View Single Post
Old 03-01-2016, 08:20 PM   #6
Eric
Senior Member
 
Eric's Avatar
 
Join Date: Jul 2004
Location: Hudson Valley
Posts: 229
iTrader: (3)
Default

Hi All.

I've just changed my driveshaft, and wanted to post up some information, as I was not able to find much out there when I looked.

First, to be clear, the common reason to replace a driveshaft is because the universal joints wear out.
The U-joints are pressed into the yokes and staked in place at the factory in a machine that places them in the best position for proper alignment and balance. There are no machined lands to locate the cup retaining clips, as there are on earlier American driveshafts, so replacing them yourself can be an adventure in fabrication and improvisation, with no certainty that you've done it correctly until it is installed and you find out whether it vibrates.

Quality-rebuilt driveshafts are available from several suppliers, but Driveshaft Specialists in San Antonio seems to be the place that comes most highly recommended. I bought mine there, it was about $375, plus a core charge, with free shipping, and it arrived in NY in 3 days.
You MUST also change the guibo, which WILL be in sorry shape. I bought a Febi/Bilstein unit from Pelican for a decent price, which had completely identical markings on it as my original BMW unit.

I've been driving and fixing cars for a lot of decades, and have replaced U-joints a number of times over the years in American cars and trucks. I am accustomed to their typical failure signs, which include clunking with throttle, gear, or direction changes, and whining.
I was NOT accustomed to the signs of BMW driveshaft failure, which include exactly NONE of the above.
In my case, I spent a couple of months experiencing a harsh vibration that feels like it's coming from the rear of the car (occasionally left, occasionally right, usually middle), that I could feel mostly in my butt, like a back massager gone haywire.
No vibration in the steering wheel.
No vibration in the gearshift (MT).
The vibration was affected by throttle position and road speed - it was worse at steady throttle, better with acceleration or deceleration, worst at about 40mph and again at about 70mph (could be bone-jarring when it was just right), and smoothed out pretty well at about 80-85.
It was not affected by engine RPM.
There was no sound associated with it - no howling, growling, or grinding.
Taking sweeping turns in either direction did not change it.
I had gotten under the car and messed with the axles, wheels, and driveshaft, and I didn't notice any slack or problem (the rear U-joint is barely visible, and you can't get your hand fully around it, and the slack that there was felt to me like the slack I would expect to find in the differential, so I didn't think anything of it).
My best guess was a rear wheel bearing, because of the relation to throttle position, but, of course, I was wrong.

The driveshaft could be changed on the ground, on jackstands, by the determined, strong, and young, but I would highly recommend using a lift.

In order to change the driveshaft, you need to first remove both the catalytic converter and muffler sections of the exhaust system. I have never been able to get the downpipe flange nuts off without first heating them to orange-red, except in cases where I had previously replaced them with stainless. This applies to both plain steel nuts, and to BMW factory copper nuts. You do NOT want to really whale on these nuts to remove them, as the studs sometimes have been corroded away to some extent at their bases, and too much of a pull can shear them off, which would then oblige you to drill them out and replace them. I always chase the threads with a die (M10x1.5 if I recall), as they are always crappy. You will need a new flange gasket for reassembly.

Unless they were recently replaced, you WILL destroy the two 85-100mm bolts that hold the two pipe sections together at the flare joint, so have a new pair, as well as nuts and washers. Again, stainless is your friend. The springs are often stainless, and if so will be fine (they aren't cheap to buy).
You may have to drill or drive parts of the old bolts out of the flanges - heat helps here, too.

The two heat shields covering the driveshaft have to be removed - this usually goes well, but if you live in a rock-salt area, this is a good opportunity to replace the little washers with larger washers and even larger plastic spacers (cut from coffee can lids), because otherwise galvanic action will eat little holes in the heat shields exactly the size of the washers, and they will begin to fall off.

The driveshaft is attached to the differential by 4 screws with 16mm hex heads. 16mm is the size that is not included in any socket or open end wrench set. ⅝" is the same size as 16mm, so grab an American box wrench (a socket won't fit). You will need to apply the parking brake, loosen 3 screws, release the parking brake, rotate the driveshaft 180°, and loosen the fourth screw.

The driveshaft is attached to the guibo, which is attached to the transmission by 3 nuts and bolts. These fasteners all have 18mm heads. This is the other size that is uncommon in wrench sets, and there is no American substitute.
You will need to use a deep extension from the rear, with an open end on the nut on the front.

Don't forget the center bearing's 2 nuts, and the little steel support bracket for the rear heat shield, which also have to go.

Once all the fasteners are off, the driveshaft just drops out.
Right.
Actually, after 1- to 200,000 miles, its spline joint will be frozen, and it will be locked in place. You will need two good prybars to work the ends off, and then manipulate the thing out.

The new driveshaft will come sans vibration dampener, so you will have to swap yours on (unless it's destroyed, in which case you will need a new one, for over a hundred bucks). The bolts that fasten the guibo to the front of the driveshaft have round flat heads and splined shafts, and are splined into the driveshaft flange holes, after going through the balancer's holes. A few good shots on each bolt with a sledge will pop them out - screw the nuts back on to just above the ends of the bolts, to protect them.
I replaced all 6 of of the nuts, as they are special lock nuts, but I'm not certain whether that's necessary.
Once the bolts are out, the balancer can be rotated 60° and removed.

Installation, as they say, is the reverse of removal (only easier).

To be continued...
Eric is offline   Reply With Quote