My jag started giving a bit of hesitation for the first second accelerating away from a complete stop - engine rpm doesn't reflect this and revs normally, just the movement of the vehicle hesitates, a similar feeling to driving a manual and having the clutch partially engaged and then after a second fully releasing the clutch (and then it drives normally).

I'm somewhat heavy footed, so it's quite noticeable to me and it's been consistent, starting just a few days ago. It's not particularly bothersome, just concerning that it's not a slipping first gear in the transmission.

 

Is it sluggish when selecting gears? first thought would be low trans fluid level - can't recall your car model or year??

 

You don't state what year the car making it hard to give advice. If it is an early model with the cable accelerator then I would say you have developed slack in the accelerator cable.
If you do a forum search for throttle cable adjustment you will find pictures of the adjusting procedure.
You can check it for slack by pulling on it with your finger and see how much play you have. The cable is held to the throttle body with a tie-wrap. You cut it off and lift the retainer out of the slot and rotate it to remove the slack. Place it back in the slot and install a new tie-wrap.

 

2002 VDP (it's in my signature, but that doesn't show on mobile)

I've adjusted the throttle cable slack when I first got the car back in 2011, easy procedure - but the engine revs appropriately for the throttle amount, just that the car doesn't initially get moving much.

Other gear shifts seem great, very smooth - sometimes even imperceptible, and timely.

 

Your sig isn't showing on the website version either. Maybe you changed a setting and turned it off?

Is it only off the line that it hesitates, or while you accelerate hard in general?
Hesitation under acceleration on my car was caused by a dying MAF. Cleaned it a few times, but the only proper fix was a new one.

 

No, just off the line. Also, the engine sounds like the car is taking off normally, but there is a delayed burst of movement, like your resting on the clutch of a manual. If it were caused by the maf I think the engine would not sound like it's accelerating normally.

 

Sounds like the A drum failing if the fluid level correct.

 

The problem got notably worse during 50 miles of driving today it now has that same hesitation-sensation paired with a noticeable vibration/rumbling and it happens on other gears too now (besides off-the-line in 1st), seems like it only happens in other gears when I give it enough throttle to trigger a downshift.

It is happens fairly consistently when passing on the highway, when cruising at around 50-55mph and then give it enough gas to drop a gear (presumably that is downshifting into 2nd or 3rd, but not sure.) The engine sounds exactly how it should but it feels like the transmission is struggling to engage the lower gear and during those 2 seconds or so there is about 1/3 the normal acceleration pick-up, like trying to floor-it in 5th gear, then it engages the correct gear and all is normal again.

FYI, this is probably totally unrelated, but the rubber on my transmission-mount is broken, I just got the replacement today but it is not installed yet - any possible relation? If the transmission flexes/torques too far it still would not have effect like these symptoms, right?

Ugh, if that is the case, does that necessitate a transmission swap?

 

I'd be looking to get your transmission mount sorted ASAP, but I'd also be looking to get the fluid and filter changed too if you've not already done it. The transmissions on these cars need looking after if you want them to last, especially if you're doing a lot of stop start driving.
The reason my old car's gearbox let go was because I was doing a short commute of 2 miles, which wasn't letting the box warm up properly. This eventually took it's toll on the gearbox. Get the modified TransGo pressure valve fitted to your car whilst the gearbox fluid is changed.

 

There's a Transmission fluid filter? Where is it located, in the Bell housing?

 

The filter is in the pan which has to be removed, cleaned and refitted with a new gasket as part of a transmission fluid service. If you search for ZF5HP24 on this forum and there will be a wealth of information available to you.

 

How do I go about diagnosing this? Step 1 check the transmission fluid, then what?

 

Fit the kit Stu suggests is what I would do right now, the car maybe warning you of impending trans doom.
The solenoid valve kit fixes the pressure spikes due to a worn valve block wall, these pressure spikes show up as odd behaviour initially, as the wear gets worse the shifts become worse until enough pressure (rev...bang into gear) breaks the circlip and the A drum is then free to move.
A routine oil/filter service - along with the new valve and seal transgo provid into the valve block - should fix it.
Plenty of info out there on how to carry it out, google transgo Jaguar.

 

My car is an '02, what I've read is that the valve was updated in '01 so the transgo may not be needed (?), also, there's a post stating if you've already got problems the transgo only buys a few months of time and a Transmission swap is still going to be needed in another 6 months (is that accurate info?)

I'm also hesitant to experiment with fixes without some way to systematically confirm that this is actually the issue. Transmission work is beyond my ability and I'll be paying a mechanic for the labor.

 

I agree that it probably has the updated ZF valve. The transgo might offer an advantage if the bore of the valve body is worn, but it may not be a permanent repair.

 

Taking it to a trans shop my next day off from work, but in the meantime the problem has gotten worse. At certain consistent down shift points the car just shutters away instead of dropping into gear. Nothing stops the shuddering besides lifting off the throttle or hammering it hard forcing it to downshift - remaining at that throttle will keep the car shuddering indefinitely as (what seems like) it tries unsuccessfully to engage the lower gear.

This happens consistently around 50-60mph when you add gentle acceleration like reaching an incline or passing another car. It also occurs at other points, but with less consistency.

Any idea what would cause this behavior?

Fyi, New trans Mount has been installed, so that was unrelated...

 

Trans shop put the code-reader on, no codes at all.

Put it on the lift and there is nothing is leaking.

They said if the problem is getting worse and there are no codes and no obvious external signs the only thing to do is to open it up, and once you do that you might as well rebuild it already - otherwise there is the labor for changing the seals/fluid and you may still have the issue. Rebuilding would cost around $1800

He expressed that the symptoms imply an issue with the torque converter as it happens at the speed-points that the converter locks-up (or something like that), off-the-line and around 50mph.

He also said there was no point to check the fluid because there is no sign of leaking and the old fluid would likely be full of metal shards (~150k miles) and changing the fluid without disassembly/analysis/rebuilding the transmission could make it worse due to the detergent-characteristics of new fluid.

Does all this sound right? Should I get a 2nd opinion? Is there anything else that they should be checking?