Moving on from the previous post about the front axle, we arrive here, at the rear axle as promised.
Again, as with the front axle, I had to remove all the braking and suspension components. This obviously includes the spring platforms, dampers, brake calipers and the A-frame. All the bolts were rusty as with the front axle. However, this time I was prepared. I used a combination of 1600 Celsius blow torch, and –40 Celsius freezer spray. It really made (almost) everything easy to undo, I did have to use a few other techniques to remove some things. But for the most part the fire/ freeze method worked.
So onto the axle.
You can see clearly how the rear brakes are connected, a simple T piece. This means that the Disco’ doesn’t brake opposite corners as with most other cars. It has individual circuits for the front wheels and a single circuit for the rears. This means should the worst come to the worst and the rear line breaks somewhere ahead of the T piece, you lose all rear braking. However the handbrake could be used instead. Although, saying that, there is only one master cylinder. That means all fluid has one original pressure source, which means the car only really has a single circuit.
Below are a couple of pictures after I removed the dampers, spring platforms and brake calipers. I removed the dampers using a nut splitter, as you can see one of them is a bit bent.
The only thing left to remove was the A-frame, which is obscured by the axle as it was upside down when the picture was taken.
The A-frame is connected to the axle by a ball joint, which is secured by a 30mm king nut and split pin, oh joy! All the fun of a rusted split pin in a very confined space, super! I took the easy route and just cut it off and used a nail punch to remove the legs. Now for the nut, because it was in such a confined space, the only thing I could fit on it was a 30mm spanner. This meant I couldn’t get enough torque on the nut to undo it.
So, I drilled the edge of the nut and used a chisel to split the nut, after which it came out by hand.
As an aside here is the seized bush, it is ruined. The inner metal ring of the bush had rusted to the bolt rendering the bolt immobile. This meant I would not have been able to remove the A-frame from the chassis without cutting the bolt. I won’t be able to remove the bush without a hydraulic press, unless I drill a large hole through the bolt.
Below is a picture of the axle after I removed all the external parts.
So now is the part of the walkthrough that is important.
Pre-preparation: Drain the axle of its oil. As before note the colour of the oil. There is a chance that if you do any off-roading, in deep water particularly, the oil will be water contaminated. It will be white and a bit frothy, or if the oil has been contaminated for a long time will be mixed with rust, and be rust coloured and frothy. This is the reason you should check the colour of your diff oil after every deep water session. As it happens, the colour of my oil was a deep black, indicating it was time for a change anyway. There were no silver particles either so, I’m fairly happy.
Step 1: undo the 17mm axle bolts (5x).
Step 2: pull the axle shaft out from the axle.
Step 3: bend the locking tab away from the 52mm locking nut and remove both.
Step 3: remove the 52mm hub adjusting nut and spacer.
This reveals one of the two wheel bearings behind the hub. As you can see the grease has seen a lot of mileage, it is contaminated and there also isn’t much left in there either. At the very least it requires a re-grease.
Step 4: pull the hub from the stub axle. In the picture below you can see where the bearing sat on the stub axle.
Step 5: put an oil receptacle under the stub axle. Undo the 17mm stub axle bolts (6x).
Step 6: remove the stub axle.
Repeat for the other side.
Step 7: undo the 15mm final drive housing nuts (10x), and remove the final drive unit in the same way as the front axle.
Finally, wrap up the open ends of the axle and put it away ready for sand blasting. This rear axle is in a worse state than the front axle, mostly because the front axle is sat under the engine, and this being a rover engine has a few leaky bits. But in all honesty, it isn’t really that bad.
Not like the spare axle casing which is toast. There are more than a few holes in it.
At this point, I thought it would be interesting to show you my brake calipers. On the front, they are 4 piston calipers, and on the rear they are 2 piston calipers. They are surprisingly high spec for your average road car, which tend to have sliding calipers. You would tend to find similar calipers on fairly sporty cars, such as a Porsche Boxster. They were manufactured by AP Lockheed a.k.a. AP Racing. They have 4 quite large pistons, which means a large, fairly uniform contact area on the pads. Which in turn means the pad is pressed more evenly onto the disc (than a single piston caliper, which will tend to bend the pad slightly), which mean a greater area of the pad is used against the disc and results in a larger stopping force for the same pedal input (with everything else being assumed to be equal). Having multiple opposed piston calipers allows for larger brake pads as well, which means heat is dissipated more quickly (as a larger surface area can absorb/ dissipate more heat than a smaller one). This results in a braking system that is more resistant to brake fade over a series of heavy braking situations than a sliding caliper (in general). Which is a plus on the Disco’, as the discs are not ventilated.
These brakes are good, but not the best. They are bolted together rather than being mono-block. So when I brake (simplifying the problem down by ignoring all material deformation, mechanical or thermodynamic, heat transfer and friction, and assuming a completely incompressible hydraulic fluid), the pistons press the pads onto the disc, which exerts an equal and opposite force on the pistons. This equal and opposite force will try and force the caliper apart, which is prevented from happening by the caliper bolts. Caliper bolts will not be as good as taking the load as a much larger cross-section of uniform material, as in a mono-block caliper. In the real world, the bolts are a source of loss of efficiency of the calipers.
However good/ not good calipers are theoretically, it doesn’t change the fact that my calipers don’t actually work. At least not as they should, some of the pistons are seized. They could do with a rebuild, which is what I am going to do. Probably new pistons (dependent on condition), new seals and new bolts (maybe), as well as a de-rust and fresh coat of heat resistant paint. Ideally, I would like them as new, we’ll see how long my patience holds up whilst doing this, I have 8 to do. As long as I end up with a working set I won’t be too unhappy.
Anyway, that is it for another edition. I have lots to be getting on with, like removing thousands of bushes, sand-blasting lots of things and rebuilding these calipers (and eventually axles). Cheerio.
