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Rb25 Gearbox To R31 Speedo

FordyR31
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FordyR31 Mentor

FordyR31

Posted
Posted

Well guys I have an HR31 GTSX and there is an RB25DET manual gearbox going in it. The 25 box has an electrical Speed sender and the R31 a cable sender. I am hearing a few things work like a Nissan navara sender but have been told they can be inaccurate. Been told my most accurate option is an R32 GTR sender. Any1 have any more info on this topic, how its done and what else is needed?

Thanx

Liam

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BHDave Grand Master

BHDave

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Posted

It just looks like a navara drive with an r33 cog on it. Nothing special. It will still be inaccurate if you don't have the same diff gears as an r33 (4.11s).

Some one has mentioned ripping the back off the r33 drive and fitting the back off the stock 32gtst drive. If it works it saves having to source any new parts (assuming you have the 33 drive). AFAIK the r31 drive is mechanically the same as 32.

B0oStEr Mentor

B0oStEr

Posted
Posted

I've posted numerous times how to do this to help people out.

It takes me less time to actually do the job than it does to type up how it's done.

Mainly because I type with one finger so I copied the following from one of my old posts.

The cheapest and best way to put a cable speedodrive in the RB25DET box is to use Navara speedodrive part no 32702-02G17.

It is very similar to the R32GTR speedodrive and only costs about $20.

Both these units require modification to work properly.

It requires some basic tools and skills.

There maybe a speedodrive available that bolts straight in but not at this price.

The Navara speedodrive comes with a 17 tooth gear that

you'll need to remove and replace it with the red 20 tooth gear from the rb25det box electronic speedodrive.

For an R32 with the stock 4.36 diff and tyres the ideal number of teeth is 21.

I estimate the 20 tooth gear will read about 105kph at 100kph but would be closer if you're running larger tyres.

You need to punch out the rollpin so you can pull the shaft out of the Navara assembly.

Use a hacksaw to make a helical cut along both sides of the 17 tooth gear being careful not to scratch the shaft. It should pry off.

Remove the circlip and pull the red gear from the electronic speedodrive.

The red gear located on a flat spot on the end of the r33 shaft

Use a round file to make the hole in the gear round.

Be careful not to make it sloppy on the shaft.

Support the red gear and drive the Navara shaft in until the splines press all the way through leaving about 2mm of shaft sticking out the end of the gear.

It's a tight fit so it should stay put without any glue.

Care needs to be taken to make sure the gear will mesh correctly with the wormgear inside the box.

You will notice the shaft is slightly off centre in the assembly.

Nissan rotate the assembly to compensate for the difference in diameter of the various gears they use.

Depending on the gear diameter they cut the retaining slot in a particular location to secure the assembly at a certain rotational position to achieve the correct gear clearance.

When putting the 20 tooth r33 gear on the Navara assembly you'll need to cut a new retaining slot exactly 180 degrees opposite the original slot.

I cut the slot with a hacksaw and cleaned it up with the edge of a small file. You need to be accurate here.

Put the shaft back in the assembly and drive the rollpin back in.

Check that it has about half a mm of end float between the body and the gear.

Now it should be ready to go in the box.

As stated in a previous post this assembly is accurate for speed with a 4.1 diff ratio.

What ratio are hr31 gtsx diffs?

FordyR31 Mentor

FordyR31

Posted
  • Author
Posted

I dont know what ratio the diffs r in stock HR31's. My speedo is already out, as my speedo reads 110km/h its actually doing approx 95km/h so maybe an owner in Japan has changed the diff already. If it is now reading more than my actual speed this modification sounds like it will make it more accurate. At 60km/h on the speedo I am doing closer to 50km/h etc. Thanks for the info, sounds like the way to go and would make my current speedo a little more accurate than it already is. Good info. Exactly what I wanted to hear lol.. $20..

Thanx

Liam

B0oStEr Mentor

B0oStEr

Posted
Posted
In my r32 with 4.3's my speedo reads about 10% high with the navara drive/r33 cog, checked with gps. So 110km/h on speedo = 100km/h actual speed

The difference between the 20 and 21 tooth gear can be expressed as a percentage (4.76%) which will be the same percentage the speedo will be out (+4.76kph@100kph) relative to what it was before swapping the cogs.

If it was out before the swap then of course you have to add that to the difference.

Fordy if your speedo reads 110 when you are actually doing 95kph then it is out the same way but it depends how many teeth the speedodrive has in your current gearbox.

Have you checked?

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

I had a GTR speed sender, around $140 second hand.

Just swap the gear over and put back into the 25 box i believe.

I was going to go the Navara route, but it was too much dicking around back in 2004 when i needed the car done.

mr_rbman Grand Master

mr_rbman

Posted
Posted
It just looks like a navara drive with an r33 cog on it. Nothing special. It will still be inaccurate if you don't have the same diff gears as an r33 (4.11s).

Some one has mentioned ripping the back off the r33 drive and fitting the back off the stock 32gtst drive. If it works it saves having to source any new parts (assuming you have the 33 drive). AFAIK the r31 drive is mechanically the same as 32.

did you use the 21/17 tooth navara drive? I heard on the grape vine that you can't get one of them any more.

Have my 25 box now and i'm trying to get all these parts together!

BHDave Grand Master

BHDave

Posted
Posted

I actually used a s/h gtr drive as i could get one straight away. Swapped cogs with the 25 drive.

The navara drive is better because it has a longer shaft better suited to the long 21 tooth gear. It's only a matter of swapping cogs, not a big issue (unless you didn't get a stock speed sender with the 25 box)

Booster, your calc is backwards. 20-21 tooth would mean a reduction in output shaft speed (everything else being equal) and result in a reduction in the displayed speed, not an increase. You are assuming that the drive gear in the box's are the same also.

mr_rbman Grand Master

mr_rbman

Posted
Posted
I actually used a s/h gtr drive as i could get one straight away. Swapped cogs with the 25 drive.

The navara drive is better because it has a longer shaft better suited to the long 21 tooth gear. It's only a matter of swapping cogs, not a big issue (unless you didn't get a stock speed sender with the 25 box)

Booster, your calc is backwards. 20-21 tooth would mean a reduction in output shaft speed (everything else being equal) and result in a reduction in the displayed speed, not an increase. You are assuming that the drive gear in the box's are the same also.

ye i got the 25 gearbox speed sensor, i think u can't get the 21 tooth drive any more, will the 17 tooth one be sufficient?

neo32 Experienced

neo32

Posted
Posted

lol i have a 32 with neo and r33 g box ordered direct from nissan the nivara cog 32702-02G17 and then realised that the 17 on the end was the teeth number

the 17 tooth drive origanaly cost $18 now is like 45 and you can buy it from holden as well as a vl turbo speedo drive but they will sting you anywhere between 80 and 140 as i found out originaly buying one of these cause the mx7 gear box in vl turbo is very simalar to r33 turbo so i brought one of these from holden then realising that was in a nissan box rang my mate at nissan and then promptly took bad the one to holden long story talked to my mate at nissan we ordered a 32702-02G21 ex jaan and presto off the shelf 100 % bang on and only $56 so you guys that are paying $300 for this you have been shafted i hope this helps but aparently the 21 tooth has been finished or nissan aus wont get them anymore

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