Dif change from 3.54:1 to 3.07:1

[mbailey]

Hi Guys,

I have a late 67 S 1.5 E type (USA) & I'm converting to RHD. I have also changed over the diff.
I'm told that this will effect how accurately the existing speedometer works. I keen to get it spot on.
Does anyone out there know what modification would be required to my existing speedo for it
to be used with the 3.07:1 diff and obtain the correct speed reading ?
Best
Marc

[malcolm]

Not sure if you can adjust the existing speedo, or if you need to get a new one. With your current speedo, you'll be underreading your speed by over 15%. 80mph in top on the 3.07 is 3225 revs, at 3225 revs your speedo will read 69 mph. These figures are right for the series 2, I assume also for the 1.5
Mind you, as my speedo OVER reads by 10%, if yours is the same you'll only end up about 5% out!
Personally, I tend to use the rev counter more than the speedo.
I can post a table of revs/speed by gear for the 3.07 if it helps

[Alty Ian]

Yes its easy, I just did the same with mine.
Just send it to speedograph Richfield and they will do it for you quickly and professionally.
http://www.speedograph-richfield.com/
Go on their website as you need to take a couple of measurements to get it accurate to suit your wheel/tire size.

[abowie]

What Ian said. They will get the speedo and odometer to work perfectly.

[chrisfell]

Mind you, as my speedo OVER reads by 10%, if yours is the same you'll only end up about 5% out!

My speedo and axle are as from the factory and the car is fitted with 185 full profile radial tyres (Vreds). The speedo is not 10% out, it is pretty accurate, reading 72 at a real 70mph. If it had original cross plies, it would be dead accurate. Surely an E-Type speedo the reads 10% high has the wrong tyres, or the wrong axle, or both?

[malcolm]

I've got normal 185s, and the original axle. Just an over ambitious speedo.

[mbailey]

Great Thanks for your advice guys

[JagWaugh]

Surely an E-Type speedo the reads 10% high has the wrong tyres, or the wrong axle, or both?

Chris,

Speedos can go out by 10% or more just within the Instrument.

One way to check this is to travel a reasonably long distance on a highway and compare the Odometer value to the known value, or use a GPS. If the Odo is out then tires/axle/angledrive/instrument aren't matching, if the Odo is right, then the speedo just needs calibration.

Here at least having the speedo only calibrated is less expensive than having the Speedo calibrated and Odo corrected.

Worth the extra cost, in my opinion, if you intend to go on a rally the navigator ends up having to apply a correction value to each distance in the book, and some of them aren't very good at that. (Isn't her fault, she's doing the best she can.)