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Flex Disc & Center Bearing

Author : Al Gray, Pictures from Steve Venn Posted on : 03/12/2004
Model : BMW, 5 - Series (E34) 1989-96 Category : Driveterrain - Transmission
Source : http://www.bmwe34.net
 

Procedure courtesy of Al Gray, Pictures from Steve Venn
If your driveshaft is staring to make some noises when you take off or at low speed, it is time to get a close look at it. Sometimes changing the flex disc and/or the center bearing will do the trick. Sometimes you will have to change the whole driveshaft and bite the bullet.

Procedure

My weekend project was the replacement of the flex disc and the center bearing support on the driveshaft of my 1992 525i. I want to personally thank Winfred Dixon for his excellent comments, advice and support for this project.
My car was making the usual progressively worse noises associated with driveshaft related problems. I just didn't know how bad the flex disk was until I looked at my new part and compared it to what was left; basically just the bolts in the steel sleeves surrounded by the remnants of the rubber and strings of thin cord that was imbedded in the rubber. I am amazed the car even moved!

Before attempting this project I purchased a 3 1/2 ton floor jack and 4 substantial jack stands. The Bentley manual mentions at 1/2 page intervals that the car should be on jack stands at the jacking points before getting under the car.
The reason I wanted to attempt this job was primarily to save several hundred dollars but also to prove to myself that I could do it. BMWs are made well but they can also be a tough to work on.
COSTS:
The BMW stealer wanted $110 for the flex disk and $88 for the center support bearing. I paid $39.95 and $32.00 respectively for the parts from BMA. I also needed to order 6 new self-locking nuts for the driveshaft and 6 self-locking nuts for the flex disk; I ordered them from the stealer for a cost of $8.00. The floor jack I picked up for $60.00 and the jack stands cost me $62.00. I also picked up a 19mm combination box wrench and a 1/2 inch drive 19mm socket for a total of $14.00. Lastly, I purchased a 1/2 drive 1 1/4 extended socket for
$7.00. My total costs including the tools I purchased was $222.95

THE REPAIR:
1. The first thing was to raise the car up with the floor jack. I positioned it under the rear differential and raised it up approximately 20 inches. The jack stands were then carefully positioned at the jacking points on the body just in front of the rear wheels. For the front of the car I positioned the floor jack on the cross member just behind the oil pan making sure I did not touch the oil pan and raised the car approx. 20 inches and then positioned the jack stands under the jacking points on the car just behind the front wheels.

2. The next thing to do was to lower the exhaust as much as possible. The Bentley manual says to remove the exhaust, however, that is a lot of work and not necessary. Before lowering the exhaust I positioned the floor jack under and just touching the rear muffler. Working from the rear muffler there are two muffler clamps that require a 13mm socket. Moving forward and just before the center resonator on the exhaust there were two more muffler brackets requiring a 13mm socket for removal. Finally, there is a bracket at the front secured to the rear of the transmission that required a 13mm socket to loosen the two bolts. Once everything was loose, I slowly lowered the exhaust with the floor jack as much as possible but still supporting it.

2a. Next was the removal of the heat shield. There were approximately 6 bolts that required either a 13mm socket or 13mm combination box wrench. Once the bolts are out you need to finagle the heat shield out and put it on the floor
and out of the way.
3. The next item was the removal of the bolts from the flex disk. Keeping the car in park (I have an automatic trans)I found that BMW really puts these bolts in tight. I couldn't even budge them with my breaker bar. Using my 19mm wrench on the nut and 19mm socket on the bolt, I finally broke the nut loose by sliding and 18 inch piece of pipe over my wrench for some leverage. To access each bolt I had to turn the driveshaft by hand after taking the car out of park and repositioning my wrench.

4. The next job was to remove the nuts from the rear of the driveshaft. Before you remove the driveshaft paint on marks where it pulls apart for proper alignment when being reinstalled. They required a 13mm wrench and the length of pipe to break them loose

5. The center support bearing was next. It was held in place by two bolts that require a 13mm socket.
6. Once the driveshaft was loose, I lowered the exhaust a little more and worked the driveshaft out and onto the floor.

7. Although my center bearing was not damaged, at the suggestion of Winfred Dixon I replaced it anyway, just in case. The center bearing is pressed on between the front and rear drive shaft. In order to access the center bearing, the front and rear drive shaft have to be taken apart. There is a 19mm bolt that holds them together. Before taking the driveshaft apart I pained marks on the front and rear driveshafts near the center bearing for proper alignment later. I had to put the rear of the driveshaft in my bench vise to work on this. The bolt holding the two together is really in there! Using my 19mm box wrench with the 18 inch pipe slid over the wrench for leverage, I finally broke it loose. The bolt was a tough out requiring small turns and effort to the last thread. I needed to take a few turns and tap the rear of the driveshaft to loosen it from the front spline until it finally came off the spline. The center bearing is pressed on over the spline. I used a hammer and an old dull chisel to carefully loosen the center bearing and then slide it off.
8. Replacement of the center bearing was easy; you just have to make sure that it is positioned correctly. I used my 1/2 drive 1 1/4 inch extended socket to firmly tap the center bearing into place.
9. The driveshaft was now ready to be bolted together. I put a little CRC on the inside threads of the spline to make putting the bolt in a little easier. Positioning the front and rear driveshafts according to the painted marks, I bolted them together in the same fashion as I took the bolt out. Be sure that the bolt is tight.
10. Now the driveshaft was ready to be installed. I bolted the rear of the driveshaft up first using the new 13mm self-locking nuts. You can access 3 of the bolts at a time. I had to position a screwdriver through the area where the front and rear shafts meet to keep the drive shaft from turning while I was tightening the bolts. Also, I found it easier to mount the center bearing only putting the bolts in finger tight during the process.
11. Next was to intstall the flex disk. In order to do this I had to unbolt the center support bearing so that I could slide the front of the driveshaft into the center bearing and onto the transmission spline. Its important to note that there is a certain way that the flex disk is installed. There are 3 flanges on the front drive shaft that will positioned at the rear of the flex disk and 3 flanges that are on the transmission spline that will be positioned at the front of the flex disk. The flex disk has arrows imbedded in the rubber that point to either the front transmission spline or the rear drive shaft spline. Those arrows need to aligned correctly. Once done, intstall the bolts and nuts and tighten appropriately with 19mm wrench and socket wrench.
Finally reinstall heat shield, exhaust brackets and lower car.

Thanks to Al Gray and Steve
 

Pictures

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Click on the thumbnails to see larger images.

 

References

  • http://www.bmwe34.net
    •  


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