Tach fix for the RB25DET

[NISMO_RB25]

In my quest to make my gauge cluster read correctly (I am using the KA cluster with my RB25DET), I have found something that will hopefully help the rest of you guys.

Nissan was apparently was nice enough to use the same pattern for their Tach and speedometer in other cars. What this means is that I was able to pull the tach from a 1989 Nissan Stanza V6. At least I think it was a Stanza, but it could have been something else(the junkyard was not kind to it).

Anyway it works, it was about 200 RPM to high, but it had plenty of adjustment to fix that problem.

Quick how to.

1. pull out both Tachs. (it is a wopping 3 screws, after you finally get the cluster out of the dash)

2. pull the needle off of both tachs.

3. Now you can remove the 2 screws that hold the face on.

4. Remove the face, and the plastic backing. (This is the part where you need to remember which tach was from the Stanza and which one was from the 240)

5. Now put the plastic backing, gauge face, needle from the 240 cluster on to the stanza tach.

6. tighten up the 2 front screws

7. put it back into your 240 cluster and you are done.

8. The Tach has an adjustment on it, if yours happens to be a little off. you will need to turn it to the left to increase the RPM readout, right decreases it. I turned mine a little to the right and it works perfectly now. (I used my Apexi RSM to verify it was working correctly)

I haven't tried the speedo yet, but if I can get that to work correctly, I will let you know.

[NISMO_RB25]

One orther thing. This leads me to believe that the best speedo solution for people with the RB25, will probably be the 300ZX speedo. Only problem is I have only seen one 90+ 300ZX in a junkyard so far and it did not have a cluster.

If anyone else finds one and gets it to work, please let me know.

[rbsileighty]

Thanks for the info! You have an S14 right? I may have to try this with the S13.

[NISMO_RB25]

Thanks for the info! You have an S14 right? I may have to try this with the S13.

My car is an S13.

[Wulfgang]

Great info!

Maybe this is a stupid question, but why would a Stanza tach work and not a 240SX tach? Is this something specific to an RB25?

My S14 tach reads my RB20 output fine, but the adjustment is off. Do you know if the S14 tach has this adjustment screw?

[rbsileighty]

Most cars have a different resistance for reading a 6cyl vs 4cyl tach signal, and ours should be the same. I am not sure why your tach reads correctly in the S14. Have you compared it to another rpm measurement?

[rcodea]

from what i ahve been told, you would need to use the KA speed sensor in the trany and put it in the RB trany. that is suposed to work, but i have yet to try it

Ryan

[rbsileighty]

Doesn't seem to work with the KA trans speed sensor and the 25 motor.

What other trans's have you found that are similar to the 25's Ivory? I know you said that the KA and 20 trans are similar, and the KA speed sensor works in the 20 trans. This might be able to help Nismo and other 25 owners with their speedo problem.

Might want to start a new thread if we continue on this speedo topic... unless the mods and Nismo are cool with it.

[NISMO_RB25]

The N/A 300ZX transmission is supposed to be very similar to the RB25. That is why I think the speedo from a 300ZX N/A will probably work for us RB25 owners. The reason the the Stanza tach works is because the car I got it out of is a 6 cylinder.

[Wulfgang]

Most cars have a different resistance for reading a 6cyl vs 4cyl tach signal, and ours should be the same. I am not sure why your tach reads correctly in the S14. Have you compared it to another rpm measurement?

No, my S14 tach doesn't read correctly, but it does read well. I get no jumping or anything, just a rock-steady signal. So that makes me think I can just adjust it to get a correct reading.

[EDIT] Ok, I understand now. I thought the Stanza was a 4-banger. My bad.

[PROJECTRB240SX]

YOU SURE IT WASN'T A MAXIMA? ANYWAY I WONDER IF THIS WILL WORK SIMILARLY TO THE RB20? BUT THE S13 TACH FACE DOESN'T GO HIGH ENOUGH.

[Wulfgang]

Another question then. Why couldn't you have put the RB25 tach into the 240SX cluster?

[PROJECTRB240SX]

I HAVE THE RB20 TACH IN MY S13 CLUSTER.

[NISMO_RB25]

Another question then. Why couldn't you have put the RB25 tach into the 240SX cluster?

I bought a motor set, so I did not get the R33 cluster. I had thought about all this before I bought the motor set, but since I didn't really want a speedo that is in km/h I didn't bother getting it. http://www.mckinneymotorsports.com did my wiring, and they wire for the stock cluster anyway. They also sell modulators to make your speedo and tach read correctly.

I am trying to go the cheap route on my cluster so I can use that money for all my other mods. I already have an Apexi RSM in the car, so I don't have to get the cluster working, I just want to.

Alot of the people posting seem to have the RB20, which you can just swap speedo sending units and then your set.

Us RB25 guys aren't so lucky, but we have more stock power

[PROJECTRB240SX]

HAS ANYONE TRIED THE 300ZX SENSOR WITH ITS PLUG? FOR THE SPEEDO THAT IS.

[NISMO_RB25]

that is exactly what I want to know. I need to go back to the junkyard to get a part I left off of that Stanza(or whatever) speedo to see if it will work until I can find a 300zx to try.

[IvoryJ30t]

Doesn't seem to work with the KA trans speed sensor and the 25 motor.

What other trans's have you found that are similar to the 25's Ivory? I know you said that the KA and 20 trans are similar, and the KA speed sensor works in the 20 trans. This might be able to help Nismo and other 25 owners with their speedo problem.

Might want to start a new thread if we continue on this speedo topic... unless the mods and Nismo are cool with it.

Z32 speed sensors. someone post their rear tire size so i can figure which one is better.

the TT uses a sensor for a 3.692 rear and a 245/45-16 rear tire.

the N/A uses a different gear ratio.

calculations for a TT Z32 speed sensor-

with a 240 that has a rear tire close in overall diameter to 195/60-15 and a standard [4.08] rear, the speedo will read 9% high.

in a 240 that has a rear tire close in diameter to 195/60-15 and a J30 LSD rear end, the speedo will read 5% to high.

you can either increase the size of your rear tire, or swaqp to the skyline cluster, and use a VSS recalibrator, so the speedo will read accurately and up to 180 MPH.

[PROJECTRB240SX]

USE A NA 300ZX. WHICH IS A SIMILAR REAR END TO THE S13 AND S14 AND NEAR THE SAME SIZE TIRES.

[IvoryJ30t]

trans-

KA=SR=RB20 sensors interchangeable.

VG=RB25=RB26 sensors interchangeable.

[IvoryJ30t]

USE A NA 300ZX. WHICH IS A SIMILAR REAR END TO THE S13 AND S14 AND NEAR THE SAME SIZE TIRES.

i wasnt sure of the rear end in the N/A Z32. if the gear is close and the diameter of the rear tires close, then use that one.

[PROJECTRB240SX]

YEAH I KNOW THE TIRE DIAMETER IS DIFFERENT BUT NOT BY MUCH. YOU CAN ALSO TAKE THE CAR TO A SPEEDO SHOP TO GET IT TO READ RIGHT.

[IvoryJ30t]

how much different is the plug on the JDM speed sensor?

[PROJECTRB240SX]

I DON'T KNOW AS I DON'T HAVE A RB25..... REMEMBER I'M THE 20 GUY. I WAS JUST GIVING YOU GUYS AN IDEA TO TOY WITH.

[PROJECTRB240SX]

THE RB25 IS A CABLE DRIVEN SPEEDO WHEN THE S13 AND S14 KA'S ARE ELCTRONIC.

[IvoryJ30t]

oh. good reason. i remember asking a while back, and i thought the 20 was mechanical and the 25,26 were electronic.

oh well, makes no difference, its just a sensor swap.

[Joe]

THE RB25 IS A CABLE DRIVEN SPEEDO WHEN THE S13 AND S14 KA'S ARE ELCTRONIC.

the 20 is cable.the 25's are electronic.

[IvoryJ30t]

thank you, thats what i thought.

[NISMO_RB25]

The RB25 is not cable driven?? Or at least mind isn't. Everyone made really good points, thank you. All of this information that I have seen around, is what has lead me to think that the N/A 300ZX speedo is probably the way to go, but unfortunately I never see them at the junk yards

Even if it is off by a small %, the speedo's all have some adjustment that would cure that problem.

And so the hunt continues.

[IvoryJ30t]

one thing i would be leery of when adjusting the speedo with the PCB potentiometers, is that the speedo is reading correctly, but the odometer is racking up miles wrong.

[rbsileighty]

The RB25 is not cable driven?? Or at least mind isn't. Everyone made really good points, thank you. All of this information that I have seen around, is what has lead me to think that the N/A 300ZX speedo is probably the way to go, but unfortunately I never see them at the junk yards

Even if it is off by a small %, the speedo's all have some adjustment that would cure that problem.

And so the hunt continues.

Might want to call/write http://www.woodfins.com and see if they can hook you up with a sensor.