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.