2005 XC70 Transmission Bugs

[precopster]

Those CFE+ units are truly remarkable.....but I could buy a much needed CVVT exhaust hub with that money......or should I use that old one off that spare head I have and order the CFE+ ??

[vonbaron]

Well, after a drive back into the city today I am happy to say there appears to be a big improvement in the way the transmission is working. I went through quite a bit of start stop traffic and up and down multistory car parks and other places I needed to go today. There were only a few slight problems on my way back out to the country, mostly a few not so smooth down shifts when approaching stop lights.

But after a single drain and fill, I wasn't expecting it to behave as well as it has done today. It will be interesting to find out how long this will last for, or if in fact it will degenerate quickly back to its old bad tricks.

I guess I know that at least it does seem to be down to the quality of the AFT. Maybe the previous owner who had it flushed last time where they used a flush treatment did not clear the treatment enough.

But, I had another thought I want to pass by you good folks:
If the problem only appears once the transmission is hot and from my fault code it appears to be the lock up solenoid, would doing a little SLU solenoid gym workout help the situation once I arrive back home and turn off the engine ?

What I am thinking is this: the three larger solenoids are PWM to give linear position control, correct?
And it seems that from videos I have seem of people pulling out these solenoids and pulling them apart to clean the bushing the pintle slide up and down in, by using a correct size drill bit, winding it in backward and then rotate forward to clean the inner wall of the bushing. Doing this helps removes the muck buildup on the inner walls where the pintle binds to.

So, my idea is, while transmission is hot and problems exist, stop and turn off engine. Then a nifty little electronic device is connected to the problematic solenoid and applies a nice sinewave, going from 0 volts to perhaps 10 volts, or maybe 12 volts. Enough to move the solenoid plunger back and forth at some cyclic rate, say maybe a few Hz, not much more.

My idea is that while the system is hot and the solenoid plunger is exercised for a duration say some minutes, then this may also help keep this solenoid cleaner. Does the plunger expand in size to to thermal rise, more than the bushing it slides within. Dissimilar metal will have different properties of course. Is this the root cause, and the muck that binds it the very thing needed to bring the problem to life ?

Of course this can not be done while engine is running.

What are your thoughts on this, has anybody ever tried such an idea before, do you think it has any merit ?

Oh, looking at the CFE devices, Mike, I think we should totally build our own, oui ?
I take a small microcontroller with CAN bus and start decoding packets. Plus, there is a lot of good info out there on hacking volvos, which gives me some hope. The CFE+ device listens on both the low speed and high speed CAN bus networks.

Anyhow, just want to pass on thanks to Mike for his initial advice and ongoing support.
Von Baron

[Sardine]

Hi Vonbaron,
I have a 2005 V50 at 140000Km that perhaps has the same Asin transmission, AW50-55SN, and with similar problems of flares, thuds when hot. After a transmission flush with the same Nulon stuff did not work, I pulled out and cleaned the three solenoids SLU/SLT/SLS from the valve body. The car transmission is still perfect after more than half a year now. You may want to do the same. But beware, it's a lot more work than some people want to do. The thing is just not designed to be removed easily.

[precopster]

It will improve as the additives in Nulon adhere to the bushings in the solenoids and the transmission computer adapts to the quicker response times of changing gear. Do another drain and fill and keep driving. In around 500-800 kms adaptation will smooth out the shifts. The Penrite synthetic ATF actually made no improvement on any of our cars.

The small bushings at either end of the pintle were rumoured to be of inferior quality until 2003 and would magnetise by induction, making metallic sludge stick to them. In your case it could just be heat alone but without pulling them apart you may never know.

Omega Machine and Tool has the tools to properly disassemble these solenoids as well as high quality bushings. The drill method is temporary for most folks that have tried it. Perhaps to use an oversize drill may help? I tried the Transgo shift kit
on our 2002 XC70. However I feel the Nulon overcomes these issues.
My 1-2 upshift is not totally gentle now in my T5 after 2,000kms on Nulon but was awful and so jarring that my wife didn't want to drive the car. The 2-1 downshift is now imperceptible.

[vonbaron]

Thanks Sardine and Mike for your input.
Does anyone have any thoughts on my idea I mentioned above on solenoid massage device ?

[precopster]

When we do the Transgo modification kit, the drill bit goes through the bushing, therefore the bushing must expand more in a hot environment than the pintle. I have no idea if passing a signal through the solenoid while hot will help but it sounds like it has merit. It would be the equivalent of drilling it out when cold, I suppose. With enough cycles while hot it could ream out the bushing.

[vonbaron]

Update March 25, 2019:
Well, actually, update 26 of March after server update went AWOL, always keep a copy of posts in case things go wrong

After doing the last drain and fill, that is, number two drain and fill, the car firstly improved for some km and then had a few bad issues again, and then resumed to being nice again. It seems it does need some time and some km for the ATF to work though and do its magic.

I think I have put on a total of around 500km on the second drain and fill now over the past weeks.
I don't drive it too much, as I work from my little mountain cabin.

During this time, I ordered more of the magic Nulon AFT from the online store I buy from, as suggested and recommended by precopster, sparesbox.
But this time, it was not only affordably cheap, they refunded my the whole amount back due to an error on their web site with a online special of 5% discount. I proceeded to the online checkout and nowhere was there a spot to enter the 5% coupon code, so I call them up and they said, "oh, yes, okay, we will refund the 5% difference back to you", to which I thought, okay, no problems, you are selling this Nulon AFT pretty cheap anyhow.

A couple of days later, I have an email that they have refunded the whole amount. That is what I call a super discount
Plus, the freight by courier to my place was free as well. A good reason to do more shopping at this online store I think, oui

My plan is to do another drain and fill in the next week, which will be number three.
I am still keeping in the back of my mind that the valve body solenoids will need some work, but am happy so far.

Also, time to write up an article on my new project, another XC70 that I bought the other day, mostly for the trailer hitch, oh ohhh
Von Baron

[MacNoob]

I didn't see any interior pics of this car - wood wheel too?
Transmission valve body troubles seem to be mostly a 2001-2002 thing. Some searching around will find you info on replacing the valve body with a more generic GM item (some GM cars use the same transmission) that is available a lot cheaper than the official Volvo part.