Hey guys,

Just bought my first Jag, have been doing a fair bit of work getting it up to road worthy condition.

At some stage in her life (fairly recent) and the guess is that the speedo gear has been replaced incorrectly as I am getting a reading about 25% out. I have been told rather reliably that it is supposed to have a brown gear. I have never replaced one before and dont even know where to look.

Any help would be great thanks

 

hi,
what model & year Jaguar?

 

1988 sovereign v12

 

sounds like you have a Daimler Sovereign, aka as XJ-40, aka as Series 4.

does it look like the picture below? if yes, post your question in the XJ-40 Forum.

 

Steve,

When I gave you the link to this section from your Intro, I assumed you have a V12 Series III.

Jaguar introduced the V12 XJ40 in 1993, one year before the series ended. If you have a 1988 V12 XJ40, someone has done a transplant.

If it is the Series III, this is what you're looking for bolted to the side of the gearbox casing:



The Speedometer Driven Gear (item 1) fits in Driven Gear Housing (item 2) and is secured by Retainer (item 6).

Graham

 

Thanks Graham. You are correct series 3.

Jose in Australia and the uk its a jaguar sovereign, Same as an xj12 slightly higher spec, not as high a spec as a Daimler double 6.

Thanks for the help

 

yes, after 1986 it can get really confusing, since the XJ-40 was first built and sold in 1986, and then you have the Daimler Sovereign models which can either be a Series 3 or a Series 4 body.

 

Jose,

I had a 1972 Daimler Sovereign Series I in 1974.

If you've an idle hour or so to fill, count up the number of models Jaguar has badged as 'XJ6' and/or 'Sovereign' across the years from 1969 when the Series I replaced the MK10/420G

Absolutely crazy way of naming different models!

Graham

 

Hey,


A quick follow up question my reliable source that had told me it was supposed to be a brown gear may have been incorrect it.


So do any of you know what colour the gear is meant to be?

I was hoping to have this replaced this weekend as the car is going in for its Road Worthy Cetificate (MOT) on Tuesday.

 

Steve,

According to the Parts Manual, the Speedometer Driven Gear for the 5.3 litre has 39 teeth - no mention of colour. ( didn't know you Australians were so fashion conscious. )

Is it possible the wrong Gear with a different number of teeth has been fitted hence giving the 25% inaccurate speedometer reading?

Graham

 

Graham,

What can I say mate we like our colours!!

So the brown gear does have 39 teeth. I have found a site that says for every tooth removed increases the speedo reading by about 2.5% do you think its a worth while proposition to change the gear to a say 29 or 30 odd tooth gear?

OR can you think of another reason that this generally would happen?

 

Steve,

As the gear has the correct number of teeth, the only other reasons for incorrect speedo reading must be either non-standard tyre size or, more likely, a changed diff ratio.

Graham

 

Or an incorrect speeo *drive* gear.

Remember there are *two* speedo gears. The 39-tooth brown gear is the "driven" gear. That's the one that slides into the side of the transmission.

The speedo *drive* gear....which turns the driven gear....is inside the transmission on the output shaft. These, too, are available with different tooth counts.

The most likely scenario for an incorrect drive gear is if the gear was broken and somebody replaced it with whathever they could get their hands on at the moment. Or someone did some incorrect mix-n-matching during a trans overhaul.

Since the reported speedo error is a full 25%....quite a lot....a different rear axle ratio is the most likely scenario IMHO

Cheers
DD

 

Cheers guys