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I noticed while taking the rear suspension out, that the bracket that bolts to the diff case which support the inner fulcrum of the lower wishbones is lose.
It's held on with two wire locked bolts. Same on the other side.
I assume the play is deliberate to allow the diff room to move about slightly?
Cage out, upside down, is the best way to do it. Also a chance to do everything else on the brakes.
And when you retighten them (having made damn sure the shimming is dead on and the fulcrum pins goes through easily) forget the lockwire and use the strongest loctite (270 coloured green) on the threads, the stuff you need to heat to 500 degrees C to loosen.
Give the same treatment to the diff to cage fixings too.
Orangeblossom has a very good thread written earlier this year on how to do the job. Also this is a short thread on the matter, far less comprehensive than Orangeblossom's one. https://www.jaguarforums.com/forum/x...ration-193055/
Last edited by Greg in France; 09-14-2021 at 09:47 AM.
Which model of XJS do you have, and if a V12, is it a DANA or a Salisbury diff? Dana has no drain plug on the bottom of the diff.
Also, here is an exôlded diagram of the setup: https://parts.jaguarlandroverclassic.../brand/jaguar/
Last edited by Greg in France; 09-14-2021 at 12:01 PM.
Also, my car isn't an XJS, its a custom, so I don't have the cage.
I am swapping from a 4.55:1 to a 2.88:1 diff.
The 'new' diff comes with brakes but thats all, so I have to swap the suspension over too.
I'm not sure the best approach to sorting out the shimming to set camber etc.
From my intial measurments the 'new' diff is 2mm wider measured across the brake disks, where the UJ's and shims sit. (with no shims in).
Measuring across the dogbone fulcrum holes, the 'new' diff is 1mm narrower than the old one! (But given the bolts were all lose, I will double check this when they are tight!)
The old diff had no shims in the fulcrum brackets but the new diff had a very thin one (0.1mm) at one end and a couple at the other end, which were rusty to hard to measure but maybe 0.5mm. I guess this sets a tiny bit of tow in/out?
I'd like to get the camber close if poss, but I suspect it's going to be difficult without putitng everything back into the car and checking it in situ.
Also, my car isn't an XJS, its a custom, so I don't have the cage.
I am swapping from a 4.55:1 to a 2.88:1 diff.
The 'new' diff comes with brakes but thats all, so I have to swap the suspension over too.
I'm not sure the best approach to sorting out the shimming to set camber etc.
From my intial measurments the 'new' diff is 2mm wider measured across the brake disks, where the UJ's and shims sit. (with no shims in).
Measuring across the dogbone fulcrum holes, the 'new' diff is 1mm narrower than the old one! (But given the bolts were all lose, I will double check this when they are tight!)
The old diff had no shims in the fulcrum brackets but the new diff had a very thin one (0.1mm) at one end and a couple at the other end, which were rusty to hard to measure but maybe 0.5mm. I guess this sets a tiny bit of tow in/out?
I'd like to get the camber close if poss, but I suspect it's going to be difficult without putitng everything back into the car and checking it in situ.
The shims are NOTHING to do with toe. The shims are there to ensure that the dogbone holes line up precisely with the holes in the OEM cage, thus allowing the fulcrum pin to slide in through all four holes. I presume your custom arrangement must have equivalent holes in the chassis frame?
The rear toe cannot be adjusted on the standard setup. The OEM setup caused a certain amount of toe change on cornering, owing to the design-in geometry changes under cornering loads allowed by the rubber radius arm bushes, and the rubber cage mountings. As outlined in a post elsewhere, on the subject of solid poly bushes in the rear and the disastrous effect they have:
"The poly bushes wreck the ride/handling because the compliance of the metalastik bush is an integral part of the design of how the suspension works mechanically. If all the rubber parts of the rear suspension were solid bearings, the rear suspension could not move up and down at all, as the radius arm's geometric path through its arc is not the same as the up and down path of the rear wishbone/driveshaft/hub. The two arcs (which are at 90 degrees to each other) intersect at the normal stationary suspension height, and any movement from that has to be accommodated by the large radius bush, mainly. The cage mounts also allow flex to an extent. The entire cage/suspension assembly is meant to move slightly also, to produce some toe-change effects on cornering. This all works wonderfully because of the correct rubber specification of the parts concerned.
Poly bushes effectively have no compliance, so the rear suspension cannot move as designed by the great Bob Knight - who allegedly was telling William Lyons in 1955 that the cars needed an independent rear, so Lyons told him to design one; which he did over a weekend and drew up the detailed design in a month.
The solid large radius arm bushes force the cage to accommodate the geometry changes caused by the suspension movement in un-designed ways, mainly stressing the cage metal and the cage mounts, so the intended toe-changes on cornering, and other designed-in movement, cannot happen. Hence the rubbish handling.
Incidentally, this is also the reason that racers modify the mechanics of the rear suspension, ICSAmerica, on here, alters the radius arm pickup points (as did TWR with their ETCC XJSs) in order to eliminate the road-going designed-in geometrically conflicting arcs. Obviously in racing you want no compliance, and an adjustable suspension too, so the radius arms are turned into A frames with their car-mounted bearings in line with the diff-mounted inner fulcrum of the lower wishbone; thus eliminating the conflicting arcs, and with that the need for rubber compliance."
On your custom setup, how are the hubs located, apart from by the lower wishbones? Do you have a radius arm of some sort, or an A frame, or what?
The shims are NOTHING to do with toe. The shims are there to ensure that the dogbone holes line up precisely with the holes in the OEM cage, thus allowing the fulcrum pin to slide in through all four holes. I presume your custom arrangement must have equivalent holes in the chassis frame?
The rear toe cannot be adjusted on the standard setup. The OEM setup caused a certain amount of toe change on cornering, owing to the design-in geometry changes under cornering loads allowed by the rubber radius arm bushes, and the rubber cage mountings. As outlined in a post elsewhere, on the subject of solid poly bushes in the rear and the disastrous effect they have:
"The poly bushes wreck the ride/handling because the compliance of the metalastik bush is an integral part of the design of how the suspension works mechanically. If all the rubber parts of the rear suspension were solid bearings, the rear suspension could not move up and down at all, as the radius arm's geometric path through its arc is not the same as the up and down path of the rear wishbone/driveshaft/hub. The two arcs (which are at 90 degrees to each other) intersect at the normal stationary suspension height, and any movement from that has to be accommodated by the large radius bush, mainly. The cage mounts also allow flex to an extent. The entire cage/suspension assembly is meant to move slightly also, to produce some toe-change effects on cornering. This all works wonderfully because of the correct rubber specification of the parts concerned.
Poly bushes effectively have no compliance, so the rear suspension cannot move as designed by the great Bob Knight - who allegedly was telling William Lyons in 1955 that the cars needed an independent rear, so Lyons told him to design one; which he did over a weekend and drew up the detailed design in a month.
The solid large radius arm bushes force the cage to accommodate the geometry changes caused by the suspension movement in un-designed ways, mainly stressing the cage metal and the cage mounts, so the intended toe-changes on cornering, and other designed-in movement, cannot happen. Hence the rubbish handling.
Incidentally, this is also the reason that racers modify the mechanics of the rear suspension, ICSAmerica, on here, alters the radius arm pickup points (as did TWR with their ETCC XJSs) in order to eliminate the road-going designed-in geometrically conflicting arcs. Obviously in racing you want no compliance, and an adjustable suspension too, so the radius arms are turned into A frames with their car-mounted bearings in line with the diff-mounted inner fulcrum of the lower wishbone; thus eliminating the conflicting arcs, and with that the need for rubber compliance."
On your custom setup, how are the hubs located, apart from by the lower wishbones? Do you have a radius arm of some sort, or an A frame, or what?
Hi Greg, OK, I assumed toe in/out as the shims were uneven front to back, but clearly you explaination also explains why my car didn't have any!
So I will be ok to not bother with them.
My arrangment (not built by me) is that the top of the diff is bolted directly to the chassis. The upper shock mounts are also welded direct to the chassis.
There are radius arms which go forwards and inwards to the chassis and these pivot on bushes.
There are also 'drop links' for want of a better word that go from the chassis down to a bracket on the front of the diff, which runs under the prop shaft. This bracket also has both fulcrum shafts bolted to it. These drop links have bolts that may alway a little bit of movement forward and backward but not much as the bolts are tight.
There is a rear bracket which goes across the fulcrum pins but this is not attached to anyting else.
It's pretty hard to photograph the whole setup.
My main issue is getting the camber right. I have measured the width of the old diff, from the outside faces of the brake disk bosses (not the disks) where the drive shaft shims sit. If the width of the inner fulcrum pivots is the same, then and difference in width between the drive shafts is going to change the camber. Perhaps due to the new diff having bigger disks on, it measures 2mm wider.
If I re-assemble with no shims in the drive shafts, I think I will be very close to the same camber setting as before as there were three shims on the original diff drive shafts adding to about 1mm per side.
I need to double check the width bewtween the fulcrum pins on both diffs once I get the bracket bolts tightened up. Hopefully the will be same.
Luckily the angle on the top of the diff is the same so that's one thing less to worry about.
Thanks again for your expertise on this!
Some pics:
The original diff and radius arms. shock mounts drop links
Assemble it and see; then, if needed, machine a bit off the disk hub, or shim it out? in which case you could use the OEM camber shims to adjust/equalise the camber each side.
Thanks for the photos, those drop links are to stabilise the diff under acceleration and braking loads, as otherwise in the absence of the cage, all the twisting loads would be on those four bolts at the top of the diff. The radius arms are indeed A frame type ones; as they are located on the chassis in line with the dogbone fulcrums, there is almost no conflicting geometry on rear suspension movement.
Personally, I would feel safer if the dog bones' fulcrum pins went into sturdy brackets welded to fabricated extensions of the actual chassis, at both front and back of the pins! There are a lot of forces going into the cast iron diff casing alone, and it was not designed to take them alone.
Last edited by Greg in France; 09-15-2021 at 03:25 AM.
Good reading here, as usual.
I would add something I learned here, or on another forum.
For the dog bone shims, use a corner cut from a camber shim. That will make a washer that can't fall out, and they come in different thicknesses.
Good luck,
Rob
Yes, the construction is a bit odd with 3 brackets not connected to each other! There is a square 'picture frame' of 6mm steel that sits under the diff and joins the two fulcrum brackets together, so I guess this provides a bit of strength but it's not attached to anything else. I wondered why the rear bracket that just goes between the inner fulcrum pins doesn't attach to the bottom plate. Likewise the front bracket that goes between the inner fulcrum pins and has the drop links on. Anyway, I'll reassemble as is for now!
OK, so another question!
The inner bearing tubes on the inner fulcrum pins came out with the pins. Should these be a sliding fit on the pins. One is seized onto the pin, the other sides about freely. I can probably free the seized one with a little heat or loctite the free one! I guess as these are the inner races of the roller bearings, it may not even matter....
The inner bearing tubes on the inner fulcrum pins came out with the pins. Should these be a sliding fit on the pins. One is seized onto the pin, the other sides about freely. I can probably free the seized one with a little heat or loctite the free one! I guess as these are the inner races of the roller bearings, it may not even matter....
The tubes should be a sliding fit onto the pins, hey in effect provide the inner race to the entire bearing formed by the roller bearing pressed into the actual eye of the wishbone, the wishbone as the outer race, and the tube as the inner. Check the roller races in the wishbone, and the grease seal, and the outer ring; if all bad you can e an entire kit. Best to buy a new set of tubes (if that is all you need) from Manners or other good supplier. Measure the tube length, as there are two sorts.
The tubes should be a sliding fit onto the pins, hey in effect provide the inner race to the entire bearing formed by the roller bearing pressed into the actual eye of the wishbone, the wishbone as the outer race, and the tube as the inner. Check the roller races in the wishbone, and the grease seal, and the outer ring; if all bad you can e an entire kit. Best to buy a new set of tubes (if that is all you need) from Manners or other good supplier. Measure the tube length, as there are two sorts.
Thanks Greg.
I'll free the bearing tube up and crack on with reassembly.
At this stage, I just want to see if the diff works ok and if the ratio is right for the car. If it looks OK, I'll refurb the whole lot over the winter along with the front suspension...
09-14-2021, 08:30 AM
Rear suspension lower arm mounting bracket lose?
