Was driving my MDX then out of sudden it shifted back to first gear and my speedometer stopped working. I decided to take out the Countershaft pickup (vehicle speed sensor) and noticed there's a big chunk missing from the sensor. It seems like the countershaft gear got too close and made contact and scrape off a piece of the sensor. Anyone had a experience like this? Is the countershaft bearing gave out?

 

pics?

 

 

holy crap.. yeah definitely seems to be a piece of it in the transmission...

 

So, I saw this post when my Acura MDX also failed in the exact described way, and I wanted to give you some closure lol.

So, the reason that happens is because the MDKA/BDKA transmission has 3 gear posts, and on the third one, nearest the VSS output and input sensors, there is a bearing that holds that load as it spins, obviously. Well, that bearing is known to go bad, and it causes a wobble when the engine revs a bit over what it can handle. It then loses the ability to spin freely, and because of that, it disables the vehicle speed sensor by eating it in the exact way you've shown. When that happens, you can't measure speed if you can't sense it in the transmission, so you lose that, and the vehicle cannot spin that part unless it's freely spinning, so because that allows you to move up to 3,4,5 gear, you have 1,2, and R left.

Sadly, this is not an easy fix. For me, I had to remove and disassemble the entire transmission to get to the bearing, and then pull that bearing and find a company that made a replacement and then reinstall it, and reassemble the entire transmission. Not a DIY job unless you have a lot of experience or you happen to be friends with a very patient transmission builder. For anyone that may see this in the future, there are ways to rebuild it yourself, but it is a VERY involved job. You don't actually need too many special tools, but the barrier for entry here would be "you have (with or without help) bare minimum rebuilt an engine or preferably a transmission from scratch."

If you are foolish as I am, and you want to do this, know that there are a LOT of points of failure to check on this particular transmission, and the total cost for me, doing the work myself was $1190 for a full rebuild kit and the bearing and tools, so it isn't a cheap fix either. There is a kit for the valve body and separator plates that improves flow and shift response, so if you are rolling this over in your head, it's another $100 and let's be honest, whether this goes well or not, you're probably never cracking that transmission open ever again. I don't want to tell people not to do it, but I attempted it because I am very comfortable rebuilding engines, so for me, it's a different species, same kingdom.