I would recommend getting some help when installing the differential, but the method I use was created when I didn’t have the help needed. Thankfully this time my wife (who is a dab hand with an engine hoist) saved me from countless times crawling out from under the car.

The diff as supplied from Caterham (being a LSD) isn’t supplied with oil. It’s a BMW unit which has been machined to fit a carrier that matches the original Ford Sierra differential bolt pattern. The machining leaves some bare metal areas which will rust over time, so I decided to break out the Engine Enamel and paint the bare metal areas. My advice is to loosen the oil fill plug at his stage, to make filling it with oil once installed easier. For some strange reason the size of the oil fill plug is different to my previous 360R, so I didn’t have the correct size tool and I had to order a 14mm hex socket.

Next I broke out the engine hoist, which I use to lift the differential instead of attempting to lift it from underneath without a proper transmission jack. It’s one of the advantages of building on wheeled axle stands: I am able to move the engine hoist around even in a small single garage by moving the chassis to one side of the garage. I then removed the boot cover and wooden boot floor.

Two ratchet straps (rated at 250Kg each so should be strong enough) were attached to the differential. The important bit is that they exit the differential at the rear (near the aluminium back plate) so they can pass through the opening. I used pipe lagging as usual to protect the chassis.

Bottom bolt holes located

I look to locate the bottom bolts first, not with actual bolts, but with pin punches (the largest possible). It’s difficult to see the pin punch in the photo, because the handle is covered with pipe lagging.

The lifting then continues to locate the top holes, again with more pin punches.

With the differential now in place, all be it with pin punches, I decided to locate the handbrake adjuster in the differential bracket. Like the other handbrake cable brackets, it’s only possible to do this by passing the black inner cable through the bracket, which meant removing the handbrake lever installed earlier. I wish I had known this before installing the handbrake.

Once I had the handbrake adjuster in place, it was time to fit the lower differential bolts. To get the holes aligned I worked my way up through my selection of pin punches until the punch was almost the same size as the bolt.

Caterham supply a large number of spacer washer in three widths. With one of the bottom bolts pulled up tight, I could measure the gap I needed to span with the washers. Following the new manual (v1.2 and v2.0), the spacing washers should be placed evenly between the two bottom bolts. Don’t forget the Schnorr washer under each bolt head and nut, unlike the new manual’s (v1.2 and v2.0) diagram. With the gap I had I could fit four medium washers and one thin shim, so I went two each side, plus that thin shim on the left hand side. At this stage I didn’t tighten the bottom bolts.

UPDATE – See Sean’s tip in the comments if you have problems keeping the spacing washers in place during the install.

For the top bolt I needed two thick spacers on one side and one thick spacer and a thin shim on the other. I put a lot of copper slip grease on the top bolt, because the this bolt is not easy to install. To get the bolt started, I aligned the washers, pin punches again are your friend here. Initially the bolt can be pushed in by hand, but soon the dead blow hammer came into play.

As it comes to the other side, again the washers are the initial problem and pin punches can get you close to getting everything aligned but, to make that final push, a bit of tool abuse was needed. I used a 1/2” drive long extension as a drift and the dead blow hammer to push it through that final bit.

I torqued the differential bolts to 81Nm at the bottom and 61Nm at the top. At this stage I didn’t attempt to torque the prop shaft to diff bolts to 47Nm, because I didn’t have a way to lock the drivetrain. I will do this when the handbrake is working. I found fitting the bolts from above easier, mainly because the panel above hasn’t been installed yet.

Tools Used

  • 250Kg ratchet straps x 2
  • Engine hoist
  • Pin punches (various)
  • 1/2” drive long extension
  • Dead blow hammer
  • 10mm 1/4” drive hex socket
  • 8mm 1/4” drive hex socket
  • small 1/4” drive extension
  • 1/4” drive to 3/8” drive adapter
  • 1/4” drive ratchet
  • 3/8” drive ratchet
  • 3/8” torque wrench
  • 3/4” deep 3/8” drive socket
  • 3/4” combination spanner
  • Philips screwdriver