Elan – Damaged Diff Housing Repair.

Aluminium is not a robust metal, it wont take a lot of abuse or excess stress.

But, if you want to add lightness which is the Lotus ethos, then aluminium is the “go to” metal for many automotive components and applications.

As you can visualize from the collage above, the housing had bit of collateral damage to it.

If you carry out a google search for damaged Lotus elan diff housings, you may find images showing many different types of damage. The most common being broken outer mounting lugs or ears of the housing, mostly caused by broken, a combination of badly worn upper mounting bushes and insufficient support.

But that should be a thing of the past, due to the excellent Australian designed and extremely stiff diff brace cage now available. Severe damage due to internal mechanical failure can also take its toll on the alloy diff housing, and this is what we are faced with in this instance.

The mechanical failure in question was caused when a crown wheel bolt sheared off during a track day race meeting, and the broken parts became jammed between the crown wheel and aluminium housing, (Ouch) punching a large hole, and creating some bad stress cracks and fractures near the hole… it was not pretty, and virtually relegated the housing to the scrap bin.

The housing illustrated here is the early small lug (25mm Dia) style housing. This was acquired as a donated scrap bin housing from my elan racing friend Rohan Hodges. It was then employed as a template and base to build our unique race design Diff Brace cage. We also have a large lug housing to build the brace for the the same application also. Personally I still prefer the smaller lug housing as its much easier to install and remove the diff from the elan chassis, and the fabricated and very strong sheet metal diff cage brace is a very neat fit, and when installed becomes an integral part of the complete diff assembly.

I have had the damaged housing for some time now, and due to the seriousness of the damage, it was never considered as a reparable housing until recently, due to the writer retraining and reacquainting himself with the art and skill of TIG welding aluminium, the purpose of which was to build a new aluminium elan fuel tank… but that’s a story for another time.

One couldn’t help wondering if this repair was going to be successful or not, the very nature of the part presented a bit of a challenge. It really depended on whether the decades of oil contamination could be removed, (Yes, it can migrate into the granular structure of cast aluminium).

The metal of the housing was thoroughly de-greased and washed several times. It was also left to bake in the hot Aussie sun for several days, and before any welding was attempted, it was washed again with brake clean fluid, and blown dry with compressed air, and more baking in the sun.

If you’ve ever been involved with TIG welding, you would understand that cleanliness is godliness when it comes to getting the best aluminium weld possible… but cast aluminium metal can throw some strange things at you, especially if its been contaminated with gear oil over a long period of time.

Not having previously attempted this type of repair, the preparation before hand was thorough to say the least, we needed to have as much as we could going in our favour.

To help dial the TIG and the operator welder into this job, the first weld operation was to build up a badly worn area on one of the arms, well, as you can see that was not all that difficult, but there’s no fancy laying of dimes, which is a common TIG weld description.

So, a couple of beads of weld put down on the worn area, the weld bead will be ground and hand finished to blend the metal into the existing profile. Now as a TIG weld its not all that pretty, remember what I said about cast aluminium, and this item is probably more than fifty years old… one cant expect a perfect weld, compared to welding new, clean 2mm thick sheet aluminium,

But please stick around and check out the finished diff casing at the very end of this article.

One of the mounting lugs edge and face was also badly chewed about, so some additional metal was added, remember that all of the welds will be ground and dressed and finished by hand.

That’s a bit of an ugly dob, TIG is very touchy with metal contaminants, and no matter how much cleaning and prep work is carried out the results are not always up to what you expect, but this weld will clean up OK. The edge of the large hole was cleaned up with a carbide bit in the die grinder, and a small piece of aluminum shaped to fit, then welded in.

The large hole in the casing caused by the crown wheel bolt, was plugged with a small piece of 4mm thick aluminium parted off from machined bar stock, it would have been better to actually use a bit of cast aluminium flat, because the two different types of metal had a bit of a fight and a crack (Look closer) appeared on the first weld attempt, but after grinding the first weld bead back, and giving the housing another pre-heat, then welding again, no more cracks appeared.

To jog your memory, the photo collage below details the various damaged areas of the diff housing.

The collage above illustrates the six points of damage on the diff housing. It is quite visible where the welding and rebuilding repairs were required. We should also point out that this wasn’t a repair in desperation, rather, it was more in the interests of “can a badly damaged elan diff housing be actually repaired and brought back into service again”.

Perhaps, like me, you were wandering how the this damage could occur? A quick email to Rohan revealed the reason.
To quote Rohan;
The circlip area damage occurred 40+ years ago in 2 separate incidents as far as I can recall.
1: A donut bolt broke soon after I rebuilt the car in 1980 and hit the diff when it came loose.
2: A couple of years after this, a donut itself broke and the bolt again hit the diff as it flailed around also damaging the chassis. The diff itself performed well for the next 35 years despite the damage until the crown wheel bolt failure. The wear and damage in other areas reflects the hard racing life it had over those years.
And here is another part of the story that has intrigue for me; “These incidents were the incentive for me getting the first VW CV adapters made by you for the Elan. (Circa late 1980s early 1990s, not sure.)

The bearing housing cage edge being built up with applications of several layers of aluminium filler rod. Once the build up is complete, the edge faces will be machined true.

Both bearing housings required a considerable amount of rebuilding. The weld pool is not always perfect, but this is as good as it got under the circumstances.

It was fortunate that the diff housing was able to be mounted and swung in the lathe without it fouling on the bed-way, or other parts of the lathe. The opposite side of the housing was also supported via a mandrel mounted on the live centre inserted in the tail stock. A small boring bar that would reach the edge face was then used to carefully machine and true the housing face, a small amount of internal machining was also required to clean up the inside edge of the bore. The OD irregular surface of the bearing housing was ground back later with a course flap wheel mounted in the angle grinder, it all looked quite neat when completed. Things were looking good at this stage.

After both of the bearing housings were edge face machined and trued up in the lathe, it was time to re-cut the inner circlip grooves. Its pretty much impossible to re-weld and build up the bearing housing with out losing the integrity of the groove, but its just a matter of setting up and clamping the diff housing to a machined parallel mandrel bolted to the mill table, then dial in and align the micro adjustable boring head cutter to re-cut the groove. This is painstaking work, with the mill spindle and boring head actually rotated slowly by hand, because it is so easy to make a mistake throughout the process. The boring head groove cutter tool can be advanced into the groove just a few thou at a time until the job is done.

Two brand new sets of 52mm circlips, they are 1.82mm thick, they fit perfectly in the grooves cut into the housing. As a matter of interest, these were bought at the local industrial bearing supply shop for AU$1.25 each.
Some people refer to these type of circlips as “garden variety”. I think that is wrong, they are high grade industrial, we’ve used this type of product for more than forty years, and have never experienced any issues with quality.

The job is almost complete. The circlip grooves on both sides have been re-cut in the mill, after which the circlips are inserted as a test to make sure they do actually fit. Look a bit closer, and you will also notice that part of the housing has been milled down to the circlip groove. This is to provide easier access with circlip pliers to insert the tool into the eye’s of the circlip. This trick is of enormous help when inserting and removing the circlips, with the outputs in place, because you can actually see what you are doing, as anybody who has done this job would attest.

Our S2 elan diff housing has had this mod for well over forty years, and I can only assume that the people who used to race our S2, got a bit tired of the fiddly job of trying to grab and removing the circlips in order to rebuild the diff, or to change over ratios… who knows why, but its a great time saver mod.

We’ve just about wrapped up with this repair or restoration diff housing project. But there’s a couple of things that we have to do yet. We need to mount the diff housing on a 90 deg angle plate to machine and true the upper and lower surfaces of the outer mounting lugs, plus machine the gasket surface where the filler screws in, and also the gasket face surface of the housing breather that sits on top. The following photos show the process.

Milling the top surface of the lugs, it is surprising how much wear occurs over time, the upper faces were not true at all. Photo shows the housing mounted to the angle plate, which is mounted solidly to the milling machine table.

The machining work continues on the underneath surface (Housing is upside down here) of the mounting lug, the out of true surface of the lug can be clearly seen, but three light milling cuts had all of the surfaces nice and true again. You might think this is over kill and that the upper bushings will counteract for any irregularity. That may be true to a point, but as we’ve said many times before, the elan is a finely tuned automobile, if every component is the very best that it can be, it must help to produce an even more amazing car to drive.

So when this diff housing is put into service again, it will be fitted with our race proven fabricated diff brace cage support, and we expect no further issues with it.

To close off this project, we had the diff housing vapor blasted to remove years of ingrained stains and to tidy the work up, we had a gear box casing done recently and it presented like new afterwards, as is the case with the elan aluminium diff housing, this I think is the icing on the cake.

Rear shot of the housing after wet blasting. The process puts a beautiful satin finish on any cast aluminium surface.

This is the left hand bearing housing, after weld repair and re-machining.

The right hand bearing housing after weld and repair and machining.

The moral to the story is that, damaged parts can be repaired and brought back to provide a serviceable life again. While cost is always a consideration, this repair would have been somewhere between a quarter and close to half of new cost…. if you were stuck for time, or as in this case, you wanted to save a badly damaged diff housing from the scrap bin, its probably worth it.

The bearing housings have had bearings assembled and removed to check that the tolerances were still OK.

Now that the project is all done and dusted, and you’ve digested the article, its odds on you might be curious about what type of TIG welder was used. (No financial connection suggested here).

The brand is Bossweld AC-DC 200X Inverter with HF function for welding aluminium, and several other metals. The shield gas is Argon. They are very versatile welding machine, and a popular choice here in Australia.

The next aluminium fabricating and welding project is already in progress, there will be another article to read on this blog in the near future… Watch this space.