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Discussion Starter · #1 · (Edited)
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Because a leaky butt really drops you down on the cool meter. :( :laughing:


Okay, let me quit it! Here's the scenario. You pull your baby out of the garage and notice that something has leaked out of the rear of the car. The odd thing is that the leak is not dead center of the rear, it’s more to the left (or right if you're really having a bad day). What you are probably experiencing is the failure of the output shaft seal (normally the driver's side in the C5). I say probably because doing a little "wide open throttle" (or WOT as it is known here) can also cause you to wake up to a wet spot. In the case of WOT, this is a normal occurrence, as the differential has a exhaust outlet in which differential fluid will leak out of in order to relieve case pressure.

If you're more of a cruiser, then you probably just have a leaking output shaft seal. You have 2 ways of identifying the source of the leak.

The professional way if the leaking source is not obvious is to add some Black Light Oil Dye to the differential and then check the area with a black light after some normal driving. The fluid will glow either a bright yellow or bright green. This allows you to identify the leak without doing unnecessary and costly repairs. If you want the GM dye, one place you can order it from the GM Special Parts website (this site only works with Internet Explorer). The part number is J-28431, which can be used in engine, transmission, and rear axle oils, as well as power steering fluids. (Note: part number J-29545 is only for use in engine coolants)

The second way if the leak is obvious enough, is to do a visual inspection. Look at the picture below.

You can clearly see how the leak is confined to about a 180 degree area of the seal. The differential side covers have been known to leak due to a design flaw although in this situation, this is not the case (just be aware of that possibility). We know that this is not the case here as oil does not leak in a upward direction.

Now that we have identified the leaking source, let's get that baby fixed!

The first thing you should do is get some replacement differential fluid. Now would be a good time to replace that old, stinky stuff. The service manual calls for SAE 75W-90 Synthetic Gear Lubricant or equivalent. The manual also states to add 4 ounces of Limited-Slip Differential Lubricant Additive. Today, you can buy this gear oil already mixed. Mobile one and Red Line are two brands that I found with the limited-slip additive already built in.

NOTE! After replacing the differential gear oil, do not go WOT for a minimum of 300 miles. Doing so may result in scoring of the ring and pinion gears leading to differential noise!!!

Some of the tools that were not in my "shade tree" collection that you may have to get, or that will make the job easier are:

Torque Wrenches - the nuts and bolts in this repair have specific torque settings. Since your life is depending on the tightness of these nuts and bolts, it would be smart to spend a few dollars and make sure that you torque them to the GM specifications. I have attached a PDF document to the bottom of this post that contain those settings.

A 21mm wrench for the lower arm ball joint nut, a short set of Hex sockets (notice the sizes in the picture - that 10mm is for the differential drain and fill plugs), and a 33mm deep-socket for the axle bolt. If you don't screw up your parking brake assembly and do not have to separate the stabilizer from the upper and lower control arms, then you will not need the 21mm wrench. Ask me how I know...:rolleyes:

A drift punch or something equivalent.

Last of all, you'll need the replacement seal.

Notice the grease that is inside the interior lining of the seal. Do not wipe that off!

Here's something you should consider. The differential has 2 output shaft seals. The right seal is not known for leaking but you never know. I bought 2 seals for a couple of reasons. One, because the differential has two of these seals. Two, the seals were dirt cheap; they were something like $12 each. Lastly, knowing how much of a shade tree mechanic I am, I wanted to have an ace in the hole just in case I screwed up one of those seals. Well guess what happened. I screwed up one of the seals when installing it. This is something you may want to consider if your mechanic skills are anything like mine.

My method of doing this repair differs from Cajun Dude's in that I actually removed the drive shaft. The reason I did so was because of the limited amount of space that I had to work in while trying to seat the seal. Look at this picture:

Even after I removed the drive shaft, it was still somewhat awkward to get up in there and figure out how to swing my hammer to seat the seal. One thing that Cajun Dude said that was right on target was tap, tap, taparoo... :yesnod:

As some of you may know, I bought the J-46405 tool that the TSB concerning this repair calls for. I have mixed emotions about its effectiveness when doing the repair the way I did. If I had taken the entire differential out of the car, the tool would have been a must have for me. However, using it in this situation was helpful, but what probably would have worked best was if this tool had a 3-foot shaft. That way, I could have stood back from the wheel well and whacked away on that seal. I did use it to do the install so I guess it ended up paying for itself.

The Repair

Okay, let's get started! I'm going to keep this as close to the manual as possible. Note: One thing that I did when removing nuts and bolts was to put them back where they originally went so that they would not get lost, and so that I would know where they went when it was time to reassemble everything. Good rule to follow for a shade tree mechanic!

1. Shift the transmission into PARK (A/T) or NEUTRAL (M/T).

2. Work the parking brake a whole bunch of times and then apply it. This will loosen the shoes up from the rotors. If you don't do this, your rotors may be a PITA to get off. They may also rip the parking brake shoes!.

3. Raise and suitably support the vehicle.

4. Remove the tire and wheel assembly.

5. Insert a drift or punch into the brake rotor cooling fins and against the brake caliper to prevent the wheel hub and bearing from turning.

6. Loosen (do not remove) the spindle nut retaining the rear wheel drive shaft to the hub.

7. Remove the drift or punch.

8. Release the parking brake.

9. Using a 15mm socket, remove the caliper bolts. You'll need to hold the caliper pin still using a 5/8" wrench. Be careful not to stress the brake line going to the caliper.

10. At this point, use your jack to support the lower control arm.

11. Remove the 2 bolts at the top of the shock absorber.

12. Remove the 2 bolts that hold the upper control arm to the frame.

13. Separate the outer tie rod end from the knuckle and reposition the tie rod toward the rear of the vehicle.

Here's the way I removed mine before I got smart enough to go buy some Hex sockets:

14. Disconnect the wheel speed sensor electrical connector.


Premium Member
30,448 Posts
Discussion Starter · #2 · (Edited)

15. Disconnect the parking brake cable from the parking brake lever. Now here comes the fun part. First of all, if you skipped step 8, you'll never get this cable off so make sure that you performed step 8.

You're also going to have to free the parking brake cable from the bracket that holds it in place. This is a real PITA. Do not get frustrated and break those tabs off. A new parking brake cable is not cheap! Look at the picture below:

Here's a trick that JDaniel over at CF used to get his cable off. I quote: "After I unhooked it from the hook and needed a way to get the prongs collapsed to get it out of the bracket, this is what I did. I grabbed a 1/2 combo wrench and used the boxed end. Its a tight fit but you slide the end of the cable theough the wrench and up to where the prongs are. Just push it up around the prongs and to the bracket and they all collapse and pops right out. Then you just slide the cable through the wrench and out of the bracket! Easy as 1-2-3!". That may be of some use when you get to this step.

If you get frustrated and decide to remove the bracket bolts, here they are:

At this point, you are ready to take a break and have the Junkman Special "Dagwood" Pizza!

For those of you on a budget, please substitute a bologna sandwich and get back to work. :lol:

Shaft Removal

16. At this point, the service manual calls for part number J-42129 to separate the axle from the stabilizer, and J-29794 to separate the axle from the differential. Here's what we're going to do.

First, jack the lower control arm up so that the axle is somewhat straight (not hanging down). Loosen the spindle nut up about a half-inch. Grab the top of the stabilizer. You're going to use it like a slide hammer to "bump" the drive shaft out of the differential. Just bump it firmly toward you and the drive shaft will eventually work its way out of the differential. At the same time (if you're lucky), the bumping will loosen up the axle at the stabilizer too. If not, you may have to give it a slight whack to disengage it from the stabilizer.

Note: Do not whack the end of the shaft while it is still seated inside the differential. There's no telling what damage that could cause. Also, if you get the shaft out of the differential and have to give it a whack to dislodge it from the stabilizer, pay particular attention to the end of the shaft by the differential as to not allow it to bang up against anything - especially the differential!

Be careful not to whack the wheel studs also.

Whatever you do, do not make the mistake of removing the stabilizer with the axle attached to it like this:

If you do, you've just created a lot more work which is now why I'm so good at removing the entire shaft and control arms. In 3 days, I must have put that thing in and pulled it out of the car at least 5 times. Like Michael (Mike94ZLT1) said in one of my other post, you get real good and quick at this after you've done it a few times. I couldn't believe how fast I put it back together the last time I did it.

Once you have the axle loose at both the differential and the stabilizer, you will need to bend the end of the shaft and simultaneously rotate the stabilizer out of the way in order to remove the axle. Check out the picture:

17. Now that you have the shaft out of the way, clean up the differential. You want to be able to see any new leaks if you don't install the seal correctly.

18. Now you're ready to remove the old seal and replace it with the new one. The old seal does not come out easily. It does however have a slight lip around the outside edge of it that you can feel and I used a seal removal tool to grab that lip and pull out the old seal. Be careful around this area. You don't want to gouge the differential and create a permanent leak.

19. Seating the new seal will be the fun you get to have. Whatever you do, you don't want to start tapping the edge of the seal and working your way around. You want to use something that will allow you to seat the seal evenly as you tap it in. Again, I used the tool that I bought that the TSB called for. I heard a block of wood works well and I've heard that they make universal seal installing tools. Whatever you decide to use, make sure you keep these tips in mind or make sure you buy a bunch of seals. :willy:

20. After you get the seal installed, you want to physically and visually inspect your work. Run your fingers around the edges of the seal. You should not feel any gap between the edge of the seal and the differential. If you do, you still need to tap, tap, tap-a-roo.

One thing that you want to inspect is the wiring harness back here. The factory electrical tape that was on mine had began to come unraveled. Thus, I re-wrapped it with one piece of tape and zipped tied the ends. I didn't have a black tie wrap but at least it doesn't show with the wheel on!

21. Now you are ready to put everything back together. Just reverse these steps and you should be fine. Remember to use the torque settings that I provided above for everything but the brakes bolts. I've provided the torque values for the brake bolts at the bottom of this post. You need to take the car for a ride in order to check for leaks and heat up the differential fluid. DO NOT GO WOT FOR THE FIRST 300 MILES!!! The fluid needs to be changed while it is hot and care needs to be taken so that you don't burn yourself.

22. Once you get back in the garage, draining the differential is no major undertaking. The drain bolt is located directly on the bottom. Remember, you want to drain the fluid while it is hot. Make sure that the car is level when you drain and fill the differential. Here's where a 4 post lift would come in handy.

23. After you have drained the fluid and replaced the drain plug, you'll need to fill the differential with new fluid. As you can see by the location of the fill plug, this is a tad bit difficult.

Fill the differential up to the bottom of the fill hole. It holds about 2 quarts of fluid.

You can drop by you local auto store and buy a siphon to fill the differential. This is what I bought, although its crappy design is why I have to clean up the garage floor now:

If you get one of these (I think it was $10), make sure that when you are using it to siphon any type of thick fluid that you hold on tightly to the output side hose! Not doing so will cause it to blow away from the siphon pump and shoot a healthy wad of whatever you are pumping all over the place. As you can see by my garage floor, it was not a pretty sight!

Once you get the differential fluid in, make sure that you do not go WOT for a minimum of 300 miles. Doing so may result in scoring of the ring and pinion gears leading to differential noise!!!

I will probably be updating this over the next few days if I see any mistakes so give me a few days before printing it.

Here she is, all assembled and cleaned up:

Alrighty then! You now have the knowledge necessary to tackle this job. I will have Rosie O'Donnell inspecting your butts for leaks at the next gathering and I hear she hates wearing gloves! :D

The Junkman :thumbsup:
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