GU Speedo's

Submitted: Thursday, Jun 01, 2006 at 13:10
ThreadID: 34501 Views:2994 Replies:7 FollowUps:3
This Thread has been Archived
G'day All

I am looking to get a engineering certificate to make the 33in tyres on my patrol totally kosher with the regs and insurance companies. Before you all say not this again, I have read a lot of the archived posts and have two specific questions:

Firstly does anyone know exactly what the allowable speedo error specified in the ADR design rules is?

Secondly I have read about changing the speedo cog(s) at the gear box end, how difficult is this, is just undo a few screws/bolts, take the old one out put the new one in, or is there a lot more to it?

Thanks in Advance

Back Expand Un-Read 0 Moderator

Reply By: Leroy - Thursday, Jun 01, 2006 at 13:18

Thursday, Jun 01, 2006 at 13:18
apparently the ADR's allow for a 10% discrpency.

to change the speedo gear drive would probably entail removing the extension housing on the gearbox. Is it really worth worring about? When I'm doing 100kph my speedo isn't more than 10% out and I have on 285/75's in a BFG MT and they are a 'large' 285/75. Different brands have different rolling diameters.

AnswerID: 176123

Follow Up By: Patrol22 - Friday, Jun 02, 2006 at 09:07

Friday, Jun 02, 2006 at 09:07
....but unfortunately in some states (especially Victoria) they don't allow that same margin of error in their speed cameras and police radars.
FollowupID: 432288

Reply By: Truckster (Vic) - Thursday, Jun 01, 2006 at 13:22

Thursday, Jun 01, 2006 at 13:22
I think the 3.0 has electronic speedo, so the gear thing wont work, Think that came up on the patrol forum ages ago.

10% for speedo, but I wouldnt worry, try it with a GPS and see how far out you are.

How much is the engineers? Gotta get mine done too
AnswerID: 176124

Follow Up By: Snowy 3.0iTD - Thursday, Jun 01, 2006 at 13:32

Thursday, Jun 01, 2006 at 13:32

Don't know what the one off cost is yet, but in Country SA atleast apparently it is just find one of the Transport SA registered engineers he has a quick look at it, takes it for a quick drive does a handling and braking test, and signs off on it, or gives you some bits you have to do before he will sign off on it. There is no increase in registration costs, and going from a original 32inch tyre to a 33inch I am hoping it will just be a paperwork formality. Will post the outcome including costs once I get it done.

FollowupID: 432164

Follow Up By: Voxson (Adelaide) - Thursday, Jun 01, 2006 at 13:52

Thursday, Jun 01, 2006 at 13:52
I am talking to engineers every day,, i am answering this question as the engineer is telling me..... He says "anything over 15mm in rolling diametre from standard is to be checked by engineer at Mallala in a controlled braking and swerving test with special measuring instruments attached to vehicle"..
If vehicle passes it is then inspected as a whole at Vehicle inspection station and then a bill of around $1500 plus the hire of the racetrack is required" another $800..
Not many pass this test...
I have only repeated this from an Engineer...
FollowupID: 432166

Reply By: Member - Sam (NSW) - Thursday, Jun 01, 2006 at 13:27

Thursday, Jun 01, 2006 at 13:27
According to Marks 4x4 Adaptor website (click here), the GU uses a 2 wire inductive sensor for its speedo.
AnswerID: 176125

Reply By: Robin - Thursday, Jun 01, 2006 at 14:45

Thursday, Jun 01, 2006 at 14:45
0% under indication and -6% over Snowy, got Nissan to swap out a new speedo on that one for my GQ before I realized the electroinc speedo had a cal knob on the back.

You probably need to do nothing as GU speedo reads over (faster) about 6% by design.
My 33's almost spot 100 reading=99 actual and 60reading =61 (note speedo is non-linear)

Jaycar convertor kit is lowest cost option - if you don't mind building things

Robin Miller
AnswerID: 176135

Reply By: bobsa - Thursday, Jun 01, 2006 at 16:06

Thursday, Jun 01, 2006 at 16:06
Hi Snowy,
I had the same problem with my 3.0L GU 4
There is no adjustment on the back of the speedo.
The driven gear is very easy to change. Find the sensor on the back of the gear box on the extension housing, there is a 10mm bolt remove that and pull it out a small amout of oil will be lost, I just plugged it with a piece of rag.
There is a small circlip remove this and the cog can be removed and changed to suit your needs.
Here is a list of part numbers for the cogs
32743-74P18..........18 tooth
32743-VB017..........17 tooth
32743-VB016..........16 tooth
32743-VB015..........15 tooth
the original cog in the GU 4 with 17" standard rims is a 16 tooth, went to 285 75 16 and changed to a 15 tooth cog and the speedo now read about 4 km fast.
AnswerID: 176142

Reply By: dan26aus - Thursday, Jun 01, 2006 at 18:20

Thursday, Jun 01, 2006 at 18:20
Hi there Snowy,

I have been thinking about increasing in size on my patrol also, and found something to supposedly suit on ebay. I don't know how to send the link via this site, so if you go into ebay and do a search for a " speedo correction switch" you should get a hit for your patrol. Dunno if they're any good or not but let me know how you go if you decide to try it out. Also i did a comparison on a tyre calculator for you and depending on what size tyre is recommended on the inside of your glovebox, i did the comparison as if it were my patrol which was : recommened tyres: 265 x 70 x 16. compared to 33 x 12.5 x 15 = 6.27% difference & 33 x 12.5 x 16 = 11.17% difference.
If you would like me to send you the link to ebay or the link to the tyre calculator you can send me an email to: and i would be happy to send it to you........

Good Luck

AnswerID: 176170

Reply By: Member - JohnR (Vic)&Moses - Thursday, Jun 01, 2006 at 20:32

Thursday, Jun 01, 2006 at 20:32
Snowy as far as the speedo is concerned do you know how far it is out with the original tyres. Mine was out 4kph at 100 indicated under so was actually 96 kph. It's easy enough to work out the percentage difference and 285/75s give it nearly 6% to 101.5 approximately at in indicated 100 dependent on the tyre and tread chosen
AnswerID: 176198

Sponsored Links