My recently acquired XK140MC OTS has a disconcerting tendency to shift it’s rear under quick acceleration or deceleration. A quick application of the throttle can shift the rear to the left what feels like an inch or two while lifting off the throttle quickly shifts the rear similarly to the right. It doesn’t happen consistently, but more than occasionally. It’s all left/right movement and not up/down so I don’t suspect shocks. The wire wheels are on tight with no broken spokes. Has anyone else experienced this? Could the axle shaft be slipping in/out a little? A binding leaf spring? Any advice or suggestions are greatly appreciated.
Most likely a leaf spring issue: could be a broken leaf, or a shot shackle bush.
Check the wheelbase, side to side, and see if there’s a significant discrepency.
The leaf springs have a center bolt on which the head sticks up and catches in the saddle welded to the axle tube. If this head was sheared off, movement of the axle on the spring would be a possibility.
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Thanks guys.
Up on the lift it went. It looks like I have some broken leafs in the springs on both sides, as well as a leaky right shock. I think new springs and shocks are in order.
I don’t see anything in those photos that would allow or cause a sudden transverse dislocation of the entire axle. Are you certain it’s actually moving? If you are hearing a sudden noise on acceleration or compression braking, I would bet you have a failing u-joint.
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Mike, there is no noise and it does not feel like a u-joint.
The first picture looks like there might be a witness mark on the lower spring sheave indicating movement?
i had similar symptoms on 140 - was not moving that much but steering. several leaf fractures , bushings worn away and axle tube welds broken on both sides of housing. easy to find these problems with a bar and flashlight.
You can plainly see the axle tube welds in the photos above. Not compromised. That only leaves the bushings and rear shackles.
i had this exact same issue on my 120. it was the welds at the diff end of the axle tube. i have a short video but can’t post that here. thesis are the before and after
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Welding usually shifts things. Did you have any problems with that or how did you make sure that the far end of the tube remained in line?
Replacing/remaking the factory plug welds didn’t give me any alignment issues the additional seam welds were done after the plug weld
John’s original description of rear end shifting and the pictures showing broken leaves suggest to me that unequal springing is allowing the rear to behave strangely on hard acceleration and deceleration, and give the impression of axle movement when it is in fact irregular movement in the chassis and body.
In any case, new springs or at least replacements for the broken leaves are clearly on the table.
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Johns’ description sounds like intermittent change of rear thrust angle under higher levels of change in acceleration/deceleration. A change in acceleration is called a “jerk” and a change in “jerk” is called “jounce”.
In the automobile world jounce often is used to refer to just vertical rear axle rise conditions, hence shock absorbers are key players in vertical jounce. Because John reports inconsistent effect and no vertical issues, it seems unlikely to be traditional shock absorber jounce problem.
Because John says inconsistent horizontal shift, variable spring-related response to horizontal jounce seems strong contender if no witness marks on axle tubes are showing. Measuring thrust angle prior to disassembly steps would add a useful number to the understanding.
Photos and description point towards spring-related problem. When replacing springs caution is deserved in getting the right spring constants in the leaves as well as ride height.
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Felt compelled to add, typically such sliding sensations are also attributed to bad wheel bearings.
I would jack up the rear and do some checks of all of the above.
Be curious to know what you find.
Try and refrain from going crazy replacing such significant items without knowing more is my suggestion.
Frankly, i don’t see particular issues with the springs…nevertheless, good info above.
Kind regards
I had exactly the same issue with my XK120. Turning to the left after lifting off after hard acceleration. In fact it was found that rear axle tube was cracked and coming away from the Differential. It was very similar to the problem that Philip Dobson had on his 120. We both had ours welded by the same company and they said it was not an uncommon problem they had seen before. Initially it was thought to be the obvious rear spring bushes until the car was lifted up. It has been suggested that the cause is people jacking the car up by put a jack under the diff and stressing the 65 year old tube welds to the diff.
Thanks for all the input and ideas guys. I’ll get the rear in the air this week and see if I can detect any lateral movement and have a good look at the axle welds. In the meantime I’ve ordered leaf springs and shocks as they needed to be replaced anyways.
Well, I got it up on the lift with the wheels off the ground and could not detect any lateral movement at all. Also the diff housing welds look solid and show no evidence of slipping. The springs on the other hand are quite compromised. 3 broken leafs on the right, two on the left. New springs and shocks are inbound.