Tran not upshifting
 

Im the new owner of a 2005 XK8 with 50K, great shape and transmission in first week was smooth. Starting yesterday it doesnt upshift in all gears at least half the time. A little tap on the gas and it will usually will shift from a high rpm. Any ideas at what the issue is with such low mileage?

The first step is to check and make sure that the fluid level is correct. Sounds like it might not be.

I would agree on mos cars but it seems these are like my Infiniti where there is no dipstick. Is thsi true, manual tells you nothing.

Correct, there is no dipstick for the ZF 6HP26 transmission (which is what you have). The ATF drain-and-fill procedure is sort of a Rube Goldberg operation that must be performed in the proper sequence at the proper temperature. There are many threads here in the XK8 forum that instruct you how to do it. The fill procedure is best done by two people - one in the drivers seat putting the gearshift through its paces, and one underneath the vehicle pumping the fresh ATF into the pan. Many of us switched to Mercon SP ATF, available at any Ford dealership. It is essentially the same product as ZF's much more expensive Lifeguard 6 ATF....

I would start by doing an ATF drain-and-fill and see if that improves your transmission's operation significantly. If your car is still running the factory fill of ATF, its additives and friction modifiers have long since worn out. Fresh fluid is always a good idea in these cars. Most of us long-time owners do ATF drain-and-fills at least every 50,000 miles or so....

I appreciate the information. I would guess that if it was anything to do with the fluid it would have been a gradual problen. It started yesterday and wont upshift on most accelerations. Im only handy with car but again, if it was fuid issue wouldnt be an ascalting issue? Not sure what it means but it shifts withoiut issue on the manual side of the J.

I have been here on this forum a long time and have owned two of these ZF 6HP26 transmissions (one in my previous 2005 S-Type and one in my wife's current 2006 XK8). I know from experience that if you cannot document at least one previous ATF drain-and-fill for your now 15-year-old car, that is where I would start....

The other bit of info that you need to be aware of is that strong batteries are mandatory in these cars. Even marginally weak batteries cause all sorts of issues, including transmission misbehavior and throwing spurious warning lights on the dashboard. How old is your battery? It should have a production date (month/year) sticker or embossed digits on it somewhere on the casing....

Thanks for the input and the battery issue would make sense.The battery is 2017 however car has a mod for daytime running lights to bring into Canada and if you leave lights in auto they stay on. I learned this the hard way and drained the batter a couple days ago. Maybe this is a cause?? Ill trickle charge the battery and see if that makes a difference Thanks again, from replys it mau also be worth changing 15 year old tans oil

Jon, I cant thank you enough. I put the tester on and surprisingly "week". Put the charger on for 2 hours and gave it a try. 5 times from stop all gears changed as they should. Wow, what a surprise and I cant beleive I havent seen this issue flooded on the forums. Thanks again for making the effort to help! My only other issue is the cruise aunavailable and rear light message that should be fixed when I get the brake switch.

Put your shifter in the manual mode in 5th gear and drive the car if it shifts ok then I would say you need to have the shifter cable adjusted.

Guys
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Thanks Gus, appreciate the help very much. To my surprise the suggestion prior regarding the battery was the issue.

Also, manual shifting was fine, but if left in 5 I had the same issue.

Fingers crossed for you that it is just the battery :)

I'd recommend that you take Jon's advice and do the filter/fluid change. The 6HP is pretty robust, but a little help along the way won't go amiss.

Yes Sir after 15 years it woul dbe time even with 30,000 miles.

This is probably your brake switch. The adjustment is likely off, and the car "thinks" you foot is on the brake and will not shift up. You can test this by of course determining if your brake lights are on when they should not, or, as suggested above, move the shifter from "D" to "5" back and forth for each upshift.

For the fix, you need to look some pictures up, but the switch trigger has a built-in ratchet that need to be adjusted. This is tricky work mostly for access reasons (narrow footwell, up to the brake pedal). This is likely $0, though, if DIY.

Best of luck, keep us posted.

Hey folks, well I spoke to soon on the battery and should have tried from stop more, fuly charged battery and stil wont upshift. I do have a brake switch issue with the "cruise unavailable" and "check rear lights" message on gauge. If starting from stop in 5 I still wrake wont upshift. I have ordered the brake switch (LJB 642 0BB)after taking it out to chect for corrosion, there was none. Not difficult but was tight under there. It would be great if the brake swich replacement fixes all but the shifting was fine even with these error messages prior. This shifting issue wasnt gradual, it just came on hard one day.

Start in D and gently accelerate from a stop, then gently switch from D to 5 and then back to D, back and forth, multiple times, as needed to reach the proper higher gear.

If you have your brake switch on hand, check the plastic teeth/ratchet on the trigger. That is the adjustment I am talking about. It is likely completely collapsed right now, and no longer makes contact with the brake pedal stem, hence your transmission thinks you have your foot on the brake.

Im wondering of we are talking about th esame switch. This is th eone I removed, is there a different switch behind the pedal that you are refering to?
https://cimg6.ibsrv.net/gimg/www.jag...9db828f1d5.jpg

The white area is actually two pieces that can be adjusted for actuation. (photo complements of member astromorg from post 22 thread: https://www.jaguarforums.com/forum/x...-171849/page2/
https://cimg0.ibsrv.net/gimg/www.jag...61522eebc1.jpg

Thank you, I should have the new witch soon and will keep you posted on the results. My brake lights do work as they are suppose to.

Hey Craig, on you pic I see the prongs are grabbed by a dark grey clip of some sort, Looking at my switch this isnt present. Is this the teeth you are mentioning?