Gears not engaging when car has warmed up

[michalsoch470]

Hi,

I am new to the club, having recently bought a 1995 xjs celebration. I am sure that this question has been asked before but I am finding that the car changes gear ok when cold but when warm the gears start slipping, or won't do into gear when moving off from a standstill.

However, once I have turned the engine off and let it stand for 15/20 mins, the gears work again until warm.

Please could someone advise me as to what the potential problem(s) could be. I live in Cheshire East but can't find a garage that knows anything about Jaguar XJS'.

Many thanks in advance.
Mike

[davidr]

Hi Mike and welcome to the XJS Forum. Congratulations on purchasing the Celebration model - a fine choice!
Maybe we could start with a few basic questions?
Do you know the service history of the car?
Have you checked the transmission fluid level?
Your car has an OBD2 port. Have you scanned the gearbox for fault codes?

[michalsoch470]

Hi David,

Thank you for the quick response.

I did check the transmission oil when the engine was warm and it looked like it was at a good level, maybe even a little high.

I do not have any tools to check the OBD2 port (I assume that this requires a diagnostics tool?). I did call a couple of local garages today but they do not work on XJS'. In fact, I haven't been able to find a local garage that will even consider looking at the car.

I have put all the cars papers in a very safe place (including service book). So safe that I am trying to find where I have stored them at the moment. I do remember that is was MOT'd in Nov 2022 and has done approx 3,000 miles in 3 years.

I was thinking of having all the fluids changed as a starting point but I don't even know if this transmission needs special oil and if so, what oil it needs.

I realise that it isn't very helpful but not being mechanically minded, I am at a loss as to where to even start.


Regards,

[andypryce]

In terms of servicing there is a couple in Liverpool who specialise in Jags and you have North Wales Jag centre not far away. A fluid change definitely as a start I would say.


https://www.northwalesjag.co.uk/

[ptjs1]

Mike,

When you say the car "won't go into gear when moving off from a standstill", do you mean that the engine revs will go up when you're in Drive but doesn't move forward? Is that different from the "gears start slipping"?

The ZF boxes on these cars are very tough but also very dependent on clean fluid. Gear "slip" on these ZF boxes is a typical symptom of very low fluid level, although you've said that the fluid level seems ok. I know it can be difficult to accurately assess the fluid level on these boxes. You need to have the engine and box at full operating temp, then with the engine running you need to cycle the box through all its gear positions pausing for a few seconds in each position. Do this a couple of times. Then quickly check the fluid level with engine still running. (Ideally, you'd do it with selector in Drive, one person safely holding car with brake on. But unless you can fully do this safely, then put it in Park and check yourself) You need to fully withdraw the dipstick, wipe it, fully insert it, then withdraw and check level. It only tends to show clearly on one side, so be careful which way round you have inserted the dipstick. Wipe and repeat until you are comfortable that you are seeing it clearly. Really clean fluid is just about completely colourless on the dipstick, so it can be very difficult to see it clearly.

If you don't absolutely trust the history of the car and know that the fluid has been changed in the last year, I would be changing it. A straight drain and refill of the fluid will change less than a third of the total fluid, so it might need to be done more than once. (In 2016, I did mine 5 times with a 10 mile run in-between. I've then done it every year since even if I've done only 500 miles). The fluid type is nothing special, a good quality Dexron III is fine. If you don't know when it was last done, I'd also change the sump filter. If you do, be careful, the Jaguar part number on their system (and, therefore, the number quoted by all the major independents) is WRONG and will not fit. Drop a message back here and I'll give you the right part number.

Start with a known situation of the right amount of good clean fluid in the car and then you can reassess the situation.

Good luck

Paul

[michalsoch470]

Thanks all for the great advice.

I have been under the impression that the gearbox was a GM4L80E (just from internet searches). I didn't realise that it is a ZF box. Do you know the model number by any chance so that I can give the correct information to a garage? I have been telling everyone that it is a GM box.

I have now located all the paperwork but unfortunately, there is a note from a previous owner in 2015 that the service book was lost in a fire. There are lots of receipts from companies like KWE for upgrades and mechanical work carried out but the only 'service' receipts that I have found for the last 7 years are for a very ambiguous 'Gearbox Treatment' - £9.99 in 2022 and 'Engine Oil' -£10 in 2019.

As suggested by all, I will go for the Transmission Oil and Sump Filter change first. It anyone could give me the correct part number for the filter and the best oil to use, I would be very grateful.

Many thanks,

Mike

[michalsoch470]

Further to my previous post and re: 'do you mean that the engine revs will go up when you're in Drive but doesn't move forward? Is that different from the "gears start slipping"?

I have only driven it 3 times in the last 9 months and the last time (6 months ago), the gear change became less smooth as it get the car warmed up but The issue started after I had driven it for 20 minutes. On the bypass, it was fine but when I stopped, and tried to reverse the engine just revved, I tried to engage drive but the same thing happened. After a few more attempts, it engaged drive but when I slowed at a 'T' junction, it once again wouldn't engage drive and just revved.

I turn the engine off thinking that I would have to call the AA, sat there for 15 mins and then decided to give it one last try. Strangely, it engaged drive 1st time and allowed me to get home but it felt as though there was a little slipping between the gears.

The next day, I decided to take it back to the place that I keep it and it was fine for the 10/15 min drive. It moved off from lights, slowed/accelerated ok. Admittedly, as I got my friend's barn, the gear change became less smooth.

All very strange to a laymen like myself

[ptjs1]

Mike,

If its a 6 litre, it's a GM box. If it's a 4 litre it's the ZF box.

Paul