Reverse switch for 71B 5-speed

[Digger48]

I replaced the stock 4-speed in my 1973 620 with a rebuilt 5W71B 5-speed, reportedly from a '77 620.  It didn't have a reverse or neutral switch when I first got it so I used the reverse switch from my '73 4-speed.  Now my back-up lights are on whenever it is not in reverse and off when it is in reverse.   The switches I have from the 4-speed are "on" (continuity between the two wires) when the plunger is not compressed and "off" when the plunger is compressed.  Did Datsun reverse that switch configuration for the 5 speed? 

 

I am assuming the proper tapped hole for the reverse switch is the one in the main (or front) casing), as indicated in the service manual, and that the only other tapped switch hole (in the rear housing near the shifter) is the neutral switch.  Is it possible the fork rod for reverse-5th was improperly installed?  If that were the case, why would all other gears besides reverse allow the plunger in the switch to be extended?

 

Any advice appreciated.  (And, yes, I know I don't really need a back-up light ?  )

[datzenmike]

 

1/2

3/4

5/R....... front>>>

 

This is an FS5W71B and the notch you see on the lower 5th / reverse rod, just below the roll pin above it on the 3/4 shift rod, is where the reverse light switch sits. You can see the round light color wear pattern. Shifting into reverse the rod moves to the right and the switch plunger rides up that ramp, closing the switch. Shifting out of reverse the plunger extends as it rides down the ramp and the switch opens.

 

The old F4W63 you had has a different arrangement and is the wrong switch for this.

[DanielC]

Check all the switches from your old four speed transmission.   One of them may work.  I would check the switches by screwing them into the transmission, and using an ohmmeter to find a switch that only has continuity when the transmission is in reverse.

Datsun used switches on the transmission to electrically control some exhaust emission systems, and some of the switched are normally on, and other switches are normally off.

Edited January 15, 2019 by DanielC

[datzenmike]

You want OFF when the plunger is extended and ON when compressed.

[Digger48]

That's what I thought.  Thanks, guys.  All the switches I have are ON when extended.  I'll look for a new switch.

[Gery]

After switching an automatic to a 5 speed, my reverse lights are always on.  From this thread, I’d assume that I need to replace the switch.    If so, for what specifically am I searching?  Or could the leads just be reversed.?  (‘78 620)

can I scavenge the switch from the automatic to use with the 280z 5 speed?

Edited February 11, 2019 by Gery

[datzenmike]

Automatics use a totally different switch on the shift linkage, that won't work.  With a light bulb it doesn't matter which way the electricity flows for it to work. It's like a sandwich tasting the same if it's upside down.

 

The reverse switch rides on the rev/5th shift rod. The rod has a groove cut in it. When shifted into reverse the plunger on the switch drops down into the groove and the contacts connect and the lights come on. Other switches work the opposite and this won't do. Someone may have swapped the reverse light with another switch. Look on the passenger side rear for other switches and try them. BTW if there are other switches on the transmission it's from a truck not a 280z, not that it really matters as they are internally the same.

[Gery]

No other switches present.  I pulled the switch to check function.

Plunger extended = no continuity

Plunger depressed = continuity 

while under, I tried directly connecting the truck’s reverse wired together (removing the switch from the circuit).  No reverse lights.

Because the truck was an automatic, there are two wires that were attached to the old internal neutral switch.  These two wires are now connected together.  If not connected together, the truck won’t turn over.

i ended up just disconnecting the switch so there would be CONTANTLY ON” no reverse lights.

So what seems to be occurring is: when the switch is in place ... the plunger remains depressed regardless of gear selection, or even neutral.  If so, that is problem #1

Problem #2 then would be why wouldn’t the reverse lights just stay on if the switch is bypassed?

is there a lost ground connection with the switch out?  Or?

i wish this was as simple as having the wrong type of switch installed.

ideas?

 

 

 

 

[datzenmike]

7 hours ago, Gery said:

 

Plunger extended = no continuity

Plunger depressed = continuity 

while under, I tried directly connecting the truck’s reverse wired together (removing the switch from the circuit).  No reverse lights.

 

 

 

 

On the FS5W71B when the switch plunger is extended the contacts are open and the lights are off. If wiring them together and no lights... fix this first.

 

 

Find the middle shift rod.... see the roll pin? Look directly below the roll pin that notch is the reverse / 5th shift rod and when shifting into reverse the rod moves forward. The switch plunger rides up that ramp (on the left) and the contacts close turning the lights on.

[Gery]

Very helpful.  Turns out a fuse had blown which explains the lack of reverse lights when the switch was bypassed.

Your photo and explanation help me better understand the problem.  

Am I right in thinking that the pin is dropping into the notch (and thus, not extending to break continuity)?

if so, what might cause that situation?

The plunger moves relatively freely and has consistent spring tension pushing it outward.  There is minor scraping when moving, but nothing that seems restrictive to movement.

 

Perhaps my next step thould be to remove the switch, insert a thin rod into the switch hole, and the feel what happens as the truck is shifter in and out of reverse? (Ignition off, of course)

That might add some info, but won’t give me reverse lights....

 

Better ideas?

[datzenmike]

The rod moves to the right when shifting into reverse so the switch is in the hole or extended to begin with. It is forced to slide up the ramp compressing the plunger

[Gery]

I sent off for a new switch.

[Gery]

The problem persisted with the new switch....

I then stepped things up and used a meter to check all the wiring.  

Turns out that the relay was frozen in on position.  Replaced the relay and problem solved.

Thanks everyone.  🙂