A gentle auto gearbox shudder!

[Big Wigg]

Good evening fellow Jag owners.

My S Type diesel auto has what can best be described as a gentle shudder from the gearbox.

It happens from about 1500 rpm up to about 2500 rpm.

It feels like I’m driving over ripples in the road!

The Oil level is correct.

It had an Oil and filter change before I got it.

Although I have very little experience with this car (not had it long) the gear changes seem to be very smooth, and I think everything else in the gearbox works as it should.

Any ideas please?

Bonne soirée 🙂

[mrmike]

Change the gearbox Oil, be sure it is for the 6 speed box don't be fobbed off. Many mechanics put in the cheap 5 speed box stuff and that is instant grief.

Mine had had judder at between 1700 and 2000 rpm when under light acceleration. When you change the transmission fluid you can only change about 3 of the 8 litres with the drain plug and top up system. The first time there was a definite difference. ( I had 3 new litres of fluid and 5 now of the old ) After A couple of months I repeated this (Now I had 3 new litres and 5 litres of the previous mix) More improvement and no juddering at all. Just recently I have noticed a very slight judder at around 2K rpm. I will shortly repeat the 3 litre change again. As you can imagine this is a crap method.  I understand that the best way is to use the proper machine, dissing the connections to the Trans Fluid cooler and flushing and then refilling with 8 litres of the correct trans fluid. My drain plug (10mm) was stuffed, I made a tool to remove it and  then I got a new one for an automatic mini. (No jag dealer here) the filler uses an 8mm allen key Which needs to be cut down because of chassis clearance and then use an 8mm ring spanner on the inseted piece. It will undo with a bit of force. This is the cheap solution, there is a kit with filter and seals for the valves if you have really good access or deeper pockets for the better solution/

Good luck

[LairdScooby]

On 9/27/2022 at 11:51 PM, mrmike said:

 

 I will shortly repeat the 3 litre change again. As you can imagine this is a crap method.  I understand that the best way is to use the proper machine, dissing the connections to the Trans Fluid cooler and flushing and then refilling with 8 litres of the correct trans fluid.

 

As someone who has had autos for many years (decades in fact) i can assure you the method you used isn't crap, unless your car is near new with very low mileage and has previously had the ATF changed regularly, the method you used is in fact the best method.

Using the flushing method you describe and cite as "the best way" introduces all new fluid in one hit. That new fluid will be much thicker than the older, worn, thin stuff currently residing in your box. The additive in ATF commonly called "seal-swell" will also have worn out, allowing the rubber seals, "O" rings etc to dry out and become brittle.

When you dump a full load of new, thick fluid in, this can cause pressures to rise considerably and those brittle seals etc don't always cope.

Introducing it in a series of "part-changes" as you've done means the new fluid comes in gently, allowing the seal-swell to work on the seals and revive them before the next lot of new fluid comes in. This is a much gentler method on the gearbox and less likely to pop any seals as you drive. Normally 3-400 miles between each part-change is ideal, depending on the state of the fluid when you started your series of part-changes, you'll need to do 3-4 part-changes and then do one a year to maintain the fluid in a good, clean condition.

I did once (about 18 years ago!) try the flushing method on an old Volvo 740GLE, seemed fine until i gave it the beans one day about 3 weeks after (bearing in mind i'd been doing about 250 miles a week in between so the seal-swell should have done its bit of reviving) and caused a harsh change between 2nd-3rd which even happened on a gentle throttle after that. Needless to say i p/x'd the car soon after and never again tried using the flushing method!