Jump to content
HybridZ
zbigtim

'95 Maxima Gauge Retrofit

Recommended Posts

I've been looking for an inexpensive way to install modern, electronic Speedometer and Tachometer. Right now I have the stock gauges with the speedhut EL Glow Overlays, which looks awesome (in my opinion) but the speedo reads 10 mph low and the tach does not work sometimes under 1200 rpm, and is off by about 200 rpm according to megasquirt. So, browsing through the local pick 'n' pull I decided to give the '95 Maxima Gauges a try. $20 got me the entire gauge cluster.

 

cluster.jpg

 

I had to trim the corners of the gauges to fit in the original "cups". A dremel tool made quick work of this. I'm not quite done with the assembly yet, but well on my way.

 

speedotrimmedtofit.jpg

tachtrimmedtofit.jpg

tachwbezel.jpg

bothinbezel.jpg

 

After researching with the Maxima Factory Service Manual, I believe that the tachometer will work with no problem on the megasquirt Tach Out.

 

But, the speedometer scaling is my next biggest hurdle. I have connected a speed sensor from a 5-speed 240SX (which fits the stock 4 and 5 speed transmissions) and tested the speedometer with a power supply and a drill. It works fine.

 

speedtest.jpg

 

Back to the scaling. Does anybody know if the frequency to speed ratio can be changed with the "adj" points on the speedometer circuit board? Please look at the next pic in the red circle. Or will I need some kind of signal condition circuit in between the speed sensor and speedometer (frequency to frequency conversion)?

 

speedocircuit.jpg

 

-Tim

  • Like 1

Share this post


Link to post
Share on other sites

Does the manual say anything about what those adjustment numbers do, can you just experiment jumping different ones? I'm not familiar with those, is it like a small percentage multiplier for different size tires etc? Never heard of being able to adjust a stock speedo like that. If only you could figure out how the circuit actually converts the frequency into mechanical movement of the needle and set it off by a little bit with a resistor or something simple like that.

 

I was trying to convert a speedo once and couldn't for the life of me find signal multipliers that weren't in whole numbers, and your gauge apparently isn't off by a factor of a whole number. I have seen speedo adapters that are supposed to be universal though and can be programmed to make any gauge work just like you would calibrate an autometer, but the price of those probably defeats the purpose of using the maxima gauges in the first place... If you're lucky you can find a cog for the speed sensor that gets it close enough but that's a long shot.

 

Have you given up on the stock gauges? It sounds like your new speedo is in the same boat as your old one. If the tach doesn't read real low, it's probably not high enough input voltage. It couldn't just be off by a certain amount though, there has to be a ratio that it is off, which should tell you it's hooked up to the wrong signal source. Just thinking out loud.

Share this post


Link to post
Share on other sites
Have you given up on the stock gauges? It sounds like your new speedo is in the same boat as your old one.

 

I have no idea what the maxima gauge is going to read. I have not had it in the car yet. I can only assume it will be off because of the mismatch of parts.

 

The universal converter is about $80 from Dakota Digital, which yes, defeats the purpose of using the junkyard gauges.

 

I am going to experiment with the "adj" solder pads. I assume it is a binary coded multiplier. Im going to set my fluke meter on the sensor and read the freq. and compare to the speed reading. Then change the adj setting and repeat, till I figure out the math.

 

Thank you for the replys!

 

-Tim

Share this post


Link to post
Share on other sites

Thanks Alonso. I think I found what you were talking about.

 

(Thanks to Knate's post off of zilvia.net forum, here is the following value of each jumper on the binary divider)

 

Quote:

Originally Posted by knate

Here's how it works. It uses the adjustment points as a binary divider. The more switches on, the lower the speedometer will go. 9 is the most significan bit, and each switch below that will have half the effect on your needle. Here's a list of how they affect the needle. All these numbers are based on my eye reading the needle and some calculations, so they are not 100% perfect.

 

ADJ 9: -49.4%

ADJ 8: -24.7%

ADJ 7: -12.4%

ADJ 6: -6.2%

ADJ 5: -3.1%

ADJ 4: -1.5%

ADJ 3: -0.8%

ADJ 2: -0.4%

ADJ 1: -0.2%

ADJ 0: -0.1%

 

 

I have confirmed some of this. The maxima speedo had 4,5,&7 bits "on". I ran the speedo again with the drill, reading 49 mph. When I removed the solder on bit #7 the speed indication increased to 56mph, which is approx a 12.5% increase. According to the post from JBrant on 240SXFORUMS this adjustment only works on the speed indication and not the odometer. I will try some time trials hopefully tomorrow to confirm this. Hopefully this is not the case.

 

http://www.240sxforums.com/forums/do-yourself-section/130489-240sx-speedometer-error-s14-s13-speed-sensor-reads-double.html

 

-Tim

Share this post


Link to post
Share on other sites

Yeah that doesn't make any sense. Why would they have the two circuits independent of one another such that the odometer can only read correctly in the factory position? I would think that there's one circuit that counts the frequency and sends it both to the odometer to count the miles and then to the needle to average it out. The needle is basically the odometer with a clock added on that it divides by, so they would only conflict with each other if it was the clock you're altering with those adjustments to fool it into thinking it's moving faster.

Share this post


Link to post
Share on other sites

Well, I did the time trial tonight and the results were not what I wanted. I chucked the speed sensor in the drill press so I would have a consistent speed, as opposed to the cordless. With bits 4 and 5 on (7 is still removed), I ran the drill, speed showing 116.5 MPH, for one minute. At this speed for one minute, the odometer should have registered 1.94 miles, but it only registered 1.7, which is a 12.4% error. So I believe that confirms what JBrant said, that the adjustments only affect the speedometer and not the odometer.

 

At this point, if I still want to use the Maxima speedometer, I will need the dakota converter box or build my own. Now that I have my car back from the shop (state safety inspection), I think I will install the sensor and see how far off the speedometer really is.

Edited by zbigtim

Share this post


Link to post
Share on other sites

That's because the speedo is not supposed to be calibrated to the car, but to the gauge face. You use the proper speedo cog in the transmission matched to the rear end ratio, in order to make the speedometer correct.

 

solder the jumper back, put it in the gauge cup, and it's done. Just use the right speedo cog and you're finished.

Share this post


Link to post
Share on other sites

Well, I'm not sure what I'm going to need yet. I have not actually installed this setup in the car yet. I just got my car back from state inspection, and I have the 4-speed out, installing a freshly rebuilt 5-speed. I plan on doing some temporary wiring for the speedo to see what cog I will need. To do the conversion right, I'm going to remove the dash to install the wiring from the megasqirt for the tach. I also need to route the speedo sensor wiring from the tranny through the firewall, and up to the dash harness. This will all be much easier with the dash out. All that being said, it will probably be a few weeks before I get to that point. I will certainly keep posting my progress.

 

Thanks for all your input guys...

 

-Tim

Share this post


Link to post
Share on other sites

Getoffmyinternet...the 95 maxima uses the same type of speedo cogs as the F4W71B and FS5W71B and C manual transmissions...they use the same R180/R200 rear ends...the rear end ratio for a '95 maxima can be determined and the appropriate speedo cog obtained.

 

It's just like when you swap rear end ratios, and keep the cog matched to the rear end.

 

zBigTim, what color speedo cog is on the sensor? how many teeth are on it? What rear end ratio are you running?

Share this post


Link to post
Share on other sites

Sorry, been out for a while! I just installed the rebuilt 5-Speed today. Still need to finish up all the loose ends. But, the 240SX sensor installed just fine, and it has a red, 20-tooth cog just like the mechanical one that came out of the 4-speed that I was using. On the surface this seems like good news, but thats only if the maxima has the same final ratio and tire height as my Z. My Z has the stock rear end for '76 as far as I know. And, correct me if I'm wrong, I think it is a R200 with a 3.545 ratio.

Share this post


Link to post
Share on other sites

You will need to find a VSS sensor that has the correct color/toothcount cog on it if you want your speedometer to be correct. There's really not any other good way to do it unless you have a programmable speedometer.

 

I THINK the 3.545 rear end uses a black speedo cog; but somewhere in these forums is a good list of what color/tooth cogs are for what rear ends. The red/20 tooth cog is for a 4.11 rear end.

Share this post


Link to post
Share on other sites

Thats interesting Xnke, I'm not sure I've ever seen a black one. I have a red and yellow one, and the electronic one I pulled from the 240sx was red also. I'm sorry, I haven't posted any results. Truth is, the car is now off the jacks w/ 5-speed installed but I havn't wired the speedo up yet. I hope to do that this week.

 

Did have some fun today at the local Z-Car show put on by the Gateway Z Club.

 

Thanks,

-Tim

Share this post


Link to post
Share on other sites

Ok, my mistake; the Black speedo cog is for the 3.545 rear, blue for 3.700, white for 3.900, and red for 4.110. I'm still looking for the correct cog for my 3.36 rear end; I have a black one in my transmission at the moment.

Share this post


Link to post
Share on other sites

I have no news yet. But I am close. Recently I have pulled my injector rail, sold it, and am buildig a new one with 440cc injectors. Pulled the tranny because of a massive oil leak in the bell housing. I just received my new wheels (Rota RB-R, 16X8). So, hopefully in the next week or so, my car will be back together, able to test the speedo. I will absolutly post my findings.

Share this post


Link to post
Share on other sites

Correct Cogs:

teeth Color Ratio

16 yellow 3.364

17 black 3.545

18 Blue 3.70

19 White 3.90

20 Red 4.11

21 Purple 4.38

 

 

Sounds like you need the speedo cog to set the odometer and the dip switches to scale the speedo. On the old speedo cogs you could switch the cog itself out from the body. Is that possible on the speed sensors?

 

I like the design with the dip switches. This will enable you to make a new face if you wanted a 200mph speedo without major work. I might end up doing this mod to get an electronic speedo.

 

Hope that helps.

Edited by rejracer

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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 by rejracer

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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 by rejracer

Share this post


Link to post
Share on other sites
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?

 

VSSSide-1.jpg

VSSTop.jpg

 

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.

 

VFCircuit.jpg

differentiatorcircuit.jpg

 

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 by zbigtim

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×