Differential and Swingarm Install

Having earlier cleaned and painted the differential, the plan for this entry is to install this into the chassis. Once the differential is installed, the rear swing arms can be attached.

Installing the differential

Before installing the differential into the chassis, I first had to find all the required parts. This included the front pendulum, tie bar bracket and assorted nyloc nuts and washers supplied by AK. With these parts found, each bolt/shaft and bushing surface was given a healthy coating of copper grease. Then the cleaned and painted pendulum from the donor car is re-mated with differential. This slides over the differential nose and onto the large studs. 

Installing the differential into the car is certainly not a one-person task. I, therefore, enlisted the help of my better half and a trolley jack. The plan was to raise the differential using a trolley jacket, with one person to supporting and navigate the differential whilst the second person gently pushes the trolley jack and differential into place. Although this is certainly not an easy job, with a little care the differential soon slots into place.

There is then a range of nuts which need to be added to secure the differential in place. All the nuts shown below are provided within the AK kit. The back of the differential is secured with a pair of the M12 x 70 mm bolts, washers, and M12 nyloc nuts. AK also supply four 35mm x 14 mm washers, which are used as spaces between the rear of the differential and the chassis.

Rear ot differential secured to chassis, with spacers shown.

The two main differential bolts (which pass through the pendulum) require a 1”1/4 x 5/8” washer and an M16 nut. The differential nose is secured in place with 4x M10 nylocs.

Differential securely bolted in place.

Attaching the Tie Bar Bracket

With the differential secured in place, the rear swing arms can be a fastened onto it. This requires another rummage around the garage to find the relevant supplied AK and donor parts. With the exception of the swing arms, the majority of the components needed for this step come from the donor vehicle.

Parts required to install rear swing arm.

The swing arms attach to the pendulum (already installed between the differential and the chassis) and a rear tie bar bracket which fastens to the rear of the differential. To install the tie bar bracket, first slide the small right angle bracket (cleaned and painted from the donor car), and a pair of rubber domed washers onto the already cooper greased studs on the differential. 

Installed differential with exposed stubs.

Here I am using the rubber domed washers from the donor car. This is because after given them a good clean they appeared to in good condition. 

Right angle bracket and two of the doomed washers installed.

As well as applying copper grease to the studs, I also put grease on the inside of the tie bar bushes. With the troublesome memories of removing this from the donor vehicle still fresh in my mind, I am certainly going to apply extra copper grease here. Then the tie bar itself slides on and is secured in place with an additional set of dome rubber washers and M12 nuts. Whilst AK does not directly provide the nylocs for the tie bar, I seemed to have extra M12’s, so will use these when it comes to tightening things down.

Tie bar installed onto differential.

Now the swing arm is installed by passing the lower fulcrum shaft through from the tie bar, through two holes in the swing arm and finally through the pendulum. The fulcrum shaft is then secured in place with an M12 nyloc nut (according to AK). There are, of course, numerous washes and a protective metal tube placed in between. From rear to front, the fulcrum shaft should pass through the following: swing arm, tie bar, 2 washers, a protective tube, swing arm, 2 washers and finally the pendulum before being secured with a washer and nut. 

The washers which sits within this assembly are 1”1/2 x 7/8”. Annoyingly, these are not supplied by AK and given the lack of washers I found online, they don’t appear to be standard size. Since AK does supply the same size washers for the front lower fulcrum shaft (used in setting the chamber), I gave them a quick email to find out where they buy them from. The response was from Welland Engineering, but when I phoned up they seem to only really sell to manufactures with washers in boxes of 500, not ideal for my needs. The dimensions of these washers are not too dissimilar from the metric M22 washers and so I chose to use these instead. These can be ordered in packs of 10 from Amazon for very little money.

Missing Metal Tube

The protective metal tube (mentioned above) should have been supplied with the donor parts, but whilst this was originally part of the XJ40 chassis, through its life span the chassis was given continual ‘improvements’ which lead to this separate part being omitted in later models and changed for an integral part on later swing arms. Since my donor car was a later model, I do not have this separate part. The tube in question is part number CAC9384 and is advertised online for around £3, but no one seems to have any in stock (Bummer!). I then contacted Simply Performance who did have a few salvaged units lying around but by their own omission, they were not in great condition. However, Mark was able to get one posted to him so that we could measure its dimensions and investigate sourcing our own tube. Upon measuring Mark’s original tube, we obtained the following dimensions:

• Outer diameter: 28 mm
• Inner diameter: 21.2 mm
• Wall thickness: 3.4mm
• Length: 196.5mm

With these dimensions, I began searching online metal merchants. Matching the inner and outer diameters was not as straightforward as I had first hoped, as this doesn’t appear to be a standard size for stainless steel, even when its converted to the nearest imperial measurement of 1" x 14 SWG. I found these dimensions for plain steel but I didn't want to buy this as I would have to paint the internal surfaces to avoid them rusting.

The closest match for the radial dimensions I found was 25 mm outer diameter with a 1.5 mm wall thickness (22 mm ID). Whilst most major online metal stockiest had this in stock and would cut the tubes down to length, they generally had very high shipping fee (£30+). A better option was to order a 1 m section of this tubing from eBay, which cost £13 including p&p. I would have to cut this tube down to length, but I could make two new sets of tubes for both mine and Mark’s cars easily. Ordering this tube was a no brainer and it arrived within a few days. 

Tube section on workbench ready to cut down to size.

Despite having the dimensions of the tube above I did check the oversized diameter and length of the tube against my actual chassis.

Comparison of fulcrum shaft and purchased metal tube.

Having offered up the freshly cut tube to the temporarily assembled swing arm, I could check its length and trim it down with the grinder. After all, was said and done, the actual dimension of the tube matched Mark’s original measurements very closely. 

Offering up the cut tube to the gap between the swing arm.

Two spacer tubes down to size. I also made an extra set for Mark.

Assemble of the Swing Arm

With the protective tubes cut to length, it was the normal process of taking everything apart (again) to then re-assemble it with the new tube. The final layout of parts is now shown in the image below. For final assembly, it is important to ensure that all metal to metal surfaces (washer to washer included) are given a liberal coat of copper grease. When it came to fastening the nut at the end of the fulcrum shaft, it appears that AK’s statement of it being an M12 nut, is wrong (at least for my vehicle). Luckily, I still had my donor nut safely stored away and so with a coating of POR15, this was pressganged back into service. I will have to add some lock tight to it as well. 

Final layout of parts used to install a swing arm.

Fulcrum shaft going into tie bar

Close up of swing arm with the protective tube.

Installed swing arm with the metal tube.

With the process repeated, the second swing arm is installed. 

Both Swing arms installed.

Now that the swing arms are installed, the next step is to build up the half shafts and rear hubs. These separate items will be the focus of the next posts, before returning to installing them on the chassis.

Front Corner – part 2

Using the parts ordered from SNG, it is time to rebuild the front hubs with the new bearings and races. Once these are rebuilt, they can then be installed directly onto the part built front corners.

More Angle Grinding

The typical approach to install the bearing races is to use a hydraulic press with the correct sized race press tool. As I had neither of these tools a second common approach is to drift the races in. Whilst this process initially appears to be the reverse of the removal process, extra care needs to be taken not to damage the concave race surface. To avoid damaging these new races, the old race can be placed on top of the new races, with the old race then taking the direct impact from the hammer. To avoid getting the old races stuck in the hub, a clever trick which I found on Marks blog was to cut a slot into the old races. This slot allowed for the old race to deform and pop out of the hub if they get stuck. A short term borrow of Andrew’s angle grinder and slots were cut in the old set of races. 

Front races with slots cut in them.

Rebuilding the Front Hubs

Having created a race ‘insertion tool’, it’s now time to tackle their installation. I started by laying out all the parts on my workbench to ensure that I hadn’t lost anything. There was a small split pin in the SNG rebuild kit which I could see myself losing, so this was put in the top drawer of my tool chest for safe keeping. 

Parts and tools required to rebuild the front hub.

The plan seems simple: drift both new races in with a lump hammer using the old races to protect the new ones. 

The process of installing new races into a front hub.

After several good hits with my trusty hammer, the tone of the impacts changed to signify that the race is finally in its new home. The old races then came out easily, thanks to the freshly cut slot, exposing the installed race. I couldn’t believe how simple the process was.

New races installed in the front hub.

This process is then repeated on the other side of the hub. Both sides went in without too many problems. Although the hardest part is certainly getting the race to sit true in the recess during the first few impacts.

Once both races are installed, the messy jobs start as the bearings need to be greased. Since I didn’t want to get any grease on my phone or camera, there are no pictures of the process. The method was to rub general purpose grease into the new bearings internals, by rotating the outing surface in relation to the inner surface. A few good scoops of grease and the bearings can be dropped into the corresponding race. I should note I also put a small amount of grease on the race surface as a precaution before installing each bearing. 

Greased front hub.

Installing the inboard race is the same process, although there is an additional grooved oil seal that keeps the inboard bearing in place and keeps dirt out from the bearing. The seal supplied by SNG seemed to be slightly larger than the original donor part, which I had kept. After trying to install this seal with varying tools from a hammer to my vice, I decided to resort to the original seal. The old seal isn’t in bad a condition and so should suffice. I will undoubtedly come back to this and try and install the new SNG parts at a later date but will wait to discuss this with Mark when he gets there.

Installing the hub onto the chassis 

With both hubs rebuilt, the next step is to finish building up the front corners. Before installing the hubs, I decided to split from the AK manual and install the front hub covers, from the donor car. These have already been cleaned and painted ready for installation. Whilst the build manually does not say to install this part, they don’t appear to foul on anything (unlike the front splash shield) whilst offering additional protection to the bearings from the elements.

Final parts required to rebuild the front left corner.

This cover is secured to the upright with three T30 headed bolts. To ensure they don’t vibrate loose, the threads are given a coating of lock tight. This might be foolish and may come off later, but let’s see.

Greased stub axle with hub cover installed.

Returning to the AK build manual, the next step is to apply a small amount of grease to the front stub axle; which I duly did. The rebuilt hub then slides over the stub axle and is held in position with the large cone-shaped washer and fastened to the axel with a 15/16’’ nut. Both these parts came from the donor car and have been cleaned prior to installation. This assembly is then torqued to 27 Nm, released and then re-tightened finger tight. To ensure this nut doesn’t come loose, a castellated cover sits over the nut with a split pin passed through. Since this assembly might come apart again, either to replace, to grease seal or to remove the hub cover, I will not fully install the split pin yet. 

Front hub secured to stub axle.

To complete the installation of the front hub, a small domed cover fits over the end of the stub axel. This is a friction fit and includes a large O ring. For now, I have decided to re-use the original O ring from the donor car as it seemed in good condition.

The final stage of building the front corner is to install the front shock absorbers. This is a simple process, using the AK supplied 4 x 7/16” x 2.5” + M12 washers & nylocs to secure the top and bottom of the shock absorbers to their respective mounting locations on the wishbones and chassis. The one thing to note, is that the build manual recommends to ensure the adjusting knob on the shocks is facing inboard. This was impossible with my shock absorbers, and after a quick email to AK, they confirmed this does happen with modern shocks and they suggest placing adjustment knob forwards. 

After repeating this extensive process (over a few weekends) on the opposing front side, we are left with an assembled front end. 

Assembled front suspension!

With the front end assembled, the focus now shifts to the rear and installing the heavy differential. 

As an added bonus, I took this slow motion video of me using the angle grinder one evening. I was not cutting anything important, and this was done just to make the video. 

Front Suspension – Part 1

Now the real excitement can begin as I get to attach the first components to my new chassis. Since for now, at least, I’m following the manual, the first step is to build up both corners of the front suspension. All the large components for this are supplied by AK, but you will also need 4 new ball joints (which I ordered from SNG Barratt), as well as the refurbished front hub (a topic for another blog post).

My first task was to dig through the large pile of bubble wrapped parts supplied by AK to find the top and bottom front wishbones for both sides. I will also need the four M10 x 75 bolts and nuts required to fasten the top ball joints in place and the pack of 1”1/4 x 5/8” washers (all AK supplied). Then I will need the two top and bottom fulcrum shafts from my donor parts pile and the new ball joints.

Parts required to assembly front right corner.

New Ball Joints

Before assembling anything onto the chassis, the new ball joints need to be installed into the bare wishbones. The top ball joints fit into a crevice, without any additional shims (this is different to the donor vehicle). They are secured in place by passing the supplied M10 x75 bolts through both the crevice and ball joint. These bolts are fastened in place with the pair of M10 washers and nuts. The ball joints and bolts fitted easily and there were no issues with excessive powder coating, so a nice simple job to get me started! 

Front top wishbones with new ball joints - not installed yet.

The bottom ball joint is secured in place with four ‘special bolts’ ordered from SNG. According to AK the actual dimensions of these bolts are 5/16” x 1”, although I did not verify this. To avoid these bolts coming lose I added some additional lock tight and spring washers. Whilst spring washers were used on my original donor vehicle, I have replaced these with new ones.

Components needed to install lower ball joint.

Ball joint assembled with M6 bolts for caster angle measurement installed.

Installing the Wishbones 

With the new top ball joints secured to the wishbones, they can now be fitted to the chassis using the clean fulcrum shafts from the donor vehicle. To ensure the caster angle of the front uprights is correct, the build manual suggests distributing the 1”1/4 x 5/8” washers placed between either side and in between the wishbone and the chassis. Starting with the top front wishbone, two washers are placed either side of the wishbone (same on both sides).

Front wishbone fitted to chassis. The first part which I fitted :D.

When inserting these fulcrum shafts I had no issues with excessive powder coat and the shafts slide in easily. I applied copper grease to the shafts at this stage, which in hindsight might have been a mistake as it makes this job a lot messier when it comes to removing the fulcrum shafts to redistribute the washers.

One thing I did notice was that after installing both top wishbones, and resting them along the center line of the chassis they did not align correctly. I queried this with Jon to ensure I had not already made a dreadful mistake, and he assured me this is normal. Although a little unsure, I will take his word for this is and move on.

Top front wishbones rotated inboard. Notice they do not line up along the chassis rail below

The bottom wishbones are then installed, bypassing the donor fulcrum shaft through the chassis and wishbone, whilst placing a set number of washers between the wishbone and chassis. Since the number and their location affects the angle, AK suggests the following initial order.

• bottom right wishbone, place 3 washers to the front and 1 to the rear.
• bottom left wishbone, place 4 to the front and none to the rear.

Bottom wishbone installed and supported on a trolley jack.

With the bottom fulcrum shafts installed, it was apparent that my donor shafts were a little too long. The build manual states that the length of the fulcrum shaft is dependent on the age of your donor vehicle. To compensate for this, I placed 2 additional M22 washers at the head end of the shaft to shift the shaft’s position.

Fulcrum shaft too long, before adding additional washers.

With both top and bottom wishbones installed, the next step is to secure the upright to the ball joint. The easiest way I found to achieve this was to raise the bottom wishbone with a trolley jack and whilst it was being supported, secure the bottom ball joint in place. Then the top wishbone can be rotated into place and it’s ball joint loosely attached to the upright. 

Assembled front corner. Spirit level used to ensure wishbones are level.

Setting the Caster Angle

Now comes the setting up of the caster angle. After reading other cobra builder blogs, this job appears to be either very quick or a time-consuming nightmare. The first challenge is to level the chassis by altering the location and height of the four jack stands.

Then a pair of M6 bolts (lower bolt is packed with washers) are fastened into the upright. The caster angle is then measured against these two bolts, with a target of between 6 and 8 degrees. The further challenge is to ensure that the angle is the same on both sides.

To measure the angle between the two M6 bolts, AK supply a paper gauge and suggest using this with a plumb line. I had two concerns with this approach, firstly how straight was the edge of the paper now and after I have used it a few times, and how accurately can I secure the plump line to the central mark on a thin piece of paper. I, therefore, choose to use an application downloaded on my mobile.

The angle of the upright is then altered by redistributing the number of washer’s front to back on each wishbone. This is certainly a trial and error process but didn’t actually take that long. In the end, I had the following washer distribution and an angle of 7 degrees on both sides.

• Left top: 0 to the front and 2 to the rear
• Left bottom: 3 to the front and 1 to the rear
• Right top: 2 to the front and 0 to the rear
• Right bottom: 1 to the front and 3 to the rear

With the wishbones installed, the next step is to rebuild the front hubs and finish off the front suspension.

Cleaning and painting the Differential

The last major dirty job which I had to get done before the body arrived was cleaning the differential. This was slightly delayed due to a problem with removing its rear cover, as mentioned in an earlier post. Whilst the majority of the dirt and grim was removed prior to the body/chassis arrival, the final cleaning, sanding, and painting was completed after the chassis arrived and hence this post appears online now.

Let the Cleaning Begin

From the image below, the extent of the dirt/corrosion on the donor differential is evident. Given the time and energy, I am investing into building this car, there is no way I am going to install the differential whilst it’s in this state. The plan is to give it a clean and fresh coat of black paint. The dirtiest areas of the differential are certainly towards the bottom (no surprise there). The problem is that even with the oil removed from the differential, it is still a very heavy and cumbersome part to move and clean.

Differential prior to any cleaning.

To make life easier and to test out the new chain hoists (purchased for the body lifting), the differential is lifted over a bucket of soapy water. With plenty of hot soapy water, copious amounts of thick oily mud easily came off the differential. This cleaning was repeated multiple times and with the differential rotated at different angles until it was clean to the touch.

Differential supported by chain host whilst cleaning.

With the diff clean, it was put to one side as I needed to get the garage cleaned for the arrival of the chassis.

A few weeks after the chassis and body had arrived, I turned my attention back to the differential. The next step was to give the main casing a quick sand down with some medium grit sandpaper to remove any loose paint and to key the surface. With all this cleaning and sanding I am not sure if the differential looks any better at the moment.

Cleaned differential prior to painting.

 Having wiped the casing down with white spirit, it was time to give it a few coats of black POR15 paint. Whilst painting the differential I removed the rear cover as this needed to be cleaned separately and painted grey/silver. Since painting within the lines was never a strong skill of mine, I covered the parts which didn’t need painting in electrical tape. After a few coats of POR15 the differential was beginning to look a lot more respectable.

Freshly painted differential.

Cleaning the Aluminum Parts

With the differential casing now looking at it best again, my attention turned to the rear aluminum cover. Whilst the soapy water removed a lot of the surface dirt, the aluminum surface of the cover was still very corroded and needed further attention. In addition to the differential cover, the two rear hub carries, which are also aluminum, despite being cleaned with soapy water are also not looking at their best. Given the similar metal, and because I wanted to paint them the same final color, I decided to tackle the cleaning and painting of these parts together.

Note: to make cleaning the differential cover easier, I removed the breather, parts 7, 10 and 11 in the diagram below. This is a simple process of carefully popping off the top cover (11) and then removing the cir-clip. The remainder of the breather can then be pushed through to remove. I did look at replacing this part and after some online research found it to be part number JLM631.

Schematic diagram of the differential casing (No internals shown).

I didn’t want to place these parts in the Deox-C to remove the surface corrosion as I wasn’t sure how the aluminum would fair. Other bloggers have sent their parts off to be soda or vapor blasted. A search online found a few local-ish companies, but I wanted to see if I could service these parts myself first. My first plan was to try Cillit Bang Power Cleaner as this is designed to clean metal items around the kitchen, and I had some under the sink. After spraying the damp surface and leaving it to sit for 15 minutes before scrubbing off, I found it removed some more grim and corrosion, but definitely not all. Since the surfaces were not good enough for painting, I tried to mimic vapor blasting, using a household steam cleaner, which did nothing! My last plan before giving up was to see how easily the surfaces sanded down. Being aluminum it was very easy to sand and quickly looked a lot better. Although this would be a long process, since I had started I decided to stick with it. A comparison of a sanded/cleaned rear hub carrier next to a non-sanded carrier is shown below. 

Rear hub carries – left cleaned and sanded, right cleaned but not sanded.

The best part of a day later, both hub carriers and the differential cover had been sanded down and ready for a final clean and paint. Since I will be spraying these parts, I filled any bearing regions with newspaper and then covered in duct tape. Then, after a final wipe down with white spirit, these parts were given a few coats of silver spray. For this, I chose to use Arctic silver, as I had a can of this in the garage after doing a small painting job on my Citroen a few years ago.

Cleaned differential cover and hub carries ready for painting.

 After 3 coats, the parts looked amazing… I am very pleased with the result.

Freshly painted differential cover.

 With the differential cover painted it was time to re-install the breather. After comparing my breather parts with the online images, it seemed as though mine was in good condition and so I chose to reuse the original breather, but replace the cir-clip.

The rear hub carriers are also looking very smart with their new coat of paint. I will deal with the rebuild of the hubs in a separate blog post at a later date. For now, they are placed to one side.

Freshly painted rear hub carriers, front and back view.

Differential – Reassembly

Having cleaned and painted the differential cover and casing separately, they can now be re-assembled into a complete unit. With some research online, it is apparent that there is no pre-made gasket seal for this differential and instead you need to use LOCTITE SI 5980 Flange Sealant to create the casket.

Before applying the sealant, both mating surfaces (differential and cover) were rubbed down very gently with sandpaper to remove any excess sealant or dirt and then wiped over with white spirit. After leaving this to dry, the sealant was placed on the cover. The process was to add a continuous bead around on the inside of any bolt holes. Additional sealant was then placed on the outside of the bolt holes. With the sealant applied, the cover was then carefully positioned back onto the differential.

Differential cover before and after adding sealant.

Using the original 6 x ½ inch bolts and fresh m8 spring washers, the differential cover was reinstalled onto the main differential casing. The bolts were tightened down in a crisscross pattern in incremental stages to avoid warping the cover and to ensure even pressure on the sealant. As these bolts were fastened, a small amount of sealant began to ooze out the edges, which I guess means there is plenty of sealant in place. 

The two large bolts/shaft which has originally caused so much trouble were then re-installed and tightened using a few gentle taps with the slogging spanner.

Fully re-assembled differential, sealed and painted!

With the rear hubs carrier and differential cleaned, it’s now finally time to start building up the chassis. Hopefully, the parts will start to resemble a recognizable car.