So... been looking into my aging ZF 6HP26X and considering my next move..
But first a little history..
Got the car a decade and 120,000kms ago. Full dealer service history and no mention of any transmission work.
When I first got the car, I asked the dealer to check the transmission as it had a bad 2-1 slam - they said they checked the fluid level and condition (fine and fine) and said they reset the transmission adapations.
Didn't help so I learned to drive around the 2-1 slam (easy enough).
Four years and 30,000kms later, I replaced the power divider oil on the transfer case and reset the VTG oil wear adaptations using DIS. No issue but... the 2-1 slam was gone!! What the heck... I'll take the win...
Fast forward another year or so and the 2-1 slam was back (like the cold, it creeps in...). I knew the mechatronic seal on the transmission was starting to weep a little, so I bit the bullet and replaced it, along with the bridge seal and the four "jump" seals, pan gasket and filter. I used the old fluid again, as I was worried about causing an issue with a full fluid change. I did use a liter or two of new fluid, as you always lose some doing a mechatronic drop (most of it was on me!).
In the last six months, the shifting has gotten noticeably harsher. Not bad but I noticed it, as a I drive the car pretty much every day.
OK - time to try a fluid change. Yeah, I know - a fluid change isn't going to fix hard wear on parts but I figured I'd be dropping the pan again and so I wanted to get as much new fluid into it as possible when I DO drop the pan. Rather than doing 2-3 drain/fills after putting new parts in there, I opted to do the first 2 drain/fills, then drop the pan etc.
Car was now 20 years old and at 285,000kms - on factory fluid.
First drain/fill caused no issues - shifts largely unchanged, possibly a bit smother (plecibo?).
Drove it for a month (500kms?) and then did a second drain/fill. Again, no issues. Initially, anyway. Ater about 200kms it suddenly developed a nasty jerk in 5th gear at low rpm (~1,500rpm). And I mean nasty. It's like the power is chopped hard on/off for a quarter second or so. This repeats 2-3 times in a couple of seconds, then it settles down.
Higher rpm (over 2,000rpms) and high loads (pulling a loaded trailer up a hill at 100km/h in 5th gear) are fine. Sweet as. Zero issues - that I can feel anyay!
Same issue in D, S or M mode. Makes no difference.
Around town, it drives fine - but then it never gets higher than forth gear, so the problem doesn't bite.
Hmmmm... So I load up ISTA and query the solenoid adaptation values....
Not good. They are all way high... way, way high....
Fill times seem ok - at least the first three.
So are high adaptation values on all solenoids a sign of overall low fluid pressure? Is my pump failing or the bridge seal leaking badly?
I was thinking I needed to replace the solenoids but given the fact the adaptations are all high, I don't think this is (just) a solenoid issue.
I guess I'm looking at a full mechatronic rebuild but I'm not throwing over $2k at this only to find the issue remains...
I do so hate loving this car...
