speedo drive on lt77

a1100ndy · Post by **a1100ndy** » Tue Mar 10, 2009 9:06 pm

have lt77 box in my sierra with cosworth back axle the gearbox has an electronic pick up for the speedo but need to change to mechanical drive to run cable to standard speedo does anyone have any idea which drive i need and where can they be got

many thanks

harvey · Post by **harvey** » Tue Mar 10, 2009 9:15 pm

The standard early cable driven gear and its sleeve from an early SD1 is a direct replacement for the later electronic sender. In fact any cable LT77 box should get you a gear, after that it's just a matter of recalibrating the head to make it accurate.

a1100ndy · Post by **a1100ndy** » Tue Mar 10, 2009 9:26 pm

thanks m8 thats good to know ive been told that there are different sized drives have not been able to find anyone who sells them

harvey · Post by **harvey** » Tue Mar 10, 2009 9:31 pm

The driven gears will have different numbers of teeth depending on the original application, but as the LT77 was never fitted in a Sierra you can fit any one as you'll need to recalibrate the head anyway.

Try Rimmer Bros for new driven gears, and they probably do the sleeve it sits in as well.

Pocket rocket · Post by **Pocket rocket** » Tue Mar 10, 2009 9:32 pm

Rimmer Bros did do them - but they ain't cheap

http://www.rimmerbros.co.uk/rimmer/rove ... Transducer

SORRY - just noticed they don't appear to be in stock. Might be worth phoning them anyway..

a1100ndy · Post by **a1100ndy** » Tue Mar 10, 2009 9:34 pm

will do never thought about them is it tricky to recalibrate the speedo or is that a specialist job

harvey · Post by **harvey** » Tue Mar 10, 2009 9:37 pm

a1100ndy wrote:will do never thought about them is it tricky to recalibrate the speedo or is that a specialist job

Google "Speedy Cables" and they can do it, and their site shows you how to do the calculations for them to be able to do it for you.

They can also custom make a cable to fit both ends as well.

harvey · Post by **harvey** » Tue Mar 10, 2009 9:40 pm

Someone on here must have the speedo gear and sleeve secondhand that they would be able to sell you.

a1100ndy · Post by **a1100ndy** » Tue Mar 10, 2009 9:42 pm

thanks for all the help, gives me a point in the write direction, been working off and on the car for a while and need to get the finger out and get it running this summer,

or so i keep telling myself

ged · Post by **ged** » Tue Mar 10, 2009 9:49 pm

Hi a1100ndy,

There are 2 mechanical speedo drives that I am aware of, you'll have to pick the one nearest to your final drive ratio.

3500-20 teeth orange for 3.08-1 axle ratio or

2600/2300 23 teeth black 3.45-1 ratio.

Hope this helps

Ged

CastleMGBV8 · Post by **CastleMGBV8** » Tue Mar 10, 2009 10:17 pm

Yes final drive ratio, and tyre size come into the equation.

http://www.v8forum.co.uk/forum/viewtopic.php?t=5079

Might do the job.

Kevin.

ChrisJC · Post by **ChrisJC** » Wed Mar 11, 2009 8:04 am

Some speedometers can be recalibrated, some cant. When I put the 150MPH speedo in my Sherpa, I investigated this point, and found that it's too new (only 20 years old!) to be recalibrated.

Instead you have to buy a correction gearbox which sits in the middle of the speedo cable (which in effect becomes two cables) to make the adjustment.

I did the various calcs, and specificed that a certain RPM on the speedo drive from the gearbox was 60MPH road speed.

I now have a speedo that is c*ck on. However, because the manufacturers make the speed part optimistic and the odometer accurate, I now have an accurate speedo but lousy odometer!!!

Chris.

Post by **katanaman** » Wed Mar 11, 2009 5:01 pm

There are loads of options on the ratios. Last set I bought was from an LDV van dealer so try one of them.

a1100ndy · Post by **a1100ndy** » Wed Mar 11, 2009 9:03 pm

got a speedo drive thanks Keith, and thanks to all for your help