RPM fluctations
 

This winter I have experienced some RPM fluctuations that I for some reason have associated with the gearbox. What I experience is that the motor RPM is moving between 1400-1600 rpm when driving on gear 3 and 4. It may be present on gear 5 too. This happens both when using cruise control and having my foot on the throttle.

The phenomena seems only to present after start, after driving for 15 minutes or so it seems to be gone. I have no fault codes that seems to be related to this (even though occasionally get an EGR fault code on one of the valves).

The gearbox is JEF, it has 280kkm on it and I'm pretty sure the transmission fluid never have been changed. I'm now considering my options. Can low fluid level result in these fluctuations?

If level indeed is low (plan to check that), should I consider changing the fluid? Not that keen on a full flush and not sure if it is worth it on this old car. OTOH I plan to keep it for a few more years.

Can't comment on the symptoms, but if it is low on oil, then best to top it up in accordance with proper procedures (temperature range), even if it doesn't eliminate the problem. As to doing a full flush that's a tricky one to answer. Some would say that the car has done 280k km and doing a full flush may dislodge gunk that could wreck the transmission, so best to leave alone.

No harm in checking fluid level or doing fluid change. Don't think you get any gunk settling in D3 boxes, modern fluids are keeping all the **** suspended in the oil, was only problem in older boxes that used older versions of gearbox oils.

I think it's just a software disengaging torque coverter lockup clutch as rpm drop. I have noticed on mine too but I would say more like 1200-1400rpm and more noticeable before it's warmed up while the fluid is thicker. Fluid has been changed on mine.

Thanks for the input, will check the fluid when the weather gets a tad less cold....

Looking at the instructions for checking the level it seems like one could change the fluid and filter while on it. Only part that seemed hard was how to get the wheels off the ground while running it in.

Have been driving the car in a tad warmer temperatures now and it's obvious the transmission doesn't change gears as it should when doing up-shift. It is like it is releasing the the torque converter but instead of shifting to next gear it keeps slipping too long which results in running this non-locked converter mode with too high motor rpm (lower gear).

Changing fluid is of course a good first thing to do but is there anything else I can prepare or check out to be prepared when doing the change? Anything else that commonly fail on these gear boxes like valves or anything? Have no fault codes when checking with VCDS at least.

Check the plastic tube on the top of the pan for leaks where the wiring harness goes in. This sleeve seal is common for all ZF leaks. In addition, you may want to order the 4 rubber tube seals and the bridge seal and have them changed when you service the box. These seals can leak fluid internally and cause the gearbox some issues

The sleeve seal leaks externally and the ZF box doesn’t enjoy low fluid at all.

The ZF 6HP26 is capable of operating the solenoids to overcome internal and external fluid leaks and therefore pressure changes. So once repaired, simply reset the adaptation for the solenoids.

Google ZF 6HP26 seal and it will come up with many things. Otherwise these boxes are pretty bulletproof

Just logged in and saw your reply mcs, thanks!

A actually did what you suggested. When I realized the gearbox is a common ZF 6HP26 was wide open ;) So much to read on BMW/jaguar pages.

I came to the decision to start just changing the ATF fluid. Couldn't see any notices in the service booklet about it ever being changed event though that doesn't guarantee anything. Reason for the change was that better to start off replacing some of the potentially really old fluid to see any improvements before doing more work. Agree that just pulling the mechatronic unit and replace the seals wouldn't be that hard. Save that for later.

Reading Jaguar forums I noticed a method that used the internal ATF pump to pump out fluid via the cooling outlet and then just doing refilling through the return line. That sounded like a good idea to replace more than the accessible fluid. So that is what I did...

First inspection indicates some kind of leak. Can't really say where it's coming from so it is hard to say if it even is ATF fluid or engine oil. Pretty messy around the sensor at the bottom but didn't bother. Need to do my homework on what it is before.

https://whatever.nu/byggahus/atf1.jpg

Pulled the ATF cooler, started the engine to find which is the exit/return lines. The front one is return, the ATF fluid comes out of the rear one. Fine.

Drained the transmission, pulled the pan and filter. Let it drain during the night, new filter, pan gasket and then assemble. Made a simple adapter to connect hoses in place of the cooler. I printed the green plastic thingies on my 3D printer. The plywood piece has holes for two M6 screws and the hose connectors. Center measurements for screw-hose-hose-screw are 0-36-70-128 mm.

https://whatever.nu/byggahus/atf2.jpg

idea was, according to my Jaguar fellows that the return line dumps into the pan. The pump then sucks up new ATF fluid through the filter and pushes out old through the cooling exit. In theory, one would see fresh ATF fluid coming out but that didn't happen. At least the fluid spit out at the end was less black than what I first drained.

https://whatever.nu/byggahus/atf3.jpg

I first pressure-filled about 6 liters of fluid to replace what I drained during the night. Then started engine to drain one liter, filled up with a new liter and so on until I realized I had put 12 liters into the whole thing.

My plan was to just fill up the transmission with too much fluid and rain it off during the level check. Unfortunately I didn't have enough fluid so when doing the level check it was too low. I had then mounted the cooler. Had to wait a day to get more fluid and fill it up the normal way.

In the end I think the transmission was about 500ml low on fluid and the fluid seemed to be in really bad shape. Deep black. Magnets looked good though, just some minor metal slush on them.

So how did it work out then? Fine. I haven't done the adaptation reset yet, just took it for a test drive of about 20km in different conditions. Shifts are smooth and happens when expected, gears are locked and so on. Still assume I need to reset the adaptations and do the adaptation runs on an empty road?

Lessons learned:
- Buy more ATF fluid than you think you need when you order it from a cheap reseller to avoid having to buy additional at a steeep price...
- The flush method using the cooling lines may not really work that well on the Audi version of the 6HP.
- I will need to redo this sometime in the future due to the potential leak.

I also learned a lot about the ZF gearboxes and gained more hands-on experience. Nice.

If I encounter more new problems I will gear up with new sealings to the mechatronic unit and replace them when having things apart.

Cool picture. With all those pipes pumping different coloured fluids, the only thing missing is the heart monitor.

The reason you won't find it in the service schedule or book is because Audi claim it is 'sealed for life'.