What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

LS-Swap VSS Headache

S

skinnytones

Registered Member
Joined
Mar 31, 2025
Posts
8
Reaction score
2
Location
ontario
Hello!

This is my first post on this forum. ive been working on my 1987 GMC Jimmy full-size i did an ls swap about 3 years ago and i got it woking good enough to drive but because of the redneckery that i had to do to get the VSS (vehicle speed sensor) to work it sometimes stutters trans and/o drops to first gear as the VSS signal drops out. Ive attached some pictures of what i did to get this to work. I ended up JB-Welding a vss into a whole drilled in the extension housing between the 4l60E and the t-case alltho its been so long now i cant even remember what it is i think its a NP-208 whatever was factory on the 87 Jimmy. what im getting at is does anyone know of a better way to get this hooked up? i would like to keep my speedo cable for my factoy cluster speedo and i just want this shifting problem to be fixed. it works perfectly but when watching the live data on a scan tool the VSS signal drops off randomly as its not perfectly square which makes it think to go to first gear which is a little scary at like 60KM/h

Any help would be greatly appreciated :)

( BEFORE I GET ROASTED THE VSS IS NOT THAT FAR AWAY THAT WAS JUST SITTING THERE FOR REFRENCE IT IS ALMOST TOUCHING THE GEAR )



484496826_464544020073491_1962836334306601096_n.png
485087722_2421869528162518_6020266406558032635_n.png

336630685_3087061314922302_6608916488121548702_n.jpg


^ this is the rig love her to bits!!
 
Is your vss wiring twisted? If not that could be issue.

Twisting wires is a common practice in electrical wiring to reduce noise and interference, and this principle applies to VSS wiring as well. It helps to ensure that the signal from the VSS is clear and reliable, which is crucial for functions like speedometers and cruise control systems.
 
You could change direction and go with an external encoder. I'm not sure this is the right pulse count, but it's an idea: https://jagsthatrun.com/products/speed-sensor-4pac

1743508815753.png

Theoretically, what you have could work. What holds the sensor in place? Make sure that you route both wires from the sensor all the way to both pins on the PCM without sharing a ground connection. As stated already, twisting is better. If the sensor is too far from the ring, the problems are normally worse at low speed. The VR creates higher amplitudes as the rising/falling edges are faster. So dropping out at high speed implies interference or that something causes the sensor alignment to change.
 
I cant believe how much help I've gotten just overnight I've tried other forums and had no success thank you everyone for all your input so far!! makes me so happy there's a community out there that wants to help :)) i will have to check the wiring as i cant remember if i have it twisted or not that'll be step number 1 i suppose. as for the mounting of the sensor i just basically hogged a hole with a die grinder and jb welded the sensor into the hole. i do have another housing i can try to re install a sensor but the problem is the gear is so far from this sensor that the sensor basically has to be "countersunk" into the housing in order to be close enough to the gear, hence why i had to jb weld it in and not able to thread in. i would love to be able to find a sensor that would send the right style signal that was longer or even a full thread one like they use on big rigs but i havent been able to find a sensor that would put out the right ppm and sine wave style signal....

This is what i mean by a full threaded big rig wss
07-071010_2__53012.1682470271.jpg
 
Blue85 said:
You could change direction and go with an external encoder. I'm not sure this is the right pulse count, but it's an idea: https://jagsthatrun.com/products/speed-sensor-4pac

View attachment 501063

Theoretically, what you have could work. What holds the sensor in place? Make sure that you route both wires from the sensor all the way to both pins on the PCM without sharing a ground connection. As stated already, twisting is better. If the sensor is too far from the ring, the problems are normally worse at low speed. The VR creates higher amplitudes as the rising/falling edges are faster. So dropping out at high speed implies interference or that something causes the sensor alignment to change.
Click to expand...
the sensor is held in place with JB weld into the casing. this was a temporary fix to be able to get it driving which has worked but i want to fix it for good now. i will definitely check and if not i will twist the wires. i do know for sure that the wires go right to pcm as i dont use it for anything else on truck other then the trans shifting.

as for that link on jags that run i tried a similar one off amazon and it did nothing but it may have had the wrong output im not sure this was before i learned how complex this stuff is haha. the only problem i see with that one is that it shows 4000 ppm and i thought i read somewhere that these LS motors require a "high frequency" something like 128k ppm but that might be wrong also im not sure. i would love a setup like that one though because then i wouldnt have a problem withmy speedo cable for my dash also which i dont really want to pay to change to a new digital style.
 
The 4 bolt dide is the 4l60 side and the t case is a 6 bolt round in that linked kit. ORD has lots of good square body stuff, browse around the sight.
 
Wes Harden said:
The 4 bolt dide is the 4l60 side and the t case is a 6 bolt round in that linked kit. ORD has lots of good square body stuff, browse around the sight.
Click to expand...
On the newer transmissions with the removable bell housing they went to a 6 bolt on the trans as well. I think the "K series" case has the 4 which is for the 97 down.
 
skinnytones said:
i can try to re install a sensor but the problem is the gear is so far from this sensor that the sensor basically has to be "countersunk" into the housing in order to be close enough to the gear, hence why i had to jb weld it in and not able to thread in. i would love to be able to find a sensor that would send the right style signal that was longer or even a full thread one like they use on big rigs but i havent been able to find a sensor that would put out the right ppm and sine wave style signal....
Click to expand...
This may not be as hard as you think (but of course I haven't thought about it as hard as you :whistle: ), but "sine wave style" is usually just a misnomer for "variable reluctance", to separate it from "square waves" that come from active sensors like hall effect or reed relays. It's really just a coil of wire on a magnet, so every time an iron edge passes by, a voltage is induced in the coil.

1743528805040.png

As the wheel speeds up, the spikes get closer together and larger in amplitude. The PCM has a circuit designed to filter these and just count the distance between the zero crossings. This is why it's important to keep both legs of the sensor off of ground. The point is, VR sensors are available in all shapes and sizes. The PPM is strictly determined by the tooth count of your wheel (plus final drive ratio and tire size, but you get the idea).

Best-case would be some kind of bung welded on that lets you adjust the gap between sensor and wheel and then hold it with a jam nut or similar.

Notice that neither wire should be connected to ground:
1743529304050.png
If you have 2 dedicated wires, twisted the whole length and it still looks like interference, shielded cable (STP) would be an option, but it's normally only required if you route this wire near the ignition system or something else generating a lot of electrical noise.
 
Blue85 said:
This may not be as hard as you think (but of course I haven't thought about it as hard as you :whistle: ), but "sine wave style" is usually just a misnomer for "variable reluctance", to separate it from "square waves" that come from active sensors like hall effect or reed relays. It's really just a coil of wire on a magnet, so every time an iron edge passes by, a voltage is induced in the coil.

View attachment 501080

As the wheel speeds up, the spikes get closer together and larger in amplitude. The PCM has a circuit designed to filter these and just count the distance between the zero crossings. This is why it's important to keep both legs of the sensor off of ground. The point is, VR sensors are available in all shapes and sizes. The PPM is strictly determined by the tooth count of your wheel (plus final drive ratio and tire size, but you get the idea).

Best-case would be some kind of bung welded on that lets you adjust the gap between sensor and wheel and then hold it with a jam nut or similar.

Notice that neither wire should be connected to ground:
View attachment 501081
If you have 2 dedicated wires, twisted the whole length and it still looks like interference, shielded cable (STP) would be an option, but it's normally only required if you route this wire near the ignition system or something else generating a lot of electrical noise.
Click to expand...
Thank you for helping me with some clarification on this.

So yea i just need to find a sensor that's a non-hall effect style switch and kinda long and preferably threaded to be able to reach my tone ring better and twist my wires
 
Fastereddie said:

Variable Reluctance (VR) Sensors - ATEX & IECEx Certified Explosion-Proof Sensors | Magnetic Sensors Corp.

Magnetic Sensors manufactures long-lasting standard & custom variable reluctance & ATEX-certified explosion-proof sensors. Rely on our experience—request a quote now!
www.magsensors.com www.magsensors.com
Click to expand...
Oh mannnn that looks perfect!!! so i already have the 40 tooth tone ring wedled onto my trans output shaft so if i were to use this sensor you think it would work? meaning it would put out the correct data?
 
skinnytones said:
Oh mannnn that looks perfect!!! so i already have the 40 tooth tone ring wedled onto my trans output shaft so if i were to use this sensor you think it would work? meaning it would put out the correct data?
Click to expand...

I found this one on amazon that i think should work on the same theory as the one you sent, nice thing about amazon is if it doesnt ill just return it haha. i will try this in the upcoming weeks and see if it works and let you know.

Thanks for your help!!
 
You must log in or register to reply here.

Latest Posts

Top Bottom