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Differential Cover Removal & Replacement

I couldn't understand why all of a sudden the differential started leaking oil everywhere. The whole rear underside of the car was a right mess and I feared the worst. Upon closer inspection, it became obvious that the differential cover plate had rusted so badly that there was now a hole in it ! The cover plate is made of very thin metal and apparently this is a big problem. So much so that The Capri Club have recently started selling replacement diff covers. Couldn't have happened at a better time. I duly ordered a new cover for £37.50 and had to get a new paper gasket from Ford for £1.50.

Before tackling this job, make sure that you have purchased some new oil. For the Sailsbury axle which is on all late model Capri's, you need about 1.5 litres of SAE90 differential oil. You will also need some blue gasket sealant and a square socket adapter to remove the oil filler plug.

The diff cover supplied by the Capri club comes unpainted so the first thing to do is give it several coats of paint - I recommend the Hammerite black which looks good. Don't paint the gasket surface or the interior. Allow plenty of time for the paint to harden.

Nobody really understands why Ford didn't put a drain plug on the differentials. They say that the oil should last the lifetime of the car but many others believe it should be replaced say every 50 - 80 thousand miles. Jack up the rear of the car and secure two axles stands on the ends of the axle tube. You need the rear up as high as you can get it. Make sure the hand-brake is off and the front wheels are chocked. The first problem you will see is that the rear anti-roll bar is in the way. You only have to undo the rear-most fittings to give enough movement to get the bar out of the way. Undo the two bolts on each side that are either side of the large rubber bush. The anti-roll bar will now lift up away from the differential cover.

Next problem is the brake pipe which passes over the back of the cover and is indeed clipped to it. Very carefully prise up the metal clip and pull the hose away from the cover. You should also free the pipe from the two clips on the axle tube itself. Be very careful, the pipe is reasonable flexible but take great care not to bend or kink it.

Hopefully there is enough slack in your handbrake mechanism to allow you to get the differential cover off (sideways) without dismantling the handbrake itself. Now is the time to make sure that you have an oil basin at hand. One at a time, carefully undo all the bolts that hold on the differential cover. Some are quite tricky to get to. This is when you need a good socket set ! Don't worry that the cover will fall off before you want it to - the old gasket will hold it tight. Now with bucket in place, take a chisel or something similar and prise the cover open at the bottom. You will get lots of disgusting black oil pour out into your bucket. Wait for all the oil to drain out before prising the rest of the cover off. The handbrake mechanism is still attached so you will have to work the cover off sideways. It is a bit tricky but it will go; watch that you are not putting a strain on the brake pipe.

When my cover came away I could see daylight through the metal in about three places ! I suggest that you now spend time with an old rag mopping the rest of the oil out of the diff and using a chisel, scrape away all the old gasket. Check this very carefully as it often looks like it has all been removed when in fact the gasket is still there. Clean up the surface with wire wool.

Please take time to marvel at the amazing array of gears inside the differential. They really are a very clever device and I for one don't really understand how they work. More importantly, get your inspection lamp in and rotate the teeth checking for signs of damage. Broken or chipped teeth require immediate attention. Mike all looked OK thank goodness. Fortunately, the Capri diff is extremely tough.

Now is the time to replace the cover (in my case with the new one). If you are using your existing cover, can I suggest you clean off all the rust, and treat it to a paint job? If you are swapping the covers, you will need to remove the rubber grommet into which the handbrake rod slides and fit it to the new cover. Make sure that all gasket surfaces are clean and apply a slither of blue gasket sealant to the cover plate using your finger to smooth it out. Place the new gasket on and match up the bolt holes. Allow ten minutes for the solvent to evaporate. Now add more blue sealant to the top of the gasket and work the cover back into place. Fit one or two bolts to keep it steady, while making sure that the handbrake mechanism and brake pipe are all in the right place. This is the point where you need three pairs of hands. As you refit the cover bolts, smear some gasket sealant onto each thread. Eventually when all the bolts are on, tighten them diagonally and torque each one to 25 pounds ft. Wait another ten minutes and re-torque the bolts to the same setting. This allows the gasket and sealant time to settle down. Remove all the excess sealant that will have oozed out. Now re-attach the brake pipe using the metal clip on the cover plate. I used a piece of wood to tap the clips down. Make sure that the brake pipe is not able to move about. Replace the anti-roll bar fittings, re-torque to 30-35 pounds ft. All that remains is to re-fill the diff with new oil. Most oil bottles have a filler pipe to make this easier to do. The filler plug is at the top LHS of the diff casing and requires a square socket adapter. Keep filling the oil until it begins to ooze out of the filler hole. Re-fit the plug - put some copper grease on the thread to make it easy to remove in future and hand tighten the plug.

Make a final check that everything is back in place. Lower the car down and go for a spin. Keep an eye on the diff to make sure that there is no oil leaking out. You may have to retighten the bolts again if there is. Allow two hours for this job.

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