The chassis restoration of Octavius is simply two parts: the front axle and the rear axle. To ensure the safety we will install rear axle first, the front is more heavier which might cause the tilt of Octavius’ body on the two post lift. Therefore, after completing necessary part of Group 60: Shell, Grommet that will be blocked by the rear axle installation, the rear axle is assembled as a separate part.
015 Rear Differential
Apparently, as a relatively hardcore area, no one has ever worked on Octavius’ rear differential. The obvious problem was the sludge on the driver’s side flange, where the leak occurred. After we removed the entire rear axle, it wasn’t a surprise to see that almost all the seams were leaking.
The ideal example of differential restoration would naturally be factory spec, but I have lingering fears about it. Apparently, it’s Mercedes’ custom to paint the entire rear axle together, as evidenced by the black paint on all the bolts and nuts. Even the axle shaft boots were once covered by black paint, as the area of the axle shafts covered by the boots was unpainted. When I was involved with the restoration of a 1953 300 S cabriolet (W 188) at McPherson College Automotive Restoration, my team painted the chassis parts including the rear axle. Our director, Brian Martin, after communicating with the school’s Advisory Board (composed of leading figures in the restoration industry in the United States, including the chief of the Classic Center), learned that the entire rear axle would be painted black after assembly.
When I saw the rear axle being transferred from the paint booth back to the studio, the paint on the axle boots had cracked from twisting, in the factory way. When we reported to the Advisory Board at the end of the term, one of the senators asked us, perhaps teasingly, why you painted the entire rear axle together. The team looked at each other, and I was pushed up to answer the question. “Because the rear axle needs to be assembled before it can be painted”, well, that seems to explain some, and it also seems to explain nothing.
On Octavius the answer is obvious. In fact, for non-V12 models and late V12 models, it is not easy to unite the answer, because only early differentials have independent covers on both sides. This means that to assemble the differential, you must first insert the bearings and gears, then install the side covers. Then insert the axle shaft and secure the axle shaft with a locking piece inside. So before the differential rear cover is in place, the axle shaft is already connected to the differential. And before you install the axle shaft, you have to insert the boot, so it’s all there.
We managed to acquire the complete rear differential rebuild kit, Mercedes aftersales don’t retail kits anymore, only by individual part today. So we decided not to use all the new parts because the differential overall drives fine. After inspection, we kept the original side bearings and did not remove the gears. The differential rear cover was open at this point, we sealed it and sent it to the paint booth, where the rear cover was also painted separately.
I suddenly wanted to challenge the patterns I was following. Since all the bolts for the differential have been replated by me, they shine like gems and it would be a shame to bury them under mediocre black epoxy paint. So I decided to have some creation here, protecting each fresh bolt from the painting. It’s not easy because the steps in assembling the differential are unique, to get unpainted bolts, either mask the bolts or treat the painted ones. The ideal situation would of course be to have these bolts absent from the differential painting, so the solution is to use non-critical replacement bolts to hold the side cover in place and replace these after painting is complete.
The replacement bolts on the side covers soaked up all the fire, after they were completely dry they were replaced by new yellow screws, D-Day of the new ones. We replaced the seals on the front and sides and that should be enough to fix the leak. Then insert the axle shaft, secure it, close the rear cover. The beautiful bolts of the back cover are now also in place. The differential is done and we torqued all the bolts.
030 Axle Shaft
The axle shaft itself also needed repair, here a difficult problem arose. The bearing caps near the differential can be opened and the O-ring is replaceable, but not the side near the wheels. I think we brute force disassembled them and replaced the old ones with the above o-rings, that part is considered an assembly by EPC, you shouldn’t disassemble and service them. I must say that it took guts and skill to disassemble this part, if not careful it would damage the bearing and we actually lost a circlip. Leaks can be exacerbated if not installed properly. But we did it, and the axle shaft and flange were connected with new bolts. Many parts were starting to rust and I zinc plated the attachment parts but forgot to take pictures.
Regarding the paint of axle shaft, in order to prevent the boot from participating in the painting, we cannot assemble the axle shaft to the differential, but pint the axle shaft separately. This touches on another issue, theoretically the axle shafts and flanges are assembled and then painted so they appear to have no seams on edges. But if they are sprayed separately, there will obviously be gaps in the casting iron color, so a slight over spray is necessary.
We encountered a last minute parts issue: the EPC provided the wrong binder part number. The V8 and V12 share the same diameter axle shaft, so naturally I took the binders from the V8 NOS repair kit, but they were not long enough. Then I ordered new binders based on the EPC number, A1249973090, surprisingly they were still not long enough. In the end I had to re-galvanize the original binders, during installation we broke off 2/4 of them, these thin guys don’t like to be bent multiple times, and galvanizing them will cause them to become brittle and damage is almost impossible avoided. I still haven’t found the correct spare part yet, maybe I’ll have to wait to find the old part on another donor. The axle shafts are not tightened at this moment, they should be placed on the car and tightened once the working angle is reached.
045 Rear Subframe
Earlier, the rear subframe had been processed, along with many of the suspension parts that also needed to be painted. In order to protect the original rust-proof performance, I did not blast the original black E-coat, which is actually more time-consuming since hand sanding takes a lot of time. For the inside, I used compressed air to blow it out for a long time and there was a lot of dirt in it. Painting includes sanding, degreasing before painting, marine primer finish, and black epoxy paint.
The focus of the rear subframe is to replace the four rubber mounts connected to the body. They are crucial to the NVH experience. The typical failure is that the rubber in the middle of the mount cracks or breaks directly. On the Octavius, two cracked. For a job of this depth, don’t leave anything to chance, even if all 4 looks good, don’t expect much life from the 30 year old rubber. Given that replacing them requires removing the entire rear axle, I would just replace them regardless of their health. When purchasing parts, I insist on ordering them from the German warehouse directly from the dealer. They are all made recently. For rubber parts, it is best not to use NOS that are more than 20 years old.
The second job is to install the differential to the subframe. There are three connection points between the differential and the subframe. A long longitudinal screw at the front connects the differential to the cross member of the subframe, and several rubber pads are connected in series. Here, the design of the buffer rubber was changed in structure, the original design had 5 spacers, 2 of which had rubber. Since the rubber is not the critial here and they are limitedly attached to the spacers, I did not use the new design parts. The front end of the differential is almost completely fixed. At the rear end, the fixed bracket of the differential is fixed to the subframe by two transverse screws, and two bushings are connected in series on the screws. These bushings are definitely worth replacing because once they are damaged, the job is even harder than disassembling the entire rear axle. After comparison with the original parts, the design of the new parts has also been improved.
075 Rear Axle Mount
The rear suspension of the 140 is composed of a relatively complex multi-link-compared to other brands. For Mercedes, this is standard equipment from the 190 E onwards. Wheel carrier is classified into this group, it is the first job, we need to replace the rear wheel bearing. When all suspension parts are painted, the bearings are not disassembled to avoid over spray causing difficulties in assembly.
There is also a small u-joint at the rear end of the carrier that will connect to the torsion bar via a tie rod, also replaced. According to the EPC, the torsion bar is classified to Group 32: Suspesion and Springs, but it should be installed here, not forgetting the two rubber bushings on the torsion bar. The Lower control arm also requires two new bushings.
To ensure factory comfort, all arms are new, in die-cast aluminum color. I mentioned that the factory installed arms were covered in black paint since the entire rear axle was painted together. Here, instead of painting it black as is, I found a way to preserve the true color of the die cast aluminum. Due to being in stock for a long time, and lack of packaging, these arms are showing oxidation and wear. After some research I decided to send them to magnetic polish store. Magnetic polishing is widely used in the treatment of die-cast aluminum automotive parts, such as generator shield. The shop owner told me that after passivation, they can withstand salt spray for 48 hours. Considering I won’t be putting the Octavius in any wet conditions, this durability is acceptable.
I have accumulated a lot of NOS fasteners, but they are not completely usable either. Since calendar year 1997, all fasteners became Dacromet, in repair kits they were mixed with yellow zinc. Be careful if you use any OEM parts such as LEMFÖRDER. I used a pair of LEMFÖRDER tie rods, paired with the restored original nuts. As a result, their threads did not match, causing damage to the original nut during the tightening process. I had to look for the nuts on other cars. It also took several months to collect all the fasteners and restore them.
Tightening also requires extra attention. Theoretically, they need to be placed on the car and tightened when the inclination of the axle shaft reaches the working angle. However, many bolts on arms will be inaccessible after the rear axle is married to the body. So refer to other vehicles in shop, mount the axle shafts to a similar height, and then tighten those nuts that cannot be tightened later. Here is the complete rear axle. I also put in shock absorbers and springs to make it closer to the completeness of the press photo. This set will be introduced later. Below is a large collection of After & Before pictures.
Overall rear axle
Rear differential
Rear sub frame
Arms and fasteners
Wire harnesses and brackets
Torsion bar
At the end there’s the free browsing mode, I’m enjoying it.
The next chapter will introduce how we worked on Group 32: Suspesion and Springs. After completing all the hydraulic lines underneath, we can marry the rear axle onto the body.