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Discussion Starter · #1 ·
Got a power lock diff to put into the Morris which currently runs a 4.55:1 Jag diff.

The new diff has the brake assemblies on and the inner fulcrum mounts and that's it.

Is this a case of 'just' dropping the old one out and putting the new one in or are there alignment procedures? Does anything need measuring or shimming?

Any special order for bolting it all back up again?

Anyone done this before and remember any gotcha's?

Any help appreciated.
 

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The driveshafts are shimmed at the inner end to set the wheel camber, where the UJs bolt to the diff flanges

The rest just assumes a modicum of ability, pretty much, but plenty of info online
 

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A lot of folk have been caught out when changing complete jag irs diffs as the top pad that takes the 4x mounting bolts comes in 3 types,
The pad on the top is tapered forward by a few degrees, something like 4, 7 & 10 so check both before swapping,
The diff will bolt up fine to the crossmember but may push everything else either forwards or back depending on the pad degree change.
 

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As well as shimming the driveshaft for camber you shim the inner fulcrum shaft that the wishbone mounts on to adjust the rear toe. Depending what car the diff is from, XJS models have bigger discs so the calliper is mounted slightly further out, I found this out when I ended with a lip on the edge of the pads. Diff mounting angle normally only affects diffs mounted in other cars such as the Aston martin, not sure if Jaguars used different angles, I've had three different ones and they've all been the same
 

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Discussion Starter · #6 ·
A lot of folk have been caught out when changing complete jag irs diffs as the top pad that takes the 4x mounting bolts comes in 3 types,
The pad on the top is tapered forward by a few degrees, something like 4, 7 & 10 so check both before swapping,
The diff will bolt up fine to the crossmember but may push everything else either forwards or back depending on the pad degree change.
That's excellent info! Exactly what I hoped to find out. Thanks.

If there is a difference in mounting angle, I can machine something up to adapt it.
 

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Discussion Starter · #7 ·
As well as shimming the driveshaft for camber you shim the inner fulcrum shaft that the wishbone mounts on to adjust the rear toe. Depending what car the diff is from, XJS models have bigger discs so the calliper is mounted slightly further out, I found this out when I ended with a lip on the edge of the pads. Diff mounting angle normally only affects diffs mounted in other cars such as the Aston martin, not sure if Jaguars used different angles, I've had three different ones and they've all been the same
I guess I can look at the shims in the current rear axle and see where its at. Maybe worth trying to measure castor and toe on the axle now, before I start taking it all to bits!
 

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That's excellent info! Exactly what I hoped to find out. Thanks.

If there is a difference in mounting angle, I can machine something up to adapt it.
You could certainly machine up a tapered adaptor but that would lower the diff with several knock on effects;
The driveshafts will now point upwards more to the outside,
Ride height will slightly chance along with torque straps if you run now not bolting up without adjusting,
A far better option would be to find a complete diff with the same angled top as yours or rebuild your casing with the gear ratio etc of your choice,
It’ll then bolt straight in.
 

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Discussion Starter · #9 ·
You could certainly machine up a tapered adaptor but that would lower the diff with several knock on effects;
The driveshafts will now point upwards more to the outside,
Ride height will slightly chance along with torque straps if you run now not bolting up without adjusting,
A far better option would be to find a complete diff with the same angled top as yours or rebuild your casing with the gear ratio etc of your choice,
It’ll then bolt straight in.
Any idea which diff was fitted to which Jag?

I need to get underneath again to check, but I don't think there is a Jag subframe/cage on my car.
 

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just drop the old one (after taking camber etc measurements) and with it flat on the floor/bench check the angle of the top flange and compare to the new one. they may be the same, there's a 1 in 3 chance so......
 

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Discussion Starter · #11 ·
just drop the old one (after taking camber etc measurements) and with it flat on the floor/bench check the angle of the top flange and compare to the new one. they may be the same, there's a 1 in 3 chance so......
Just had a nose under the wheel arch to see whats what. My diff doesn't have the Jag cage/subframe thing, so the top of the diff is bolted direct to the chassis. The tops of the shocks are also attached direct to the chassis. There are 2 drop links from the chassis to the cross bracket that goes between the two inner fulcrums and 2 radius arm rods which go to the wishbones/lower links.

632616


632617

So looks like I take off the shocks, the drop links, the radius arms and then prop. Then the 4 bolts into the top of the diff. Oh and disconnect the brake lines!

Angle wise, best I can measure with respect to the bottom of the diff where the suspension arm brackets are, one is 4.4 degrees, the other is 5.4 degrees. I hope that's close enough!

632614
632615
 

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you got to get them both on the floor/bench level to make a proper comparison of the top angle. if it is different get your local engineering firm to make you a tapered shim to fit between the diff and chassis. it won't alter the geometry to any noticeable amount as the shim can be 1mm thick at the thin end going to whatever is needed to correct the angle at the thick end, which may be only 3-4mm. so not enough to worry about. you need to worry more about shimming the driveshafts/discs to the diff flanges correctly so the wheel camber isn't altered.
neil.
 

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Discussion Starter · #13 ·
you got to get them both on the floor/bench level to make a proper comparison of the top angle. if it is different get your local engineering firm to make you a tapered shim to fit between the diff and chassis. it won't alter the geometry to any noticeable amount as the shim can be 1mm thick at the thin end going to whatever is needed to correct the angle at the thick end, which may be only 3-4mm. so not enough to worry about. you need to worry more about shimming the driveshafts/discs to the diff flanges correctly so the wheel camber isn't altered.
neil.
I zeroed the angle gauge each time on the bottom of the diffs where the fulcrum bracket attaches as it's flat there.

I've got a mill so I can make a wedge if needs be.

The new diff came with at least 3 shims each side to go on the drive shaft flanges so should be able to get it close. I'll see if I can get some decent measurements of the camber with the existing setup. I guess the easiest way is to measure the distance from the top of the hub carrier to the edge of the brake disk with the suspension hanging? Or with it under normal load? (I'd have to set the car up on ramps to get under it to measure the distances.)

The tyres are soooo wide that I'm not sure they'd do much cambering anyway!
 

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that's the problem with wide tyres, if there's too much camber they'll wear the inside edge of the tyres away. with the car on the ground put a straight edge top to bottom against the rear wheel and use your angle finder to check camber. or as you say with it hanging and the wheels off check against the wheel flange and shim the new one to match. that'd probably be easier too.
great that you can mill an angled shim so it's all the same after the swap, definately worth the effort.
neil.
 

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Discussion Starter · #15 ·
that's the problem with wide tyres, if there's too much camber they'll wear the inside edge of the tyres away. with the car on the ground put a straight edge top to bottom against the rear wheel and use your angle finder to check camber. or as you say with it hanging and the wheels off check against the wheel flange and shim the new one to match. that'd probably be easier too.
great that you can mill an angled shim so it's all the same after the swap, definately worth the effort.
neil.
Been having a measure, looks like there is about 0.5 degree camber but it's hard to be 100% sure. Measuring from the top of the hub carrier to the side of the brake disk gave different distances on each side, by about 5-6mm? I might try and find a different measuring point...
 

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Been having a measure, looks like there is about 0.5 degree camber but it's hard to be 100% sure. Measuring from the top of the hub carrier to the side of the brake disk gave different distances on each side, by about 5-6mm? I might try and find a different measuring point...
You could measure the camber directly off the wheel using your angle gauge.
 

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Discussion Starter · #17 ·
You could measure the camber directly off the wheel using your angle gauge.
Yes, I've stuck it onto the hubs, the car isn't on level ground, but I've zeroed the bevel box on the bottom diff brackets and got 0.5 degrees camber. No sure if that's typical or not? This is with the suspension hanging, no wheels on.
 

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as long as you keep it the same once the diff's swapped over it'll be fine as nothing geometrically has changed. as you found, measuring from the hub carriers won't work as they're castings so only the machined surfaces are the same which i guess isn't where you measured from.
neil.
 

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Getting your geometry from the existing setup assumes that that is correct!
it almost definately won't be exactly as per stock jag geometry but it's an established build and it works so no reason to change it from what's there. he's only swapping to a better ratio diff, not changing to a new setup. (y)
neil.
 
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