Driveshaft Overhaul: Flex Disc & Center Bearing

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Driveshaft Overhaul: Flex Disc & Center Bearing

Postby EBSF » Fri Mar 28, 2014 12:40 am

So, gearing up and getting smart about E30 driveshaft overhauls, specifically flex disc and center bearing replacement. I've observed vibration at 70mph but not 50 mph after dropping the final drive in connection with a rear suspension overhaul. Still diagnosing but suspect the guibo/giubo and am wondering what I might be getting myself into in attempting the center bearing.

The question is whether center bearing replacement requires a puller and a press or whether it can be removed and installed by hand with some penetrant or gently tapped off and on with a hammer and punch.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby M20_fever » Fri Mar 28, 2014 2:29 am

You can do it without a punch, just need to be patient and work it off gently with a flat tip punch. Hit the splines with some penetrating oil before hand and it will help it come off. Make sure you mark the two halves of the drive shaft so it goes back together the same way it came apart, they are balanced as a single unit. If you don't have a Bentley manual you should get one, it will detail how to preload the CSB when you reinstall it.

I highly recommend buying a hard copy of the Bentley, but we have a hosted copy here somewhere, can't find it right now.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby EBSF » Fri Mar 28, 2014 3:34 am

I've got the PDF, and thanks. The Bentley talks about using a puller and a press, which is the reason for my question. Pelican's article is for an E36 and the Haynes I've found online is missing this chapter, so I don't have much else to go on--the ETK is only good for schematics and part nos.

A key take-away from the available resources is replicating the balance on re-installation, so I take your point about marking everything so it will re-mount correctly. Even the bolt direction seems to matter.

What do you mean by preloading the center bearing? It seems to come as an assembly, already pressed into the mount, and (but for clearances and working it onto the shaft) all that seems necessary is just mounting the two dust caps correctly and getting the circlip back on.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby Yoshi » Fri Mar 28, 2014 2:43 pm

Bad CSB manifests as a vibration on hard accel. usually only in first or second gear. If vibrations are at a specific speed (not RPM), it's a wheel related problem. RPM related problems are usually drive shaft-ish area.

IMO, don't replace the CSB if it passes visual inspection.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby 87e30 » Fri Mar 28, 2014 2:58 pm

Yoshi wrote:Bad CSB manifests as a vibration on hard accel. usually only in first or second gear.


Not disagreeing at all here, but not 100% agreeing either... I thought my CSB was bad because I got a bad vibration on hard accel in 1st and 2nd mostly, but it turned out to be just one of the bolts holding the CSB in place had backed out and the mount was slapping up and down. Make sure those bolts are tight before assuming CSB is actually where the vibration is coming from.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby EBSF » Fri Mar 28, 2014 4:25 pm

The vibrations are, indeed, at around 70mph (and not lower speeds), and observed at around mile 7 of a test drive following rear suspension upgrades that required lowering the final drive. In another thread, the diagnosis was flex disc. I thought it might be the CV joints but one response was that they were fairly robust. I still haven't ruled this out.

Note that it's an automatic transmission.

What I want to do first is get a new lock nut onto the final drive mounting bolt. The Pelican procedure I was following said nothing about putting on a new one, so I used the old one.

Also, it's sounding as if I should do a more detailed inspection of the CSB and flex disc before ordering a pile of parts.

I'm in the midst of replacing a defective strut mount. Once its replacement arrives, I can get the other end of the car jacked up and take the thing on a few more test-drives, swat some bugs, do some more inspection, and get more information. Stay tuned, and any thoughts or hypotheses in the meantime would be most appreciated.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby Yoshi » Fri Mar 28, 2014 4:32 pm

guibo is easy to check. If it has cracks, replace it. CSB will be also easy once you get access. If it's cracked or missing bits, replace it.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby EBSF » Tue May 27, 2014 10:42 pm

So, the problem seems to be the final drive mount lock nut. This came off to lower the final drive so as to install new rear springs. The procedures I was following (Pelican's and Bentley's) made no mention of this point, so I re-used the existing lock nut, albeit with some trepidation. I observed the vibration on the test drive and ordered a new part. I've been testing on an increasingly demanding basis for a few weeks since replacing it, and not a hint of the vibration I observed.

Interestingly, the nut that came off was a lower-grade nylock nut, while the stock replacement that I re-installed was a higher-grade self-locking nut.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby Yoshi » Tue May 27, 2014 11:30 pm

I'm having a hard time picturing the part you're talking about.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby EBSF » Wed May 28, 2014 12:04 am

The final drive has a mounting bushing about 2" in diameter and 1" thick, and is held up by a bolt mounted longitudinally that goes through the bushing and corresponding flanges, probably in the subframe.

See ETK DTU 33-0124. The bushing is part no. 33 17 1 135 242. The nut that goes on the mounting bolt is part no. 07 12 9 900 047. The mounting bolt is part no. 07 11 9 914 536, but is discontinued. The hardware should be grade 8.8 or better. Torque spec is around 65-70 ft.-lbs. if I recall correctly, but of course check a definitive reference on this point.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby EBSF » Wed May 28, 2014 12:09 am

Also see Bentley Section 11 Fig. 5-4 on p. 16.
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Re: Driveshaft Overhaul: Flex Disc & Center Bearing

Postby Yoshi » Wed May 28, 2014 12:49 pm

ooooooooooooh yea that makes sense then.
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