944 Rear Bearings

 

A part of the 85.5 re-design of the 944 included alloy rear trailing arms (aka guiding arms). With these alloy pieces came new rear bearings. Each of these bearings is actually a double ball bearing design that must be pressed into the trailing arm. Porsche used this same bearing in a number of their other cars too. 

Note: this page is really oriented to the 944; however, this same bearing is used on a number of other cars and sometimes in the front.

Extracting and inserting the the bearings can be a real headache.  If you talk to those Porsche owners who have tried this task, you'll find they have tried torches, sledge hammers and even freezing the bearings in an attempt to lessen the nightmare, If this task is in your future, consider this tool before you break out the hammers.

Rear Bearing Removal

This write-up was done using a 85 Porsche 944, other models are similar.

The first thing I needed to do was remove the axle gland nut. This puppy is torqued to 300 inch-pounds so some serious persuasion is needed to break it loose. This big torque wrench can handle the job easily. To get to the nut, a small hex wrench can be inserted into the center cap and be used to pull the cap. Not all Porsche wheels have the small holes in the center cap though.  

With the cap out of the way I can simply set the parking brake and with the big torque wrench, remove the gland nut. If you're going to do both rear bearings (right side and left side) then go ahead and loosen the other side's gland nut now. 

CAUTION: Do NOT utilize the transaxle to assist with holding the wheel from turning. If the transmission is in gear, a good deal of force can be placed on the tranny components and they are really not designed for this kind of stress.

 

Next, get the rear of the car up on jack stands and remove the rear wheel. Remove the brake caliper and hang it with a piece of bailing wire (you need not open the brake lines). Release the parking brake and remove the Phillips screws that holds the rotor to the hub and set the rotor aside.

Next up is the hub. This is another difficult job made easy with the right tool  - a hefty slide hammer.  With the hub clear, the snap ring is exposed and easy to access. It is a large snap-ring but shouldn't be a problem with a little patience and maybe a small screwdriver to help in getting it clear of the bore. 

Moving now to the inside of the trailing arm, I need to get the axle and half shaft out of the way. First I remove the half-shaft.  Notice the tool I'm using here. These cheesehead or triplesquare bits can be found if you look around. Try to get ones that are long like the one in this photo. The length helps you to work out away from the boot and that means it is easier to hold the bit square in the head of the bolt. THAT is critical to not-stripping the heads of these special bolts.

CAUTION: The CV joints are designed for positions only a few degrees off center. Be careful not to let one end of  the axle half shaft hang - doing this can break the CV's cage.  

The stub is now clear to be pushed through from the wheel side. A small hammer and a block of wood work well to push it the out. This will probably break the seal on the bearing.

 

Finally, we're ready to pull the bearing. Start by assembling the tool on the trailing arm. The 2 photos above show the orientation. On the inner side of the trailing arm, be sure to use the the smaller of the two disks - the large one will work only for inserting a bearing. Position the tool so the cylinder rests along the edge of the trailing arm - the cylinder lip must be clear of the inner diameter. OK, we're ready to bring up the pressure. Any number of tools will work here.  A ratchet on the outer side of the tool and a breaker bar (with a deep well socket) on the inner side is my preference. Expect break-away torque to be in the neighborhood of 90 lbs. As you tighten up the tool, the bearing will pull straight out.  

Position the tool just as you see it in the pics above. The small gap, in the cylinder, is helpful for seeing into the situation.

 

In the photo above you see the removed bearing. Notice how one of the inner races has separated and pulled out the bearing seal. This happens routinely when removing these bearings and usually means the bearing cannot be re-used.  The race separates from the rest of the bearing because the race is stuck to the hub, (also shown above). 

Side note: if you're in a real bind for parts the bearing can be re-assembled by first pulling the ball bearing & cage, insert the race into the cage and then insert the pair back into the outer race. Re-shape the brass/plastic seal and it can be pressed back in. If needed this can all be done with the outer race still captured in the trailing arm.

That race will need to be removed from the hub and there are few different ways to do that. 1) You can take the hub to a machinist and pay him to remove it . 2) You can cut the race with a Dremal tool or small grinder - difficult. 3) You can use a bearing separator.  I chose number 3.

I brought in a bearing separator and snugged it up under the race. From there it is a simple job to mount the threaded rod and extract the race.  The only problem here is that the hub is hollow and the threaded rod needs some sort of surface on the hub to press against. And that surface has to be small enough to go through the bearing race. Luckily, the axle nut washer is exactly the right fit. With the help of a piece of bar stock, this becomes an easy job.

Rear Bearing Installation

Note: although not necessary, insertion of the bearing will be easier if you place the new bearing in a freezer for a few hours prior to installation. Of course, this trick only works for insertion and insertion will still need a good deal of pressure.

Installation is actually easier than removal. First, wipe out the trailing arm bore and coat the cylinder with a lubricant like WD-40. Place the new bearing in the cylinder - it won't go in far without some real force but it will go far enough to support itself. It's critical that the bearing be placed square in the bore. What works best for me is to gently tap the edge of the bearing (with a soft-face hammer) just enough to get it to hold there without falling out. Then I measure at 3 different points around the bearing. These quick depth measurements tell me if/when the bearing is squarely situated. Make small tapping adjustments until it measures square. Once I'm satisfied with that, I bring in the tool again, only this time the cylinder is positioned on the back (inner) side of the trailing arm. Also be sure to use the insertion disk - it's the larger of the two machined disks. 

Situate the tool so that the insertion disk is centered on the bearing. Like before, hold the tool in position and then snug up the nut to hold it there. OK, hold the threaded rod with some sort of tool (wrench, ratchet, etc) and tighten-up the nut. Expect a torque of about 80 inch-pounds to move the bearing. If it takes much more than that,  STOP, double check your squareness and continue pressing the bearing into the bore.  If it becomes difficult to tighten the threaded rod, STOP, and recheck the squareness of the bearing in the bore. This is most likely to occur during the first 1/2 inch or so of insertion. As before, remove the tool and use a small hammer to re-square the bearing in the bore.  

You will know when you get the bearing fully inserted because it will suddenly get difficult to tighten. Remove the tool and verify this by checking the snap-ring groove. It should be exposed. Re-insert the snap-ring to secure the bearing. 

You're now ready to re-assemble the axle shaft/ half shaft and re-install the hub, rotor & caliper.  Using the axle nut to pull the two pieces together is much better than using a hammer. 

With the axle back together, you can put on the wheel and lower the car to the ground. Once there you can tighten the axle nut and re-install the wheel center cap.

Miscellaneous Wheel Bearing Info

Here is a good example of bad wheel bearing. Its a bit hard to tell in this photo but 2 of the balls are have chips broken from them.

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