Drivetrain Advice?
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Mountain Pass
Joined: Apr 2000
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From: Arkansas
Drivetrain Advice?
If the rear differential ratio in my 01 Navigator 2wd was changed from 3.73 to 3.08 or 3.31, what affect would it have on sensors, speedometer, anti-lock brakes, etc. ? Would it screw up things big time? Would a trip to a dealer be required to make adjustments to the computer program? Has anyone here ever done this? Not that I'm set on doing this but we hardly ever tow anything. And I know I should have considered the ratio before purchasing the vehicle. Just want to know what my options are.
Fleet Owner
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Yep, the speedo would be off. Of course if you have 4WD you can not change the rear ratio without changing the front axle ratio to match. If you don't, the two axles will fight each other as they try to turn at different speeds.
Fleet Owner
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Hmm, I'm now wondering if the ABS will be effected until the reprogramming is done? Changing the ratio will affect the number of ticks the sensor receives per axle revolution. If this doesn't match the front wheel ticks, then the ABS might think the rear brakes are locking up. Any takers on this thought?
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Freshman User
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Wouldn't the Navi have 4 wheel ABS with individual sensors at each wheel rather than a driveshaft sensor for both rear wheels? With individual sensors the axle ratio will have no impact on ABS.
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Just my $.02, but going from a 3.73 to a 3.31 is going to drop your rpm @ 60MPH about 150 rpm. You could probably go to a slightly taller tire and get the same effect, but I doubt you would see any appreciable change in fuel economy.
Elder User
Joined: Dec 2007
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From: royal oak, mich
I changed the rear end gear in my 9.75 where the ring gear has the sensor ring. ABS works fine but I had to use my tuner to set the speedo right. Another thing I found out was the trans shift schedules were off. It was shifting so early, in your case a little later, that I changed it to shift normal again.
Posting Guru
Joined: Oct 2005
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From: Longwood, Fl
differential sensor
I may be way off here, since I dont know if the later models use the diff sensor for the speedo input. In 93 the diff sensor is the rear ABS sensor as well. I dont know how much later they used that sensor.
If a diff sensor is used (pulse ring behind ring gear) then changing ratios will not affect speedo. The only thing that affects readings is a change in tire size. I have done the PCM correction procedure myself.
If a diff sensor is used (pulse ring behind ring gear) then changing ratios will not affect speedo. The only thing that affects readings is a change in tire size. I have done the PCM correction procedure myself.
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Mountain Pass
Joined: Apr 2000
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From: Arkansas
If the anti-lock pulse ring is attached to the ring gear/carrier (9.75" diff?), he should be okay, as the ring gear turns with the axles.
Just my $.02, but going from a 3.73 to a 3.31 is going to drop your rpm @ 60MPH about 150 rpm. You could probably go to a slightly taller tire and get the same effect, but I doubt you would see any appreciable change in fuel economy.
Just my $.02, but going from a 3.73 to a 3.31 is going to drop your rpm @ 60MPH about 150 rpm. You could probably go to a slightly taller tire and get the same effect, but I doubt you would see any appreciable change in fuel economy.
Fleet Owner
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If for example, the smaller diameter ring has 15 ticks and the larger diameter ring has 16 ticks, then the speedo will be off about 6%. If the spacing of the ticks is constant, it's a reasonable assumption that a large diameter ring will have more tick points.
Posting Guru
Joined: Oct 2005
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From: Longwood, Fl
Differential speed sensor
The original poster was talking about changing gear ratios in the rear end, not to change rearends to accomplish that---thats the way I read his original post.
When changing gears, the pulse ring (forget what they actually call it) mounts behind the ring gear, between it and the carrier assembly. I have not seen any gear sets that include a new pulse ring with the set. Even if it did, it would probably have the same # or teeth as the OEM. I doubt you could even find, anywhere, a ring with a different # of teeth, even with a different rear end.
Certainly, if you change the tooth count that would change the reading-----.
But then, thats not what I said, so I stick by my post on that subject, that is that changing the ratio will not effect the speedo reading
When changing gears, the pulse ring (forget what they actually call it) mounts behind the ring gear, between it and the carrier assembly. I have not seen any gear sets that include a new pulse ring with the set. Even if it did, it would probably have the same # or teeth as the OEM. I doubt you could even find, anywhere, a ring with a different # of teeth, even with a different rear end.
Certainly, if you change the tooth count that would change the reading-----.
But then, thats not what I said, so I stick by my post on that subject, that is that changing the ratio will not effect the speedo reading