How did this happen

[Hagbard]

My center support bearing bracket has snapped on both sides resulting in a huge pain in my ass. Taking the exhaust off and taking the drive shaft apart is simple but it's still a pain.
IMG_0024.jpgIMG_0025.jpg

How did this even happen?

My hypothesis is that my engine mounts have turned into flan, causing the engine and transmission to torque backward on acceleration and that has rammed the drive shaft into the center support bearing bracket enough times to crack it and snap both sides of it.

Is that insane? What other cause could there be? I've got a new $30 bracket on order from Amazon that should be here Tuesday. Until then my boss is picking me up to commute to work.

Rebuilt engine is running great by the way. I am seeing some oil leaking from around the edges of the oil pan. I should've RTV'd all the way around it. Can I just tighten the bolts and make the leaking go away?

[jclausen]

Typically the center support bearing gets worn out because the u joints in the driveshaft are either frozen or barely moving, check those joints

[epmedia]

I can visualize some possible excess vibration there, if the csb was not 'pre-loaded'. Glad to hear the engine is doing well

[Thecatmilton]

Could have the bearing seized? My CSB failed once, but the rubber ring ripped instead.

[Hagbard]

The bearing appears to not be seized and moves freely. I agree that the rubber should have ripped before the bracket snapped but it also appears to be intact. I'll know more when I take everything apart and replace the CSB.

As far as pre-loading goes, when I installed this current CSB about a year ago I pushed it forward about 0.5-1.0" approximately what it recommended in the Hayne's manual. Do you guys have a different take on that procedure?

When it comes to the U-joints on the drive shaft, if those were seized, wouldn't that cause a shit ton of vibration? That joint failed on my E36 and it felt like the back end was falling off the car. My E21 has a fairly smooth ride, especially after I had my alignment redone recently, except for the usual slight shimmy around 55mph and I believe that can be traced to my steering coupling. There's some play in the joint where the steering wheel shaft attaches to the steering rack. But that's neither here nor there.

The crazy thing here is that the CSB bracket snapped off completely on both sides. That's the last thing I expected to find when it started making this noise.

[320iAman]

What was the drive shaft angles ?
Did you use an inclinometer to measure these angles ?
Did you have the drive checked for balance and u joints good ?

One side breaking could be old weak metal, two sides breaking you have some serious torque there, what you caught on not knowing these is the notion of that if the Centre Bearing has not been changed no need to measure the drive shaft angles and the side to side angles perpendicular to drive shaft angles, even if these are good--the extended inspection may have short circuited or found the issue before it happens. Since the power in your motor has stepped up old-small vibrations in the drive line that are acceptable to this lower HP are magnified when HP is stepped up, Do the extra work, your car will thank you in english and german.

Stepping up HP is a very detailed item, can the rear end handle it, is there enough fuel, air and spark and so forth.

Arm chair analyzing I'd say say either the Centre bearing had issues or the drive shaft was out of alignment and wobbled and snapped off both support bolts or as another arm chair analysis said u joint issue.

If you go to a shop to rebalance the drive shaft ask questions and find a professional not just any rebalancer--I went thru this ages ago and found several that were clueless, just getting a paycheck.



Randy

[epmedia]

I just realized that it's missing the Protection plate/heat shield (#16). I wonder if the csb rubber may have hardened a tad, causing some unusual stress on that aluminum (small vibrations). The Protection plate maybe could have added some additional strength to the aluminum as well

http://www.realoem.com/bmw/enUS/show...diagId=26_0001

[amarino]

I had this happen to my E30:
IMG_20131027_145439.jpg

[Hagbard]

I removed the heat shield so that I could get a good view of the CSB without removing the exhaust. It has been running with the heat shield. I'll have to remove the exhaust to replace the CSB but I'll do that tomorrow night. Anybody know what all I need to do? Aman's post makes it sound like rocket science. I've done this job twice before and all I did was remove the old CSB and press the new one on and then put everything back together again, making sure to push the CSB forward to "pre-load" it as much as I could within the recommended amount prescribed in the Hayne's.

I did have to jack the engine up to get the oil pan off and back on again when I rebuilt the engine. Could that have twerked the CSB and caused it to succumb to vibration?

Thanks

[amarino]

I did have to jack the engine up to get the oil pan off and back on again when I rebuilt the engine. Could that have twerked the CSB and caused it to succumb to vibration?

I hope not because I recently did the same to my E21 (remove and replace oil pan my jacking up the engine)

[okieflats]

... pushed it forward about 0.5-1.0" approximately what it recommended in the Hayne's manual. Do you guys have a different take?

I see the Haynes says :

0.08 inches = 2 mm


That is just a little. Not much. Sounds like you put a lot of stress on it.

[okieflats]

My Chilton's doesn't even mention preloading. It says for the 7-series (733i) the preload is 0.078 inches. For the 320i it just says installation is the reverse of removal and does't even mention preloading. I have a Haynes for the pre-facelift 1977-79 and the Chilton's for 1970-82 all models.

[320iAman]

I think you missed the point , its not rocket science to check drive angles it a little more work to make sure its within specifications. haynes is better than nothing, the bmw service manual has the drive angles and is the basic service manual for these cars.

Good Luck

Randy

[epmedia]

I see the Haynes says :

0.08 inches = 2 mm


That is just a little. Not much. Sounds like you put a lot of stress on it.

My haynes says .08" too.

[okieflats]

I think the OP must have misread that to say 0.80" and that could have overstressed it. Also I think I push mine too far forward as well as I seem to recall not looking for any spec and just pushing it a quarter inch or so, maybe more. So the correct 2mm is not much at all. Easier to think of it in millimeters. There is 25mm in and inch so 2 of them is not much. .08" is a little more that 1/16th inch. Much less than 1/8 inch.

[Hagbard]

Ya, I confirmed I pushed the CSB too far forward. I'm going forward with the assumption that this is what caused my CSB to fail. I will make sure to only pre-load by 2mm (0.08") this time around. Hopefully it runs for a while after this.

[Hagbard]

I cannot get new csb driven onto the drive shaft. Any tips or tricks? Things to check? Does it matter, functionally, which way the dust shield is positioned?

[Thecatmilton]

I cannot get new csb driven onto the drive shaft. Any tips or tricks? Things to check? Does it matter, functionally, which way the dust shield is positioned?

I gave up on the dust shield. The one on the bearing should be sufficient.

[pommeree]

Leave the shaft out in the cold overnight.
Put the CSB and dust shield in the toaster oven and get it toasty.
Should go on without too much issue.

[Hagbard]

I got a shop to put the CSB on my drive shaft for $10. It seems to spin freely, which is a better result than I've ever been able to achieve the past two times I've done this job, both on this car and on an E36.

So I reinstalled everything and it feels great. In fact, it felt better than ever. Then I drove it to Chattanooga from Atlanta this weekend. In low gear I'm getting some weird feels on occasion.

At one point I got kind of a judder when starting out in first gear. But it only happened once.

I have two questions: One, how do I know if my U-joint is failed/failing. Two, how does having a worn out "dog bone" bushing affect driving? Mine is completely toast. I have a new one and am going to replace this week. I'm just wondering how that can affect drive feel.

Thanks guys

[epmedia]

The toasted dog bone is probably the "judder" you feel and may also cause the rear u-joint to wear out faster than usual, wheel-hop, etc..

Did you feel the u-joints when the shaft was out? If a u-joint has any play in it, it's bad. There should be no binding or tight spots during full travel (this sometimes means the grease has dried/contaminated). If there is rust or metal dust on the grease seals, the u-joint is bad. Some grease leakage means the u-joint may fail soon, but not always the case if the u-joint is serviceable (grease fitting).

* the new dog bone should make a world of difference because it holds the rear subframe from twisting.

[Hagbard]

I am having trouble finding a good procedure for replacing the dog bone diff mount.

I think it's pretty simple. Is this accurate?

1. Put rear end body on jack stands. (At designated jacking points)
2. Put jack under differential.
3. Replace dog bone.

Is that correct? Or is there more to it?

Also, torque spec? I can't find it in the two manuals I have.

[Hagbard]

Got the new hanger on but not sure if it’s torqued correctly. The jester mounts are difficult to get up in there!

Had to bend the edges of the chassis bracket slightly.

Still have a judder in reverse gear. Forward gears feel stiffer/better.

[Hagbard]

I felt the drive shaft and it has a tad of play in it. It jiggles a bit just twisting it lightly by hand. Does this mean there's play in my differential?

Also, felt some play in the steering shaft where it meets the rack and pinion. Has anyone ever refurbed their steering rack? And if so, which components? Was it easy? Did entire rack have to come out or can it be done with it in the car?

[Thecatmilton]

I felt the drive shaft and it has a tad of play in it. It jiggles a bit just twisting it lightly by hand. Does this mean there's play in my differential?

Also, felt some play in the steering shaft where it meets the rack and pinion. Has anyone ever refurbed their steering rack? And if so, which components? Was it easy? Did entire rack have to come out or can it be done with it in the car?

It's probably the steering u joint and not the rack. You can try adjusting the rack with the allen key bolt coming out.