In the process of reassembling the rear wheel bearings on my 85XJS.
The splined driveshaft slides into the hub and there is a small collar which has to be adjusted to get the correct amount of end play in the bearing set up. The axle has a shoulder on it , then a spacer for the oil seal to run on, then the small collar to adjust the clearance on the inner bearing race, then the inside diameter of the hub, then the hub, then a washer and a 3/4UNF nut. All the stuff listed above is sandwiched together by the torque on the 3/4UNF nut. Do not OVERTORQUE this nut. The “normal” torque setting for this size nut is over 200 ft-lbs…depending on the grade of the fastener…but the manual indicates 100 ft-lbs…because this torque setting creates a moderately high compressive stress between the little collar and the oil seal spacer. If you overdo the torque you will overstress the connection on each side of the collar and the bearing clearances will be affected. On my XJS the collar on one side is a bronze material and the bearings are not Timken …so have been replaced …and the collar made to measure from material that can have a wide range of mechanical properties…the collar on the other side looks like steel but is quite roughly machined…but those bearings are Timken…but the collar machining does not look like OEM…I don’t have the gear to fix this so I am going to get a local machine shop set the hub bearing end float with new collars machined from mild steel…then I’ll reassemble to the CORRECT torque of 100 ft-lbs(136N-m) I don’t understand why Jaguar didn’t design this bearing arrangement with the adjustment on the OUTSIDE bearing so the end float could be set with a feeler gauge between the outside bearing race and the washer under the nut…or …SOMETHING easier to set up!!!
As mentioned in the Book, the threaded portion on the end of that shaft has a nasty habit of breaking off. In fact, when GT Jaguar was around they offered a kit to fix a broken shaft, basically a bolt and washer; just cut the broken end off clean, then drill and tap the shaft to fit the bolt. Jan Wikstrom provided some tips on how to modify the shaft to prevent it breaking in the first place.
Hi Kirby
Ah HAAH…Forgot to research this in your fantastic book!!! I REALLY don’t want this thread breaking off.!!
I’d be tempted to tighten it to a much lesser torque setting. If they are failing it will most likely be due to the stress levels at the root of the thread or the lack of attention to detail at the transition from the thread to the shaft. This basic stress level is determined by the torque setting and the driving loads then add and subtract from this base level. I roughly figured that the torque imposes 3 1/2 tonnes of compression on the items sandwiched. Seems to me that …say…half that value would be enough…so maybe 50 ft-lbs torque on the 3/4 nut. Problem is …just checked this and this still stresses the bolt above the magic endurance limit…so likely it will fail in fatigue at some stage. Plan B…machine a suitably sized radius to relieve the stress at the transition from the thread to the shaft . Luckily it is in the machine shop this week to get new clearance collars machined up so I’ll have a look in your Book (Capital B) and see what the radius idea looks like!! Thanks for the timely info!!
Actually, I don’t believe they add – unless they exceed the preload. That’s why the preload needs to be above a certain minimum, so the driving loads can come and go without exerting a cyclic stress on the fastener. That means you’d be ill-advised to reduce the torque on that nut to 50 ft-lb.
The bearings are sitting on the hub carrier and are unstressed with 0.001" clearance. The shaft is stressed by the tension in the bolted connection. Now pull the wheel away from the car with 20 lbs force. The 20 lbs is added to the shaft stress. Now push the wheel in to the car. The bearings push on the inside retaining collar and the shaft stress stays at the preload level…so I think the cornering load possibly just adds to the shaft stress… In a fatigue situation it is still a fluctuating stress which, unless properly considered, will cause the weakest part to fail…either the root of the thread or the transition from thread to shaft.
No, it’s not. The shaft is in tension by the bolted connection, and the surrounding sleeve is in compression. Pull the wheel away with 20 lbs force, and that 20 lbs is subtracted from the sleeve compression.
The shaft is in tension. The sleeve is in compression. When you pull the wheel away from the car the tension in the shaft increases and the compression in the sleeve decreases. Sketch a force diagram. The nut ultimately holds the wheel in position…and will be subject to any outward force you apply ON TOP of what is already in the shaft due to preload.
It is an attempt by the Jaguar Engineers to reduce the magnitude of the stress fluctuations because of the stiffness difference between the collar and shaft…but both are similar so it won’t make much difference. If it worked the joint wouldn’t fail…
Hi Matt,
What torque setting, or machining did you end up with? Are you satisfied with your result?
Regards,
Chris
Hi Chris
I had a machinist turn the largest radius he could achieve between the threaded portion and the main shaft. Any radius here will help the stress situation…even a small amount of undercut in the threaded portion.
I tightened to 75ft-lbs instead of the 100ft-lbs(?) specified. The nut is retained with a split pin so is not retained by friction. I had a bet each way with the 75ft-lbs. Need to have enough friction from the nut torque to ensure the spacer with the radius which presses on the driveshaft and the shim and the hub itself rotate as one piece. The reduced preload will decrease the static stress in the threaded part of the driveshaft.I have only done a few hundred kilometres on the rebuilt rear end so too early to say …