2.8 speedo problems

Post by **Andrew 2.8i** » Tue Feb 11, 2014 6:11 pm

Hi Everyone,
The speedo on my 2.8 under-reads. When I'm doing, say, 40MPH indicated my satnav says I'm actually going about 43MPH. Does anyone else have this problem? The speedo under-reading like this might cause a problem, so I am keen to fix it.
Can anyone suggest anything to check?
All the best,
Andrew.

Post by **stevemarl** » Tue Feb 11, 2014 6:23 pm

Normally you`d suspect the rear axle/gearbox has been changed, but your 2.8 has the highest ratio so fitting say a 2.0 axle would make it *over* read. As I understand it the gearbox for 2.8 has a different nose so it`s also unlikely that the gearbox is from a 4 cyl model (with a different speedo drive ratio) which is the only way I can think of which would give this problem.
I`m thinking maybe it`s the actual speedo itself? On the bright side - easier than changing the axle anyway!

Just thought - have you got lower profile tyres etc, anything which reduces rolling diameter??

edit: I meant *increased* rolling Diameter of course....

Post by **Andrew 2.8i** » Tue Feb 11, 2014 6:47 pm

Hi Steve,
Thanks for your help.
I have standard 205/60 13 tyres on the car, so it can't be that. The dash pod is from a 6 cyl, so I don't think that the problem is there either.
So do different models have different gearing on the speedo drive gear? perhaps that might be the problem. Any thoughts?
By the way, is there a way I can tell what ratio axle is in the car without taking it apart?
All the best,
Andrew.

Post by **stevemarl** » Tue Feb 11, 2014 7:02 pm

Didn`t they used to have a metal tag with ratio on?, .. very vague memory, and it will probably have rotted away by now anyway.
The gearboxes do have different speedo drive gears - but can`t imagine a scenario where that would be changed? And as said, I don`t believe the 4cyl type 9s are *suitable* for the V6 models, and that`s the only way you`d under read.
I didn`t mean it had the wrong speedo fitted necessarily, just that it may be faulty?

Post by **Andrew 2.8i** » Tue Feb 11, 2014 7:24 pm

Hi Steve,
You're right about the 2.8 'box, I'm sure somebody said that the 4cyl T9 does not fit because the input shaft is too short. With that in mind, I suppose it's unlikely that the speedo drive gear in mine would be the wrong one.
You could well be right about the speedo itself being faulty, it might be worth me changing it at least to eliminate it if nothing else.
Next time I'm under the car I will look for the tag on the axle. Do you know where it is located?
Thanks for your thoughts so far, much appreciated.
All the best,
Andrew.

Post by **stevemarl** » Tue Feb 11, 2014 7:39 pm

I think it was a thin pressed steel tag held on by one of the back cover bolts. (I`m even doubting its existance myself) I think I took it off when I had cover off for painting but didn`t put it back again.

Post by **Big Mike** » Tue Feb 11, 2014 8:38 pm

I'd be inclined to say don't worry too much about it, I've driven my Capri, my Mazda 6, a works Transit Van and 44 tonne artics with my sat nav in place and it never 'agrees' with the figure the speedo is showing - sometimes it's under, sometimes it's over (depending which of the above I'm driving) but it's always within a few mph either way. If it was say 8 - 10mph out perhaps I'd be wondering why, but I really don't think there's anything to worry about that warrants major investigation with just a few mph?

Edited to add: Debate here: http://forums.moneysavingexpert.com/sho ... ?t=3135556

Mike.

Post by **Andrew 2.8i** » Tue Feb 11, 2014 9:06 pm

Hi Mike,
Thanks for your thoughts on the subject. You could well be right that it's not really worth bothering with over a few MPH. Maybe I was worrying a bit too much because on all of the vehicles I drive the speedo always reads slightly over the actual road speed but never under, except for the Capri. I thought there may be a simple fix for when I have a spare hour or so.
However, I will probably leave it for now and keep an eye on it in case the margin of error increases.
All the best,
Andrew.

pbar · Post by **pbar** » Wed Feb 12, 2014 8:01 am

Big Mike wrote:I'd be inclined to say don't worry too much about it, I've driven my Capri, my Mazda 6, a works Transit Van and 44 tonne artics with my sat nav in place and it never 'agrees' with the figure the speedo is showing....

Same here, never had a satnav which agrees with a speedo in any car.

Post by **stevemarl** » Wed Feb 12, 2014 8:29 am

The problem is, say speed limit is 30, you do 33/34 (as everyone does...)you`ll generally be safe, (prosecution guidance is speed limit + 3mph +10%, so 36 ) but given an UNDER reading speedo you`re actually doing 36/37 - just prosecutable. I believe the tolerance for speedos was always +10% -0% ie they would usually read over for this very reason. Personally I`d be happier with one which over-read slightly.

Post by **Andrew 2.8i** » Wed Feb 12, 2014 5:48 pm

Hi,
Steve, that is very sensible advice about the speedo reading. Your belief about the tolerances are exactly what I thought too. It was in the back of my mind that it was against the law for the speedo to read under the actual speed, although it is not tested for the MOT.
I may get a another speedo pod and replace it when I have some more jobs to do that involve removing the instruments. As I only use the car for approx. 2000 miles a year the job can wait for a few months.
Thanks for all the advice so far guys.
All the best,
Andrew.

Post by **Andrew 2.8i** » Tue Mar 18, 2014 8:42 pm

Hi,
Unfortunately I still have this problem. I understand that the type 9 has different speedo drive gears depending on which capacity engine it was mated with.
Can any brainy types answer these questions?
1) Are the different speedo drive gears interchangeable?
2) If I had the 24 tooth gear from the 2.0 in my 'box instead of the proper 22 tooth gear, would the speedo under-read as I've described in my original post?
3) Am I barking up the wrong tree completely?
Any thoughts?
All the best,
Andrew.

Post by **Caprigear** » Tue Mar 18, 2014 9:18 pm

The drive gears are interchangable, you can alter the speedo readings by using different ones but if you have the correct speedo drive gear, standard rear diff, wheels and tyres then there's not too much else you can do.
I have a set of instruments just removed from a 2.8i this afternoon if you're loking for a set of spares.

Post by **Andrew 2.8i** » Tue Mar 18, 2014 9:32 pm

Thanks Martin,
I've got one more thing I'm going to try first before I change the instrument cluster.
Andrew.

Post by **stevemarl** » Tue Mar 18, 2014 10:41 pm

peers.dupp wrote: If I had the 24 tooth gear from the 2.0 in my 'box instead of the proper 22 tooth gear, would the speedo under-read as I've described in my original post?

If you had a DRIVEN gear with 24 teeth, it would turn at a lower speed than the 22 tooth gear, and hence give you an under-reading speedo (obv. by a factor of 24/22 or circa 10%)

-JC- · Post by **-JC-** » Wed Mar 19, 2014 2:19 pm

peers.dupp wrote:Re: 2.8 speedo problems

Personally, I would recommend trunks rather than speedos.

Post by **stevemarl** » Wed Mar 19, 2014 3:33 pm

Esp. speedos with teeth.....

pbar · Post by **pbar** » Wed Mar 19, 2014 6:27 pm

Neither speedos nor trunks, those tiny things are of no use

Post by **Andrew 2.8i** » Wed Mar 19, 2014 7:38 pm

-JC- wrote:Personally, I would recommend trunks rather than speedos.

pbar wrote:Neither speedos nor trunks, those tiny things are of no use

In future I will keep problems with my speedos private.

Andrew.

r2vdh · Post by **r2vdh** » Fri Mar 21, 2014 1:34 am

Your most simple option is to remove the gauge cluster and using two small screwdrivers lever off the your needle and press it back on into the right position.

Have you got white dials in your car??
If it reads over the same amount across the range this will be the fix you will need.
The Indicator can slip if it hasnt been pressed on correctly.