Guys
As some will recall, I have just redone my inner fulcrums on the rear lower wishbone. The "dog bone" casting, bolted to the diff had come loose. All now so very good. But I have been thinking why, when I tested the bolt I could get to a few months ago, it did not seem loose.
But, having decided to remove the axle and find out what was the cause of my on/off the power clonk and vibration at certain speeds, I found the bolts were less than finger tight, even with the axle still in the car when I tested them again.
The reason, I am pretty sure, was my way of supporting the axle on my retirement present 2 post lift. In order not to stress the cage mounts, I place the rear lift arms not on the jacking point, but just an inch or so rearwards from the centre point of the radius arm large bush. This takes significant weight off the cage mounts and also ensures the axle cannot suddenly fall on my head if the mounts suddenly fail. They are not designed to be in tension and have no failsafe safety device.
However, because this time I was going to remove the axle, I used the jacking points, then I raised the car and tested the dog bone bolts again, and both were very loose both sides.
So I reckon, if there is any weight on the lower wishbone arms, they effectively jam the dog bones in position and their fixing bolts too, meaning that a test with on their tightness will probably not show up any looseness.
Therefore, as a tip and in case it is useful for anyone else, and as this test is now on my regular service list every time I grease the rear axle, I think it is important to ensure the wishbones are completely unloaded before anyone does this tightness test. Axle in car, you can only get an open ender on one of the two bolts, but that is better than no test at all.

 

Hi- you didn’t mention lock wiring the bolts. Did you lock wire them? I cheated once and used threadlock and have had no problems. -John

 

I agree Greg, loaded, and there is a lot of force on those dogbones.

I cheated years ago (early 80's) with Loctite, and have done so for many, many years since, no loose bolts anywhere.

I doubt thread lock was around in the '50's, and lock wire was very common on most cars etc, and the practice simply carried over.

 

The OEM bolts I used 18 years ago were not drilled for lockwire, but came with jaguar's own Loctite already on them. This time I bought some specially strong Loctite 730 and used it all over including on the countersunk cones, as Grant advised, and did them up with a 2 foot lever.

 

Thanks for the input Greg! Something I was never considering. Though I doubt an axle wall fall out...

Look at the front for example... The front axle is held in place by 2 screws and 2 small nuts (not screws) and doesn't fall out with a 400 kg engine on it. The XJ40, X300 and X308 have the same (albeit 180° turn around with the large screws at the rear) setup... The rubber V mounts aren't "fail proof" and do delaminate (mine were starting to).

in MY personal opinion, I think that the 4(!) rubber mounts at the rear are more than enough for that axle to hold in place. Hence the jacking points away from the rear axle... It must be a really bad day for all 4 rubber mounts to delaminate. I am sure you'd notice it driving prior to that!

 

Im really surprised the OEM bolts 18 years ago were not drilled. My 95 has drilled bolts.

 

Thanks for yet another tip Greg. All help gratefully received not just by myself I suspect. Nice one

 

No chance. The rearmost dog bone bolt you can get an open ender on, axle in place. This one can be checked regularly. The front one not; because that bolt is countersunk further into the casting only a socket will engage. And a socket cannot be engaged because of the spacer pipe you refer to. It does mean even totally loose bolts cannot fall off though!
I am pretty confident in Loctite 270. The properties sheet says you need to get the bolt up to 300 degrees C to undo it, and must undo it while it is still that hot! And yes, the threads in the diff and the bolts were completely degreased. This is not a job I wish to have to repeat.
LOCTITE 270 - Threadlocker high strength - Loctite
The trickiest bit of the whole repair is ensuring the shims between the dog bone and the diff completely accurately align the four holes (cage:2 and dog bone: 2) so the fulcrum shaft slides in without fouling. Anyone doing this is welcome to a couple of tips I use if needed. Just ask.

 

Though I doubt an axle wall fall out...
They do Daim, they do. Many garages place a wooden vertical post under the diff when the cars are on two post lifts.
Look at the front for example... The front axle is held in place by 2 screws and 2 small nuts (not screws) and doesn't fall out with a 400 kg engine on it.
Daim. the front subframe's rear V mounts have safety bolts through them. The fixing nuts and V mount stud they go on will withstand many many tons of tension. Also the front subframe front mounting fixing bolts are bloody enormous!
in MY personal opinion, I think that the 4(!) rubber mounts at the rear are more than enough for that axle to hold in place. Hence the jacking points away from the rear axle... It must be a really bad day for all 4 rubber mounts to delaminate. If all is in good order, you are right, after all the axles do not all fall out! But ultimately it is a glue bond, and only a glue bond between rubber and steel that holds the axle in place when the car on up on its two rear jacking points.
So better be safe than sorry, say I.

 

Hmm, the XJ8 ones don't have any safety screws in them but heck, I see your point.

 

i said before , when 1st got XJS , non runner, unloading from tilt hauler, backing down ramp, car started to roll faster, so i pulled the E-Brake, the complete cage ripped loose sideways, and locked the rear wheels against the body, Catta wumpass!!

ALL four mounts had broke loose!!?? hind sight only thing keeping out of the street was drive shaft.