Hi all, I recently bought a Jaguar XJ8 X350. It's visually quite clean. It does have lots of fault though, primarily air suspension and a gearbox issue. This is what I have noticed from the transmission:
- When driving away, the car sometimes puts way too much throttle without me pressing the gas pedal at all. This happens in 2nd and reverse gear only. I haven't driven it in sport mode, so I don't know if the problem is also there in 1st gear.

- When it's downshifting from 3rd to 2nd, it's almost always clunky. If I brake lightly and there's a smooth deceleration, it's less clunky. The whole car also vibrates at low speeds when braking, it has trouble adjusting the rpm. It doesn't clunk in any other gear, neither does it do this when upshifting.
From what I've read, I'm guessing this could be caused by:

- A-brake

- valve body

- transmission sensor

- transmission fluid
Which or these would most likely cause the problem, or are there other possible causes? It must be noted that the transmission oil was probably never changed in 260k km, as the brake fluid dates from 2011.

Do you think the problem could be solved by changing the transmission oil and filters?

 

The first thing to do is to have the car scanned for error codes.

I am thinking that the putting too much throttle when driving away could be caused by a defect related to the throttle body or a sensor, and that should give an error code.

The transmission will benefit in any case from a fluid and filter change, and I would say that the downshifting should improve. If you do the fluid change, I would recommend to replace the cable plug sleeve and the seals between the mechatronic (or valve body) and the rest of the transmission, as well.
The seals I mean look like this:


The trouble with adjusting the RPM could also be caused by either a defect related to the throttle body, or come from the transmission.
When I test drove the car that I eventually bought, at steady speeds the RPM were not constant, but fluctuating a bit, and this was cured with a trnsmission fluid and filter change.

The vibration when braking at low speeds may be caused by a sticking brake caliper or a warped brake rotor.

Best regards,

Thomas

 

I had a similar experience. The XJ "lurch" is a well known thing on these cars usually caused by zero maintenance on the transmissions. Fortunately they are robust and will take a beating. I got bad shifts if coming to not quite a complete stop making first engage with a severe lurch. Also "rev hunting" and torque converter not locking which was mistakingly associated with a bad torque converter making the previous owner drop the price to peanuts. Took a risk, bought the afore mentioned valve body kit, oil flush, new filter/pan, and solved the issue. Also noticed low oil from previous bodged attempt at a fix which probably caused the torque converter to not lock. I did 2 x trans oil flushes just to be sure! Important to note that it can take a relearning cycle for everything to clear up. Mine took a couple of weeks.

As said, check for codes first. I use an iCarSoft V3.0 and keep it in the glove box. Very handy tool...