HOW TO… CHANGE A DIFFERENTIAL
1 Remove the brake drum
With the car raised and supported, remove the road wheels and slacken the rear brake adjusters. Remove the rear brake drum retaining screws and remove the drums.
2 Remove halfshaft
Under the car, remove the axle drain plug and catch the old oil in a drain pan. Remove the half shaft retaining screw and withdraw the halfshafts. Take care not to damage mating surfaces by using levers.
3 Unbolt propshaft
Release the bolts securing the propshaft to the differential drive flange (1/4 BSW). Support the propshaft, but avoid removing it from the gearbox, which will allow gearbox oil to drain past the seal.
4 Remove brake union
Unbolt the brake union that fixes to the top of the differential’s aluminium casing (7/16in AF). Carefully move this on it’s copper pipes clear of the differential. Be careful to avoid stressing the pipes.
5 Remove diff securing nuts
Remove the eight 5/16in UNF nuts and spring washers which secure the differential to the axle casing via it’s mounting studs (1/2in AF). Inspect the spring washers and replace if they are imperfect.
6 Remove the differential
Gently tap the aluminium differential casing with a soft face hammer to release it, then ease it off it’s securing studs. Keep the drain pan underneath, as more oil may drip.
7 Clean, clean, clean
Particularly if you’ve removed a differential because it’s showing signs of wear, cleanliness of the inside of the axle casing is imperative to avoid swarf being transferred into your new diff’s bearings.
8 A note on gaskets…
In our experience, quality and thickness of hub to halfshaft gaskets varies dramatically. Our preference are the thicker gaskets on offer, but we are using two thinner gaskets here with a smear of sealant.
9 Fit differential gasket
Ensure both axle and differential flanges are clean then apply a smear of gasket sealing compound to both sides of a new gasket and coax it over the differential’s mounting studs.
10 Fit new differential
We’ll assume here that you’ve checked the condition of, and thoroughly cleaned, your replacement differential. Carefully offer it up to the mounting studs and push it ‘home’ into the axle casing.
11 Tighten securing nuts
Replace split washers if in imperfect condition and replace the differential securing nuts. Ensure the differential is square to the axle casing and tighten nuts gradually in a crosswise sequence.
12 Refit propshaft
Align the propshaft’s mounting flange with the holes in the differential’s drive flange (they are unequally spaced) and re-fit the securing bolts with new Nyloc or aerotight nuts (5/16in BSF).
13 Fit hub ‘O’ rings
Having first cleaned all remnants of old seal and gasket from the hub’s face, seat a new ‘O’ ring seal into the corresponding groove on the hub’s face. Sealant isn’t necessary, but a smear of grease helps.
14 Hub gaskets
Apply a small bead of sealer on both sides of the new hub gasket. Note step 8, here we are using two gaskets per side as those supplied are of the thinner type, which we have experienced failures of.
15 Refit halfshafts
Slide the halfshafts down each axle tube and lift slightly to align the splines with the differential. Ensure they are correctly orientated and fully seated then secure with their countersunk screws.
16 Refit brake drums
Refit the brake drums, secure to the hub with countersunk screws. Use a flat blade screwdriver to turn the brake adjuster until the drum locks, then back the adjuster off until the hub just spins freely.
17 Fill with oil
Replace the axle drain plug and fill with oil until the level of the filler plug is reached. Oil specification is EP90. Importantly, the oil should conform to API GL4 to protect the differential’s yellow metals.