Inaccurate Speedo on Patrol GU

[Zhing1]

Hi. I have a 01 GU with TB45 Autotrans. I noticed that my speedo reads 60kph but is actually running only 50Kph via a GPS speedo. It gets worse if I go faster. While running 120 Kph the GPS only shows that I am only going 105kph. I got the rig with 32s and I understand the stock tires are 31s. Does this have anything to do with my speedo problem? Can something be done to calibrate the speedometer?

[NP99]

http://www.jaycar.com.au/productResults.asp?keywords=speedo+corrector&keyform=KEYWORD&SUBMIT.x=0&SUBMIT.y=0


There's a few options out there...

[threedogs]

stock tyres are 265's x 16
my speedo reads correct with 285's [33's]

[Zhing1]

I guess your rig has everything in in place. I plan to regear my axle ratio a step higher. I think my axle ratio is 4.11. I'm thinking of going 4.3. Will this help? Anyone else willing to render advice?

[Stropp]

there is a table i have somewhere that gives you the teeth gears for the drive gear on the gearbox that you can use to change the speed on the speedo to corrct it, i will see if i can find it.

[jff45]

I guess your rig has everything in in place. I plan to regear my axle ratio a step higher. I think my axle ratio is 4.11. I'm thinking of going 4.3. Will this help? Anyone else willing to render advice?

The final drive ratio is on your vehicle ID plate.
I think you might find a 2001 4.5 auto will be 3.9.

[Stropp]

Thanks to ET for the table, this the pinion gears table for speedo correction at the gearbox.

Diff ratio Tyre size Speedo gear (pinion) Part Number 32703 - 31G 17
Change last 2 digits (in boldface) for gear you need using the table below.

Be aware that is manuf spec so speedo will probably overread slightly IE at 100KPH GPS the speedo will possibly be 103 maybe 104 KPH as req'd by ADR's

Your diff ratio will be on the vehicle build plate

3.9:1 Ratio
TyrePinion
31 16
33 15
35 14
37 13

4.11:1 Ratio
31 17
33 16
35 15
37 14

4.375:1 Ratio
31 18
33 17
35 16
37 15

4.625:1 Ratio
31 19
33 18
35 17
37 16

[happygu]

Zhing,

Has your truck been modified at any stage - Bigger Tyres or Changed Diff Ratios for bigger tyres?


All my four Patrols ( Diesel ) have been 6 Klms under at 100KPH ( IE : Speedo shows 100 - actual speed 94ish ), and I haven't measured super accurately for 60, but it is only out by a couple of Klms.

Putting on 33 inch tyres makes the speedo virtually spot on, right throughout the range.

I would expect that the Petrol would be the same, so to be that far out, something has been changed.

Mic

[threedogs]

with 305s I had to drive a tad under to stay on the limit
265s had to drive above what was shown
285s spot on

[Zhing1]

Thanks guys. I learned a lot from this thread. I'll see what's applicable to solve my problem. I'm thinking of upgrading tires (31s to 33s) and doing a regear up by 1 step (3.9 to 4.11) anyways . Hope this works.

[BigRAWesty]

Your readings seem a long way out.
To me either your running smaller than 31" tyres, or you have higher ratio gears already installed.

If your unsure of diff ratio up for a bit of work pull the front or hear diff center and count the teeth on both the crown gear and pinion gear.
Divide the crown by the pinion and that's the ratio.

[Wizard52]

Talking to a long time Nissan worker who said latest Patrols speedo are spot on where the older ones (2 or 3 years old I think) have about 3 or 4% safety margin when standard. It has save me a couple of times as I did not know.