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Reverse Gear Question


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I have a 5 speed out of a 280zx in my 240z. At first the reverse lights worked correctly but now when the sensor (in the transmission) is connected, the reverse lights constantly stay on. 

I have tried multiple brand new sensors to no avail. When I put my pinky finger in the hole (where the sensor goes) it feels like something is there pushing in the button on the sensor and I guess not moving away regardless if I’m in reverse or now.

My question is this…


What inside the transmission pushes up against the this reverse light sensor?  Is it possible for it to get stuck?  I was hesitant to stick a tool in there to try to push (whatever is touching the sensor) back to its resting position. 

Thanks in advance!

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Take a photo of where the switch is mounted on your 5 speed. I have a truck 5 speed in my 240Z that never had a working reverse switch until last year. However, at first I didn't have it in the right location. Fortunately @Zed Head posted a great picture showing the correct location for the switch. 

I didn't realize there was the "top gear" switch, and that was where I was trying to connect the reverse switch.

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Thanks for the reply. I’m 99% sure I have it in the right spot because it worked originally when I installed it but after about a dozen or so times of going into reverse and back to 1st gear, the light came on endlessly so I just decided to unplug it. 

I would love to get it working again so I wanted to find out what specifically inside the transmission is pushing up against that button on the sensor…. and is it possible for it to get stuck?

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Have you tried connecting the electricals with the sensor removed?  It's not clear that the switch itself isn't stuck.

There's not much to it.  The rod has a section cut out with a ramp.  The ramp pushes the switch contact point closed when the rod moves.  If the switch is good the only other reasonable possibility is that the rod is moving inside the fork.  That would not be good.

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@Zed Head  thanks so much for these pictures. It’s great to understand what is pushing the sensor internally. 

I have tested the switch out of the transmission and it works perfectly fine. I push it in with my thumb and the light goes on and I let go and the light goes off. When I put the switch back in the transmission, the light stays on constantly. 

I can take a picture but my understanding is that I have the 280zx 5 speed. The reverse sensor is in the passenger side of the transmission right next to the drain/fill plug (which has a square end on it). 

when you say that the rod may be moving inside the fork… what does this mean?  Would I have any other symptoms if this is occurring?

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It's not common but occasionally the roll pins that hold the fork to the shaft break or fall out.  You can see them in zKars's pictures.  I'm not saying that's what is happening in your case but the transmission is a very mechanical device.  Gears and rods and other parts made of steel and aluminum.  If it worked before and it's not working now, that implies that something moved.

It might be that the switch contacts are so close that a fraction of a millimeter has caused it be on all of the time.  Who knows.  You could get your eye or a camera up by the hole in the transmission and see what's in there.  If it still looks like zKars's pictures then it's probably the switch.

Funny, but one of zKars's roll pins looks like it's working its way out...  @zKars



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Thank you. I’ll see if I can pull out the reverse switch and take a picture in the hole. 

I purchase the transmission as a rebuilt/remanufactured transmission so hopefully it was done right. 

The only other issue I have is that once in a while it can be a little tough to get it into gear when the engine is cold but I just attributed that to being that the engine/transmission isn’t warmed up yet. It always gets better/normal once the engine/transmission is warmed up. 

The diagram that SteveJ showed me looks like there is a “top gear” switch right next to the “reverse” switch but I don’t remember seeing another switch that close to the reverse switch. 

is it possible the square head plug that I’m seeing was put in place of one of those switches?  Or is that the proper location of the fill/drain plug?

Edited by eastcoastz
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IT’s just the ramp machined into shift rod. It would have to be bent pretty badly to keep the switch “on” all the time. I would expect shifting performance to be “different”.  If the roll pins were loose/out, you could not shift.

If shifting into reverse and 5th works fine, then it’s unlikely that its in the transmission. So you can take the switch out and move the tip by hand and the lights work correctly? If so, then I guess the shift rod must be bent. I’m baffled. 

Now all this said, I have a customer with a similar problem…. Hmm…. No his won’t come on. Crazy

And did you know they make special pin punches for roll pins? Just got some last week. And those roll pins above are in no danger of going anywhere…


Edited by zKars
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I kind of doubt it's screwed in too tightly... I didn't torque it... only did it tight enough so that I wouldn't have anything leak out of it.


@Zed Head@zKars - is it possible the square headed plug that I’m seeing (next to where the reverse sensor is installed) was put in place of one of those switches?  Or is that the proper location of the fill/drain plug?

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