Rebuilding a Harrop Elocker (1 Viewer)

[DivByZero]

Earlier this year, I picked up a A9334 Harrop Elocker for $200, which had suffered a mechanical failure. It had been used in the rear of a Hilux, and came still fitted in the diff centre. My plan was to rebuild it and fit it to the front of my 80, which uses the same locker.

The problem was an apparent failure of the cross shaft inside the locker. The shaft is designed with one rod straight across and two half length rods that lock together in the centre with three head cap screws. The screws themselves had sheared, allowing the rods to float out of the housing and grind against the ring gear.

First step was a full tear down, to see what I was dealing with. This turned out to be easier said than done, because the bearings were stuck on solid. Well, one side at least. One finally let go with the 20 ton press after a lot of stuffing around, but I had to resort to slicing the other one off with a mini cut off wheel. Here's some teardown shots once I had the thing open:

Cross shaft was totally rooted:

You can see there how worn down the surfaces are where the spider gears ride, and you can see in the shots above what almost looks like graphite power - that's fine metal dust from what remains of the screw heads and the missing material from the cross shaft. It was dry, which leads me to believe the diff was running without any gear oil at all for an extended period of time, which is what caused the damage. There was also problems with the spider gears themselves. The gears are made of harder material than the cross shaft, and the teeth themselves were acceptable to my eye, but the internal surface that rides on the cross shaft had suffered badly.

At this point I contacted Harrop support to see what they could provide in terms of parts. I could see I wanted a new cross shaft, spider gears, and thrust washers. Harrop support were good. Even though the locker was out of warranty, an older model they no longer made, and I wasn't the original owner, they still raided the parts bin and sent me a new cross shaft, no questions asked. I struck out with the gears though, apparently they use a different gear now, and they had none of the older one left. I contacted Eaton, no luck there either.

So, at this point I could scrap it for parts, or try and resurrect it with what I could source. I opted for the second. Part of the rationale is this - I have a HZJ80, part time model. Most of the time, the front hubs are unlocked, and the diff assembly is totally stationary. If I had a problem with this locker, I could just drop to 2wd and keep on driving until I have time to deal with it, so I see it as low risk in my case. If this was a full time model or going in the rear diff, I would have been more reluctant.

 

[DivByZero]

So then, how to proceed. I had the new cross shaft, which was vital, the old one was trashed, but the spider gears were an issue. They didn't have problems with the gear surface, just the internal face that rides on the cross shaft. The gears are hardened high carbon steel though, the cross shaft is some kind of weaker alloy. What you see in the picture above isn't as much damage to the internal surface, as it is material that's been ground/melted off the cross shaft, and fused with the gear surface. I actually had to drive the parts of the cross shaft out of the housing with a brass drift, because the internal diameter of the gears was now narrower, and they didn't fit properly over the less worn parts of the cross shaft. I also found the new cross shaft from Harrop wouldn't slip into the gears, same problem. I was able to take a measurement from the inside of one of the gears on one side that was in good condition, and confirmed the cross shaft had a diameter of 17.4mm, with the gear having an internal diameter of 17.5mm. I ordered a 17.5mm reaming bit, and ran the gears carefully though the drill press, on a very low speed, with lots of cutting oil:

Enlisted some help too from one of the kids:

The reaming was successful, and the gears now all slipped easily over the new cross shaft, but the inside was not yet smooth, and contained ridges and grooves. I didn't want bits of softer metal from the old cross shaft peeling off under load and tearing into the new cross shaft, so it was time for the next stage - honing.

I used a compact two leg brake cylinder hone, which goes down to 15mm, allowing it to work in these gears. It took quite a lot of honing, a very slow process with oil and a handheld drill for quite an extended period of time, slowly grinding off minuscule amounts of material to try and get back to a clean surface underneath. I went through an entire set of grinding stones for the four gears, but in the end it looked much better:

Not perfect as you can see from the second pic above, there were a few nicks in two of the gears, but that's the worst of it. I felt this was acceptable for the low speed intermittent work the spider gears have to do. With the gears cleaned up, I took to fully cleaning, the other parts, grinding a lot of it with a copper wheel, sanding back the thurst washers and any other parts that needed attention, and in the end it was all ready for reassembly:

I used some assembly lube for all the sliding surfaces, and carefully put everything back together. Stages of reassembly:

There was one issue with the housing too that I thought might require more attention. There was some flaring at the housing where the cross shaft peices acted on the housing like a jackhammer when they hit the ring gear. I ground the edges back a little, and was thinking of brazing around the edges if required to make the cross shaft stable:

In the end nothing extra was required. The two half-length shaft peices did the most damage. In the end I was able to change the orientation of the cross shaft, and the shaft that goes all the way across had enough support from the two opposite sides to sit properly, so I left it like that. Since the shaft doesn't rotate, it doesn't need to be pretty, it just has to be supported.

 

[DivByZero]

Final assembly:

Gears feel smooth and tight, hoping it'll perform well and not be noisy. All looks good on the bench, as much as I can test it out of the vehicle. It just needs bearings pressed and it's ready to install in a front diff, and I happen to have a spare front diff centre on the shelf, but that's a job for another day. I'll follow up here once it's in the vehicle.

 

[fjbj40]

Great job saving this from scrap

 

[BILT4ME]

Having trouble uploading final assembly pix, I'll add one tomorrow.

Gears feel smooth and tight, hoping it'll perform well and not be noisy. All looks good on the bench, as much as I can test it out of the vehicle. It just needs bearings pressed and it's ready to install in a front diff, and I happen to have a spare front diff centre on the shelf, but that's a job for another day. I'll follow up here once it's in the vehicle.

Did you Loctite the screws holding the cross shaft?
I've had the cross shaft pin screw come out of another differential, so I am forever paranoid about it.

 

[DivByZero]

Great job saving this from scrap

Thanks. Can't complain about a $200 elocker either!

Did you Loctite the screws holding the cross shaft?
I've had the cross shaft pin screw come out of another differential, so I am forever paranoid about it.

Yep, the screws they gave me for the new cross shaft came fitted with thread locker. Torqued them good and tight too, or as much as I dared. I put a little blue loctite on the two screws holding the two halves of the split case together too for good measure.