Shop claiming transmission "clunk" is the differential

[1955moose]

If your not married, your SUV is telling you to knock on the door at that spot. Sounds like a Hallmark syrupy movie, with your vehicle acting like Herbie the love bug, trying to get you laid!

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[Matticus]

Hmm....i get an occasional clunk slowing down going uphill to coast to a local stop sign

Nothing bonejarring

Pretty much always in the same place, maybe 0.5 - 0.7 mi from my local grocery store, speed ~25mph

Should I be worried? Or just a quirk of how it reacts when it's not up to operating temperature yet?

2012, 140k mi

In my case, it will do it when the trans temp is cold or up to temp. It tends to do it more when up to temp. I don't think it's ever bonejarring, though. Per moose's comment and many nights laying in bed thinking about it previously, I've wondered if it's a worn driveline component and/or transfer case component. Something where the torque/strain on the drive train when slowing down hits a perfect "sweet spot" that the downshift to 3rd causes something to knock. But man...sure is an odd coincidence if that is the case.

Can anyone confirm my question about manually putting the vehicle in "3" vs "D"? Should it still downshift when I manually put it in 3?

 

[Sgt Darkness]

There are a lot of rip off joints out there. A lot of transmission rebuilds are half ass done. Sure they order the rebuild kits but only end up using one part outta the whole kit because your trans only needed that one part....is that what you paid for, no you paid for the whole kit but the shop only uses one part and keeps the rest of the kit. Do that 50 times and you got enough kits to fix 30 more transmissions plus you still end up paying for a kit that they will use later on. I know some of you know exactly what’s happening......but lots of people get juked everyday. There are also lots of honest shops out there that do you right, every time. Get smart on how to rebuild transmissions and engines and do the work yourself, you will feel a whole lot better and your wallet will b a lot heavier.

 

[Sgt Darkness]

In my case, it will do it when the trans temp is cold or up to temp. It tends to do it more when up to temp. I don't think it's ever bonejarring, though. Per moose's comment and many nights laying in bed thinking about it previously, I've wondered if it's a worn driveline component and/or transfer case component. Something where the torque/strain on the drive train when slowing down hits a perfect "sweet spot" that the downshift to 3rd causes something to knock. But man...sure is an odd coincidence if that is the case.

Can anyone confirm my question about manually putting the vehicle in "3" vs "D"? Should it still downshift when I manually put it in 3?

This is the first Ford I have owned since the 70s. Now, on my Silverado it will not downshift if you start in 3rd and continue slowing down. On the other hand the 16 CX-5 will downshift as you slow down. I just gave those two examples because I haven’t used the manual mode on the Expy yet and no one had dialed in on your question yet. Hope someone who actually knows for sure will give you an answer soon.......

 

[1955moose]

The whole purpose of putting the transmission in a set gear is for either assistance of brakes going downhill, or for acceleration up a grade, especially if your towing a heavy weight. Most transmission valve bodies are designed not to shift up or down out of that gear. It closes off flow to the other passages and valves that allow up or downshift. When you move shifter back to drive, pressure is transferred to that drive position valve, allowing full automatic shifts.

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[Matticus]

The whole purpose of putting the transmission in a set gear is for either assistance of brakes going downhill, or for acceleration up a grade, especially if your towing a heavy weight. Most transmission valve bodies are designed not to shift up or down out of that gear. It closes off flow to the other passages and valves that allow up or downshift. When you move shifter back to drive, pressure is transferred to that drive position valve, allowing full automatic shifts.

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Yes, I'm aware of the purpose. But my experience with my previously owned 03 expedition, current minivan, and every other vehicle with an automatic transmission I have driven has been that, when manually selecting a gear, that simply made the transmission not shift any higher than that gear. It would still downshift just like it would if it were in drive. This is a first for me

 

[TobyU]

Yes, I'm aware of the purpose. But my experience with my previously owned 03 expedition, current minivan, and every other vehicle with an automatic transmission I have driven has been that, when manually selecting a gear, that simply made the transmission not shift any higher than that gear. It would still downshift just like it would if it were in drive. This is a first for me

That's how GM's work. Many/most Ford's start in 2nd if you put them in 2. They don't start on 1st and go no bother than 2 like a GM does. Some of the newer trans will go the same for 3rd but not many older ones. All my Town Cars and Expedition, Navigator and Excursion 4speed autos do this...start in 2 and stay in 2 if you choose that position.

 

[Matticus]

Going to bump this thread again with a question:
Automatic transmissions eventually lock the torque converter up so that it is directly driving the drive train as opposed to the fluid acting as the coupling, for maximum efficiency, right? What are the general conditions that need to be met to lock/unlock it?

The reason I ask is because I'm wondering if this "clunk/thud" I'm hearing has something to do with a sudden release in stress in the drive train. So, for example, let's say I have some worn driveshaft components. As I am slowing down, if the torque converter is in this lock up mode and then suddenly releases while the engine is being driven by the wheels, that sudden release on the drive train could conceivably mean those parts under stress would sort of "lunge"/clunk into place as they find their normal equilibrium. Since this "clunk" I am hearing is always at the exact same speed when I am slowing down and the trans shifts into 3rd, I'm theorizing that this is also the point at which the computer tells the torque converter to unlock (provided it was locked up in the first place).

There is a lot of "ifs" in this theory....does it seem sound?

 

[Trainmaster]

You're absolutely right. The clunk could be anywhere in the drivetrain. The most common place is the U Joints, but it can be in the spline joint, rear trans mount, the differential or internally in the transmission. Could be a worn bearing or shaft. Stuff wears and has play. There's play somewhere, and if it's internal you're not going to find it without disassembling the gearbox.

Don't rule out that transmission mount. I've seen them permit the tail of the tranny to clunk around.