So this past week, the transmission acts up and won't shift to a higher gear by itself when accelerating from a stop. But if you pull over and shut the car off and then start the engine again, all returns to normal. But just last night, it got even stranger. Now from a complete stop, the car slowly accelerates as if the parking brake is on. It makes a similar sound like the calipers are holding the brakes on. So I bring her in to my shop and jack her up and check all the brakes. All check out as being perfect. I did reset the brakes as per the procedure of disconnecting the battery and then going to some procedures to recalibrate both the foot brake and the parking brake. But after test driving it, the issue persists. So I jack up the rear of the car and start the car, put it in to reverse, then in to neutral, and then in to drive. When in reverse, it makes the sound as if the brakes are on. When in neutral, the tires rotate forward as if it was in drive with no sound as if the brakes were on. But when in drive, the sound returns as the wheels move in the forward position. It almost sounds like reverse and drive are both engaged. On closer inspection, it sounds like the brake squeal sounds are coming from the transmission. So I am assuming that it indeed is a transmission problem. This is weird for a ZF transmission that reportedly is supposed to be very reliable.

I am wondering if anyone has insight of this or even has experienced this problem with their XF or even another make of car that has this ZF trans in it. But the real question is whether the problem is actually with the transmission, the selector switch, or the transmission control module/computer? I already have a new transmission on the way. But could it be something else that is causing this? There are no fault codes popping up.

Anybody want to chime in and help an XF 5.0 owner who is thousands of miles away from the nearest Jaguar dealer? I really could use the help.

 

I'll go out on a limb, given my limited knowledge of automotive computer controls, and say that you may have a traction control or stability control system problem, rather than a transmission problem. Maybe a wheel speed sensor is failing, causing the car's systems to think it's seeing wheel slippage, and trying to counteract it.


Just for the sake of clarity, when you say the transmission "acts up" and won't upshift, what is the engine doing? Is it increasing RPM without any increase in vehicle speed? Does the engine appear to be "laboring" against the brakes?

 

Yes, it seems like it is laboring, as if the brakes are holding it back. The reason why I suspect it to be a trans problem and not a sensor problem is that the trans is actually in the forward gear when the selector is in neutral. Also, I forgot to mention that when you start the car and the shifter knob rises, the car jumps as if you had put it in to a gear. You hear the traditional thump and the engine jerks slightly indicating a load from the transmission. But I could also have a selector issue or even a transmission module issue. I am not sure how to diagnose that, but eventually I will figure it out. Would a wheel sensor cause these types of symptoms?

BTW, I appreciate all your ideas and thoughts.

 

I think that I am going to do all the repairs myself starting with the seals and spacers to the valve body assembly. I will probably change the solenoids while I am in there too. And of course, I will change the pan and filter along with a fresh oil treatment. I will let you know how that works out and if I get her fixed.

 

If you're lifting the car off the ground and putting the car in gear while running the engine, I'm amazed that you don't get an ABS and DSC fault warning. Or do you?

 

No, I did not get any fault codes. That is what was weird. It was just for a second or two in each gear. But the one that got me was that it was spinning forward in neutral.

 

If I were doing the troubleshooting, I might be suspicious of the shifter module, first. If you don't have an effective way to troubleshoot the issues, and are forced to try a few part replacements first, I would think that this would be the easiest/cheapest part to replace. If it's a transmission issue, it could get costly. Along that line, the shifter must plug into the transmission somewhere on the outside of the housing. Have you tried cleaning both sides of the connections, with spray "contact cleaner" and compressed air? Maybe, it's just a dirty or wet connection?? Did you, by any chance, drive through any deep water, prior to these problems occurring?

 

No deep water or even mud puddles as we are in a very dry season right now. I was going to replace the selector and module which apparently one assembly. A used one is about $250 from sellers on eBay and others. A new one is more than double that. I did some research on line and have come to the conclusion that it may be a block between the valve body and the transmission case. Apparently the part is made of plastic and cracks at about 50,000 miles. My car is just over that. It seems to be a common problem and 95% of all ZF 6HP26 issues are a result of that. I have one on order which takes a week to get to me. I did buy all the plastic spacers and a tube also. I am changing pan, oil, and filter at the same time. And as a consolation plan b option, I have a tested used transmission that is arriving in two weeks. I also bought a complete dealer diagnostic tough book computer just so I could be able to service my XF thoroughly without having to guess anymore. I love this car and plan to keep it. So hopefully, I can learn to maintain an repair it as needed.


Thanks for your input!

 

Glad to see your enthusiasm about tackling the transmission issues. If you are able to take some pictures, when you tackle this repair, I think it would be a great help to other XF owners!


Good luck!

 

So I completely went through the brakes inside and out including testing the parking brake switch and module.

I even spent some big money buying a Jaguar SDD computer which is exactly like the dealers. All the software was included in the Toughbook and current updates also. I updated all the software on the car and cleared all the codes as well as did a full diagnostics on the car.

The car now runs fine with the exception of a sound that mimics the brakes. So I installed small microphones on the bottom of the car to see if I could detect the location of the noise. My results were that it was coming from the transmission.

Also, if the car is put in neutral with the parking brake in the "off" position, you can rev the engine and it will slowly pull forward.

So now I know where the source of the noise is. So I did tons of research on the web. And I asked lots of ZF techs and most were not absolutely sure what it could be.

But after careful research, I have found that the possible problem is the spacer block that goes between the megatronix valve body and the transmission housing. These parts are made of plastic and can break from pressure and heat. A loss of pressure in the block from the crack can cause all kinds of strange things to happen.

So I ordered the block and some of the other sealing parts as well as a pan, filter, and oil and will rip her apart tomorrow. At that time, I will report back on my findings.

 

Can you point to some info on this plastic spacer?

I have been using the 6 speed ZF for almost 8 years in my 2005 STR and currently over 125K miles on the transmission and have never heard of this problem.
Now the sealing sleeve fluid leak is well known and the "Lurch" is a software/programming issue.

Have you contacted Klaus at CTSC?
They seem to have the most knowledge and parts selection of any supplier. I got my fluid and service kit from them.

Genuine ZF Parts
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I did lots of research and contacted nearly everyone that I could. The "lurch" that you described is not the issue if you have read my posts. I do have a Jaguar proprietary SDD laptop and have run the updates and diagnostics. It did not cure the issue that I have been encountering. The part is like the one in this eBay sale.

OEM ZF 6HP26 6HP28 Valve Body Sleeve Connector Seal kit 6pcs BMW Transmission | eBay

 

Right that is the sealing sleeve I mentioned. The other plastic in that kit is not needed and has not caused problems. Would not hurt to replace them since your in there anyway.

Do you have the up-rated pan bolts? They are pretty easy to mess up and Jaguar increased the size to help prevent that.

The sleeve just causes a leak and also does not affect anything else.

Don't forget to get the drain plug busted loose BEFORE trying to do any service. That plug almost sheared odd my Allen wrench it was so tight. At that time I did not have a lift and access is very tough.
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Update: So I did all the upgrades including the oil pan and filter change. I replaced the Megatronix sleeves and block Is suspected. I did not see any damage or reason that this might be the problem. I even inspected all the solenoids. Nothing out of whack. So I went to test drive the car and it still has issues.

I am now not sure if I am even looking in the right place. So I test drove it again and no codes show up. Most of the time, the car drives fine. But after coming to a complete stop and then idling for a minute, the sound comes back and stays as if the brakes were dragging. But if you move forward and then accelerate, the sound goes away and the car drives perfectly fine. The odd thing is that this noise also occurs when you are stopped and in park idling. But if you raise the rpms in the motor, the sound goes away.

I am now going to check the ABS system. But their are no codes and no faults. So I am going to hook up the SDD computer and do a two man test drive with the computer hooked up to see if I can detect it some other way. Is it possible that the ABS pump is making the noise and that it affects braking at low speeds?

 

Latest Update: The transmission has now failed and is making a terrible whining and grinding in low and reverse. There is no noise once it shifts to higher gears. So this week, it will come out and be replaced with another. I will then do a tear down and see what failed. I suspect that it was a defective solenoid.

 

Wow. Crazy stuff. Subscribing for analysis. I wonder if it's the torque converter that failed? Doesn't it decouple from the trans, which would explain why in low gears it squeals, but not higher gears?

 

No, the tq. converter never decouples, it just hydraulically 'stalls' while the car is stopped.

 

With the symptom of starting in gear maybe the TQ lock up is too blame?
They can appear to hold the engine back and can stall the engine at idle sometimes.

Please post back but sorry to hear you need a new transmission.
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Did the new transmission get rid of the noise?

 

So here is where I am at now. It takes about four to six weeks to get anything shipped by a container vessel to Guam. In case you don't know where I am, Guam is a US Territory in the Pacific Ocean very close to Japan.

I got the replacement transmission a couple of weeks ago but had to go to Los Angeles for a week and just got back this past weekend. So I replaced the transmission yesterday and everything seems fine. I ran the Jaguar dealer authorized computer and reset the codes. So for now everything seems good. I guess I shouldn't jinx it and keep my fingers crossed for a few days.

I did remove the pan on the old one and removed the valve body. There were lots of shavings and particles from the clutches in the oil. I am going to tear it down. But what I suspect happened is something that I should have done before the issue got serious. It looks like I had solenoid failure. Maybe even more than one solenoid failed. And because I tried several cures while still driving the car, the transmission eventually had catastrophic failure.

I will disassemble the trans and wash all the parts and send the solenoids back to be tested. Then I will rebuild it and save it on the shelf in case I ever need it. I will give another update when I do the rebuild.