R34 manual gearbox swap to RB20DET (SMALL BOX)

[RB25inside]

Hi all, I have recently brought an engine (RB25DE) / manual gearbox (small box) from Facebook Market place for a good price which I will be putting into my R34 RB25DE sedan.

As you are probably aware the gearbox is an RB20 box which the N/A manuals had.

The problem that I'm having is with the boxes sensors. There are 3 ports on the box 2 of which are missing cables

I'm not sure if the speed sensor will fit my loom / it looks to be missing a cord? ( On purpose?) And its bracket is broken so a replacement is required. Would my 4 speed automatic one fit?

I have attached the photos below including speed sensor

 

Any help would be much appreciated 👍

 

Edited January 6, 2024 by RB25inside
Need to add tags

[RB25inside]

Under some more research would a KA24DE speed sensor work? It seems to have the same connector? I have read on another form about pulses from the speed sensor?

[Duncan]

I'd start by seeing if your auto speed sensor does physically fit. If you go for something from another car it will need to have the same diff ratio to give you the right speed.

Also, both the neutral and reverse sensors seem to have their wires broken off too...whoever you go this from really looked after it. You probably don't need the neutral switch but without the reverse one you won't have working reverse lights

[GTSBoy]

Auto speed sensor won't fit.

You will need that speed sensor for that car/gearbox combo, because the pinion gear on the sensor must match/mesh with the one in the box.

[RB25inside]

Thanks for the replys guys. I am yet to take out my auto gearbox but believe the R34 has two wires plug for the speed sensor? But currently the one in the box has 3 wires.

Does anyone know the exact model speed sensor I need?

I'll count the teeth on the sensor that it came with.

[GTSBoy]

I can't imagine a 3-wire speed sensor. They're just (effectively) an electric motor that produces an AC voltage waveform as you spin them. 2 wires that go to the speedo. You should look at the R34 wiring diagrams to see if the auto speed sensor really is a 3 wire.

[RB25inside]

So the 3 wires is from an r31 and it's called a hall effect unit. That sensor with its 3 wires will not work on my car. I have found that much. I did see that the KA24DE has 2 wires

[GTSBoy]

11 hours ago, RB25inside said:

So the 3 wires is from an r31 and it's called a hall effect unit.

Jap 31 or Aussie 31? I didn't think Nissan Japan did any Hall effect speed sensors.

[RB25inside]

Yeah how interesting right! As I am in Australia maybe it was from a Commodore at some point? If I look up VL gearbox speed sensor it looks awful similar.

While searching this morning I found this https://vegaautosports.com/products/speedo-sensor-and-pinon-to-suit-nissan-silvia-s14-and-skyline-r33-n-a-gearboxes not sure if this would fit into my box seeming its an RB20 box of some sort. The images don't really show if there are any plugs. But yet again it shows Silvia parts in RB20 Boxes. What do you think?

[GTSBoy]

I don't know enough about the CA/SR gearboxes. They are very similar to the small RB boxes, but as with all Nissan stuff, there are small and annoying differences everywhere you look.

I can say that there is no difference at all between an RB20 turbo and R33/4 NA box. Well, alright, again small differences. I'm pretty sure 3rd gear was a different ratio between R32 turbo and R34 NA boxen (I had both in my car). But the speedo drive (cable, for R32) just goes directly into the R33/4 boxes like it was made to, because it was.

 

[RB25inside]

19 minutes ago, GTSBoy said:

I don't know enough about the CA/SR gearboxes. They are very similar to the small RB boxes, but as with all Nissan stuff, there are small and annoying differences everywhere you look.

I can say that there is no difference at all between an RB20 turbo and R33/4 NA box. Well, alright, again small differences. I'm pretty sure 3rd gear was a different ratio between R32 turbo and R34 NA boxen (I had both in my car). But the speedo drive (cable, for R32) just goes directly into the R33/4 boxes like it was made to, because it was.

 

So If that's the case and the R32 speed (Cable) sensor goes into the rb20 box would that mean the R33 sensor should fit into my rb20 box?

[GTSBoy]

Yes, so long as we're talking about the RB20 turbo box and the R33 RB25DE NA box. I cannot promise you that the R32 NA box is the same as these though. It probably is, as again it is effectively the same sort of box as the CA/SR boxes, and almost the same as the 20DET box. They are definitely not all the exact same though. The 20DET box is stronger than the 20DE box, for example, even if it is only a little stronger.

[RB25inside]

Okay so I have done some R&D the RB25DE sensor has 21 teeth and is a lot longer then my model.

 

RB25DE sensor model (purple)codes are:

25010-79T01 – Sender

32743-71T21 – Gear / Cog 

 

As you can see this is much larger then my speed sensor shown above. Further research has found that the S13 / SR20 / KA24DE sensors are the same size as the RB20 (R32) and still offer 21 teeth while supplying two output wires (As seen in red cog)

So I'm 99% sure it will fit into my box but the question is will it out put the correct voltage pattern??????

[GTSBoy]

Most of them are 2 pole. Apparently, some are 4 pole and put out twice as many pulses per rev. I have no idea how common that it. I'd suggest if the gear meshes, you have a better than even chance of it being good.

[RB25inside]

I don't suppose you know how many pole the r34 is?

[Duncan]

Don't worry about the wires so much, you need to make sure the diff is the same ratio as your car or the speedo will be out by the difference.

[RB25inside]

Correct me if I'm wrong but the box is going to be connected to my car's original diff? That shouldn't make a difference as the speed is picked up in the box?

[Duncan]

Well, the speedo sender is trying to work out road speed from the gearbox's output shaft speed...therefore the diff ratio (and tyre height) must be assumed in the speed sender. So, if your car/diff (r34 auto) matches the speed sender you are looking at it will be fine.

[RB25inside]

Okay so correct me if I'm wrong my R34 is RC40 and according to this website it means my car is:

R34 GT – RB25DE – auto – 4.083

 

https://www.eatsleepboost.lt/tech-info/nissan-tech-info/nissan-r200-diff-ratios/

 

This website also lists the S13 diff ratios as the following:

S13 – KA24DE – USDM – manual/auto – R200/R200V – 4.083

S13 – CA18DE – JDM – r180 6 bolt – manual/auto – 4.363

S13 – CA18DET – EDM – manual/auto – R200/R200V – 3.916

S13 – CA18DET – ADM – manual/auto – 4.363

S13 – CA18DET – JDM – manual/auto – 4.363

S13 – SR20DE (ABS) – manual/auto – 4.111

S13 – SR20DET – manual – 4.111

S13 – SR20DET – auto – 3.916

PS13/RPS13 – SR20DE (ABS) – JDM – manual/auto – 4.083

PS13/RPS13 – SR20DET – JDM – manual – 4.083

PS13/RPS13 – SR20DET – JDM – auto – 3.916

 

So if my understanding is right I need a KA24DE USDM or a JDM version. Probably the KA24DE would be the easiest and safest bet to get?

[Duncan]

Yes, I agree with that logic. I don't know enough about the spec to confirm the list is correct