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Subject: My Differential Project with instructions and photos Author: ejonesie22 : member since March, 2004 : 1108 posts Posted on: 2008-04-11 15:19:04

My car needed a new differential. I ended up getting one from an E30 which will fit our cars with some switching of parts I will detail later. This swap took me from a 3.25 open to a 3.73 with limited slip.

Since this maybe a job faced by other I thought I would detail it here:

Parts and supplies needed:
- New differential
- Differential housing gasket
- Four new differential mounting bolts with washers.
- New nuts for the drive shaft yoke.
- New bolts and lock washers for the differential housing.
- New Allen bolts and reinforcement plates for the half shafts (24 bolts and 12 plates)
- It’s a good time for CV boots if they are getting old, the shafts have to come out anyways, so get four of those and some good grease.
- Good time to do a fuel filter, since it is easier to remove the pump/filter assembly to reach the top differential bolts.
- Lots of WD40.
- Loctite blue.
- Gasket dressing.
- 2 quarts of Red Line gear oil.

I got the nuts and such from Maxmillian

Some notes on some tools
- Big 19 MM closed in wrench for differential to sub frame bolts
- A ratcheting 19mm box wrench is very helpful.
- A good quality 8mm hex head impact bit.
- Small pry bar to pop out half shaft flanges from differential
- Dental pick or stiff wire.
- Must have a transmission jack, it will make it much easier than using a standard jack. Harbor Freight has a scissors style one that doe 450 pounds and works great for 60.00.

This is not a long project but it will take a couple of days, only because you will want to soak the hell out of the mount bolts for the differential itself as well as the 24 Allen bolts that hold on the half shafts. By soak, I mean blow a can of WD40 if you have too and leave the car sitting for a day or so. You don’t want to take a half assed approach to getting the Allen bolts out, if they strip or break you are in a world of hurt.

Getting started:

- Relieve the fuel pressure by pulling the pump fuse and briefly starting the motor, then disconnect the battery.
- Jack up the rear of the car as high as you can, at least a foot or more if possible.
- Unbolt the 4 17 MM bolts on the driveshaft yoke.
- With the parking brake on to keep the shafts from turning, start on the Allen bolts on the half shafts. Clean the hell out of them and used the pick to pick out any remaining goo in the hex hole. The Allen socket needs to rest fully in the hole. Mine came out with my ½ socket wrench and a good tug, but you may need an impact wrench. Be very, very careful because if you break one of these you will be in for a good old time. When you have loosened the bolts you can get to, release the brake and give the shafts half a turn to get to the other bolts. You want to have as clear a shot at the bolts as possible. Then remove the half shafts.
- Remove the rear differential mount completely and unplug the speed sensor.
- Remove the fuel pump and filter.
- Now the fun begins. Since the differential is probably sagging toward the rear from removing the rear mount, you will have a little extra room to reach up to the top bolts. I doubt even with pulling on the tail of the differential you will be able to get a socket up there, I couldn’t, so with the biggest box end 19mm wrench you can get, loosen, but do not remove the bolts. You may need to hammer it or get a larger wrench on the handle to bust them loose.
- Bring in the jack and just bring it under the housing and snug it a bit and loosen the front two lower bolts. You can get a socket on these.
- Now remove all four bolts. If you are lucky you may be able to hand spin the top bolts. I couldn’t but I have a ratcheting box wrench that made it easy.
- Pull back the differential towards the rear of the car to free the drive shaft and lower it.

You have now removed the differential.

As I said I sourced a differential on EBay from an 88 325I. The only difference between the two is the rear cover and the two output shafts that go to the CV joints. These pop out and the cover comes off with 8 bolts. Just drain them real good, I used a big tub with a milk crate and turned the unit up on it overnight then used the old cover and a new gasket on the new unit.


Here are a couple of pictures of the two differentials





Here is a picture of the new unit right before installation:




Installation is the reverse of removal, but a few points

- Test fit the four bolts on the top of the differential. You want them to turn as easily as you can so you can get them hand started and put in as much as possible. Chase the threads if you need to. New bolts and washers are a blessing here.
- Use blue Loctite on all the bolts you will use for the mounts and shafts. It helps lube the bolts so they turn easier as well as locking them in place.
- When you start make sure the first thing you do is ease the differential up on the jack a little shy of the drive shaft and work it onto the yoke studs, other wise you will have to drop the shaft or uninstall the differential. The jack is on wheels so this is easy. Then loosely fit at least a couple of nuts to keep the shaft on the yoke as you work.
- Don’t put in the rear mount until last, it will give you the space you need to get the bolts and bolt holes straight on the top of the differential.
- Jack the differential up to about an 1/8 of an inch from the sub frame and use the mount point for the rear mount on the cover to wiggle the differential until the top bolts find the holes and start them, but just a few turns, then fit the lower/front two bolts, again wiggling as need so they basically drop in. Do all this by feel and make sure not to cross thread.
- Jack the differential up flush, then by whatever means you want, tighten the bolts, by hand or with a socket or ratchet wrench on the top bolts. If you have to use a regular box wrench because the bolts are a little tight have fun.
- Once the differential is in place, install the half shafts, (do the boots if you need to first) and use the new bolts and reinforcement plates. Cinch them up and then torque them to 45 lbs. Put on the parking brake as needed to keep the shafts from spinning. Also once a few of the bolts are in you can also tighten the drive shaft yoke bolts and tighten them good and firm, I think it’s 45 lbs also, but I always just cinch them as tight as I can without being crazy.
- Reinstall the fuel pump and filter, the rear mount and the speed sensor wire.

Done, the car sounds much better, no more Sherman tank gear growl from the back, it is also a bit quicker and the LS is a nice upgrade.

Here are a few more pictures:

You can see the yoke for the half shaft that has to be changed between the two units, it just pops out:





Here is a good shot of the mound of metal on my speed sensor form the failing gear set:







Evan Jones
1984 733i(s) Polaris Metallic 214,000 Miles
1986 745i Bronzit 162,000 Miles
1984 745i Delphin Gray 148,000 Miles (in progress)
1979 733i back to life supporting the others

oh and a '73 Alfa Spider, just because...

• My Differential Project with instructions and photos (pic) - ejonesie22 2008-04-11 15:19:04 (659 views)
  • Question... - mofinco 2008-04-14 00:22:32 (135 views)
    • Re: Question... - ejonesie22 2008-04-14 16:32:14 (113 views)
      • Re: Question... - mofinco 2008-04-14 20:05:04 (130 views)
        • Ok, here is what I found... - ejonesie22 2008-04-21 09:47:49 (108 views)
          • That's GREAT! - mofinco 2008-04-22 14:43:57 (102 views)
            • Re: That's GREAT! - ejonesie22 2008-04-25 16:33:29 (88 views)
              • No doubt... - mofinco 2008-04-28 00:42:59 (91 views)
    • What are you doing with the 3.46? (nt) - demet 2008-04-14 08:59:38 (112 views)
      • Re: What are you doing with the 3.46? - mofinco 2008-04-14 20:06:39 (120 views)
  • Nice write-up, Evan, Here are a couple more points - kff 2008-04-12 18:29:40 (123 views)
    • Yes. I should have pointed out it was my North American 733i I did this on... - ejonesie22 2008-04-12 20:16:49 (127 views)
  • Good info. - demet 2008-04-11 18:09:55 (94 views)
    • Its a permetex gasket dressing that comes in twist stick tube. - ejonesie22 2008-04-11 18:16:28 (114 views)
      • Is a sealer necessary? - stevebu 2008-04-27 07:49:37 (86 views)