Drive shaft bolts....?

[Yakinho]

So i've lost my 5th drive shaft bolt in a period of about 2 or 3 months. Any input on why the hell they keep falling out? It's a pain in the ass because BMW doesn't like to carry these, so I get stuck with home depot aluminum bolts holding the drive shaft and the transmission together for a week at a time. Initially I thought it was due to the self locking nuts being worn out after reusing them once i did the short shift kit. That way last may though, and now I have brand new bolts/nuts in there and they're STILL falling out.

[nando]

how are you torquing them? Drivetrain vibrations? misaligned shaft?

not to question your skill, but lots of people never have this problem.. so something is wrong, and I doubt it's the bolts.

[Naplm00]

lock tite thoes bitches

use new OEM bolts and pinch nuts and red locktite, they will not come off then

[nando]

You shouldn't have to locktite them. Something else is causing the problem.

[RickSloan]

yea and if you lock tight them good luck if you have more work to do under there. Everytime i go under to loosen those bolts to work on something it is always hard to get them loose, so there is a bigger problem here.

Bad CSB?
Un-balanced driveshaft like said.

something

[Hallen]

I am voting for improper torquing. There are two torque values depending if you have 10.8 bolts or 10.9 bolts (marked on the head of the bolt and on the nut). I think it is 53ftlbs for the 10,9 bolts. Use a torque wrench and make sure it clicks. It's hard to believe they back out even with driveline vibration because that guibo grabs and holds the nuts making it damn hard to loosen them.

Which bolts fall out, btw? The ones from the driveshft to the guibo or from the output flange to the guibo? (or are we talking about the rear U-Joint?)

[Adrian_Visser]

Unless you've been torquing them with little girly torque I think you have a bigger problem. So these are the bolts going through the guibo I presume? you do have to torque them down pretty good, not just until they bottom on the rubber, clamp those bitches down a bit.

Do you feel any high frequency vibration in the car at speed? It's possible your driveshaft is out of balance and causing the bolts to back out.


In my old eta with seized u-joints and an blown apart CSB my ds bolts were still tight when I replaced them. Oh and btw aluminium bolts have the shear strength of a stick of warm butter I would try and find a better subsitute until you get the oe's.

[abepark]

I got the same problem actually. every couple months I gotta get under there and tighten the bolts. I am using used driveshaft bolts. I'm thinking of marking the bolts I retighten to see if its the same bolts loosing up.

[nando]

overtorquing them may make it worse, bolts have a yield strength where they have maximum clamping force and the bolt is at it's strongest. That is usually what you are torquing them to.

also if you are using aluminum bolts or old used bolts, you can expect this to happen. new ones are only a couple dollars each..

[Yakinho]

These are the bolts connecting the transmission.



Tightening isn't the issue as i've torqued them to specs, and at another time torqued the shit out of them with the same results. There isn't any vibration until one falls out, then it vibrates like crazy on acceleration. Im pretty sure they all have fallen out on the highway, you can't feel it then, just when you accelerate out of a stop light. Nothing during cruising... I replaced the CSB when I did the short shift kit. The bolts and nuts are brand new, except for the aluminum one in there now, but for some reason they actaully seem to hold up better... I don't know how it would be an unbalanced drive shaft either. When I did the the SSK, the CSB was completely shreded, but I never had a problem with the bolts backing out, plus when the SSK and CSB were installed I didn't have a problem for at least 7 or 8 months. Transmission mounts are in decent shape, as well as the motor mounts, so i'm really out of guesses. Its a pain in the ass doing this every week or two. The only noticable vibrations the car makes is during braking, which i believe is due to a warped rotor.

[Adrian_Visser]

Hmm that's a doozy...I feel the need to go check the bolts on my eta now since I never replaced the driveshaft that caused the csb to die... my lil bro will be driving that car soon. I already put like 5000km's on it after doing the csb with no problems though

[abepark]

you will usually feel a vibration around 2k when these bolts loosen up I have found.

[Yakinho]

When you lose one out of the three, i guarantee it will feel like the car is falling apart.

[jlevie]

When I did the the SSK, the CSB was completely shreded,

I agree with everyone that says you should not be having this problem if the correct bolts are used and they are correctly torqued. But the failure of the CSB provides a clue as to why this might be happening. In almost all cases, a failure of the rubber mount of the CSB will be due to binding u-joints in the drive shaft. Which means that both the CSB and drive shaft require replacement. The binding u-joints will place unusual loads on the guibo and probably explains why the bolts are loosening.

[Mossman]

when u did CSB did u split the driveshaft and put back together without marking the way it was aligned beforehand?