Intermediate Shaft Bearing (IMSB)

The intermediate shaft bearing (IMSB) is used in all Porsche 996, 997.1, 986, and 987.1 vehicles between 1997-2008 worldwide. The IMSB uses a ball bearing design that was inadequate for the application it was intended to serve. The official and unofficial story is that the ball bearing was a permanently sealed design that was prone to failure due to inadequate lubrication and friction. Specifically, the seals located on each side of the bearing would begin to deteriorate and release lubricant out of the bearing and cause friction and heat. This oil starvation would then cause the bearings to have hot spots due to radial and axial forces placed on the bearings. Additionally, the ball bearings had a contact surface with the outer race (track) which was less than 2mm’s in width. Unlike an automobile tire with a wide tread pattern to assure traction think of a Tour de France type road bicycle with skinny tires. The surface that touches the road is even skinnier than the width of the tire. The intention is to reduce as much friction as possible between the two surfaces allowing for less resistance and higher speeds. The less than 2mm contact surface would seem optimal for the size used in the IMS ball bearings, but because of the pressures placed on the bearings within the harsh engine environment and the eventual lack of lubrication put the IMS at risk for bearing failure. Once the bearing has failed and turned into metal particles floating in the engine, the results could be catastrophic. Check out a video we found below that provides a nice explanation and visual evidence of how the bearings work and what they look like after damage has begun.

Porsche honored warrantied cars by replacing the engine. For those who’s cars that fell outside the warranty period the owners were hit with engine replacement and rebuild costs up to $20,000 or more. It was a devastating blow to most owners. A class action law suit was settled and that offset some of the costs for a segment of the 996 cars that were within a certain mileage and age. However, the damage had been done to Porsche’s reputation as a respected builder of bullet-proof engines and to the 996 as the next generation of water-cooled “modern” 911s. 

Porsche made three attempts at correcting the IMSB problem by modifying the design. They went from dual row bearings to single row bearings to larger bearings. All developed to eliminate bearing failure. The IMSB was failing at a rate between under 1% to 10% depending on the year and source. However, each subsequent modification to the design was not effective as IMSB failures continued through to the 2008 model year 911s, Caymans and Boxsters. 

It was a disaster for Porsche as the newer cars continued to fail even after they released subsequent design upgrades. Since Porsche seemed to be going in one direction and reality in another, pundits and desperate owners tried to combat the problem using logic. A stream of accusations, measures and countermeasures to reduce the probability of bearing failures materialized. From the internet: driving styles were blamed, owners were told to keep the RPMs above 2500, while at the same time keeping the RPMs low until the engine reached normal operating temperatures. Maintenance schedules were targeted by recommending oil change frequencies of 3 months or 3,000 miles or less in some cases! Tearing open the filters was mandatory in an effort to find shiny pieces of bearing metal. Using oil with the proper viscosity was also recommended along with avoiding temperatures that were either too cold or too hot. Low-mileage garage queens were implicated for being at higher risk for bearing failure due to stagnant oil, water accumulation, and deteriorating rubber seals. Some were advised to avoid buying later cars as those had weaker bearings. And let’s not forget the recommendation to send in oil samples for analysis of metal after every oil change. Quite a list to remember and still maintain peace of mind about one’s engine reliability. 

Further preventive measures were recommended through the purchase of IMSB metal monitors, magnetic oil plugs along with direct oil pressure feeds to improve lubrication (to a sealed bearing?!).  However, none of these provided a repeatable or reliable solution to prevent bearing failure. The IMSB continued to fail with and without these pundit precautions, recommendations, mysticism, and paranoia. These were sincere but ultimately unreliable measures. 

With Porsche still trying to design a reliable intermediate shaft bearing, the aftermarket began developing their own solution to the bearing. At first the upgrades weren’t perfect as failures also occurred, albeit at a smaller rate. Replacing a part with the same OEM part does not resolve the problem, it prolongs it. Further research and product development improved the aftermarket upgrades and reduced the risk for IMSB failure in the M96 engine. Reliability improved dramatically and with thousands of products sold has shifted the IMSB from being an unpredictable, expensive, and potentially catastrophic problem to merely a maintenance and now from two vendors a permanent upgrade for the IMSB. That’s a dramatic shift in the reliability of this car and in our opinion a resolution to the 996s major flaw. Wow! We can’t wait to see the long-term reviews on these miracle product.      

Implications of a fixed IMSB in the 996

Now that the aftermarket has created products that fixed the intermediate shaft bearing problem, what will it mean for the 996? Without a doubt the intermediate shaft bearing problem was a disaster for the 996 and with the help of the internet and continued IMSB fails, the car has gone through a very dark period. A period that continues today as seen in the car’s market values, ownership by individuals who may not keep up with proper maintenance, an active market for blown engine “rollers,” and the continued misconception about the 996 engines as ticking time bombs. In reality, the shift in perception may be slow as there will continue to be 996 and 997 owners who are oblivious to the IMSB problem, owners who don’t want to invest in the upgrade, or cannot afford it or don’t believe there’s a problem. In fact, those not keeping up with the forums, magazines or this website will probably not know about the problem, the cause, and the cure.

Regardless, there’s light at the end of this tunnel and it’s actually shining brightly. The light comes in the form of high quality high reliability intermediate shaft bearings upgrades from the aftermarket. The current IMSB upgrade comes in a few varieties. All aftermarket upgrades have addressed the lack of the oil problem by using some form of direct oil feed system to the bearing. Some have continued using the OEM ball bearing design. One maker calls their product a maintenance items with a life span equivalent to other engine maintenance items. The IMSB is checked, for instance when the clutch needs replacing and depending on wear it can remain or be changed. One vendor uses dual row bearings while the others use ceramic bearings and one uses no bearings similar to previous 911 engine designs.

The other option available is the IMSB permanent fix which its makers says it’s intended to last the life of the motor and beyond. This IMSB is not a maintenance item and is considered a fix it and forget it upgrade. They use a different approach than the OEM and other bearing designs by successfully using cylindrical bearings and non-bearing designs. They also claim a 0 fail rate.

A working IMSB with zero chance of failure may seem to have shown up a little late in the 996 story, and the chances of the manufacturer revisiting the design issue after the class-action lawsuit are pretty much nil at this point, but it’s definitely not too late. In fact, these aftermarket IMSB upgrades are changing the story of the 996. 

We recommend reading more about the IMSB options available for your 996. Below is an excellent PCA video released in November 2017 that explains the history of the design changes to the intermediate shaft bearing. Jake Raby takes us through the different IMS years and designs. It’s very educational for those interested in better understanding.

Expensive Upgrade Relative to What?

In comparison to the IMSB part, other mechanical niggles associated with the 996 like the rear main seal and air oil separator don’t seem so ominous. Let’s take a look at the expected costs for the 996 and compare them to other generation 911s with well-known and common mechanical problems. What we found was that the 996 has no more design or engineering problems than earlier generations of 911 and much less than the 964 series.

Say you’re about to purchase a well-maintained with all service records 2000 996 showing 39,000 miles from an individual who knows nothing about the IMSB. The first thing you should do is take the car to your local Porsche mechanic for a pre-purchase inspection and among other things have the IMSB, air oil separator and the rear main seal inspected.

Assuming all three items need correcting the estimated costs would be around $3500-4500 installed at a shop. If you’re a do-it-your selfer the costs drop to under $2K. Of course if this were any Toyota that level of investment would be considered unacceptable.

Compare that expense to the purchase of a 1990 964 C2 with 39,000 miles from an owner who knows nothing about the problems of that generation 911. The first things to be checked are that generation’s common problems; head gaskets, timing cover gaskets and flywheel. Assuming all three items need correcting at the same time the estimated costs would be around $7700. If the 964 were a C4 then a few more $$$ need to be added for the lateral load and acceleration sensors.

Let’s make one more comparison, and this time it’s a 1977 911 with 39,000 miles purchased from an individual who knows nothing about the problems of this generation Porsche and has no upgraded corrections. The first thing that needs to be checked are the valve guides, head studs and rear crank seal. Assuming all three items are corrected at the same time the estimated costs would be around, gulp, $14,000. Imagine what the internet chatter would have looked like had forums been around then? Suddenly, the IMSB expenses related to the 996 aren’t looking so bad.
 
These comparisons are exclusive to the common problems found in these model. If we were to also consider maintenance or running costs the 996 would be less expensive than all previous models. Let’s remember that the ownership cycle of the 996 is just beginning. This means that unlike the earlier 911s that have probably had their problems updated or corrected, the 996 owner will be facing these things for the first time. 996 owners who have replaced their IMSBs with permanent fixes and sell their cars eliminate IMSB failure for the next owner.  Finally, thanks to higher production numbers and specifically the availability of parts, the cost of suspension, body or electrical components are much less expensive than these older 911s.;

We believe the above comparisons, maintenance, replacement parts and daily driveability make a compelling argument for 996 ownership.

Important Caveat

All criticism considered, we believe the biggest factor preventing the 996 from currently reaching parity with its older and younger siblings has solely been due to the IMSB flaw. Regrettably, the three-times revised OEM bearing did not provide owners and potential buyers with the much needed reliability and assurance that the bearing would last the life of the engine. Those are not good odds in our opinion. As a result, we believe investing in an IMSB upgrade should be mandatory and will yield a greater ownership experience, peace of mind, and driving satisfaction.

Once this is taken care of, not only will the upgrade virtually eliminate the possibility of an IMSB failure, but the effects of this will be far-reaching at restoring the 996s to its rightful place within the 911 world, one car at a time.  If it worked in previous 911s with upgrades to faulty chain tensioners, pop-off valves, valve guides, and head gasket seals, etc., then the IMSB upgrade should follow the same route.  

In this section, we offer a visual representation of the intermediate shaft and bearing in the M96 engine. We hope this provides you with a better understanding of the bearing in action and how you can choose the most effective measure of protection for your car. Like other defects in the history of the 911, the best upgrades are the permanent solutions that resolve the design deficiency and have longevity equivalent to the life of the engine where possible. We anticipate the current IMSB upgrades actually provide a reliable permanent resolution to the problem rather than serve as a temporary or band-aid on the problem.  

To the right are a series of pictures showing an open M96 engine case filled with oil. You can see the intermediate shaft with gears on each end partially immersed. The right side of the shaft with the four sprockets is closest to the rear of the 996. The left side of the shaft with the two sprockets is closest to the oil pump and front of the car. The oil volume was checked and the dipstick indicates that the case is full. More important, the intermediate shaft sits about 2/3rds immersed in the oil, the way it would look with the engine turned off and the car on a level surface. The shaft is not filled with oil and since the OEM bearing is sealed, it was not intended to be functionally immersed in oil for lubrication. However, there is oil to the right (rear of car side) of the bearing. What oil does make its way into the OEM bearing with a deteriorated seal comes from this area.

In the fourth and fifth pictures, you will see the intermediate shaft spinning at about 800 RPMs. Not seen is all the oil splashing! Splashing increases as RPMs increase and splashing oil lubricates. The bearing continues to be partially immersed, which would serve a purpose had it not been sealed on both sides. Also, you will note that the piston sleeves are not immersed in oil. They are lubricated with jets and splashing. Fortunately, oil does not need to be thicker than a thin film to properly lubricate.

There are currently three methods to resolving the IMSB problem. Actually four if you include replacing the existing IMSB with another sealed OEM bearing. In mid-2017, Porsche began producing an upgraded version of the IMSB. Part number 996.105.085.80. The latest design comes with ceramic bearings, sealed and a larger stud.  The first non-OEM upgrade method is an aftermarket upgraded open-design (without rubber seals) bearing. These come in a couple of versions which also include a ceramic bearing set that can tolerate more of the axial and radial stressors placed upon it. However, there have been reports of failures using these OEM-type bearings. If failures continue even after three OEM updates and with the OEM-design aftermarket upgrades, then we have to question the choice of using this type of bearing design in these applications.  

The second method of IMSB lubrication offered by the aftermarket is to pipe in oil from a pressurized feed location that sprays the bearing. However, if the OEM seals are not removed then no amount of oil will penetrate the bearing. You can see in the picture to the right the space between the bearing and the case is minimal and so any oil that would make its way into a bearing would require some kind of assistance. The vendors recommend upgrading the OEM bearing at the same time to assure the bearings have not worn or have some pre-failure weaknesses. We agree! A pressurized feed system is rather effective at lubricating the bearing and reducing the risk of oil starvation. This method seems logical, but there continue to be reports of failures using the OEM bearing along with  aftermarket OEM-type bearing designs using this oil feed method.

The third method offered uses a different approach to the OEM-type design. It comes in two forms from two vendors. Unlike the failure prone ball bearing design, this upgrade uses cylindrical bearings which spreads the contact points to a much larger surface area and they increases the number of bearings. Similar to the above, this approach also pipes in pressurized oil but directly from the oil pump through the intermediate shaft.

The other vendor provides a design that removes the bearings to eliminate IMSB failure. Similar to the previous air-cooled engine’s design. This approach changes the oil filter type and pipes in oil to feed the bearing. Like the other design above both are patented designs and are considered permanent fixes.

One dilemma about choosing the best IMSB upgrade is that these products are still relatively new on the market and because of the type of use 996s get, high mileage cars with upgraded IMSBs are still rare.  We recommend contacting one of these dealers to help you decide what’s best for your car. What’s important to remember is that these upgrades are investments in your car and peace of mind.

IMSB Upgrade Videos

In an effort to provide 996 owners with information about the IMSB issue, we include videos of the three main upgrades by European Parts Solution / Vertex; Pedro’s Garage; and LN Engineering. You will see that they each have a different perspective to addressing the IMSB problem and we applaud their heroic efforts.

IMSB Upgrades: Types

In this section we offer a visual representation of the intermediate shaft and bearing in the M96 engine. We hope this provides you with a better understanding of the bearing in action and how you can choose the most effective measure of protection for your car. Like other defects in the history of the 911, the best upgrades are the permanent solutions that resolve the design deficiency and have a longevity equivalent to the life of the engine where possible. We anticipate the current IMSB upgrades actually provide a reliable permanent resolution to the problem rather than serve as a temporary or band-aid on the problem.

The series of pictures are showing an open M96 engine case filled with oil. You can see the intermediate shaft with gears on each end partially immersed. The right side of the shaft with the four sprockets is closest to the rear of the 996. The left side of the shaft with the two sprockets is closest to the oil pump and front of the car. The oil volume was checked and the dipstick indicates that the case is full. More important, the intermediate shaft sits about 2/3rds immersed in the oil, the way it would look with the engine turned off and the car on a level surface. The shaft is not filled with oil and since the OEM bearing is sealed, it was not intend to be functionally immersed in oil for lubrication. However, there is oil to the right (rear of car side) of the bearing. What oil does make its way into the OEM bearing with a deteriorated seal comes from this area.

In the fourth and fifth pictures you will see the intermediate shaft spinning at about 800 RPMs. Not seen is all the oil splashing! Splashing increases as RPMs increase and splashing oil lubricates. The bearing continues to be partially immersed, which would serve a purpose had it not been sealed on both sides. Also you will note that the piston sleeves are not immersed in oil. They are lubricated with jets and splashing. Fortunately, oil does not need to be thicker than a thin film to properly lubricate.

There are currently three methods to resolving the IMSB problem. Actually four if you include replacing the existing IMSB with an another sealed OEM bearing. In mid-2017, Porsche began producing an upgraded version of the IMSB. Part number 996.105.085.80. The latest design comes with ceramic bearings, sealed and a larger stud. The first non-OEM upgrade method is an aftermarket upgraded open-design (without rubber seals) bearing. These come in a couple of versions which also include a ceramic bearing set that can tolerate more of the axial and radial stressors placed upon it. However, there have been reports of failures using these OEM-type bearings. If failures continue even after three OEM updates and with the OEM-design aftermarket upgrades, then we have to question the choice of using this type of bearing design in this applications.

The second method of IMSB lubrication offered by the aftermarket is to pipe in oil from a pressurized feed location that sprays the bearing. However, if the OEM seals are not removed then no amount of oil will penetrate the bearing. You can see in the picture to the right the space between the bearing and the case is minimal and so any oil that would make its way into a bearing would require some kind of assistance. The vendors recommend upgrading the OEM bearing at the same time to assure the bearings have not worn or have some pre-failure weaknesses. We agree! A pressurized feed system is rather effective at lubricating the bearing and reducing the risk of oil starvation. This method seems logical, but there continue to be reports of failures using the OEM bearing along with aftermarket OEM-type bearing designs using this oil feed method.

The third method offered uses a different approach to the OEM-type design. It comes in two forms from two vendors. Unlike the failure prone ball bearing design, this upgrade uses cylindrical bearings which spreads the contact points to a much larger surface area and they increases the number of bearings. Similar to the above, this approach also pipes in pressurized oil but directly from the oil pump through the intermediate shaft.

The other vendor provides a design that removes the bearings to eliminate IMSB failure. Similar to the previous air-cooled engine’s design. This approach changes the oil filter type and pipes in oil to feed the bearing. Like the other design above both are patented designs and are considered permanent fixes.

One dilemma about choosing the best IMSB upgrade is that these products are still relatively new on the market and because of the type of use 996s get, high mileage cars with upgraded IMSBs are still rare. We recommend contacting one of these dealers to help you decide what’s best for your car. What’s important to remember is that these upgrades are investments in your car and peace of mind.