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Salisbury Diff Locker Fitting


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I have decided a need a locker on my rear diff and am currently leaning towards a Truetrac (for fit and forget and reasonable on road manners), however all the advice regarding Salisbury diffs is to leave well alone unless you are an expert (which I am not). I have found several suppliers of the Truetrac, but not anyone who says they will fit it (Ashcroft, for example, specifically say they do not work with Salisbury diffs).

I would take it to my local independent, but if it is that tricky I want to feel comfortable that whoever I was asking to do this had some experience and done it before.

Any suggestions for someone in the South East who might be worth approaching?

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I had the same problem with the transit diff before I realised it was a prop shaft bearing. It looked as though I needed to move up from 'garage' to 'commercial reconditioning'. The other option might be American repairers with the dana being similar? Sorry I'm not more help, but it does appear to be a bit of a black hole compared to cartridge diffs.

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I keep saying. I've done three Salisbury diffs. One at Ford school the others at work. I've always said I'd never do another...Saying that they are only time consuming in getting things right.

Do you know anybody that has any connections with a REME workshop. They are supposed to do them.

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It's simple - I have changed an axle from 3.54 to 4.71 and back again with perfect results, and with no special tools other than borrowing the axle spreader tool for getting the carrier in and out of the axle case. Since you are not changing the ratio, you don't need to replace the pinion, which is the hardest part to set up. If you do need to replace it because it's worn, then it's a simple swap anyway, as the shim adjustment is all for variations in the case tolerances, the gear set tolerances being small enough to be discounted.

Drain the diff and remove the rear cover, and disconnect the rear end of the prop shaft (you can remove the shaft completely or just hang it out of the way with string or a bungee like I did).

Mark the main bearing caps to identify which side they are from and which way up they go. Undo the two bolts in each of the diff carrier bearing caps, followed by the caps themselves. They have to go back in the exact same orientations later, so be careful to do this marking.

With the aid of the spreader, lift the diff carrier out. It's damned heavy, so be careful.

If you need to replace the pinion or its bearings, you need to undo the flange nut. It too need marking before removal to ensure the correct torque and bearing preload later, so make indelible alignment marks on the nut and pinion. It's on at a few hundred foot-pounds, so to get it off you need to lock the pinion flange by using a couple of bolts through the holes and a bar against the ground (or ramp, if your so lucky). Then use a socket and breaker bar to undo the nut. Remove the nut and the the flange and the pinion will be free to come out through the diff housing, along with its aft inner bearing race and rollers.

The outer race will still be in the casing, with the pinion heigh setting shims immediately behind it. If the outer race is in good order, leave it be, likewise the outer race and bearing on the pinion. The forward bearing will be complete inside the casing, retained by the seal. To inspect it, you'll have to remove the seal, which will require replacement on reassembly. It's probably worthwhile renewing the seal anyway, so prise the seal out and remove the bearing for inspection. You will also find a steel collar with a ridge in the middle. This is the collapsible spacer that holds the aft and forward bearings apart against the force of the flange nut for setting the bearing preload. There is no need to replace this unless you have overtightened the nut, so keep it safe.

Setting up the new diff centre's bearings and shims is easiest with the pinion out of the way, so do it now. If the pinion is still fitted because inspection of the gear and the feel of the bearings passed inspection, then you can continue setting up the main bearings as long as the ring gear is not fitted to the diff centre.

Fit the bearings to the carrier without shims and test ft in the case. Remove the spreader tool and measure the end float on the carrier. Use the spreader to remove the carrier and add shims of the total thickness of the measured end float under the inner race in the crown wheel side of the carrier (not the plain side - you'll see why later) to remove all the end float and refit. Remove the spreader and test for end float again - there should be none at all, and check for free rotation of the carrier - the bearings should be smooth and pretty quiet with little resistance. If that passes, then you have the correct thickness of shims. Resistance to motion points to excess shims, any end float or rocking to insufficient shimming. Once you have found the correct total shimming, the carrier can be removed to have its ring gear fitted (the kit's instructions will give torque settings and you should use red thread lock)

Now comes the fiddly part. You need to transfer shims from one side to the other of the carrier to set the gear mesh with the pinion. For this, the pinion must be fitted. Then fit the carrier with the ring gear to check the gear mesh. You're looking for a tight mesh, but a minimum of 0.004" (4thou) crown wheel free rotational movement to allow gear lubrication and prevent overheating. In practical terms, you can do this by setting the mash to the smallest movement you can feel by hand. This is set by transferring main bearing shims from one side to the other, and because they were all put on the crown gear side of the carrier, the mesh will have to be tightened by transferring some shims to the plain side of the carrier - if you had set the shims on the plain side during the earlier stages, the mesh would have been too tight to full fit the carrier into the casing without risking damage to various parts. This is going to be a bit laborious, using trial and error to move shims from one side to the other until the correct mesh is reached, using and removing the spreader too and removing and refitting the bearings each time. There is no way around it, though experienced mechanics would be able to make better estimates of shim adjustment and have less cycles of adjustment and testing, but they would still have to do the same thing.

Once you have set the mesh nice and small but with that minimum of 4thou, you should use a mesh marking fluid on several crown gear teeth and turn the diff several times to see the pattern left by the pinion on the fluid on the crown gear teeth. Ideally, you'd use engineer's blue, but it's expensive and not especially easily available. I have used emulsion paint to quite satisfactory effect. You want to see a regular pattern of contact in the centre face of each tooth - towards the root of the teeth indicates too tight a mesh, and the footprint towards the edge of the teeth indicates too loose a mesh. If the foot print is markedly towards the outer edge of the crown gear, then the pinion height is too low (ie it isn't sticking in towards the diff centre enough), if the footprint is markedly towards the inner edge of the crown gear, then the pinion heigh it too much.

Should the pinion height be out, which is extremely unlikely if you haven't altered its shims (even if you have replaced the pinion and/or its bearings), then it will need to be adjusted, but it's so unlikely that I wouldn't bother with the pinion height setting procedure initially. Unfortunately, if it does prove necessary to alter the pinion height, then you'll have to start the mesh setting procedure with the main bearing shims from scratch as the pinion heigh will throw the mesh out too.

It all sounds a little scary, especially from the proper manuals, but I can assure you it's very simple. I can also back up KAM Diffs comment that replacing pinions and bearings does not require the pinion height set up procedure because that is all done for the casing variation, which has already been accomplished on the initial factory build. I found that my 4.71 and 3.54 diffs had such close tolerances that I didn't need to change the main bearing shims at all either. If you have suitable measuring equipment, you may be able to set the main bearings up well enough that you do only the one test fit - you'll need to compare the distances from the gear side of the crown gear mounting flange (plus any spacer ring required for the conversion) to the bearing seat faces; just shim them to match the original carrier and shims.

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Well, that's a fairly comprehensive reply! Thanks for the intricate details, unfortunately, I am still scared.

My major fear is finding something that is not quite as you described, or breaking/losing something and then being utterly unable to work out what to do next, stuck with the diff out and in pieces and still not having an expert on hand who can take over when I stuff it up.

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I would second that

The salisbury is a not loved unit, stong - yes, but unloved. Partlt as they are horrible to work on, and also as the parts costs are far higher than you might expect - price up a Timken Head bearing .....

Its a nuts and bolts job to buy and fit a late TD5 110 axcle with a short nose diff, and swap the prop. Parts are still more expensive than a Long Nose but less than a salisbury and have a decent after maket value as the diffs also fit P38 Range Rover. You can also get an Ashlocker for the P38 / short nose axle, beats anything else hands down IMHO


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