New Owner! Tranmission cutting out on freeway :/

[OslosisJones]

Hey everybody!

Been lurking here for a little while, finally bought my first car a couple weeks ago, a 2006 XC70 with 94k miles, exciting stuff!

So far I have serviced the car by doing the following:
-Switch to synthetic, replace oil filter
-Replace TCV hoses with ipd silicone
-Drain and fill ATF with T-IV

The transmission fill is where I am having some issues. After re-filling with approximately the amount I drained, the dipstick was reading high, so I mistakenly drained some extra. The transmission was fine in lower gears, but had serious problems engaging at freeway speeds of 70-80mph after running for 20-30 minutes. It will suddenly disengage, then re-engage with some gas, then eventually not re-engage until you slow down some. Very unsettling.

After doing some research, I discovered I was not following the proper proceedure to check the dipstick (btw this should really be in the main posts of the transmission threads). Knowing that I had underfilled the transmission, I have slowly been adding more fluid over the past few days to avoid overfilling. I have a VIDA/DICE setup running, which is helpful for checking the fluid temperature which affects the reading on the dipstick.

After my drive home yesterday (w/o any engaging issues), the dipstick read at about the minimum (maybe slightly less) for the temperature of the ATF. However, on my drive to work this morning I noticed the previous engaging issues at freeway speeds, possibly the worst they've been. Was planning on only adding ~0.2L, but I had to pull off the freeway and figured it might still be low, so I added about 0.4-0.5L.

My questions for the forum are:
-Will this problem be solved by filling to the correct level?
-Do I have a worse or different problem?
-How badly did I screw up?

BONUS:
Pretty sure this isn't a problem with the engine, as revs stay consistent when the trasmission disengages. I have to take a closer look, but I did see some VIDA codes for a high fuel pressure sensor, and some other fuel trim issues. Also noticed a small amount of smoke/vapour coming from the oil dipstick and oil cap when the engine is hot and running. Is this totally normal or should I be concerned about my PCV system? (currently a bit paranoid since risking the switch to synthetic)

Sorry for the novel, glad to be a new member here and looking forward to contributing some after getting through the newbie struggles!

[vtl]

A tad of smoke is ok on a running engine. Do a glove test at idle revs as well as at above 2500 to check PCV.

Sounds like you have a valve body issue, or may be, bad torque converter. Transmission is not that critical to ATF level despite all the sayings, I did not have any problems even with 0.5 liter less when I mismeasured drained ATF and drove like that for months.

[Astro14]

I'm not convinced that the transmission is slipping. The description is too vague and could easily be an engine stumble/power loss due to bad MAF or boost sensor.

[OslosisJones]

I'm not convinced that the transmission is slipping. The description is too vague and could easily be an engine stumble/power loss due to bad MAF or boost sensor.

Will the ECU/TCU automatically disengage the transmission if it detects a stumble? If so, then this could very well be the cause.

I am fairly certain the transmission is slipping, but I will look into the engine issues if this could be the cause.

MAF is fairly new as previous owner had it replaced after throwing some codes. I think these codes are still present so it likely isn't the MAF, which I also cleaned last week.

[Astro14]

Rebuilding a transmission involves replacing the parts you mention. Generally, you replace all the "soft" parts, seals, gaskets, clutches. If they look bad, then "hard" parts are replaced as well, steels, sprag, etc. it's similar to rebuilding an engine - special tools, understanding, evaluation of components, and care are all required.

I've done a TH-400. Stone simple by comparison. Easy to do.

You might consider buying this to understand what you're getting into: https://www.amazon.com/ATSG-AW55-50-...rds=ATSG+AW-55

The valve body rebuild takes a test bench to ensure correct performance and calibration.

To be honest, I've done engines, and transmissions, but I would farm this rebuild out. You can get a quality, durable, rebuild that includes the valve body work from a variety of sources, including your Volvo dealer. But I was considering these guys if my valve body fix hadn't worked.

http://www.level10transmission.com/services.html

[OslosisJones]

Nice reference, looks like a fun read. Might look into it if it comes down to the transmission internals.

I'd be inclined to try the valve body job myself first. I'll have access to a workshop when I'm back in school in the fall; we build and maintain ocean research devices. We have some pressure testing equipment typically used for pitot tube calibration, in addition to an absurd amount of tools that I could borrow. Anything specific I would need as part of a test bench?

Transmission itself sounds like a bear, just getting the damn thing out probably goes beyond the scope of what I'm capable of. For now I'm considering this the worst case scenario.

Still curious if this could be an engine power loss or ECM confusion issue causing the transmission to momentarily drop out of gear (coast in nuetral or downshift). Sources could be:
-Slight misfires: no codes atm, but will be replacing spark plugs this weekend hopefully, along with fuel filter
-Plugged or leaking vacuum lines, PCV clogged
-Some combo of bad throttle, fuel pressure, MAF, oxygen sensors. (VIDA showed codes for MAF, fuel pressure sensor, and fuel trims. Problem might have been fixed and codes were never cleared, idk)

[JRL]

Valvebody is shifting, going completely out of gear is another thing completely.
What is so difficult about checking your fluid level, you're making a federal case out of something very simple!

Car and oil HOT, (after 30+ minutes of driving)
Place car on level ground.
Check hot level while of course the engine is running. (You DID check this while the engine is running, didn't you)?

If you did all the above properly and it still was below minimum.... that is NOT good and will cause it to go out of gear (slip)

Of course continuing to drive while this was not completely fixed did not help, you may have done some serious damage

[AKAMick]

JRL is absolutely correct, I have found his method easy to understand, just check it after a run, hot, yea it's a b*tch to reach, but that's the way it is, more is better than too little, less will trash the trans, more will make it puke it up and make a mess but not toast it.

[OslosisJones]

Like I said, the proceedure should really be included in the transmission posts... It's a bit misleading to say to just check it while it's hot and running.

The engine was hot when I first checked, but I have no idea if the ATF had cycled through completely as I didn't specifically cycle through all the gears to allow all the ports to fill. And then I probably checked it immediately after turning off the engine.

So yes, mistakes were made. These could have easily been avoided if any of the guides indicated there was more to checking the level that just looking at the dipstick. I thought I was playing it safe by draining some excess to avoid overfilling, which seems to be of higher concern than underfilling.

The question is whether it's likely I caused any permanent damage, or whether this has to do with the ATF level at all. You both seem to think it is something else.

I'll keep tabs on my ATF level and note if I experience any more slipping over the weekend. Please let me know if there is anything else I should investigate.

[hoonk]

I probably checked it immediately after turning off the engine.

Engine off usually gives too high a reading. If you are unsure - just drain and fill again - fill with 3.5 quarts (proper fluid only of course) and that will be very close. Double check to be sure - (yes that lower radiator hose is hot on your hand/arm!) Congratulations on your purchase and hopefully a proper fluid level eliminates your problem, if not you may have just found out why the car was for sale