Re-Painting the Hub Carrier

This post is less about starting a new job or finishing old tasks, but more about fixing a painting mistake on the rear hub carrier. Luckily Mark had already spotted this error and explained a better way of painting cast aluminum, which in hindsight I believe would have resolved this problem. The one downside to this was that due to my slow posting on this blog, Mark’s response to my original painting post came just after I had spent another weekend working through the steps below to fix the issues. Still, I did explain why I had observed the painting issues, which put my mind at rest. Importantly as this post will show, this problem was easily resolved with filling and re-painting.

Flaky Paint

Due to Christmas holidays, several weeks (maybe a month or so) went by between me painting the hub carries and then looking at them again. When I did, I noticed that the paint, where the splash shield fastens, was starting to peal. More concerning still was that this issue was visible on both hub carriers. It only seemed to be in this small region, which I guess is because it’s these areas which had the greatest amount of corrosion, and I didn’t manage to remove it all. 

Flaky paint on the rear hub carrier. 

Flaky paint initially sanded off.

Filling down and re-painting

A quick rub with sandpaper removed the large flaky parts. Although all the loose paint had been removed, I suspected that the problem would keep coming back unless I followed a more aggressive sanding approach. Doubting that I had not removed all of the corrosion, I, therefore, began filling down the entire flat area to remove as much of the corrosion as I could. Plenty of partially corroded aluminum quickly came off, further highlighting the error in my earlier ways. Lots of filling later, the surface was looking a lot better, although still with some deeply corroded recesses. Whilst I was able to get it looking a lot better than the image below, I was not able to remove all of the deep regions. 

Partially filled down hub carrier.

To avoid a repeat of the flaky paint, I then decided to seal this surface using POR 15. After carefully masking up the freshly installed bearings, I applied two coats of POR15 to the affected area. 

Preventative coating of POR15 on the affected area. 

After leaving this to dry, it was then time for a fresh coat of grey primer before a top coat of Arctic Silver. When spraying the primer, I used extra newspaper around the carrier to avoid getting too much overspray on the rest of the hub. 

Hub carrier, outside ready for first coat of primer. 

Hub carriers after the primer is applied.

After all this work is said and done, the final part looks as good as it did before. I don’t think you could tell that it has been partly sanded back and re-sprayed. 

Re-painted hub carrier.

The Cause

As I said at the start of this entry, Mark did explain the potential cause for why this had happened, all before he knew I had encountered a problem. The explanation was that cast aluminum is slightly porous, with containment and gasses trapped inside. To avoid this reacting with your paint, it is recommended that you place the part in an oven for 30 minutes to extract these contaminants/gasses before painting. It was this oven step, which I missed when I originally painted the carriers.

However, remember, I did put the painted carries into the oven, to allow them to expand when installing the races. I suspect this resulted in the same expansion and extraction gasses/containments from the aluminum, although this time they reacted with the paint which leads to the flaking. Although I learned of the correct approach after fixing the original problem, I’m hoping the POR15 will provide an adequate seal. I will keep a close eye on this area over the coming months and years, in case further action is required. 

Looking back, I am glad this happened, as I would never have learned about the need to degas cast aluminum parts before painting. I’m sure I will continue to make mistakes and go back and fix them! So, if anyone does spot other errors in my work, please leave a comment below, im always happy to learn from my mistakes (It certainly happens enough).

Prop Shaft Rebuild

With the rear hubs (partially) rebuilt, the last step before these parts can be assembled onto the chassis is to assemble the half shafts. This starts with finding the AK supplied shortened half shafts as well as the separate splined and differential end plate pieces which came from my donor vehicle. The ends of the half shaft have been cleaned and painted. To assemble these separate parts into one complete shaft, I have to tackle the dreaded universal joints.

Spline Ends

The AK manual suggests you start with the splined end so my first task was to find these parts from amongst the cleaned and painted donor parts. Then I dug out the new universal Joints (UJ’s) from my large SNG suppled new parts box. 

Splined half shaft end with new UJ.

Since I had planned to follow the AK method of pressing the UJ caps in with a vice, my first step was to check if these parts would fit. So I opened the bench vice to its fullest extent (125 mm) and the splined end fitted in easily. With the vice open, it was simply a case of placing a UJ cap on one side and then closing the vice to press the cap into place. Once the cap is flush against the splined end, the vice can be opened and the part removed. 

Vice pressing first UJ cap into the splined end of the half shaft.

Now the UJ itself can be fitted to the splined end. To do this, remove the adjacent cap from the UJ and place this end into the empty side (the side without the cap) of the splined end. Once this end of the UJ is in place, the opposing side of the UJ should slide easily into the already installed cap. With the UJ pushed into the installed cap, the opposing cap can be installed using the vice/press method. Whilst doing this, be careful to ensure none of the needle bearings come lose or worse, fall out. 

Initial fitment of the UJ into the splined end of the half shaft.

Once this pair of caps are installed, the UJ can be rotated to ensure it moves somewhat freely. The final step for this pair of caps is to secure them in place with their respective circlips. To fit this, the caps need to sit below the surface of the splined end to expose the circlip grooves. This can be done by placing a set of small washers or a nut onto the cap surfaces and then placing back into the vice. Once the caps are sunken correctly, the new circlips are easy to insert. 

I did find a few times that I had pushed one side of the caps in too far which meant I wasn’t able to install the opposing clips. This was easily remedied by placing the assembly back into the vice with a large nut placed on the lease recessed side and using the vice to press/shift the entire assembly through the splined end. 

UJ fully installed in the splined end of the half shaft.

With the UJ installed into the splined end, the process is then repeated to fit the splined end with the UJ into the main half shaft section. Again, start by installing one cap, followed by the UJ and then the opposing cap (almost sounds easy).

Time to repeat this process and install the opposing side of the UJ into the main half shaft.

Differential output end

Once the splined end is attached to the main shaft section, the attention then turns to the separate, cleaned differential plate end. The installation of the UJ is the same as before, with the UJ initially being pressed into the smaller differential plate end. Then the differential end can be assembled to the original half shaft assembly. 

Repeat the entire process on the differential mounting plate end.

UJ installed into differential plate end.

Final UJ cap (on this shafr) being pressed into place.

Having assembled the first of the half shafts, the above steps are repeated to construct the other half shaft. I didn’t have too many difficulties with this process other than it being a very repetitive process, which required a surprising amount of effort. 

One-half shaft assembled, now onto the next.

Completed Parts

After just over a couple of hours’ work, both half shafts had been assembled.

Both half shafts fully assembled.

Having rebuilt the last component of the rear suspension/drive system, the next step is to install all these parts on the chassis. Once these are installed onto the chassis I will then pump some grease into the UJ’s using the grease nipple.

Rear Hub Carrier - Rebuild

Having installed the differential and the swing arms, the next step is to build up the rear hubs so they can be mounted to the swing arms. In a previous post, I covered the strip down, cleaning and painting of the rear hubs and their carriers. In this post, the aim is to install the new races and bearings into the bare hub carrier. 

Freshly painted rear hub carrier.

Race Installation

The process of installing the races into the rear hub carrier is the same as that on the front. This being to use an old race with a slit cut into it and then a lump hammer to drift the new races into place. When I began to install the races, it was apparent that they are a slightly tighter fit than those on the front hubs. To aid the installation, I enlisted the help the kitchen oven to heat up and expand the aluminum casting. As I had never done this before, I was worried about applying excessive heat and warping the aluminum parts. I therefore gradually increased the oven temperature in stages starting at 80 degC and testing fitting the races after 30 mins in the oven. I finally ended up setting the oven to 120 degC. Of course with numerical simulation tools like COMSOL Multiphysics (the company which I currently work for), I could have predicted the expansion with a numerical model far more quickly. However, that sounded too much like work and so I chose instead to pick up the hammer and do the physical experiment!

Rear hub carrier in the kitchen oven. Such an odd sight!

With the little extra room, the outboard race easily drifted in. One thing to note, due to the considerable depth at which the outboard race sits, I had to use a pair of old races to drift the new race in. This is shown below, where three races are shown; the new race (barely visible), an upside down old race with a slot cut into it, and another old race sitting on top. It was here where the cut out in the old race really became useful.

Selection of old races being used to drift the new outboard race into place.

As before, when the tone of the impacts change the new race is home. Leaving you with this lovely view.

New outboard race installed.

The inboard race however proved a lot more difficult to install. This is mainly due not being able to impart much force onto the race due to the high sides of the carrier itself. Luckily, I was able to use the top of the hammer to gently drift the race in, with little taps. As a result, this race took almost as much time to install as all of the front races combined. Still, I got the job done in the end and that’s what counts. 

Installing inboard race.

Bearing installation

Now with the new races installed, their respective bearings can be greased up and installed. As with the front bearings, I used plently of grease and made sure to spin the outer casing with respect to the inner casing to work grease into the bearing. 

The final assemly of these bearings into the hub harrier also requires two new grease seals and a pair of spacers, one large and one small, from the donor car (top right in the image below). The order of the parts, from inboard to outbard is as follows: grease seal, bearing, small spacer, a larger spacer (tapped section facing inboard), bearing and finally grease seal. 

Bearing and seals.

To avoid the spacers and bearings falling out as you build up either side of the hub, AK suggests the following method: insert the greased inboard bearing and secure it with its respective seal. Then having turned the hub over insert the small and large spacer in turn. This is then followed by the remaining race and seal. Unlike the front grease seals, both rear grease seals went on without a problem. Just a small tap with a hammer and presto. The rebuilt hub carrier now looks like this.

Seals installed into hub carriers

Rebuilt rear hub carrier. The few marks on the inside of the hub occurred whilst trying to install the new races.

Lower shaft and bearing 

The last part of the rear hub carrier which needs rebuilding are the lower fulcrum bearings. This comprises of two sets of races and bearings connected with a metal tube. These bearings are held in place with an integral grease seal and a large washer/spacer. In a previous post, I have removed all these components, given them a thorough cleaning and inspected them for excessive wear. When I inspected the cleaned parts, they appeared to be in good condition and so decided to reuse them. When reusing bearings, be extra careful to ensure you remember which races belongs to which bearing. Don’t mix races/bearings when re-building the hub as this increases the wear on these parts.

As with all parts to this cobra story, the first step is to layout the require parts. 

Cleaned parts ready for being re-installed.

As I am not replacing these races or bearings, this process is very quick. Slide one of the re-greased bearings onto the fulcrum tube and then pass this through the hub carrier. Then the opposing bearing can be slide onto the other end of the tube, which should now be exposed on the opposing side of the hub carrier. 

Re-greased bearing.

With the bearings in place, there should be a small amount of the fulcrum tube exposed which the spacers/washers can be slid over. Then with this all assembled and placed on its side, a few very gentle taps with a hammer can be applied to ensure the integral seal finds its home. 

Installed bottom bearing.

Final components 

With the hub carrier rebuilt, the final step is normally to install the brake shield and handbrake shoes. However, when I got to this stage I hadn’t ordered these parts yet. I am planning another order with SNG which will include amongst other items the rear brake rotors and pads and the required half shaft spacers/shims. However, before I can order the half shaft shims, I need to have an idea on how many and what size of shims I require to achieve the desired angle. For this, I need to install the hub with its carrier and the half shafts onto the chassis. Therefore, the plan now is to skip past the handbrake assembly and just push the hub shaft through and secure it in place with the ABS ring. I can, with the correct pullers, easily separate these parts again later to easily fit the handbrake mechanism. This is certainly starting to feel like a habit: do the work once, pull it apart and repeat two or three more times. 

With handbrake step omitted, the hub can be slid into the carrier and secured in place with the ABS ring. Some gentle percussive persuasion is required to mate these parts together. 

Assembled hub carrier with hub and ASB ring.

Of course, this entire blog entry is then repeated on the other side, but apart from the inboard race, it’s not such a long task. Before these parts are installed onto the chassis, I have to first assemble the half shafts, and that will be in the next post.