at all possible to avoud damaged the cover. You could drive them out with a drift if you are super careful and work gently. - Nick at Pelican Parts  
agrimmitt Comments: This was very helpful in giving me a better understand between a Torque Bias and a Limited Slip box.
December 3, 2011
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. - Nick at Pelican Parts  

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