'95 Maxima Gauge Retrofit

[zbigtim]

Well, as mentioned a couple of post ago, I was pulling the tranny to fix a leak. While the tranny was on the garage floor, I decided to pull the speedo sensor and discovered the cog is missing! Now I have a plastic cog rolling around in my tranny, but I'm not about to pull it apart because I don't think it will hurt anything. But this means I'll need to go back to the pick and pull to get another sensor; maybe a few different ones.

 

I have now realized that the cog is offset from the centerline of the sensor depending on the size (diameter or number of teeth) of the cog. When I installed the sensor, I inserted it in the tail housing, and then turned it so that the mounting holes would line up (sorry I have no pics of this). I should have known better, because it got pretty tough to get that last 10 degrees of turn. Long story, short, I'll need to find a different way to secure the sensor to the housing to keep the proper offset.

 

My car is now off the jacks and running! Yeah! No leaks, new clutch, re-surfaced flywheel, 440cc injectors, new wheels and tires. Not bad for a tinkering around winter project.

 

-Tim

[rejracer]

Tim,

The offset of the cog bodies is different between the 70-80 bodies than the 81-83 bodies. The reason for this is the early transmissions the locking tab (flat machined section on the cog body) faces up. On the later transmissions it faces down. It sounds like you have a cog body that is mismatched to the transmission. You can change gear and use the same cog body, or swap it out. I read somewhere of someone machining a secondary flat spot on one of their cogs to make it a "universal"

 

Hope that helps.

 

Edit: The gauge electronics are most likely set up to calibrate between MPH and KPH. This would explain the difference as the gauge face would change, as would the calibration on the Odometer. The other reason for this is the same electronics can be used for different face plates 0-100 versus 0-150. It might be an engineering carryover from when cars were only allowed 85mph speedo's. Anyhow, it makes sense to me.

 

Edit to the Edit:

Nigel describes the cog differences in his trans swap guide: http://www.motortopia.com/cars/1973-datsun-240z-11118/car-pictures/240sx-transmission-swap-14041

 

edit to the edit to the edit:

Also stumbled upon this link, which articulates the same differences in the cogs.

http://www.geocities.com/inlinestroker/ratio.html

Edited May 19, 2011 by rejracer

[zbigtim]

rejracer,

 

Thats awesome information. I never knew there was a difference between the early and the late 5-speeds. Based on the pictures in those links, I have an early 5-speed. My problem is that the offset on the 240sx sensor is not the same offset as the early speedo sensor when you match up the mounting holes. I went back to the pick-n-pull and found another busted sensor, so I just pulled the cog off. I also pulled some speed sensors from a Maxima and an Altima, but diameter of the sensor body is much larger. Now I need to measure the offsets and maybe grind a flat spot on the 240sx sensor to match. I hope this makes since, at least is does in my head right now.

[rejracer]

The FS5w71B and FS5W71C I thought had the same offset between the tail housing and output shaft. I am assuming the 240sx you pulled the sensor from is using a FS5W71C, which should just be a drop in affair, at most grinding a flat spot on it.

 

I have setting in my storage shed a FS5W71C out of a 1987 300zx NA and speed sensor, a FS5W71B with a variety of speedo cogs. I can check to see if the 300zx sensor fits in the 71B transmission. My understanding is that the speedo cogs are interchangeable, assuming you change the cog, it should fit. I was planning on following Nigels writeup when I install the 71C into my 72.

 

the hole for the shaft (which the gear is connected to) is not concentric, in other words, as you rotate it, it gets closer or further away from the gear. I think you just need to clock it correctly? I think that's what you were saying above?

Edited May 23, 2011 by rejracer

[zbigtim]

the hole for the shaft (which the gear is connected to) is not concentric, in other words, as you rotate it, it gets closer or further away from the gear. I think you just need to clock it correctly? I think that's what you were saying above?

 

Yes, that is exactly what I was saying. Another thing is that the angle of the teeth are different. After a closer look at the gear I just picked up from the junk yard, it seems that the Z has a sharper angle than the SX gear. So I guess now I need to just install the Z gear on the SX VSS(Vehicle Speed Sensor). Looking at the shafts, the SX has a "D" shape, and the Z is round. If the diameters are the same, obviously the gear will fit, but how do I secure it from spinning on the shaft? Do I cross drill it and insert a pin?

 

 

Also, I've been working on a circuit to scale the speed correctly. I'm not so sure I will be able to find the proper gear to calibrate the speedo correctly. So, remembering the Megasquirt Stimulator circuit for the tachometer, I thought maybe it could be used to drive the speedometer. I breadboarded the circuit from the webpage: http://www.megamanual.com/v21stim.htm , modified the circuit to "AC Couple" the output to the speedometer. This worked great! I can drive the speedometer from 0 MPH to above the 140 MPH.

 

 

Please know that I am not claiming to have engineered this circuit. I owe credit to the Megasquirt guys and Forrest Mims for providing the information above.

 

 

My next hurdle is to convert the VR signal from the VSS to a voltage. I plan on using a LM2907 Frequency - Voltage converter to do this. I have experience with this chip. I'm sure this will be no problem. With the speed to voltage relationship between the two chips, I will be able to calibrate the speedometer to what ever gear, rearend, or wheel/tire combination I have.

Edited May 23, 2011 by zbigtim

[rejracer]

You could use epoxy to put the gear on, just rough up the gear hole and shaft surfaces, assuming you can get it on concentric.

 

If your circuit works, I would not fiddle with the gears, that's a fairly slick setup. FYI.. GM ECU's take the VSS signal, and have programed into them the gear ratio and tire size to calculate the VSS output which goes to the Speedo, Cruise control, and body control modules. You are achieving the same thing.

 

I'll get pics of the VSS from the 87 300zx. The VSS has a gear for 3.70's, and I will test fit it for my spare 280zx 5spd.

[rejracer]

I got the chance to pull the 300zx VSS.

 

 

The lineup from left to right.

1. 240z w/manual 3.364

2. 240z w/auto 3.54

3. Early 5spd 3.54

4. I am assuming 280zx 2+2 or GL model. 3.70

5. 87 300zx NA 3.70

 

I disassembled the 300zx VSS and I was able to reassemble it with the 240z gear, based on that, I assume any of the gears will work with it. The VSS will also screw onto any of the the Cog bodies. If one were to have the right adapter, it would be possible to run this sensor behind the dash. Regardless, this sensor is nice, as it can be used with any L series transmission.

 

I think it's exactly what you need, it's certainly the part I am going to use when I do my gauges. One question: does the Maxima speedo have blinker indicators on the speedo face? I did not see them in the pics.

 

Thanks for the writeup, hope this sensor solves the problem you are facing.

 

PS... I need a red and a white cog(more interested in the white), you up for a trade? I have 1 black and 1 blue to trade. No big deal, I can source one from the jy here if you don't.

Edited May 24, 2011 by rejracer

[zbigtim]

That would be great if we could work out a trade! That 300ZX sensor is exactly what I need. That would solve all the problems with getting a SX VSS to fit. Unfortunately, I do not have a white sensor. I have a red and yellow. I would be willing to pay cash (paypal). My local pick-n-pull does not have any 300ZXs, mostly 90's Maximas, Altimas, and a few 240SX.

 

As far as the blinkers are concerned, I plan on installing green LEDs behind the "0" and "8" on the tach, and blue and red LEDs for the High Beam and Brake indicators somewhere in the speedo. I wasn't too worried about this until, I figured out how to properly scale the speedo.

 

Good work as always rejracer.

Edited May 25, 2011 by zbigtim

[zbigtim]

Been talking with Rejracer about the mounting of the gauges in the old "cups", so I thought I would share some pictures and some of my findings. I would also love to hear some input and/or ideas of a few things.

 

First off, there was some concern that the electronics of the speedometer will not fit inside the old cup. If you compare the cups side by side, the original speedometer cup is shallower than the tachometer. On the Maxima gauges the speedometer guts require a deeper housing, so I swapped the cups, mounting the Maxima Tach in the original speedometer cup and vise versa. The mounting tabs and holes are exactly the same between the cups, so I will still be able to mount the gauges in there original position (Speedometer on the left, and Tach on the right). I did have to cut a slot in the top of the speedometer cup to allow the circuit board to protrude past the housing (see pics). I don't think this will interfere with the dash, and plan on using some duct tape to keep dust and ambient light out of the housing.

 

The issue I'm working with now is how to secure the instruments in the cups with the proper depth to keep the gauge faces flush with the bezels. I want to keep the faces flush with the bezel because the faces are backlit, while the originals had a gap between the bezel and face to allow the instrument light "around" the face.

 

I plan on using an additional circuit in between the VSS and Speedometer to do some scaling because I don't want to have to try to find a VSS cog with the right amount of teeth. Also this will allow some adjustment for example if I decide to change tire sizes, or rear end ratios. But, I think it would absolutely be possible to wire the VSS directly to the speedometer and find the correct cog.

 

PICTURES:

 

Tachomter. Mock up mounting. As you can see from the front picture, I need to move the face forward towards the edge of the cup (where the bezel meets).

 

 

 

Speedometer. As you can see on the top of the cup, where I had to cut a slot for the circuit board.

 

 

Speedometer. Also, need some mounting ideas here. I'm thinking of cutting a piece of plexi-glass and securing it inside the cup somehow.

 

 

 

As mentioned above, I could use some ideas on securing the gauges to the cups.

 

 

 

-Tim

Edited June 3, 2011 by zbigtim

[rejracer]

As mentioned in the PM, Nylon standoffs would do the trick. If you are concerned about the strength of the standoffs, maybe try making a rear plate out of Plexiglass that centers the rear of the gauge to the housing. If you wanted to be really fancy, Secure the electrical connections with brass standoffs, then on the brass standoffs mount the plexiglass centering ring, then behind the plexiglass plate use Nylon standoffs connected to the brass standoffs, or use brass standoffs connected to the plexiglass plate using different fasteners (not connected to the other brass standoffs.

In Ascii art it would look like the following:

 

 

1 2 3

|----------

| |

|--|--|

| | |

|--|--|

| | |

|--|--|

| |

|----------

 

1 is the rear housing

2 is the plexiglass plate

3 is the back side of the gauge.

 

Would this solve the problem at hand?

 

I think the trick becomes finding standoffs with the right threads for compatibility with the gauges

 

Edit: The ascii art looks well in the editor window, but not using the web browser. copy and paste into a an editor that uses a monospace font.

Edited June 9, 2011 by rejracer

[zbigtim]

Yes, I've been thinking about using a plexiglass plate to mount the gauge to, using the original screws. Then mount the plate to the back of the cup with spacer blocks. The blocks could either be epoxied to the cup or screwed. The plexigalss would give me the ability to mount and wire the gauge back lights in the proper locations to illuminate the clear plastic face backing.

[DMCNick]

So how did this turn out? I want to use the same speedometer behind another gauge face but I need a way to calibrate the sensor. Did you ever get the other circuit made? If so I'd LOVE to see the circuit.

 

And why is the second circuit (LM2907) needed? Cannot the VSS be read as a dc signal as well as a pulse. I recall that Ford tests the VSS with a DC meter. But I could be wrong. More recent reading indicates it is AC.

 

Check out this link... http://v8nissans.com/forums/content.php?113-S14-speedometer-correction-with-z32-tranny-the-free-way It implies that a variable resistor across the indicated resister pads (resistor removed) could be used to tune the speedo to any drivetrain. Once the resistance is determined a trim resistor or fixed resistor could be soldered in-place.

 

Inquiring minds want know ...

Nick

Edited September 14, 2011 by DMCNick

[zbigtim]

Well, I'm digging this thread back from the dead. I decided I was going to try and finish this up. I have finished the mounting of the speedo in the old gauge cup, wired the old harness to the speedo (plus a new wire from the VSS), and installed the speedo in the dash. I installed the black cog and 300ZX VSS that I bought from rejracer. On the road test, judging from the seat of my pants, the speed indication is about double what it should be. Although it was really cool to watch the speed jump 45 mph from gear to gear and eventually pegging the speedo at about 150mph, I need to adjust the speed signal. If I have time tomorrow, I will go for another drive with the garmin to see what the error really is. I'm not sure what the largest cog is for the speed sensor is, but I doubt that I can double the size of the black one.

 

 

Side view showing the mounting plate made out of a 4" blank round cover for electrical boxes. The stand-offs are make of plastic wire nuts, cut to the proper heights. I then glued the new mounting plate to the old gauge cup with 5-minute epoxy.

 

 

 

 

This is the new mounting plate glued in place.

 

 

 

 

Day time view.

 

 

 

 

Night time view.

 

 

I am determined to get this project finished. I promise I won't let this drag out for another 2-years!

 

-Tim

[Pharaohabq]

Looking nice...

 

Now, I'm curious about this same type of setup, though I'll be installing the 08 350Z Speedo in my car. It gets it s timing off a different location. I was just going to print up the mounting cup for the speedo on my RepRap.

 

But reason I was writing was that if you're approximately double the pulses from the 300zx VSS, then it sounds like your VSS isn't connected right, or that it's not made the way you expected. A couple ways to address it, one is to measure the outputs on your maxima VSS, and see that the pulses per revolution is. If it's the same then it's a wiring deal, if not then perhaps you can make a frequency divider circuit to cut the pulses in half.

[zbigtim]

Thanks Pharaohabq. That would be nice to have access to a rep rap. That would be so much better than trying to cob together a combination of old, new and extraneous parts. I am working on a new timing circuit to "re-scale" the VSS signal from the sensor; should be completed by the end of the week. I do believe the sensor is wired correctly, the wiring is very simple (+12, Ground, and VSS Signal). The VSS signal is referenced to ground and is an ac sine. The difference I guess is the RPMs required to move the mechanical speedometer, and the frequency range required by the electronic ones.

[zbigtim]

 

It works!

 

I will explain tonight, but I have to take my daughter to baseball practice right now.

 

-Tim

[Six_Shooter]

I wasn't so sure about this donor, until I saw this picture:

 

 

Night time view.

 

I haven't looked yet, but I'm hoping the Maxima came with black faced gauges, then I'll be looking into this even more.

Edited March 25, 2012 by Six_Shooter

[rejracer]

Tim and I traded speedo cogs for a cluster, clusters were half the cost of what they were out here, and our yards had quite a few manual transmission cars to pull COG's from. I got the black faced gauges. Tim and I did very similar things on the mounting, but I opted to use the backing plate from the maxima cluster, I cut it out with a dremel tool and screwed it to the 240z tachometer cup.

 

I may end up pulling a 300zx cluster to see if I can do this without a divider circuit.

[zbigtim]

After a lot of discussion, mainly through this thread, I have come to the conclusion that the only way to get the maxima speedometer to work properly is by constructing an add-on frequency converter. In theory, this is very similar to the SGI-5 model made by dakota digital.

 

-The speedometer cannot be adjusted internally. The adjustment solder pads will adjust the pointer but not the odometer. I believe this is so different faces can be used on the same electronics. (K/H vs. M/H, or different max speed).

 

-The 300zx VSS worked very nice mechanically, because is will mount on the existing mechanical speed sensor. I knew there was not a snow balls chance in hell that the speed signal would match the speedometer, but I was hoping it would be close enough that I could change to one of the six different sensors available and make it work that way. It turns out that the speed signal was off by by a factor of .435. So when I was driving at 50mph according to my gps, the speedometer was displaying 115mph! This is way too much to overcome by changing sensors.

 

How the circuit works: The VSS from the 300zx (or any Nissan that I have seen so far) outputs an A.C. sine wave with the frequency proportional to the speed of the vehicle. The LM2907 is specifically designed for this type of sensor. The LM2907 outputs a voltage (DC) proportional to the frequency being produced by the VSS. I have coupled this output to the AD654 via the 10K pot. The pot. works as a voltage divider, so that I can change the full scale voltage going to the AD654. The AD654 does just the opposite of the LM2907, it take the voltage in and converts this to a DC square wave who's frequency is proportional to the voltage on its input. Since the Nissan speedometer will not sense the DC square wave (the input must be A.C.), I used the capacitor/resistor network to AC couple the output to the speedometer. This scheme does not produce a true sine wave but it really does not matter. What matters is that the voltage crosses zero.

 

During my speed trials in the car using my gps unit and fluke multimeter, I determined that the Maxima speedometer deflects full scale (140 MPH) at 309Hz. I also found that the 300ZX VSS would output 709Hz at 140MPH (Mathmatical projection of course). So using a sine wave generator I inputed a frequency of 709Hz and adjusted the 10K pot until I measured 309Hz out. I also checked the linearity by adjusting the input in 100Hz steps and measuring the output. It seems to be right on. Of course once I install the circuit in the Z, I will fine tune the calibration to the gps.

[zbigtim]

 

I think I may try to photo etch a circuit board.

Edited March 27, 2012 by zbigtim