Rear Diff (Fluid Change)

Well, since I am at the 30K mark (actually 32K) I decided it was time to change some fluids.

I have ordered the "gaskets" that are needed for the front diff and TC, so I have not done them yet. But the rear just needs some RTV to seal the drain and fill plug.

First I have to say...if you have the M226 rear diff (OR model and Manual tranny) buy diff armor ASAP. As much as I don't like it, I think I'll be buying the AC armor for the short term. The abuse to the bottom of the diff, the drain plug, the cover and the bolts made this process more painful than it should have been.

I started out by purchasing 2 qts of Royal Purple. It's cheap ($9 a qt) and the people that use it seem to have good experiences. I figure I'll be changing out the oil every 30K so I don't have to go with the expensive Amsoil. I also picked up some Permatex Ultra Grey 82194 and this really cool funnel with a clear hose (it's got a handle, measure marks, a lid, and a shut off).

Once home I crawl under and since I had some seeping around the lower part of the cover I figure I'll check the level. I undo the fill plug and oil starts to run out (I had expected this as the pinion angle is pointed up). Due to the amount of fluid that came out the fill plug I think it was full.

So I look under and the drain plug is filled with dirt. I take a small screwdriver and clean it out. I go to put a 3/8� drive extension to remove the plug and it doesn’t fit. I look again and it’s so ground down that the hole is about half the size. So I break out the dremel and open the hole up. So now the 3/8� extension fits in, I remove the plug and nothing comes out. I look at the plug expecting to see a grey goo on it (fine metal shavings mixed with gear oil)…nothing. I stick my finger up in the drain hole and feel a “cap� of sorts. I push it up and oil starts to drain.

With the oil drained out I start to remove the cover so that I can pound it back into shape and reseal it. I loosen all the top bolts but when I reach the two bottom bolts they are so ripped up that the socket or wrench don’t have enough sides to grab on to. I break out the vice grips and they still do not budge. I start looking close and realize that the bottom of the diff and the cover are ground to the point that they are fused together and fused to the bolt. I break out the dremel and grind down the bolt enough to get a 12mm wrench on instead of the 13mm. Still no go. So a break out the torch and head them up. After about 30 mins I finally get the two bolts out.

So I go to remove the cover and find out that there is not enough clearance with the brake line. So I remove the brake line from the axle end (now I am going to have to bleed my brakes). I get the cover off and clean it up.

I go back and look at the inside of the diff, it looks good. The teeth are meshing well and no sign of any problems. I clean off the edge where the cover sits and notice a lip on the bottom where it was ground down. Figuring the cover is not going to sit properly with this lip, I break out the dremel again. Get everything cleaned up and pull the little plug of grey goo from the bottom of the diff. It’s about the size of a quarter and about ¼� thick. This is typically normal, but I can’t say I have ever seen that much metal in a diff.

I apply the RTV to the cover and stick it back on. Finger tighten all the bolts (moving the crewed up ones to the top since I don’t currently have new ones. Torque them all down to 31ft-lbs in a star pattern (just like you would a car tire). Put a little RTV on the drain plug and torqued it down to 25ft-lbs.

Now, since the pinion angle is off, I can’t just start filling or else I am not going to be able to put the correct amount in (someone needs to come out with a new cover will a high fill hole). So I jack up the back end and place jack stands under the rear axle. Even with it up this high, I still was only able to get 3.75pt instead of the 4.25pt’s that the SM calls for. That leaves me 1/2 pint short. The only way I can think of getting that extra ½ in is to park it on a very steep hill (maybe my father’s driveway). For now I am running it a bit low.

I put the brake line back on, but because I do not have a self bleeding kit, my brakes are not bled (I’ll be doing that tonight).

So what should have taken less than an hour to do took closer to three from prep to clean up.