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Trans makes a loud "bang" noise when slowing down to stop

I have a '06 Mercury Mountaineer, right over 100,000 miles. For the past few months the car has started to make a sound and even produce an “clunk” that I can feel when I am slowing down to come to a stop. It only happens when I slow down to around 3-4mph or slower. The tranmission has only around 10,000 miles on it. What could be causing this? Please help.

When was the last time the transmission fluid level was checked and when was the transmission last serviced?

Is your check engine light on?

One possibility is just worn or broken engine/transmission mounts though I would hope those were replaced if necessary when the transmission was replaced. The problem is that they might have been deemed fine when it was installed but one subsequently broke. You’d probably notice other things too though if you had a mount that bad (shaking on acceleration, clunks at other times too, etc.).

So it’s more likely that your transmission line pressures are hanging high for some reason. As missileman noted the first order of business would be to check the fluid. Other than that though I would make a trip back to whomever installed the transmission. Note that what the transmission does is related to a lot of other things that aren’t in the transmission - such as the throttle position sensor, speed sensor(s), MAF sensor, etc. If anything is causing the idle to stick a little high, that will leave line pressure high. Etc. So anyway - someone who knows needs to evaluate it which is why I would take it back to the installer. Who did install it? And was yours rebuilt or was a rebuilt unit purchased?

10k miles since overhaul? Do u have warranty?

Missileman…Just looked up how to check the trans fluid on YouTube… damn, looks like I will be trying to check it after work today.
Check engine light is not on, everything else runs fine until you slow down to a speed I would assume that the car is down shifting back into 1st gear. As for being serviced, The trans is new. Our warranty covered a new trans to be put into the Mountaineer. I do believe the new trans is still under warranty from the shop that put it in. I would have to check with my wife, it was her vechicle at the time and she handled the warranty while I was away at an Army school. Thank you all for the help. Doc Corbett.

Could a small crack in the right side exhaust manifold cause this problem. I know I have to fix that but am waiting on a friend to help go to the pick and pull to assist me.

Not in my opinion

A crack in the exhaust manifold could produce a ticking sound when the engine is cold. And when everything is warmed up, the metal would expand, the crack would close up a bit, and things would quiet down somewhat

It could also result in the upstream oxygen sensor reading the “excess” oxygen, thus generating a P0171 lean code, and a check engine light

db4690, i have the ticking and checked the manifold, found the crack and will replace it next day off with the help of a friend. I was just wondering if the small crack could in any way cause this down shifting… I did not think so but was hopeful. I am replacing the manifold on wednes or thurs of next week. I work weekends. I just hope the weather is nice. Does anyone see something wrong with going to a pick and pull place to get a used manifold?

Just an FYI, you can check the upcoming weather for your hometown at the following website. It’s the official “national weather service”.

A lurching or banging while slowing down can also be caused by a problem with the Idle Air Control valve.