Recently I put my Civic in reverse (1995, 200K, original automatic) and it made a really bad grinding noise so I put it right back in park. Tried again, same thing. Waited 10 secs, tried again and got reverse. Took it into a transmission shop and they couldn’t reproduce it. So we are driving it nervously. Here’s the kicker: the transmission fluid dipstick has a bite taken out of it just above the normal level marker. Looks like it got chewed by a gear. What happened?
Here is what I surmise happened. On Honda automatic transmission, reverse is gained by moving a slider dog clutch to disengage 4th counter gear and engage reverse counter gear. If everything is timed right, the 4th/reverse hydraulic clutch is then engaged and you can back up. If 4th/reverse clutch should engage early; the clutch plates be dragging enough; or the dog clutch servo is lazy, the dog clutch cannot get engaged before power is spinning the gears over the counter shaft causing the dog clutch to ratchet i.e. grind.
Hope this helps.
The dipstick should never be able to get whacked by any of the moving parts in a transmission. I’m guessing that bite taken out of it was taken out of it because something’s already floating around in there that shouldn’t be. Unfortunately that would be pretty hard to prove without removing the housing and peering inside, which gets very expensive. In fact, at that point, it would probably almost be cheaper to get a reman’d or even a junkyard tranny and throw it in instead of fooling with the one you have.
Before you go that route, though, I’d bring the dipstick to a mechanic who knows transmissions and show it to them. It could be that they’ll recognize the type of damage and be able to solve the problem from that.
I think this is a good one for transman. Hopefully he will stop by shortly and give advice.
Thanks guys for the input. I’m wondering whether a gear wheel lost a tooth which is now loose inside. The Civic is behaving itself for now but who knows when it might happen again.