2002 Mercury Mountaineer Transmission Rebuild

I have a 2002 Mercury Mountaineer with 150K+ miles on it. Lately the transmission seems “rough” as in it seems to ‘thud’ randomly when I step on the gas while cruising. I think it’s trying to change gears, but I’m not sure. It runs okay, but I feel like I should start thinking about rebuilding the transmission. I have access to a full set of tools and mechanics on hand for advice (on a military base, auto hobby shop), and about a weeks worth of time. Think I can do it?

How long since the fluid was changed? More than 30K?
I would start by dropping the trans pan (if it has one), changing the fluid and filter.
Use only the fluid Ford specifies (Mercon?)

Rebuilding an automatic transmission isn’t a job I’d undertake lightly. It takes years of experience to do it right, and although I do almost everything else, and auto tranny isn’t something I’d touch.

Be sure and do your fluid changes (re: circuitsmith and many others), and check your driveshaft - if it has one. I’m not sure…I think maybe that’s FWD. Grease any spots that need it.

Before ripping the transmission out and tearing it into a thousand pieces I’d scan the vehicle first and see if there are any codes present.

A thud feeling while stepping on the gas can also be caused by an intermittent engine performance problem related to the ignition, fuel system, etc.

Picking up on ok4450’s thought & extending it a bit, even if the transmission is acting funny it doesn’t necessarily mean that the problem is with the transmission. E.g. a failing throttle position sensor or contaminated MAF sensor will make a mess out of the transmission controls.

And going to what chaissos says, if you do find that the transmission needs work the odds of being successful at this are pretty low.

A few years back I started having a problem with my Lincoln and at first thought it was a transmission problem too. No codes, all maintenance up, etc. and this problem bugged me for several weeks.
At times, and usually on acceleration at moderate speeds out of a turn, the car would buck and lunge. It had the earmarks of a transmission problem, codes or not.

Looking it over one weekend I found the problem was caused by a razor type cut/split in a PCV hose. Apparently this split was so fine that the eyeball method could not detect it and at times the hose (which had softened with age) would gape open a little under certain types of acceleration. This had an effect on airflow through the MAF sensor and once the hose was fixed the problem disappeared completely.

Wow, thanks for all the comments. It’s been over 30K miles since the last transmission fluid change, so I’ll have to bring it in to Ford to get that fixed.

Recently, the ABS and the Air Bag light have come on, although I haven’t had it looked at by a Ford dealer, just a mechanic with one of those computers, who couldn’t help me.

Another symptom is that there’s a “hiccup” when I shift between drive and park. In other words, I have to kind of wait a second and release pressure on the handle when going from drive to park.

I assume you have the 5R55WS or 5R55N transmission. This is a pretty complex transmission. It is computer controlled using solenoid valves, a pressure control solenoid, and multiple input sensors.

If you decide to rebuild this, I have a couple of suggestions. Make sure that you have a good overhaul manual with the specifications specific for your year and model for clutch set up clearances; pump clearances; end play tolerances; bolt torques; etc. So far I haven’t seen a Haynes or Chilton transmission manual that outlines the overhaul of these or similar transmissions. The second suggestion is to make sure cleanliness is absolutely maintained. Grit and/or debris in the valve body or solenoids will creat all sorts of grief.

Correct me if my perception is wrong. Aren’t most transport repair operations on a military base “unit” exchanges i.e. a failed transmission or engine is removed and replaced by a remanufactured unit from the manufacture?

Hope this helps.