The howling from the differential's pinion on deceleration was ruining the driving experience for me, so I decided to address this issue over the Thanksgiving holidays. I found a used open 3.64 differential on Craigslist from a gentleman in Chula Vista for $100. He had two, but one was missing the output flanges, so I elected to take the complete one for my car. After a can of engine degreaser and some vigorous scraping, I was able to get most of the gunk off of it to expose the rusty housing. This one was an early unit (bolts securing the output flanges), so I would need to make some modifications before bolting it to the stock CV joints. The flanges on the early units are not threaded, so I needed longer hex bolts and nuts to secure the inner CV joints to the output flanges on this differential. A quick trip to Marshall had everything I needed. This differential also was sporting the rear cover from a 320i, so I am assuming that it was swapped out for an LSD unit sometime in the past, and I could just swap the rear cover from the whiney one. After masking off the output flanges and Input flange, I gave it a nice coat of etching primer and 2 coats of gloss black paint.
Removing the Old Unit
My Ansa Sport exhaust was shot, so took a sawzall and cut it off to give me some extra room. I unbolted the resonator at the down pipe and pulled it out as well. Removing the old differential was more work than I anticipated, mainly because I jumped the gun and unbolted the inner CV joints first. In hindsight, I should have left the CV joints attached and unbolted the input flange and the driveshaft first. Once the CV Joints were unbolted, I couldn't use the transmission and emergency brake to lock the driveshaft to remove the four 17mm nuts from the input flange. There isn't enough room to get a socket on these nuts and the box end wrench wasn't long enough to get enough leverage to break them free. I ended up buying a set of long handle box end wrenches from Harbour Freight and wedging a pry bar under the input flange to restrict it from turning while I broke the nuts free. Once the driveshaft was uncoupled, the rest was straight forward, 4 bolts securing the differential to the rear subframe and 2 nuts securing the rear cover to the differential hanger. I drained the gear oil and with some gentle wrangling it dropped out with support from my floor jack.
Installing the New Unit
I pulled the rear cover from the old unit, cleaned it up and gave both surfaces a thin coating of RTV. I placed a new gasket and bolted the 2002 rear cover on finger tight and let the RTV set for an hour before torquing to spec. After it was cured, I filled up differential was new gear oil and torqued the fill and drain nuts to spec. I spent this downtime cleaning up the rear subframe, CV joints, differential cradle and other areas covered in muck. I used the floor jack to get the new unit off of the floor and then angled the front by hand to ease it into the differential cradle. With some wrangling, I managed to move it forward enough to clear the differential hanger in the rear and attach the two nuts on the differential hanger to hold the differential's rear cover. I left these nuts finger tight in order to line up the 4 bolts securing the differential to the subframe and the input flange to the driveshaft. Once I had the 4 bolts securing the differential to the rear subframe in place, I used the longer hex bolts and nuts to attach the inner CV joints to the differential's output flanges. With the CV Joints attached, it was easy to lock the driveshaft in place using the transmission and emergency brake so I could torque the 4 bolts holding the driveshaft to the input flange. Once the driveshaft was secured, I torqued the remaining nuts to specification.
Fortunately, I had a couple of used stock resonators in my parts stash, so I took the least rusty one and gave it a nice coat of grey primer to clean it up a bit. After some searching, I decided to order a stock Ansa center exit for a replacement to the fake Ansa Sport I removed. It arrived sans box, wrapped in plastic, with the mounting tabs badly bent. Some trial and error was needed to bend them back to their original positions so they would line up with the stock mounting tabs. I splurged for a new metal ring between the resonator and the down pipe and a new set of shorter nuts and bolts. I attached the resonator to the exhaust down pipe, but left the bolts loose so I could adjust the resonator's clearance over the subframe and the connection at the muffler. I attached the rubber exhaust hanger to the rear mount on the body, then inserted the mounting tab on the rear of the muffler into it. This one mounting point for the muffler gave me some room to slip the front muffler pipe onto the connection to the resonator. Once everything was connected, I slipped the rubber exhaust hanger on the muffler's mounting hook and then slid the top portion onto the front exhaust mount on the body. I used a 1 7/8 exhaust bracket to secure the muffler to the resonator and used the floor jack to hold the resonator/muffler connection to clear the subframe and level out the muffler between the gas tank and the spare tire well. Once everything was clear and level, I tightened up all the nuts and removed the floor jack, added the new chrome tip and the job was done.
I took the car out for a test drive, no more whine and the exhaust note is very pleasing. Next up, instrument panel LED lamp replacement and IE sway bars...