hope its as easy in life as you make it sound
Trans Swap and now incorrect speedometer reading
Thread Starter
5th Gear
Joined: Mar 2014
Posts: 5
Likes: 0
From: Norfolk VA
Trans Swap and now incorrect speedometer reading
So i bought this car about 2 years ago and the previous owner told me he swapped the 4+3 for a 5 speed trans, only catch was he said the speedometer didnt read the right speed anymore. No big deal for a while, was just using GPS to tell me how fast im going but as i fix more and more things on the car this is becomming a real annoyance to me. I took it to a shop (that i have now come to not trust anymore) and they told me it couldnt be fixed due to how the new trans was installed. Im no mechanic by far, but does anyone else have an opion on this or have done this before? i dont know where to even start or how expensive of a fix this could become.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
So i bought this car about 2 years ago and the previous owner told me he swapped the 4+3 for a 5 speed trans, only catch was he said the speedometer didnt read the right speed anymore. No big deal for a while, was just using GPS to tell me how fast im going but as i fix more and more things on the car this is becomming a real annoyance to me. I took it to a shop (that i have now come to not trust anymore) and they told me it couldnt be fixed due to how the new trans was installed. Im no mechanic by far, but does anyone else have an opion on this or have done this before? i dont know where to even start or how expensive of a fix this could become.
Either can be done to correct the speedometer but it's likely different possible scenarios that could correct it. If it works (you hinted yes) then it's likely least expensively corrected using a DRA (digital ratio adapter). There are different products available and knowing what's present now might help.
It would seem there's likely a DRA there now so it could be just a matter of changing some "dip switches".
Post as much information as you have for starters.
What year is this car? Is it an original TPI or what? That could be important when it comes to making the ECM etc. understand what's going on for the VSS signal etc.
Last edited by WVZR-1; Sep 29, 2015 at 12:07 PM.
Thread Starter
5th Gear
Joined: Mar 2014
Posts: 5
Likes: 0
From: Norfolk VA
cool, thanks for the response. i thought there might be an adapter like that, i will look for any more specific info on whats currently installed when i get home tomorrow and can look at it.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
There should either be two wires directly from the transmission OR there could be a short cable and then an electrical device with two wires going someplace. At the end of either set of those wires there needs to be a "black box" of some sort that's considered the DRA>
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
Transmission model is as important as checking for the wires etc. Any casting information on the case etc would be very helpful.
Is the PO close to you and local OR was this long ago and far away? If the PO did this and it was a quality exchange he likely documented it quite well. With the modifications that were required for the C-beam adapters to the transmission etc. it would seem he likely did.
Take a ride with a GPS and drive the car at 40 MPH, 50 MPH and 60MPH noting what the GPS value is at those speeds. A % of error is needed to determine what's going to be required if it's a "dip-switch" controlled device.
If there's a DRA and it's not foolishly located behind the dash or some other secluded location it certainly could be easy. If you locate the DRA snapshots might be good.
Is the PO close to you and local OR was this long ago and far away? If the PO did this and it was a quality exchange he likely documented it quite well. With the modifications that were required for the C-beam adapters to the transmission etc. it would seem he likely did.
Take a ride with a GPS and drive the car at 40 MPH, 50 MPH and 60MPH noting what the GPS value is at those speeds. A % of error is needed to determine what's going to be required if it's a "dip-switch" controlled device.
If there's a DRA and it's not foolishly located behind the dash or some other secluded location it certainly could be easy. If you locate the DRA snapshots might be good.
Safety Car
Joined: Aug 2013
Posts: 4,430
Likes: 608
From: Minneapolis Mn
I don't know if this will help or not. I have an 86 that originated with a 4+3 that a Tremec TR3550 5 speed was transplanted before I bought it. There's a Dakota Digital SGI-5C adapter in the speedometer wiring that converts the transmission signal to drive the speedometer. It's wired into the harness right above the battery but I have not traced the wiring back to the tranny to figure out what goes where. I'm attaching a picture of the unit and how it was wired into the car
My speedometer was off about 10% when I bought it and they didn't have enough slack in the wire to calibrate it while driving as purchased (adapter is under the hood in a plastic box over the battery). I ended up having to extend the wires so the adapter could be gotten inside the car while driving and I was able to adjust it using the up/down buttons. It's in a plastic box under the hood and unless I have to readjust it in the future, it's fine there.
Hope it helps
My speedometer was off about 10% when I bought it and they didn't have enough slack in the wire to calibrate it while driving as purchased (adapter is under the hood in a plastic box over the battery). I ended up having to extend the wires so the adapter could be gotten inside the car while driving and I was able to adjust it using the up/down buttons. It's in a plastic box under the hood and unless I have to readjust it in the future, it's fine there.
Hope it helps
Last edited by hcbph; Sep 30, 2015 at 06:38 AM.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
I don't know if this will help or not. I have an 86 that originated with a 4+3 that a Tremec TR3550 5 speed was transplanted before I bought it. There's a Dakota Digital SGI-5C adapter in the speedometer wiring that converts the transmission signal to drive the speedometer. It's wired into the harness right above the battery but I have not traced the wiring back to the tranny to figure out what goes where. I'm attaching a picture of the unit and how it was wired into the car
My speedometer was off about 10% when I bought it and they didn't have enough slack in the wire to calibrate it while driving as purchased (adapter is under the hood in a plastic box over the battery). I ended up having to extend the wires so the adapter could be gotten inside the car while driving and I was able to adjust it using the up/down buttons. It's in a plastic box under the hood and unless I have to readjust it in the future, it's fine there.
Hope it helps
My speedometer was off about 10% when I bought it and they didn't have enough slack in the wire to calibrate it while driving as purchased (adapter is under the hood in a plastic box over the battery). I ended up having to extend the wires so the adapter could be gotten inside the car while driving and I was able to adjust it using the up/down buttons. It's in a plastic box under the hood and unless I have to readjust it in the future, it's fine there.
Hope it helps
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Team Owner
Joined: Sep 2003
Posts: 25,394
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You might check this instruction package and midway through there's an image of a VSS already mounted in the RH tail of the TKO. If it were a specialty conversion of sorts it could have this. If it were a DIY of sorts then that's where there could be the mechanical drive to an electronic converter that from which the wires to the box would originate.
http://www.shiftsst.com/images/pdfs/...anual_RevA.pdf
http://www.shiftsst.com/images/pdfs/...anual_RevA.pdf
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
If getting the speedo sorted is an issue an aftermarket HUD may work for you.
The display on mine washes out a bit when driving into early morning or late afternoon sun other than that I like it.
The display on mine washes out a bit when driving into early morning or late afternoon sun other than that I like it.