Speedo correction
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Member
Joined: Mar 2001
Posts: 11
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From: CA
Speedo correction
Hello all-
I replaced my 3.08 with a 3.73, which I am really enjoying. I had it done at the dealer, and the service person there told me that my speedo did not require correction since it was "pulse driven" (according to the mechanic who worked on my truck). Has anyone else heard of this? It does seem like the speedo is off, but not by the ~20% that the gear change would cause. I will look under the truck for the speedo cable / reduction gear this weekend, but if anybody has any feedback on this I'd appreciate it.
Thanks
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I replaced my 3.08 with a 3.73, which I am really enjoying. I had it done at the dealer, and the service person there told me that my speedo did not require correction since it was "pulse driven" (according to the mechanic who worked on my truck). Has anyone else heard of this? It does seem like the speedo is off, but not by the ~20% that the gear change would cause. I will look under the truck for the speedo cable / reduction gear this weekend, but if anybody has any feedback on this I'd appreciate it.
Thanks
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Senior Member
Joined: Feb 2001
Posts: 641
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From: Calgary, Oilberta
I did a lot of research on this when I changed my gears and there are a lot of mechanics out there who are confused.
On the 98's there is a Vehicle Speed Sensor (VSS) on the tailshaft of the transmission (4x2) or transfer case (4x4).
The "pulse" (or inductive) driven speedo was used on the pre '97 trucks using the rear ABS sensor and a change in gearing would not cause a problem with the speedo. The 99 and up trucks read speed off an inductive pickup on the transmission or transfer case.
Because the VSS sits before the ring and pinion it measures driveshaft speed and will be affected by the change in gears. The old pulse type was driven off the ring gear and therefore measured tire speed, so changing gears would not throw the speedo off.
On your truck you can change the driven gear on the VSS to correct the speedo - and you will need to do it. Check your speedo by driving a measured mile at an indicated 60 mph. If your speedo is off, it will take more or less than 1 minute to drive the distance.
Once you remove the VSS, you can count the number of teeth on it and multiply that by 3.73/3.08 to get the new number of teeth required.
Ian
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99 Expedition EB
5.4l, 4x4, 4.10 LS
WMS Tube, Bassani Cat Back Exhaust, Superchip Flipchip
On the 98's there is a Vehicle Speed Sensor (VSS) on the tailshaft of the transmission (4x2) or transfer case (4x4).
The "pulse" (or inductive) driven speedo was used on the pre '97 trucks using the rear ABS sensor and a change in gearing would not cause a problem with the speedo. The 99 and up trucks read speed off an inductive pickup on the transmission or transfer case.
Because the VSS sits before the ring and pinion it measures driveshaft speed and will be affected by the change in gears. The old pulse type was driven off the ring gear and therefore measured tire speed, so changing gears would not throw the speedo off.
On your truck you can change the driven gear on the VSS to correct the speedo - and you will need to do it. Check your speedo by driving a measured mile at an indicated 60 mph. If your speedo is off, it will take more or less than 1 minute to drive the distance.
Once you remove the VSS, you can count the number of teeth on it and multiply that by 3.73/3.08 to get the new number of teeth required.
Ian
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99 Expedition EB
5.4l, 4x4, 4.10 LS
WMS Tube, Bassani Cat Back Exhaust, Superchip Flipchip
Thread Starter
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Member
Joined: Mar 2001
Posts: 11
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From: CA
Thanks Ian-
I finally pulled the gear- it's a 19R. So I need a 23R to bring the speedo back in line. The local ford guys can't seem to find the gear, so my question is this- does the mustang gear fit into my truck? Steeda has the gears for the mustang, and I think that someone on the board mentioned that they work, but can anyone confirm this?
thanks again,
HG
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Truck:
98 Regular Cab, Short box, 4.6, auto, 3.73LS
Education:
MCRD San Diego
Cal State San Marcos
I finally pulled the gear- it's a 19R. So I need a 23R to bring the speedo back in line. The local ford guys can't seem to find the gear, so my question is this- does the mustang gear fit into my truck? Steeda has the gears for the mustang, and I think that someone on the board mentioned that they work, but can anyone confirm this?
thanks again,
HG
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Truck:
98 Regular Cab, Short box, 4.6, auto, 3.73LS
Education:
MCRD San Diego
Cal State San Marcos
Senior Member
Joined: Jan 2000
Posts: 398
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From: Hawaii
So Ian, how about a 3.55 to 4.10 swap on a '00 with the 5.4L?
What would I have to do to make the speedo read accurately?
Are you pleased with your gear swap?
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'00 5.4L AUTO 4X4 Lariat (Black/Silver)
'02 F-350 PSD CC DRW 6SPD 4X4 Lariat (order this year)
www.hawthorn-engineering.com
<font face="Verdana, Arial" size="2">The 99 and up trucks read speed off an inductive pickup on the transmission or transfer case.</font>
Are you pleased with your gear swap?
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'00 5.4L AUTO 4X4 Lariat (Black/Silver)
'02 F-350 PSD CC DRW 6SPD 4X4 Lariat (order this year)
www.hawthorn-engineering.com
Senior Member
Joined: Jan 2000
Posts: 398
Likes: 0
From: Hawaii
Thanks Ian. Did you read my question under "Will gears lower my top speed"? I'm trying to figure out how my truck will drive once I swap the gears. I'd like to avoid any surprises so your previous post was VERY helpful.
Thanks again.
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'00 5.4L AUTO 4X4 Lariat (Black/Silver)
'02 F-350 PSD CC DRW 6SPD 4X4 Lariat (order this year)
www.hawthorn-engineering.com
Thanks again.
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'00 5.4L AUTO 4X4 Lariat (Black/Silver)
'02 F-350 PSD CC DRW 6SPD 4X4 Lariat (order this year)
www.hawthorn-engineering.com
Senior Member
Joined: Feb 2001
Posts: 641
Likes: 0
From: Calgary, Oilberta
HG - I have heard that the mustang part will fit but don't know for sure - try a speedo shop. They usually stock the parts so you can compare before you buy.
GAH - You are going to have the same problem I did. There is no VSS on 99 up trucks,so you have three choices if you can't live with a speedo thats wrong (and I couldn't):
1) Get the dealer to reprogram the computer to compensate for the gears. You have to choose a factory option. In my case, the closest would have been a combination of 3.73 axle with the 16" wheel package (I had 3.55's too).
2) That wasn't close enough for me, so I had Mike T at superchips custom burn me a flip chip which brought everything back in line. Before you commit to the gears, check your computer code with Mike to make sure they can do it for your computer.
3) There are speedo correction black boxes that can correct the speedo - check out http://www.autotransinc.com/recal.htm . This wouldn't work with my truck because of the AWD system on the Expedition. I'm not sure how it would work with an F150.
As far as the gear swap goes, I am very happy. I just got my trailer out of storage and the truck is way stronger towing than it was before. I'm also at 3500' so the engine needs all the help it can get.
Ian
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99 Expedition EB
5.4l, 4x4, 4.10 LS
WMS Tube, Bassani Cat Back Exhaust, Superchip Flipchip
GAH - You are going to have the same problem I did. There is no VSS on 99 up trucks,so you have three choices if you can't live with a speedo thats wrong (and I couldn't):
1) Get the dealer to reprogram the computer to compensate for the gears. You have to choose a factory option. In my case, the closest would have been a combination of 3.73 axle with the 16" wheel package (I had 3.55's too).
2) That wasn't close enough for me, so I had Mike T at superchips custom burn me a flip chip which brought everything back in line. Before you commit to the gears, check your computer code with Mike to make sure they can do it for your computer.
3) There are speedo correction black boxes that can correct the speedo - check out http://www.autotransinc.com/recal.htm . This wouldn't work with my truck because of the AWD system on the Expedition. I'm not sure how it would work with an F150.
As far as the gear swap goes, I am very happy. I just got my trailer out of storage and the truck is way stronger towing than it was before. I'm also at 3500' so the engine needs all the help it can get.
Ian
------------------
99 Expedition EB
5.4l, 4x4, 4.10 LS
WMS Tube, Bassani Cat Back Exhaust, Superchip Flipchip