How to Recalibrate/adjust your speedometer

[MrMarty51]

FWIW, I probably rearranged the VSSB 3-4 times before I got a speedo reading that matched my GPS. Either the speed calculator is a bit off or my GPS is?

Thats when it gets to sort of like splitting hairs.
For the DOT, they started installing distance meters for setting work zone signs. Too many Tort claims because signs was off by feet or yards.
The vehicles that got the distance meters, the meters had to be calibrated. The engineer dept went out on the interstate and marked off a stretch that was two miles. Once we got the meter installed then we got to go out and drive the shoulder of the interstate that distance and recalibrate, with dip switches, until the meter read correct to the distance. It was usually off a foot or two but with the dip switch that was as close as we could get them.
If the sign said men working 1,000 feet then that distance had to be accurate within XX amount of feet in order for the state to keep from getting sued if there was an accident within that distancez

 

[NVW]

Years ago we had mile marker lines on the highways, they are no longer there.

 

[MrMarty51]

Years ago we had mile marker lines on the highways, they are no longer there.

Yup, we still have mile posts. For the most part they are all pretty close to being right on the money.
Drive with speedo on 60 and it should take a minute to go from one post to the next, average it out over three or four miles and it should be mighty close to that many minutes. 90 about 45 seconds, 120 about 30 seconds and so on and so forth.
Old 1974 T-150 Triumph Trident, about 20 seconds over five miles, between mile posts, still had some good acceleration to go. I guess they dont call them a T-150 for no reason.

 

[dbrannon79]

yesterday when I tracked my miles, I set the GPS to record using the stride mileage app when I left the front entrance at work. got home and looked at the difference between the counter on the dash and the app. the counter showed 5.9 miles and my app showed 5.14. it's fairly close but it was a short trip, longer trips can skew mpg numbers for sure.

I can try one or two settings off from where it's at on the chart and see if the counter gets closer.

 

[ak diesel driver]

On my 96 I could have either the speedo or the odometer correct, not both. Wasn't off a lot but if you were checking......

 

[NVW]

I went with the speedo, I've never got a ticket with a faulty odometer.

 

[jrsavoie]

I went with the speedo, I've never got a ticket with a faulty odometer.

I went with a speedo once. I was told to cover myself.

 

[Will L.]

I went with a speedo once. I was told to cover myself.

Ok swimmer boy...Only one in the news at a time please.

 

[THEFERMANATOR]

You're lucky if your speedo is +/-4 mph of actual across it's sweep. These clusters use air cores, and the slightest rfi change will change there reading. You can be going at a steady speed set on your cruise, shift from 4th down to 3rd, and your speedo will go up some due to the tach reading faster(hence how if you rev your engine setting still, your speedo will move from the signal going to the tach and rfi cross talk). My 99 is dead on perfect doing 30 when it shows 30, but when it reads 70 I'm only doing 67(and I went through a few air cores to get one that was this close). My 95 will read 34 when I'm doing 30, but 70 is dead on, but bump up to 75 on the speedo, and I'm doing close to 78 actual. I always set them so the odometer reads correctly, set the cluster up up on the bench with the tach at 2k rpm's and the speedo reading correct when straight up(50 mph for the 100 mph cluster, 60 for the 120 mph cluster), and call it good.

 

[dbrannon79]

You're lucky if your speedo is +/-4 mph of actual across it's sweep. These clusters use air cores, and the slightest rfi change will change there reading. You can be going at a steady speed set on your cruise, shift from 4th down to 3rd, and your speedo will go up some due to the tach reading faster(hence how if you rev your engine setting still, your speedo will move from the signal going to the tach and rfi cross talk). My 99 is dead on perfect doing 30 when it shows 30, but when it reads 70 I'm only doing 67(and I went through a few air cores to get one that was this close). My 95 will read 34 when I'm doing 30, but 70 is dead on, but bump up to 75 on the speedo, and I'm doing close to 78 actual. I always set them so the odometer reads correctly, set the cluster up up on the bench with the tach at 2k rpm's and the speedo reading correct when straight up(50 mph for the 100 mph cluster, 60 for the 120 mph cluster), and call it good.

How does the PCM read speed on my 95? I haven't checked what it sees with the scanner yet, but since calibrating with the 3.73 gears, the truck's TCC in 4th engages at 50mph now where before it would go in at 45.

 

[THEFERMANATOR]

How does the PCM read speed on my 95? I haven't checked what it sees with the scanner yet, but since calibrating with the 3.73 gears, the truck's TCC in 4th engages at 50mph now where before it would go in at 45.

The PCM could care less what your speedo sees, it reads everything from the vssb. Lockup at 50 with 3.73's is about where it should be(3.42's don't lockup until almost 55). The vssb reads the 40 tooth output reluctor wheel, it then converts the 40 tooth per driveshaft revolution AC signal into a 5 volt DC square wave signal to the PCM, it also will convert it over to a 2k pulse per mile signal to the PCM for speed input, and it does a 4k ppm output for your speedo & such. I would never go by the speedo when calibrating the vssb, scanner only.

 

[dbrannon79]

That makes sense to calibrate by the scanner. I never thought of that. back when I got the truck I found out by working on the dash that someone before me had been inside the cluster and apparently played with all the needles on the gauges. I've had to reset them one by one by verifying sensors on the scanner and other means while pulling the needles off the gauges and placing them where they should be. sounds like I might need to do the speedo in the same mannor. re-calibrate using the scanner and a GPS, then work with the speedo gauge.

 

[deerefan]

Hey guys, I know this is an older thread, but I figured I'd post here since I needed to calibrate my speedo after getting my truck back from installing 3.73? going from 4.10's.

Followed the instructions along with reading a bit on other forums too, did my calculations on the formula and going off the chart. I have 265-75R16 tires which gives a 99.37976377952756 circumference, using the chart on the site linked below gave me a ratio input of 0.7431492810130232 that shows on the chart as the closest setting 0.739258 or 1011011.

before I started I checked my VSSB pins and looked at the chart to see where it was at from factory. set at 0.874512 or 1001100 and after having the gears installed I ran the speedo against my phone's gps and saw my speedo was 5 miles faster than the gps.

switching to the lower setting still showed me the same result 5 mph over the gps. Thinking back when I got the truck how the speedo was off running the stock tires (235-75) I looked at the chart and used tire size 245-75 which gave me a lower number on the chart. After driving up the road checking at 30mph and again at 50mph I was seeing 3mph over on the speedo.

So I did one more run using the chart to set it for tire size 235-75 and 3.73 gears, gave me 0.7872153208675311 which showed on the chart two numbers that were close. 0.781738 ( 1010110 ) and 0.790527 ( 1010101 ).

A test run down the road again showed my speedo very close. About 1mph to only 1/2 mph over my gps. I am thinking there is something wired going on here but at least it’s close now.

And the link to the chart I used


I’m kind of torn in using this since I’ve never had a desire to use any type of illegal drug and have no interest in getting high. I only want to see if this can help calm my disease and anxiety.
So what am I getting myself into? I live in Ohio I don’t know if this is legal. Additionally, I’m concerned with whether or not the CBD oil would give me a positive on a drug test. Right now the disease does not allow me to have a position for a very long since if I go into a flare I end up missing so much work.
Where do I purchase CBD oil with Turmeric? How do I know I’m getting the real deal?

Here’s the before and after pics of the VSSB in my truck. Of course I replaced the solder joints with some dip switches off Amazon
View attachment 73277View attachment 73278

also thank you for your suggestion

 

[bucketoval]

I have 95 c3500 with 6.5 vssb the pin out.does not match the chart it was a 4.10 and I put.3.42 in it what should the pin be

 

[dbrannon79]

I have 95 c3500 with 6.5 vssb the pin out.does not match the chart it was a 4.10 and I put.3.42 in it what should the pin be

I don't think mine matched ether, but use the link I posted in my original post showing the chart. I ended up having to play with the switches and test driving several times using my phone's GPS as a speedometer to get it correct. look on page 2 post 32 of this thread for my post with the link and photo.