The best way to do it is to hack the software. If you do it by diverting the solenoid signal, you could probably get away with a resistor instead of an extra solenoid. Likely all that is needed is something that draws the same amount of current.

The other issue is that the TCM monitors transmission input shaft speed and compares it to engine speed. From this it calculates torque converter slip. When the clutch is engaged, it expects very little slip, if any. The only way around that is to either trick the software into thinking the clutch should not be locked up, or into ignoring the slippage.

Yes, the trans will run much hotter if the clutch never locks up. This can be particularly important if you are towing. Transmission fluid breaks down exponentially faster as the temperature goes up.

 

Is there a way to hack the software? Does the ability to do so exist? If so, I agree that'd be the ideal direction to take this.

I was thinking a resistor might be sufficient, too. I just need to identify the signal wire, and find out what the TCM wants to see when lock-up is "on." I'm going to look into this. If it can be done, I can monitor the trans fluid temps to see how hot it gets. Maybe it'll come down to more frequent fluid changes, depending on the operating temp with the torque converter slipping all the time.

On the other hand, I'm considering pulling the valve body to inspect its bores for the TCC solenoid and valves. It seems like a fluid pressure issue in those areas, since the shuddering only happens below 2000 RPM. Maybe the bores are worn and causing pressure surge (low, high, low) as the valve body tries to compensate. I know there was an extensive thread that someone posted about rebuilding their valve body that showed worn bores. Maybe the torque converter only exhibits this issue when the TCM is applying slippage intentionally in the lower RPM's. Above 2000 RPM, it seems to go into full lockup and the shuddering disappears. When I enabled the lockup indicator on the dash through VIDA, I believe the modes for open, slip, and lock-up lined up with those RPM's.

Just found a wiring diagram of a TF81's valve body. Light Green (+) and Brown (-) wires for the TCC solenoid. 5.0 to 5.6 ohms. I'll have to determine if the wiring and resistance specs are the same for a TF80.

 

I know little to nothing about transmissions, just replace the fluid on a regular basis. As well, while I own an '06, it had the VB replaced before I bought it in 2020.

As far as software mods go, I'm not sure who's doing them here on Swedespeed but Matthews Volvo Site has a running thread on CEM decoding in their XC90 forum and you might find a better audience on the subject.

Relating to valve bodies, they normally get replaced as an already remanufactured unit. I think there might be a couple solenoid rebore kits to do this if you poke around, it's a relatively common issue with the earlier TF-80s (Pre- 06J prefix on the AW serial number). Kid in Montana replaced his VB on a garage floor bunch of years ago so it's do-able (subframe needs to drop to some degree). You're doing band-aids at this point per your first post and while I cannot directly help with the TC shudder, I can offer this bit of technical info from Sonnax- Sonnax AW 6 Speeds: Valve Body Diagnosis

 

May I ask how many miles you have and how often you changed the fluid?
Does your transmission fall in the 2007 valve body issue serial #?
Have you had this since new? If not, when did you acquire it and what mileage have you done?

 

Happy to provide more context. About 170k miles currently.
Yes, the trans is below the fixed serial number iteration.
I bought it used when it had 95k miles, so about 75k since I've owned it. During that time, I've done 3 fluid changes.

• First at 105k because of shift flare. Mobil 3309
• Again at 130k because of intermittent and light shuddering. Aisin 3309
• Finally at 160k because of increased shuddering. Volvo 3309

To ggleavitt's point about the valve body procedure, I also just realized I failed to mention I replaced the valve body at 160k as a hail mary hoping it was just that. It didn't improve anything. It was a reman from Worldwide Specialty Parts, because they claimed to use Sonnax rebuild parts along with the oversize bores, etc. It still has its 1 yr warranty so I'm going to pull it and see if they can do anything - not sure what. I tend to block it from memory because it was quite a bit of work to get at it, as well as a highly disappointing outcome.

Since then, I've put nearly 10k miles on it driving with the shifter in manual mode to keep the rev's above 2000 RPM. A couple months ago I got fed up and got a couple trans shops to look at it to get an idea of what it would cost. A local shop The Transmission Man (good reviews, no specific experience with the chassis/trans) gave a vague quote of $2500 and up to rebuild. A shop further away Russ Transmissions (touted as all they do is Volvo's) said $6500 to $7500 for a rebuild. So, back to the drawing board at this point with hopes of finding some creative solutions / band-aids.

I glanced at the CEM thread on MVS -- wow, a lot of that is over my head. Still reading thru the 200+ pages to see if any of it pertains to TCM programming. Thanks for pointing out this potential resource.

 

Great information and good fluid maintenance. Regarding World Wide Specialty Parts, the issue with the Sonnax kit is as you mentioned, the overbore and ensuring it works well. IIRC, there are some difficulties with this if not done correctly due to the overbore alignment (or angle). I think this is one reason people have gone with the Volvo reman valve bodies since it isn't a Sonnax kit.

Tricking the torque converter lockup solenoid might work, but the question is if it will drive fine in all gears with it off. The last car I owned without torque converter lockup was a 3-speed auto Mercedes Benz and it was smooth, but lazy in shifts and you can feel the loss in power delivery to the wheels compared to lockup transmissions. IIRC, in the TF-80SC 4th-6th gears are full lock-up which helps in fuel efficiency.

I understand you may be trying to avoid removing the transmission to get the torque converter replaced, but that might be the only right solution. Hacking into the lockup solenoid could give negative results too from not having the lockup to the hacking itself. In the end, it still is hacking and not solving the issue at hand.

Have you thought about engine/transmission removal for the toque converter? Once removed, you will have better access to change gaskets, seals, etc., helping your XC90 last for many more years.

 

This is most definitely a hack at best, but one that might alleviate the shuddering while city driving, ie, mostly low speed low RPM driving. This is when the shuddering is most prevalent. I'd probably keep the lock-up enabled if I'm planning on doing highway driving and resort to manual shifting when RPM's get low (for fuel economy, and for less heat in the fluid). You're right about fuel economy likely suffering with lock-up disabled. On the plus side, with the TC unlocked, it keeps the effect of torque multiplication alive, so it should feel peppier. The person who posted about this in the thread I linked in the 1st post commented about this too. I think if my '87 245 had lock-up, it would feel even slower than it already is. The turbo versions of the models from that era came with lock-up, I believe.

I have considered dropping the engine/trans to replace the trans altogether with a reman unit from this company. I can live with $2200 if I can do the work myself. I just don't know if I can on the floor of my garage. You're right, it would absolutely make other maintenance items easier - leaky valve cover gaskets, etc. How daunting could it be, right? Remove front suspension, axles, undo steering ujoint, a couple wires, and 4 subframe bolts. Done. Famous last words.

My plan is to:

1. Try the hack, monitor fluid temps, confirm drivability
2. Check fluid condition, change if needed
3. Look into trans replacement DIY

 

i actually think that heat is a non-issue. once the car reaches a cruising speed (and very light throttle) there is little slippage and therefore little heat generated. even under med or heavy throttle the slippage only takes place up to a certain rpm- prob only about 2500 or so. up and down speeds (like on freeway, heavy traffic) would be the worst-case scenario.
The problem with the lock-up convertors nowadays is that they try to lock up (or stay locked) under too much load. the clutching mechanism just cant take it and it slips (shudders). Frankly, i think in the real world the mpg is actually hurt by the excessive lock-up as it then requires more right foot to get the acceleration you want. Getting it reprogrammed to just not lock-up until 40 mph or so and/or under lighter load would be the ideal.

 

The TF-80SC doesn't have torque converter lock-up until it reaches a certain temp, 20C. You can see in this video about the lock-up. Heat does play a role. Just like any friction surface (i.e. manual trans clutches, brake pads), the transmission friction surfaces are affected by heat (torque converter, friction discs, brake bands).

The load isn't the issue since lock-up happens at 3rd and higher gears. The issue is the torque converter also has a slip mode, or partial lockup to make the torque converter engagement smoother. AFAIK, this happens in partial throttle. You can read more about the Slipping Lockup (partial lockup), as well as the transmission adaptations in this VIDA document.

The shudder happens at the time of the partial lockup, mostly around the 2-3 upshift. Traveling at higher speeds may not reveal a shudder during the brief partial lockup between higher gears. Old fluid, incorrect fluid, improper hydraulic pressure, wear and tear, valve body, and electrical issues, could cause the shudder. Hard downshifting, noises, slipping while in gear, these may or may not be torque converter related. Here's an example of new Volvo replacement valve bodies needing pressure adjustment since the Volvo VB was not calibrated properly.

I've had old cars without torque converter lockup. There is a loss of fuel economy.

 

The load isn't the issue since lock-up happens at 3rd and higher gears.

Can you explain this in more detail? It seems counterintuitive since the load on the torque converter is higher in higher gears. If you've ever had a standard transmission with a worn clutch you'll recall that clutch slip appears first in the highest gears.

 

Did you manage to solve the problem?

 

No, I've been living with the shudder and doing early fluid flushes with Aisin 3309 (last flush was 9k miles old fluid a few weeks ago). It still does it, I've just been popping it into manual to keep the revs above 2000 RPM when I'm at a speed/load that induces shuddering. The car now has over 190,000 miles, and the shuddering hasn't become worse (or better). The recent flush was done prior to a camping trip up mountain roads for peace of mind.

I still want to try the TCC switch or dummy solenoid, maybe once the XC isn't part of the primary commuter line-up. I did reach out to a couple software folks that deal with Volvos and got crickets.

Ultimate solution would be a manual swap.

 

Have you ever considered trying Lubegard red or lubegard shutter fix? It seems to help a lot of people. Google it.

I dont have the same problems. I have shift flare during upshifts when warm. I put in Lubegard red yesterday and will see what happens. I dont think it will help against my specific problem but slipping TQ it seems to help a lot.

 

Been there, done that with Shudder Fix. It helped initially for a few hundred miles - the shuddering nearly went away. It came back not too long after, and additional amounts added after doing a fluid flush had no effect. It just seems like a diagnostic tool - if the shudder goes away, it tells you there's a mechanical issue with the trans and the effects are temporary.