MECHANICAL OVERHAUL
of AC's post-war 2 Litre SaloonENV Rear Axle
Checking
When checking the ENV axle for hub bearing wear, you need both rear wheels off the ground. This axle has a combined end float, since the half-shafts touch each other and there is a tapered roller-bearing at each hub. The specified end float is 0.005" to 0.008" (0.13mm to 0.20mm). You can measure it (with wheels removed) with internal calipers, between the edge of the brake back-plate and the flange of the brake drum. Take a few measurements to ensure accuracy. If leaking oil is the reason for this work, then note that oil may be seeping out via the adjusting shims, between the bearing housing and the brake back-plate, rather than the seal?
If you plan to do any work on the differential (including renewal of the oil seal), then it is best to slacken the large nut on the input shaft drive flange, before doing anything else. That is because it is much easier to slacken this nut using the handbrake to stop the shafts from turning. On my axle, the nut was so tight that the brakes slipped, so I locked them tight with the adjusters.
Unless you are restoring the car, it is usual to keep the axle casing in situ during overhaul. The 2 axle half-shafts can be withdrawn and then the differential removed. If you are restoring the car bodywork, then this is an ideal time to remove the whole axle, as it is normally very difficult to extract. In case you do need to remove the whole axle, I have included spring removal instructions. You would also need to dismantle the brakes. With mechanical brakes, disconnect the rods immediately behind the back-plates. Avoid disturbing the long adjusting nuts on each rod, as you may lose the correct setting. If you do need to dismantle the adjusting barrel nuts, then count the number of turns to unscrew each rod and make a note of this. Also remember that one end of this long nut (and one of the locking nuts) has a left-handed thread. If you need to remove the axle casing when the bodywork is still assembled, then the handbook says: Slide casing across the car, lower one end of it, and pull it out from under the car.
Leafspring removal
First of all, do not follow the instructions in the AC handbook! Spring removal is awkward because the chassis passes underneath the axle, and the chassis underpan is below the spring. Firstly, disconnect and remove the dampers, remove the hasps from over the axle, disconnect the prop-shaft, and if you have telescopic dampers, remove the damper sub-frame. Jack the rear of the car up and rest the chassis on stands. As far as I can see, the only method for safe spring extraction, is to clamp the spring straight against some suitable girders. I managed to do this by clamping each half of the spring against separate short pieces of steel girder. The later version of this spring, has a very thick and straight bottom leaf, and you can use this to clamp the middle part of the spring straight. The spring will still jump up a little bit when you then remove a pivot bolt. For easy access, I recommend removing the rear seat and the aluminium panel beneath it. There are access hatches in the boot floor, spare wheel compartment, and also in the inner wings. Then remove the other pivot bolts and the U-bolts securing the axle. An alternative approach might be to clamp the front end of the springs to the chassis, remove the pivot bolts, and then release the clamp. However, you would need a clamp with a very long travel (over 5 inches/125mm) and one that won't slip off.
After releasing one spring, it is best to remove it completely before starting on the other spring, otherwise it will add to the stored spring load that you release on the second spring.
Dismantling axle
You need enough space in your garage to withdraw each half-shaft. A garage at least 8.5 feet (2.6 metres) wide is sufficient. It is possible to do it in a typical 8 feet (2.4m) wide single garage, but only if you are removing the whole axle. After the springs have been removed, slide the axle to the left or right as far as it will go, and then turn it slightly so that it is a bit skewed relative to the chassis. You can withdraw the half-shaft by swinging it round as it pulls out. The half-shaft comes out complete with the bearing housing and brake back plate. So the intial task is to dismantle the brakes and then undo the 6 bolts holding the bearing housing. Be careful not to damage the inner oil seal that is inside the axle casing with the weight of the shaft, unless you are renewing the seals. With both half-shafts out, you can unbolt the differential and remove it. It is very heavy! Cover up the differential to keep out any dirt.
Splined end of half-shaft including thrust-button on tip, as the 2 shafts touch each other
Inner oil seal removal
Removal of outer oil seal and outer-race of hub bearing
The outer oil seals are inside the bearing housing, and in my axle, are trapped inside by the bearing outer-race, which is supposed to be removed first. This design matches the instructions in the AC handbook, but a close look at the sectioned drawing in the handbook, shows an improved design. In the drawing, the oil seal can come out of the housing without disturbing the bearing. There are extractor slots in the bearing housing under the outer-race, but these are much too small to be of any use. Any bearing puller small enough, will probably break! I hacksawed and chiselled through the outer seal and removed it, and thus gained better access to the outer-race. I found that the only way to shift this outer-race, was some "gentle persuasion"! Yes, a heavy mallet, applied via a thick metal rod. Great care needs to be taken not to do any damage. This should be done on a wooden bench to absorb the impacts, as one doesn't wish to crack the housing. I carefully measured any movement to be sure that it was coming out evenly.
The above photo shows the bearing housing with a damaged outer race still fitted. Damage may have been caused by excessive end play, and/or from installation.
Bearing removal from half-shaft
The handbook says to "press" the shaft out of the bearing. With no 20 ton press to hand, I improvised. I have a lot of nuts and bolts, so I used some of these to prise the bearing housing away from the hub. Once it had moved a little, I could remove the housing bolts, and insert long hex screws through the bolt holes, to complete the job.
Bearing housing with outer oil seal still fitted
Hub bearings
Since these axles are similar to (but not the same as) those fitted to early XK120 Jaguars, a quick look at replacement bearings indicates Timken number 25577/25522. I found that my bearings were 25578/25522. The "25578" refers to the inner part of the bearing (cone and rollers) and is 0.0005" (half a thou/0.013mm) smaller bore size. My bearings had not been fitted fully home, resulting in the distance piece being free to spin on the axle. Or more accurately, the axle had been turning while the distance piece tended to stay still, gripped by the oil seal. It also meant that there was excessive end play in the bearings. I decided to replace my bearings with Timken 25577/25522. Apart from the bore size (which is still 0.001" smaller than the axle), all other relevant dimensions are identical.
Oil seals
The originals were leather, but I have replaced mine with modern nitrile-rubber seals of the same dimensions. If fitting new leather seals, these will have to be soaked in oil before installion. The seal dimensions are:
Outer seal: ID=2.000" (50.80mm). OD=2 3/4" (69.9mm). Thickness=0.375" (9.53mm).
Inner seal: ID=1 3/8" (34.9mm). OD=2 3/8" (60.33mm). Thickness=1/2" (12.7mm).
Crack testing
The half-shafts should be crack tested, for peace of mind. The old-fashioned way is to tap the edge of the hub and hopefully it will ring like a bell! A more thorough approach is to buy a dye penetrant crack testing kit from an aerospace supplier. I used the Ardrox kit made up of 3 spray cans. A solvent cleaner, since the parts to be tested need to be very clean. A red dye which you leave on for about 20 minutes before wiping off the excess dye. Then a developer spray which you apply and then wait 10 minutes. Any cracks should show up bright red against the pale pink/white surface. Then clean off the dye with the solvent. I did this test on the bearing housings too.
Repainting
If the axle is removed, then it's a good opportunity to repaint it. I followed the same procedure as with my chassis, degreasing and a thorough abrasive clean up. Then a phosphating solution, ready for painting with 2 part epoxy-mastic and then 2 part polyurethane.
Installing the oil seals
These go in easily, but the metal casings are easily damaged. The modern seals have a nitrile-rubber coating over the metal and I coated these in oil before installing. If you are fitting the old style seal with bare metal cases, then a gasket sealant should be applied to the outer edge.
Installing hub bearing outer-race
Hub bolts
The bolts securing the bearing housings to the axle, are a non-standard length: 3/8 BSF x 1 5/16". They haven't been cut to length, which I can tell because the thread length is correct (2 x dia.). Replacing them with slightly shorter 1.25" long bolts is not recommended, so I went up to 1.5" long and added a washer under each nut. I used Phillidas all metal self-locking nuts.
Installing hub bearing assembly
This is easier to do if you bolt the half-shaft onto a wheel. Remember to fit the bolts into the bearing housing first, and the bell-shaped distance piece is slid onto the axle. Then the housing goes onto the axle followed by the bearing cone/roller assembly. This cone is supposed to be pressed onto the axle, but with no press available, I resorted to more primative methods! A thick metal rod resting on the edge of the cone is hit gently with a heavy mallet. The tyre absorbs the shock of impacts. Tap the cone evenly all around. I used newspaper to cover the bearing during this process, to keep it clean. Don't be tempted to use the ring nut to press it home, because the keyways through the thread, will damage the nut's thread (I found metal shavings in the keyway when I dismantled the axle). Make sure that the cone is pressing firmly against the distance piece, which should not be able to spin on the axle. Next, slide on the keyed washer and the tab washer and finally the ring nut. Hopefully your tab washer will still have a couple of unused tabs that should be bent onto flats of the ring nut. And don't forget to pack the bearing with a suitable grease and then cover it up to keep it clean.
Differential
I have not attempted an overhaul on the differential, and it looks like a challenging task to do at home. I inspected the gears for any damage and also the backlash between the crown-wheel and pinion. This is measured at the periphary of the crown-wheel and should be between 0.005" and 0.006" (0.13mm to 0.15mm). If you decide to tackle a differential rebuild, I would recommend obtaining an AC handbook (Series 2 or 3) for the 2 Litre, for further instructions.
You can easily change the oil seal at the front of the diff. Remove the big slotted nut (that you remembered to slacken before removing the axle from the car!), and pull off the drive-flange. Remove the old seal, most likely by destructive means, then a new one presses in easily. The original was a double leather seal, and thus an unusually thick casing (5/8" or 15.88mm). Its other dimensions are ID=1.75" (44.45mm) and OD=2.875" (73.03mm). I could not find a seal of the same thickness (double or single), so I have tried a slightly thinner 1/2" (12.7mm) thick single nitrile seal. Some restorers fit leather seals, but I don't know if there is any practical advantage to this? I would expect nitrile seals to be superior. British classics are notorious for dripping oil everywhere, and I would like my AC to be drip-free!
Gasket
You can make your own paper gasket to go between the differential and the axle casing. It needs to be thin and I used 0.4mm (1/64") thick gasket paper. What appear to be studs on the axle case, are in fact bolts inserted from the inside. I partly unscrewed them, and then spread the paper across the bolts, and used nuts to make the bolt holes, and fasten the paper down. Then I cut out the main hole with a knife, and penciled the outside edge for cutting with scissors.
Reassembly
I did a test assembly to check the axle end float. This is a combined end float, and so can only be checked with both half-shafts in place. With the bolts firmly tightened, you can measure the end float using internal calipers between the brake back-plate and the back of the hub. End float should be from 0.005" to 0.008" (0.127mm to 0.203mm). If there is too much, then you have to remove the shims that are sandwiched between the backplates and the bearing housings. My axle had 3 shims of thicknesses 0.024", 0.012" and 0.006" respectively. I found that I had to remove all but the 0.006" shim. If you need more shims, then you might be able to purchase them from a classic Jaguar spares supplier, by looking up XK120 ENV axle parts.
You can then do the final reassembly with the axle resting on the chassis. The differential bolts on first, with a liquid gasket sealent added to the paper gasket. Then the half-shaft assemblies are fitted. I used liquid gasket sealant on the bearing housing, shims and backplates, because oil used to seep out passed these. Make sure that the self-locking nuts are nice and tight, and re-check the axle end float.
Adjusting shim for hub bearings
Bearing housing with axle spacer inserted
Axle spacer
Close up of half-shaft
U-bolts
Ideally, new U-bolts should be fitted, but I have found it hard to track down anything even remotely close to the originals. These are surprisingly thin, with 3/8 BSF threads.
Finishing
The rest of the reassembly is straight forward, albeit with the usual fun and games of clamping the leaf-springs. Don't forget to use split-pins or self-locking nuts for the telescopic dampers.
Finally, fill up the differential with 3 pints (1.7 litres) of EP90 oil. EP (extreme pressure) is needed for hypoid gearing as found in this axle.
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