Today I was working on the rear axle. I’ve been busy lately with Steed puppets and cameras and ovens but today had a full day working on the car.
First I fixed some damaged wheel studs. I drilled out the old ones and then straightened the backplate with a hammer on a steel block. Then I riveted on the new studs. You simply insert the studs through then hammer them down on the other side. I did this over the vice jaws with the stud facing downwards between them.
New wheel studs.
Last week (or the week before?) I solved my diff housing undersized bush issue by taking the carrier and half shafts to Garth who reamed out the extra 1/64 for me with an adjustable reamer.
I also added new oil seals into the differential casing. Usually there is a felt seal behind the adjusters inside the diff. I replaced these with modern oil seals. These go into the metal cup that usually holds the felt then you hold them in place with the same washer and spring clip. You can get better seals that do away with the cups as it seems to me that oil can still leak between the cup and differential housing. While I have it all apart I might smear some Hylomar or something between them.
I didn’t get a picture of the spring clip. It’s a bugger to get on (and off) but to make it easier in the future I bent the ends in a little more. I think replacing it with a large internal circlip would be better. Something else I should look at doing while I have it all apart.
All of this actually goes under the adjuster used to load up the diff pinion bearings. This also doubles as an oil scroll. It has a groove machined in it which is supposed to fling any oil that comes along the half shaft back into the middle of the differential. Because the spiral scroll only works in one direction the adjusters are handed and marked with a L and R for the near side and offside of the diff. You have to make sure you get them the right way around!
So any oil has to get past the scroll on the adjuster first then past the oil seal. I guess this means if you drove about in reverse enough the scroll would make the oil drain out of the diff!
I spent this morning lapping the hubs to the half shafts. The hubs are held on only by the taper. There is a key but this is only to allow you to do things up without them rotating about each other. With the hub done up tight the key shouldn’t be doing anything. So you need good contact between the hub and the shaft taper. To get this you lap them together with some valve grinding paste. I found I needed to use the coarse stuff to make any progress. My half shafts were pretty knackered so it took lots of lapping. Of course the more you lap the further up the taper the hub will sit. Eventually this causes a problem!
If you lap too far the shoulder on the shaft ends up outside the hub. When you do up the nut it will rest on the shoulder instead of the hub and go no further. You can of course add a washer for the nut to bear on and this works fine. There is however a hidden issue with this. The half shaft has it’s spur gear integral with the end of the shaft. This is why you have to insert the shaft though the halves of the differential carrier before you assemble it.
Half shaft and diff carrier.
The spur gear on the shaft meshed with three other gears that are attached to shafts on the other half of the differential carrier. The gear sits below the three gears on it’s side of the carrier as you can see in the second picture above. The three gears on each half pair with one of the three gears on the opposite half. Three pairs of gears to share the load. In the third picture you can just see how the bottom and bottom right gears mesh as a pair. That transfers the torque from one half shaft to the other. This is also why if you stop the carrier from turning and turn one half shaft the other half shaft will rotate in the opposite direction. The half shaft going forwards turns it side gear backwards which turns it’s other side pair forwards which turns it’s half shaft backwards.
Incidentally this meshing arrangement is why you can recover from a half shaft breaking with a clever hack. The trick is you remove the wheel and hub and pus the broken half shaft down into the differential carrier. The spur gear will mesh with the gears on the opposite side of the carrier and effectively lock the diff up. You then bung a ball bearing or a brass wheel nut down the axle shaft as a spacer and reattach the hub. The hub itself is attached to the wheel bearing which is attached to the differential housing. So the hub can still spin fine it just isn’t powered. The drive will all go to the other wheel through the now locked up diff. If you don’t lock the diff all the drive goes into the broken shaft which just spins and you go nowhere.
The issue with over lapping is it effectively pulls the half shaft outwards and if you pull far enough the spur gear will hit the inside face of the carrier and lock up. The problem is you generally won’t know this has happened until you’ve totally assembled the differential and done up the final hub nut at which point you find the wheel won’t turn!
There are several solutions to this:
- Get new half shafts and matching hubs. These are available in the UK. This is the best way of course but they are expensive and for me even more so since I’d have to pay for shipping half way around the world too.
- Get serviceable second hand ones.
This is another solution if you can find them. The issue is with all this stuff now 70+ years old finding unworn ones can be tricky. You still need to lap them and you just end up in the same situation again.
- Take off some of the inside of the spur gear and/or the face of differential carrier.
This is what I imagined I would need to do. You have to grind the gear as it is hardened steel. Of course you will reduce the meshing area which could be a weakness. Machining the carrier will also reduce the meshing area. This is briefly mentioned in the green book as something you can do but it gives no details.
- Shim the taper.
I saw this on the A7 friends site but I am unsure how effective it is long term. You basically make a thin metal shim from steel or aluminium to go between the hub and taper. I did try this just so I could assemble my diff without it locking as you will see below. I used thin aluminium cut from a drinks can. It did seem to work well. Even after temporarily bolting on the hub so I could turn the shaft I needed to use a puller to get the hub off again.
- Machine the hub so the bearing sits further into it.
I also found this on the A7 friends site and it seems interesting.
Below though is the taper method. I am just using this for now to assemble everything. When I lapped I ended up with the shaft shoulder about 1/16th above the hub face. I think this is probably extremely excessive but this was with the best matched pairing of hub and shaft I could get in my small collection.
Adding the drinks can shim (which seems to be about 5 thou thick) took it to be level again.
This is enough to allow me to continue for now. I am wondering about option 5.
Basically since the hub fits on the bearing and the bearing is in a fixed position on the outside of the differential housing if you machine the hub so it fits further onto the bearing the half shaft will poke more in towards the differential carrier. Machining the hub should be easy and there is plenty of steel there so nothing will get weaker. You then add a spacer behind the bearing to account for the wear. There is already a spacer there in fact, the larger washer that keeps the felt in place. Pictures should help explain.
The wheel bearing sits on the differential casing. It’s not fully home here so you can see the shoulder it fits against. There is a large flat washer and nut to hold it on.
Hub components. The hub, the bearing, large washer, felt seal then the backing plate with the wheel studs.
You can see the recess in the hub the bearing fits into. If I machine this 1/16th (as an example) deeper the hub will sit that much closer in towards the differential. Since the half shaft is bolted to the hub it also moves in 1/16th giving the clearance needed on the spur gear. Since the bearing is 1/16th further inside the hub you need a 1/16th spacer on the opposite side of it to even things out. A simple ring under the large flat washer would do that.
What I don’t know though is how much clearance there is between the stud plate and the brake backing plate. Not much I think. OK, this is going to annoy me now not knowing….
…so I went out in the dark and cold (well, not cold) and checked. It won’t work. There is very little clearance between the stud plate and the differential housing. I measured less that 1/16th. Also if you do shift the hub that shifts other things too such as the brake drum which might then rub on the back plate. It’s a good idea in theory but I don’t think it will work in practice. There isn’t much space to play with.
I think to get the car on it’s wheels again I will use shims and look around for better half shafts and hubs. I know Ian might have one that is serviceable for me.
With the shims working I pressed on. I assembled the torque tube which meant pushing the bearing into the housing (I could do that by hand) and then inserting the shaft into the housing, through the bearing. The shaft is a tight fit in the bearing so I used a socket and the flange to hammer it home carefully.
Next you insert the bronze oil thrower but first you must add the woodruff key that holds the flange on. If you don’t add it now you can’t fit it in once the oil thrower is in place.
I need to make a lock washer before finally doing up the end nut that holds the flange on.
I also cleaned up the differential housing by running a tap into all the threaded holes to clean out the rust and muck and I wire brushed all the surfaces the bearings press into so they were a nice, smooth fit.
I then test fitted everything and it all goes together well. Everything turns as it should by hand but it’s pretty stiff. I think that’s just all the friction in all the gears. Turning things with a large spanner to give a bit of leverage makes it much easier.
Now for tomorrow I am ready to go through the whole setting up the crown wheel and pinion exercise.