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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

image.png

 

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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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The square headed plug is the fill plug. Should only be one place to put the rev switch forward of that in the bell housing. 

I’d be tempted to buy a new switch  and try that

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Yeah I've tried multiple new switches... I even got a switch that is reverse polarity... meaning pushing in the button makes the light go off (letting go of the button makes the light go on), but I doubt that would make a difference.

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Might be down to a switch with the “right” plunger length and the point at which switch turns “on” as you depress the switch.

Take one of your functioning switches and start filing off a bit of the tip so it’s shorter. Keep removing a bit at a time until it works?

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So I'm really confused here... this switch which I thought was the reverse switch seems, in fact to be the 5th gear (O.D.) switch.  When I remove this switch and put the tranny in 5th gear, I see the "ramp" show up in the hole.  When I put it in reverse, the rod moves just a little bit but the "ramp" is never visible.

 IMG_1472.jpg

 

... the only other switch that I see is this one (below - at the top of the picture) which I believe in the neutral switch. I didn't physically confirm this to be the neurtral... just assuming it's the neutral switch based on diagrams I've seen.  Please correct me if I'm wrong.

IMG_1473.jpg

 

So where the heck is the reverse light switch?  I don't see any other switches clearly evident or holes where a switch could go.

Edited by eastcoastz
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Now it all comes clear. The reverse switch is just behind the clutch slave cylinder. Right side.

Various trannies have 5th gear and neutral switches as well. All reverse switches are in the same place

04D52A92-B468-47D6-9C1F-55559FADD9F8.jpeg

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If you two locations for switches on the right side, in front of the fill plug and behind the slave, then the front one is the reverse switch.

This picture shows the “usual” location” of reverse switch on a zx 5 speed. A Z 4 speed would be the same except further back in the space between the fill plug and the spot where the switch is in this picture.

The FSM picture shows where the rev and 5th gear (top gear) switches would be

679A08A9-A09B-4169-AD9B-1AC053D41F47.jpeg

425C654B-929D-4343-9442-34C22D03C79D.jpeg

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Thank you.  Yeah, I'm not seeing another location for a switch in front of the 5th gear (O.D.) one.

Is it even possible that the rod was installed backwards to the point that it "turns into" a 5th gear switch instead of a reverse switch?

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Looks like the correct hole.  The switch button would sit right next to the ramp edge.  Just a tiny movement moves the button.

Before you start filing away at the button you could just thread the switch in to the hole partially.  You could use a meter to see when the contacts close then back it off a thread.  Then put the transmission in reverse and see if it works correctly.  If it does then a washer or some filing should get you there.

This is what you should see in the hole when it's in reverse and not.

image.png

image.png

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There are detent balls/plugs/springs in the adapter plate that hold the rod in the proper position.  Things would have to be way off to get the ramp in the wrong place.

image.png

Edited by Zed Head
- e
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