Rover P2 Rear Axle Rebuild

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47p2
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Rover P2 Rear Axle Rebuild

Post by 47p2 » Wed Oct 22, 2008 5:45 pm

Many thanks to RSR Member Chas Vyse for allowing me to post this article on the forum

Following the complete rebuild of the engine, my 1946 14HP P2 now ran well, but the whine from the differential which had been a constant feature of the car since I acquired it, seemed to be noisier than ever. This whine, combined with the sporadic ‘mystery’ grating noise I’d heard from the back end of the car while on the 2002 NTPR Rally, finally persuaded me to take the car off the road again, to rebuild the back end.
After removing the offside rear wheel and brake drum, the cause of the ‘mystery’ noise was revealed. One of the two brake shoe return springs had fractured at one end, allowing the spring to contact the drum, which had ground most of it away to powder. This discovery was a big relief, as I’d initially thought the noise was coming from the differential itself. A set of new brake shoe return springs was sourced from Mike Couldry and the drums shot blasted and painted.
On the subject of painting, I’m often asked what paint I use. I have to say that having tried many of the two pack, POR, Hammerite products etc, I always come back to good old fashioned ‘Chassis Black’. This paint which has stood the test of time, is a tough chlorinated coating which also looks good. Unlike Hammerite, it remains flexible and will not chip off a thin flexing body panel. Purists will like the fact that it is what Rover coated the chassis with originally. Those on a tight motoring budget will also like the fact that it costs less than circa £20 for a 5 litre drum, from motor factors such as ‘Partco Ltd’.
Having drained the differential, removed the brakes, drums, rear part of the exhaust and disconnected the brake rods and Luvax brake cross-tree oil pipe, I jacked the car up and put the vehicle on stands, so that the rear axle hung free.
It was apparent that the clearance between the differential housing and the chassis cross member that runs just in front of it, was ‘tight’. On the 1946 P2, there is not enough room to slide the prop shaft forwards or backwards and remove it from underneath the car as one might expect. Instead, you have to take out the rear seat, when the prop shaft can then be removed from inside the boot opening. Before doing this, it is good practice to mark the universal joints at each end of the shaft with the respective output flanges on the gearbox and differential, to ensure that the shaft is replaced in the same position. If you don’t do this, in some cases it can lead to a mysterious rumbling vibration when driving, due to out of balance forces in the drive train.
The differential is held in place by a ring of 5/16” BSF nuts around the casing, but before it can be removed, both half shafts that transmit power from the differential to the wheels, must also be removed. I discovered that on the P2, without the proper tool, this is difficult, if not impossible. The tool to use is a sliding hammer - not the body-shop variety, but the engineering kind. I managed to borrow one from the transmission specialist I intended to use, to mate the crownwheel and pinion correctly. At that time, I thought that this was the cause of the whining back axle. On the brake back plate you will see two rows of nuts. The outer row holds the brake back plate in position on the half shaft and should be ignored, as the back plate removes complete with its respective half shaft. Remove the inner set of nuts and the half shaft is free to be coaxed out of the axle housing. The slide hammer is designed to bolt to the wheel studs; which on 99% of cars it will do. The 1% that it won’t, is the P2! This is because the cylindrical piece that is fixed to the wheel bearing housing and is designed to hold the wheel to make for easy wheel replacement, holds off the slide hammer. The solution to this problem, is to cut 3 studs from standard M8 studding and you will find that the resulting long stud will loosely thread without causing damage, through the threaded holes that take the brake drum retaining screws. An M8 nut on the back secures the stud and another holds the slide hammer tight to the wheel bearing housing. Half a dozen or so firm bangs using the sliding handle and the half shafts complete with brake back plates pop out of the axle housing. With the slide hammer it is so easy. Without the slide hammer it is nigh on impossible. On the later P2’s such as mine, note that the half shafts are different lengths and must be replaced on the same side as you removed them.
According to The Manual, you can now unbolt the differential housing and remove it - though The Manual also states that on some models it is necessary to weigh down the boot to obtain clearance. Again; not on the 1946 14 HP P2! It appears impossible to remove the differential, without lowering the axle itself. I loaded my boot with an anvil and sundry scrap metal to the point I began to worry about dropping the lot through the floor of the boot! The clearance obtained is just not sufficient, between the emerging differential and the riveted-in-place chassis cross member that runs just in front of it. I lowered the axle slightly, by running the 4 nuts on the ‘U’ bolts that hold the rear springs to the axle, down to the very end of the threads. With the help of a long lever, this gave just enough clearance to remove the differential. However, I didn’t fancy my chances in replacing the differential the same way and as I also wanted to properly paint the axle casing, plus the underneath of the car above the axle, I decided to remove the axle casing completely.
Some care is needed in doing this; although the weight of the car is not on the springs, they are still held in considerable tension by the axle ‘U’ bolts. The required procedure is to place a bottle jack under the spring and just behind the axle and to jack the spring up visibly, by an inch or so and to then fit an axle stand under the spring. The axle stand will now take the tension and the ‘U’ bolts can be safely removed. Do the same for the other side and the whole axle can now be lifted off the springs and out of the car.
Inspecting the differential on the bench, it was apparent that the crown wheel and pinion were in good shape and appeared to be correctly meshed. Upon stripping the differential down, the ‘whining’ problem became obvious. The front pinion bearing, a really massive Hoffman double bearing, was beginning to break up. This puzzled me, as the bearing is totally over-engineered in true Rover fashion and should last a lifetime. With some difficulty I got the bearing apart; the following is deduction on my part. On one half of the ball bearing races, there was corrosive pitting and one could actually see where the balls had sat. I know that prior to rescue, my car had sat derelict in the open for very many years. I think the oil film on the half of the bearing that naturally sat above the static oil level, had over the years evaporated to nothing. Varying humidity and consequent condensation, had then rusted the exposed balls to the bearing surface. When the car had eventually been put back on the road, the rotating balls had broken the rust up and left a pitted bearing surface. This tied in with my rear end whine which was at its loudest when the car was under heavy load, climbing a hill. The cost of replacing this bearing was the single biggest cost in the whole rear end restoration.
While my local specialist rebuilt the differential and blued and correctly readjusted the crown wheel and pinion, I painted the axle and the underneath of the car. This, in turn, made the rear springs look ‘tatty’. I scrubbed these with paraffin and scraped off all the road dirt until I had shiny clean lightly oiled springs. The best spring protection to then apply, is the route that Rolls Royce took - Webasto leather gaiters. But you’re talking about the thick end of £300! Almost as good and visually pleasing, is ‘Denso Tape’. This is a thick 2” wide coarse cloth tape that is pressure injected with pure wax. Applying strips about 12” long at a time (it’s a bit unwieldy), one wraps the cleaned spring with the tape, when you will find that it will mould itself to the contours of the spring quite neatly. The next piece of tape will adhere firmly to the first and when you’ve finished the whole spring, you can mould the tape with your fingers to a tight fit, when all the joins will fuse together under the waxed coating. A single roll of tape is sufficient for one P2 spring. If you buy the tape from a motor factor you will pay a hefty mark-up - get it instead from any large builders or plumber’s merchants where it will cost circa £5 a roll - it’s used widely by the gas industry for protecting steel gas pipes that are to be buried.
When replacing the axle casing into the car, you will discover that the curvature of the relaxed springs means that the ‘U’ bolts are not long enough to get nuts on the end. I drilled a couple of holes in a piece of scrap steel bar and then used the M8 studs I had previously used to attach the slide hammer, to pull the axle down onto the springs. This will flatten the spring enough to enable you to secure the first ‘U’ bolt.
When replacing the rebuilt differential and painted axle casing etc, I renewed all the BSF fastenings, as all the originals showed signs of rusting. A complete range of BSF studs, bolts and nuts is available by fast mail order from ‘Namrick’ on 01273 779864. Two of my original ‘U’ bolts also had to be replaced; I found that Series 1 LandRover ‘U’ bolts obtained from my local garage did the trick.
The first long journey we undertook following the rear end rebuild, was to The Lakes Rally. Oh joy! With a strong rebuilt engine and the differential purring like a kitten, Rover had no problem maintaining a 65 mph cruise on the motorways and we took the prize for ‘furthest travelled’. However one problem that did manifest itself, was a gearbox leak that took the oil down to the very tip of the dipstick. When I removed the rear casing from the gearbox, which is easily done from inside and underneath the car, it was apparent that the oil seal had moved out of position and was no longer flush with the back of the casing. A new oil seal was procured from my local motor factor; it is a standard Payen oil seal Part No: NA564 and cost just £8.49. I smeared ‘Nutlock’ from Loctite inside the casing before tapping the new oil seal home, to ensure it stayed snuggly in position. This cured the oil leak. My P2 is now mechanically in good shape and the remaining major jobs is to return the paint scheme to all over black, to re-trim the door interiors, fit a new headlining and cure a rattling sunroof.


Photographs:
The slide hammer held to the half shaft housing by 3 lengths of M8 studding, loosely threaded into the screw holes that normally holds the brake drum retaining screws.
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The ‘U’ bolt nuts slackened off to the end of the studs, in an endeavour to increase the clearance between the diff housing and the chassis member that runs in front of it.
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Axle stands, used to take the tension out of the spring. Note: these stands are NOT supporting the weight of the car
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Axle removed; note fuel pump re-positioned from the bulkhead into the underfloor air stream. This cured all my previous fuel vaporisation problems. The pump was modified by 'Burlen Fuel Systems' to cope with the increased head required and at the same time the contacts were removed and the pump converted to solid state.
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The massive worn pinion bearing broken down to its constituent parts.
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The corroded and pitted track of the Hoffman front pinion bearing. This was not caused by wear - but because the car was 'abandoned' for very many years. The corrosion is where the bearing was above the rear axle oil level and is in fact rust damage
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Back axle parts and re-built diff.
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M8 studding and a piece of scrap steel, used to pull the axle down onto the spring, to enable the first ‘U’ bolt to be fastened
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‘Denso’ tape wrapped around the cleaned and oiled spring. Denso can be bought from Plumbers outlets and at £5 per roll, which will do one spring, is a lot cheaper than leather gaiters!
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