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  #1  
Old 10-21-2019, 06:07 PM
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Question about change dif ratios.

Will changing the ratio of the differentials light up anything on the dash? Will the speedometer automatically adjust to change in speed?
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Old 10-21-2019, 06:27 PM
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I would say(guess) not and I think speedo works off wheel sensors so diff ratio should not cause a change.
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Old 10-21-2019, 09:48 PM
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Speedo gets the speed from the back of the transmission. Change in dif will change your dash speed proportionally.

You may be able to code the ratio to get the speed corrected.

Somebody that's done it can maybe answer if there is a problem when vehicle speed doesn't match the wheel speed


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Old 10-22-2019, 09:31 AM
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haven't done it but I recall seing somewhere in NCS Expert files the speedo correction, probably put in there for winter/summer wheels.


Beyond that, I don't see an issue with doing it.



Alternative question, where do you find those parts? I'd be willing to go a smidge longer on my ratios for the 4.6?
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Old 10-22-2019, 10:51 AM
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Quote:
Originally Posted by andrewwynn View Post
Speedo gets the speed from the back of the transmission. Change in dif will change your dash speed proportionally.

You may be able to code the ratio to get the speed corrected.

Somebody that's done it can maybe answer if there is a problem when vehicle speed doesn't match the wheel speed


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In the good ol' days we either purchased a speedo gear matched to the ratio or we learned the difference and did the calculation when checking how fast we were going.

I assume it is a sending unit? Where is it located? I also thought it was the wheel sensors that calculated speed.
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Last edited by bcredliner; 10-22-2019 at 11:04 AM.
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Old 10-22-2019, 10:59 AM
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Quote:
Originally Posted by scourtaud23 View Post
haven't done it but I recall seing somewhere in NCS Expert files the speedo correction, probably put in there for winter/summer wheels.


Beyond that, I don't see an issue with doing it.



Alternative question, where do you find those parts? I'd be willing to go a smidge longer on my ratios for the 4.6?
A couple of years ago I purchased a set of lower ratio 4.10 diffs out of a 3.0 to replace the 3.91 stock ratios. Result will be that at the same speed RPMs will be higher than the stock ratio but it will reduce 0-X times. My interest is getting to 60 in less time.
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Old 10-22-2019, 12:10 PM
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Speedo picks up from a wheel sensor, not the transmission. No adjustments are necessary after swapping differential gear ratios.

The ncsexpert adjustment is there if you want to code out the 3mph optimistic speed that comes programmed into NA market bmws.
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Old 10-22-2019, 08:20 PM
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https://youtu.be/eOuNNG_mD6Q

Unless the X5 doesn't work like every other modern car, it will get the speed from the vss on the output shaft of the transmission.

24357507706 is the part number for my car, others may be different since it attaches to the transmission.

Prove me wrong. All info I can find online points to the speedometer gets the reading from the output of the transmission. (like most cars).

Point made: one of my xo buddies has a defective abs module and has no wheel speeds at all yet his speedo still works.
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Old 10-22-2019, 08:34 PM
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If you change the rear diff ratio, wouldn't you have to change the front diff ratio similarly to avoid TC wear?

AM.
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Old 10-22-2019, 08:37 PM
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Yes they have to be changed in pairs


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