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R33 Speedo not reading correctly

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I just purchased a R33 GTST sedan that was previously manual swapped.    I’ve figured out it has a Rb20 transmission and my Speedo is reading about double what it should.   At about 45mph the cluster is reading 160 kmh.    Does anyone have any info on how I would figure out what Speedo gear I need to change to ?    
Thank you ! 

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Could try one from a sr20 gearbox or a signal converter maybe easier to use. There was a topic on here not long ago about speed drives and compatibility. 

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So I pulled the Speedo gear and found the pinion gear is worn, guessing from improper mesh with the worm gear. So it seems the worm gear is skimming the top of the pinion instead of being meshed and causing it to over spin.  Looking for new pinion gears today 


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Yep change it out and treat that RB20 gearbox gently and start saving your little lunch money for a RB25DET gearbox.

The RB20 gearbox is know to be quite frail when you load it up behind the RB25DET motor.

That way, after you change it out, you don't have to cringe when you give it a boot full worrying about breaking the RB20 box.

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🤞🏻 Crossed the new gear meshes Into the trans correctly.   Found 4 listed at dealers in the country left. 

Have heard that about the 20 trans which is sad but makes sense.   From the condition of the trans and pedal assembly it all looks to have been in the car for a long time now.  Definitely wanting to change it out eventually for the proper trans ! 

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Well unfortunately the new gear didn’t change anything.    Anyone know anything about resistors?   The gauge is reading about double what it should.  So my thought is if I can cut that signal in half it should get me relatively close. 

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Could you post up a pic of your instrument cluster ?

Ive seen something similar with a R33 Nismo cluster out of an auto went into a manual car.

Tested it by putting it back into a auto and it worked fine.

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So it still had the auto cluster when I purchased it, was suggested to get a manual cluster so I found one and swapped it in.  Made no change unfortunately.     Seems what ever is translating the signal is on crack now 😂.  
 Have talked to people who said they had a 25 with 20 trans with the red gear on the Speedo drive and it worked as it should .    Starting to wonder if the drive unit is bad or have seen where people have gone and changed the lay out of things on the back of the actual Speedo but unfortunately can only find things for a auto to manual with the correct 25 trans 

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Posted (edited)
34 minutes ago, R33sedandenver said:

I wonder if it’s the auto ecu can’t figure out the manual Speedo inputs

Nah, the signal from the gearbox sender is sent to the cluster the signal is converted at the cluster to the signal for the ecu and tcu.

Rb25det does not work vtc in patrol gr

By kike_kike, December 3, 2020 in Projects, Overhauls and Build-ups

Edited by Rusty Nuts
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AC Sine wave speed sender (the transmission speed sender)

This type of sender, widely used in the 90s and early 2000's is simple and reliable but not infallible. It generates its own power and sends a weak AC sinewave signal to the speedometer by teeth spinning past a coil with 2 wires. The sender requires one wire to be grounded and the other is the signal. The wires can be reversed and the same result will work just fine due to the fact that the sender waveform is a simple sinewave. The downside is that due to the sender generating its own power by the speed of the reluctor wheel (teeth) it can often lead to an erratic signal at low speeds.

Suggest you check the output with a very good multimeter or oscilloscope. Its all in the workshop manual.

You cannot buy a workshop manual here. 


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