Ford Sierra Front Differential

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With all off the front suspension brackets welded into place the next job is to mount the front 4×4 differential assembly.

The nearside suspension brackets took a fraction of the time that the offside did. With the aid of a simple jig and a couple spirit levels, four mounts were welded in the time it took for my coffee to go cold.

I ran 1 metre lengths of 12mm threaded bar through the mounts to make sure then were aligned correctly. I then got some angle iron that I drilled with holes at exactly the right height and width. I say drilled, I actually reamed out the holes to 15/32″ (11.9mm) reamer so that the holes were tight on the thread. The angle iron was then welded together into a quick and disposable jig.

With the offside brackets already done, plus a  jig that I checked and double checked with digital verniers, welding the brackets into place was almost child’s play. It was so quick, I walked away with no burns or scraps; a miracle for me. Once complete the 12mm lengths of bar simply thread cleanly through the joints, prooving that they are perfectly inline. I’m not a great fan of digital spirit levels, but at least it backed up my trusty old fashioned bubble levels readings. A digitial spirit level is handy when you are trying to measure something not intended to be level like the anti squat geometry on the front suspension. All values now perfectly match my CAD design, so I’m quite please.

The next jobs that are just waiting to be done are:

  • Mushroom adaptors for the Sierra Cosworth 4×4 uprights. The Fleabay add said Escort Cosworth.
  • Front differential brackets and mounts.
  • Engine mounts
  • Front prop-shaft central bearing mount.
  • Steering rack mounts

I really keen on getting the front differential mounted. If I do that job first, I can double check my CAD dimensions for the front prop-shaft length and get that sent off to be lengthened. A local company makes custom prop-shafts for those posh leisure boats that only millionaires can afford. They quoted me £75 lengthened and balanced or £120 with new joints and powder coating. I thought that sounded pretty reasonable.

As you can see in the above photo, I’ve made up a custom aluminium housing to replace the section that would be part and parcel of the sump. It would have looked rather weird to have a 2lt Ford Cosworth sump mounted in front of the Rover V8 engine.

In it’s usual configuration, the front differential is floating in relation to the chassis. It is bolted to the side of the engine, with its weight supported by the engine mounts. When mounted to the engine a lot of the stress in not passed through the casing, yet they still have a tendency to crack. As weakness is already a problem, solidly mounting the diff, if done wrongly, would mean it could shatter before reaching the end of the driveway. Therefore, the custom differential actually has an 8mm strengthening plate that passes across the sump area and 5 additional mounting points. This leaves only the top outside quarter the option of flexing. Hopefully, all these extra mounts should do the trick of beefing things up.

In order to get the gear ratios a little better I’m using a Sierra 2.0s 4×4 differential (3.9:1) and not a 3.72 found in the Sierra Cosworth / Escort Cosworth or XR4x4.

Front Suspension and Differential

Sorry, not too much to blog about this weekend as most of my efforts were a mirror of last weekend.

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