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Thread: diff ratio change

  1. #1
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    diff ratio change

    hi guys and gals wondered if any of you could help me please

    i have a td5 whith automatic transmission and would like to know if any of you have changed your diff ratio? if you have does your cruse control still work? and all ya traction control n bits n pieces

    thanks in advance though this would be a great place to ask as i know your play grount is just a bit more extreme than what we have here

  2. #2
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    Quote Originally Posted by dieselcarb View Post
    hi guys and gals wondered if any of you could help me please

    i have a td5 whith automatic transmission and would like to know if any of you have changed your diff ratio? if you have does your cruse control still work? and all ya traction control n bits n pieces

    thanks in advance though this would be a great place to ask as i know your play grount is just a bit more extreme than what we have here
    Yes. In the auto everything will still operate. In the manual you would lose cruise control unless you correct the SLABS output to correct the speedo to what it thinks it should be doing.
    Cheers
    Slunnie


    ~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~

  3. #3
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    that is music to my ears definately works on an auto yes? i can do 5 hours off road on the pedal but 5 hours on a motor way my back plays up

  4. #4
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    So ever with 4.12 gears on an Td5 manual with 285s you lose Cruise control? How do you excalty fix that?
    Quote Originally Posted by Slunnie View Post
    Yes. In the auto everything will still operate. In the manual you would lose cruise control unless you correct the SLABS output to correct the speedo to what it thinks it should be doing.
    03 D2a Manual Td5 Modified, Ashcroft lockers F&R, Ashcroft R380,Atb lt230, Ashcroft Rear axles, AS manual IC, AS exhuast manifold, AS Coolant bottle, 3inch exhaust, alive GTB550 VGT, billies 7100s, 3inch lift, 4inch staino snorkel, 35s beadlocked

  5. #5
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    Quote Originally Posted by Kaaaiju View Post
    So ever with 4.12 gears on an Td5 manual with 285s you lose Cruise control? How do you excalty fix that?
    Remap the ecu, it only effects gearing changes between the back of the flywheel and the abs sensors on the wheels, running bigger tyres won't change anything

  6. #6
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    I had another disco with 4.12 manual disco and 285 and it had no cruise control
    Quote Originally Posted by shack View Post
    Remap the ecu, it only effects gearing changes between the back of the flywheel and the abs sensors on the wheels, running bigger tyres won't change anything
    03 D2a Manual Td5 Modified, Ashcroft lockers F&R, Ashcroft R380,Atb lt230, Ashcroft Rear axles, AS manual IC, AS exhuast manifold, AS Coolant bottle, 3inch exhaust, alive GTB550 VGT, billies 7100s, 3inch lift, 4inch staino snorkel, 35s beadlocked

  7. #7
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    i notice you guys are talking about 285s im assuming 285/75/16 roughly 33 inches is a 3 inch lift all ya running? over here apparently u need 4 inch lift i always thought 3 inch would be plenty providing nothing rubs.... 16x8 wheels with ET+25mm offset

  8. #8
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    Quote Originally Posted by Kaaaiju View Post
    So ever with 4.12 gears on an Td5 manual with 285s you lose Cruise control? How do you excalty fix that?
    The SLABS generates and sends a speed signal that is taken from the 4 ABS sensors. When you change the diff ratio, the driveline speed stops matching what it expects to see at the axle because of the diff change. If you use a speedo correction unit on the speed output signal at the SLABS computer it will correct this. BUT when you are doing this, you're not correcting the speed of the car, you are correcting what it should see because of the diff ratio change - this is important. So, to gain cruise control back again, correct from 3.54 diffs to 4.12 diffs. If you're running 285/75-16 (33's) then your speedo will be accurate. To do this you will need to use a pretty specific speedo correction device that needs to pass through the baseline diagnostic frequency, which most do not do. See this article I wrote about 17 years ago for fitting and a SCU that works.

    Truspeed speedo correction installation - www.slunnie.com
    Cheers
    Slunnie


    ~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~

  9. #9
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    Quote Originally Posted by dieselcarb View Post
    i notice you guys are talking about 285s im assuming 285/75/16 roughly 33 inches is a 3 inch lift all ya running? over here apparently u need 4 inch lift i always thought 3 inch would be plenty providing nothing rubs.... 16x8 wheels with ET+25mm offset
    285/75-16 is about 33" and I run that with 4" lift and factory 16x8's. They fit without guard cutting when setup like this, but my guards are cut to fit bigger tyres.
    Cheers
    Slunnie


    ~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~

  10. #10
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    Quote Originally Posted by Kaaaiju View Post
    I had another disco with 4.12 manual disco and 285 and it had no cruise control
    It's quite possible there was an issue with the actual cruise control itself, bigger tyres cannot make any difference to the speed the abs sensors pick up.

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