Drive Shaft Questions

[flumph]

So I recently got around to installing a new drive shaft in my 1984 325e. Some details: It has a newly rebuilt 2.5L swapped in, but it is using the Eta-style transmission and I'm running a full standalone.

When I went to replace the shaft, it turned out that the shaft had already pretty recently been replaced (which I couldn't have known because I have no way of getting underneath the car). I had bought a new shaft because of some pretty severe vibration problems above around 2,500 rpm and under load. The real problem was that one of the bolt holes that holds the center support bearing was pretty much completely thread stripped, and one of the bolts had backed out and was missing. Against my better judgment, I epoxied the bolt in place and drilled and tapped a new hole next to the old one because I had to move the car the same night. I also noticed that my flex disc was in very poor shape, and I have a new one on order. To my dismay, reaffixing the center support bearing and installing the new shaft did not fix the vibration problem. Now it only happens when torque is applied, but it doesn't happen at speed.

So I have four questions:

• I didn't think to check the condition of the old drive shaft centering sleeve. I bought the new shaft refurbished at wholesaleimports, and I'm really not sure if the new shaft even had a centering sleeve. Would the absence of this centering sleeve cause drive line vibrations?
• What is my best course of action to have a positive way of affixing the center support bearing? My thoughts are either weld a stud in place or drill in from the other side and fit a nut on the bolt. Thoughts?
• Is it likely that I just needed to replace my Giubo all along? Is this likely to fix the driveline vibration?
• What's the best way to remove a bolt that has been JB welded in place? Please no flame...

Edit: that's actually four questions.

[tomstin]

When chasing drive line vibrations everything is in play. So yes, I would replace the Flex Disk (AKA Giubo) and make sure you install it in the right orientation.

Next, the Center Support Bearing is critical and remember to pre-load it (see the Bentley). As for you bolts, that's going to get tricky as alignment is critical. Without looking at it, I really don't have any ideas.

See my post on aligning the drive shaft here: https://www.r3vlimited.com/board/sho...ht=drive+shaft

And of course from the motor mounts to the transmission mounts to the rear axle mounts, they all can cause vibrations and have you chasing multiple problems.

[flumph]

Interesting! It didn't really occur to me that you had to align it manually. The center support bearing is there, but may not be tightened as much as it needs, and I almost definitely didn't preload it properly. What I'm wondering about is the centering bushing that slips into the transmission side flange, and has a hole for the pin in the transmission output shaft. It's not like it really matters, because I ordered a new centering bushing along with the new flex disc. We'll know this weekend. Since WSI shipped it with a center support bearing pre-pressed into place, I can't imagine they would skimp on a $10 bushing.



I also dug around a little more and found this. Is this similar to the procedure that you went through? Pretty much just loosen up the engine and transmission mounts (gives me an excuse to install those ones from Garagistic that I ordered like 6 months ago), hang some plumb references (crank pulley, shaft at flex disc, shaft at CSB, shaft at diff), and nudge everything around until it's straight? The link above also says that the transmission is offset to one side an entire centimeter. Weird!


At this point I'm also planning on cutting a small hole in my carpet and drilling the floor pan in order to fix the CSB with a nut from the inside of the car. Really no other choice. It seems that BMW began using studs instead of bolt holes in later years.


Next up: CV axles, diff mount, and subframe bushings... The adventure never ends.

[tomstin]

drilling the floor pan in order to fix the CSB with a nut from the inside of the car.

Be careful here, in order to preload the CSB, as I recall, they are T bolts and need to slide back and forth? As a worst case, preload the CSB, mark the spot, then weld in the bolt.

Its been a while since I was under there, so whatever you end up needing to do, if the CSB is not aligned and preloaded properly, you'll have problems.

But with 30+ year old cars, problems are part of the process.

[flumph]

I realized shortly after buying the damn thing that it was pretty much a rolling problem. Nearly 2 years later, I'm still trying to get it roadworthy. Bit by bit by bit.

I will check for bearing preload (or, absence of) this weekend when I get some lift time. Makes sense to check that and check for vibration after fixing just that.

You might be right about the T bolts on some cars, but mine just has a single bolt hole on both sides, and the CSB has a slot for it to slide back and forth. One side is completely stripped. As a contingency, I got a pack of rivnuts. Even if I don't use them here, I'm sure I'll find something to do with them.

[e30davie]

Everyone goes on about pre-loading the cetnre support bearing, but in my experience it made no difference weather it was preloaded or just bolted up where it wanted to be. 2 drive shaft shops i spoke too said they'd never heard of the idea (i had my driveshaft ballanced trying to chase a vibration). I have back to back tested full on preloaded, not preloaded, half preloaded and found it made no difference.

Yes i know its in the Bentley and it takes all of 10seconds to do it, but i personally think its not going to be the cause of or fix any major vibration issues.

Anything rubber in the drivetrain has the potential to cause vibration. Engine mounts, gbox mounts, centre support rubber, diff bushes, subframe bushes, trailing arm bushes, rubber driveshaft coupling. they all have the potential to cause vibration if they are stuffed.

the straightness of the drive train is good to try and fix, but unless all the rubber things listed above are new, then its a waste of time.

[flumph]

So the new Giubo (a Febi part) came in the mail and I'm reading up on the replacement. I see the little arrows molded into the rubber, and I understand that these arrows indicate the placement of the transmission and drive shaft flanges.

If I'm understanding correctly, when facing the front of the car, the output shaft of the transmission spins counterclockwise from your perspective. If the disc is installed as the arrows indicate, this means that the thin part of the disc is held in compression when the engine is applying torque? My instinct is that the fat part of the disc should be the one transmitting the torque from the transmission to the drive shaft.

Am I overthinking this?

[flumph]

Followup:
Replaced the disc and the vibration is 100% gone. The old disc was completely destroyed. The arrows are correct and I'm just dumb. JB weld in the bolt hole for the CSB (which I preloaded this time) worked fine for now. I'll stick a rivnut in there one day.


One thing down on the list, 34 to go... Next up, trailing arms and wheel bearings. Thanks guys.