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vss to cable drivin?
- Thread starter nerraw117
- Start date
nerraw117
1/2 ton status
ok so without using a 90-91 t-case it will be extremely hard to get them to work. ok so i am listening now, i want to keep the 90 guages, so what can i do to get my speedo to work? none of them things that screw into the t-case and send somin to ecm work?
nerraw117
1/2 ton status
is the wiring harness behind the dash the same for the 87,88 and 89 as it is for the 90 and 91. if so is the computer differant? maybe i could get a 87,88 and 89 guage panal and corrosponding computer and because they are cable driven i would not have to worry about wiring up a vss to use the speedometer.
'90-91 for sure are wired differently. Dig under your dash, you'll find the opaque DRAC module somewhere if the PO put it in.
'81-89 clusters are essentially the same, trip odometer on the '87+(?) is the only difference that comes to mind quickly, and they kind of suck.
It doesn't matter whether the gauge donor was TBI or not, cruise on trucks starting about 1982, and '87-91 truck TBI used the same VSS pulse to the ECM, 2.
The only difference '90-91 is the DRAC I'm talking about converts that 40 pulse from the transfercase to what the speedometer, ECM, cruise, and ABS want to see. The '82-89 VSS on the speedometer gauge will work fine for your setup. Just need 12V, ground, and an output wire from the buffer to the ECM.
Still making sense?
'81-89 clusters are essentially the same, trip odometer on the '87+(?) is the only difference that comes to mind quickly, and they kind of suck.
It doesn't matter whether the gauge donor was TBI or not, cruise on trucks starting about 1982, and '87-91 truck TBI used the same VSS pulse to the ECM, 2.
The only difference '90-91 is the DRAC I'm talking about converts that 40 pulse from the transfercase to what the speedometer, ECM, cruise, and ABS want to see. The '82-89 VSS on the speedometer gauge will work fine for your setup. Just need 12V, ground, and an output wire from the buffer to the ECM.
Still making sense?
nerraw117
1/2 ton status
so what in the world can i do besides swap out the transfer case?
If you are dead set on the '90 cluster/speedometer, you can check out jagsthatrun.com in the VSS section for something that replaces the speedo cable output with either a 2 pulse generator, or a 40 pulse. Not sure if a 40 pulse one even exists.
There is a post on here about the DRAC that I did, that has all sorts of links and info in it. I can't recall what the speedometer needs for input, whether its 2000PPM or 4000PPM. If it's 2000PPM that the speedometer wants, I don't see why you couldn't split the output from an aftermarket 2 pulse VSS generator to the speedo and the ECM.
The electric speedometer is the only thing making this difficult, but I can see why you'd want to keep it. That's why I put one in my truck, but I did it when the '91 transfercase went in to drive it!
You can also retrofit the reluctor ring to different transfercase output shafts, (which means you run the '90-91 t-case mounted VSS sensor) that's been covered, can't recall if that article is in the tech section or not.
As well, if you browse around the VSS section on jagsthatrun, you'll notice that they make an external reluctor ring setup. I don't know as you could use it on the transfercase end, but as they show it mounted, it would last a very short while even driving in just tall grass. If it could be mounted at the t-case output, that would work ok I suspect.
There is a post on here about the DRAC that I did, that has all sorts of links and info in it. I can't recall what the speedometer needs for input, whether its 2000PPM or 4000PPM. If it's 2000PPM that the speedometer wants, I don't see why you couldn't split the output from an aftermarket 2 pulse VSS generator to the speedo and the ECM.
The electric speedometer is the only thing making this difficult, but I can see why you'd want to keep it. That's why I put one in my truck, but I did it when the '91 transfercase went in to drive it!
You can also retrofit the reluctor ring to different transfercase output shafts, (which means you run the '90-91 t-case mounted VSS sensor) that's been covered, can't recall if that article is in the tech section or not.
As well, if you browse around the VSS section on jagsthatrun, you'll notice that they make an external reluctor ring setup. I don't know as you could use it on the transfercase end, but as they show it mounted, it would last a very short while even driving in just tall grass. If it could be mounted at the t-case output, that would work ok I suspect.
nerraw117
1/2 ton status
ok well i called jags that run and they have a part # 4PRS and it sends 4 pulses square wave and he said that completely bypasses the ecm and plugs into the transfer case and i wire it to the speedo? sound like the best idea? sounds good to me
Again, 4 pulse is not what your ECM is looking for I'd bet, and you will have to do research for the speedometer input.
4 pulse is a car only thing. That means their speedometers (and ECM's) might be (and are in some circumstances) looking for different VSS signal than what the truck TBI wants.
I assume you have the 1227747 ECM in the truck, if so, I expect the VSS input is the same on the '90-91's as the '87+, which is 2000PPM.
The cable driven VSS stock is 2 pulses per speedo cable revolution, and since GM speedometer cables turn at 1000RPM (per mile) that's 2000PPM. The reluctor ring setup is 40 pulses per *output shaft revolution* which is entirely different.
Cars in some applications used 4 pulse per cable revolution, and I *believe* the box (buffer? adapter?) they used with that is similar in theory to the DRAC and is known as a "4 out" box. That's 4000PPM, which is not what your ECM wants, at least as I deduce from the data so far.
I don't have a '90-91 truck ECM, but if it too is a 1227747 like the '87-89 trucks, then you need a 2 pulse generator I'm sure. I noticed before that jagsthatrun is a little uninformed on the truck stuff, but that's understandable since the '90-91 R/V stuff is one off the C/K stuff that was out at the same time.
I can't really help much more, I'm only confusing the issue since I don't know the facts with what you are dealing with for hardware other than the cluster and the t-case, the important stuff now is the ECM. Since I don't have a '90-91 truck, I don't know the exacts.
4 pulse is a car only thing. That means their speedometers (and ECM's) might be (and are in some circumstances) looking for different VSS signal than what the truck TBI wants.
I assume you have the 1227747 ECM in the truck, if so, I expect the VSS input is the same on the '90-91's as the '87+, which is 2000PPM.
The cable driven VSS stock is 2 pulses per speedo cable revolution, and since GM speedometer cables turn at 1000RPM (per mile) that's 2000PPM. The reluctor ring setup is 40 pulses per *output shaft revolution* which is entirely different.
Cars in some applications used 4 pulse per cable revolution, and I *believe* the box (buffer? adapter?) they used with that is similar in theory to the DRAC and is known as a "4 out" box. That's 4000PPM, which is not what your ECM wants, at least as I deduce from the data so far.
I don't have a '90-91 truck ECM, but if it too is a 1227747 like the '87-89 trucks, then you need a 2 pulse generator I'm sure. I noticed before that jagsthatrun is a little uninformed on the truck stuff, but that's understandable since the '90-91 R/V stuff is one off the C/K stuff that was out at the same time.
I can't really help much more, I'm only confusing the issue since I don't know the facts with what you are dealing with for hardware other than the cluster and the t-case, the important stuff now is the ECM. Since I don't have a '90-91 truck, I don't know the exacts.
nerraw117
1/2 ton status
well like i said before it is completely by passing the ecm, so that means nothing. and well i guess you have a point about the input for the speedo. i will try and find that out. thanks appearently with the jagsthatrun guy says the ecm takes 2 pulses and the speedo requires 4 pulses so i might be good with that. i could either do that and hopefully it would work. or try and find a 87-89 wiring and ecm and guages which i really dont want to do but i might have to. what do yall think i should do? im so ****ing sick of this **** 
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nerraw117 said:or try and find a 87-89 wiring and ecm and guages which i really dont want to do but i might have to. what do yall think i should do? im so ****ing sick of this ****
It's very very easy.
Go get a 1982-ish-1989 C/K/R/V gauge cluster, with appropriate VSS buffer assembly (and a section of the wire harness that runs out of the buffer) that will be attached to it. May need a speedo cable, depends what you've got for yours. '81+ (if not earlier) speedometers use a different method to attach the cable to the speedometer. Now the cluster issue is solved, short of the cluster connector wiring. That might be interesting, the older cluster needs more wiring than the later, but that should be pretty simple, move a few wires around on the connector, splice a couple of 12V wires and grounds in, done.
Run a 12V ignition switched wire to the VSS buffer that is attached to the cluster, run a ground wire to the buffer, and find out if pin A10 on the ECM you have is where the VSS input is. Wherever VSS input is on your ECM, you run the third wire from the VSS (the output) directly to that pin on the ECM connector.
You now have a working, cable drive speedometer/VSS, and the ECM has the 2000PPM signal it's expecting.
Cost of all of this should be less than $40 as long as you can get a speedometer cable that works for a good price.
This is almost exactly what Canadianbuilder suggested, except I've broadened the breadth of vehicles you can search for components out of. It's not that difficult.
nerraw117
1/2 ton status
do yall think i should somwhow find the wiring (which wont be hard) and the guage cluster (which will be hard to find) and all the other stuff i need and try and get this working. OR go with autometer all new guages and maybe mount them like rene has them like just mount them outside to the outside plastic bezel? opinions please?
Your setup is supposed to have VSS, how do you plan on working around that?
thebigdaddyof2
1/2 ton status
Gotta give Props to Dorian for sharing knowledge and experience.
nerraw117
1/2 ton status
yea dyeager535 is a genius, thanks man. isnt the vss in the wiring? im going to pull the wiring from a 87-89 all the wiring under the dash. then hopefully find a guage cluster from a 82ish to 89.
VSS is sort of seperate in the earlier setups, since it's only 3 wires, and only one is directly linked to the ECM. On the '90-91 setups, VSS is more integrated with the wiring harness.
I really expect that pulling pre-'90 wiring harness is going to potentially make life more difficult than just retrofitting the earlier VSS. I'd *expect* but not blindly trust, that GM changed only the wires at the ECM required to make the '90+ stuff work. However, there are what, 40 some pins on the ECM? GM could easily have swapped those around, especially if they changed the ECM.
Someone that has had a later (say '87-89) gauge cluster apart can perhaps answer what the printed circuit board looks like. The '90-91 printed circuit board is much different, as most of the "common" grounds and 12V is on a single wire, quite a bit earlier, the printed circuit and wiring was a bit more complex. If the '87-89 cluster PCB is "improved" like the '90-91 (doubtful) then the re-wiring will be easier.
As far as I know, the transmission end of all speedometer cables (GM) are the same, so you will just want to grab one that is long enough and mates to the cluster you end up with.
I really expect that pulling pre-'90 wiring harness is going to potentially make life more difficult than just retrofitting the earlier VSS. I'd *expect* but not blindly trust, that GM changed only the wires at the ECM required to make the '90+ stuff work. However, there are what, 40 some pins on the ECM? GM could easily have swapped those around, especially if they changed the ECM.
Someone that has had a later (say '87-89) gauge cluster apart can perhaps answer what the printed circuit board looks like. The '90-91 printed circuit board is much different, as most of the "common" grounds and 12V is on a single wire, quite a bit earlier, the printed circuit and wiring was a bit more complex. If the '87-89 cluster PCB is "improved" like the '90-91 (doubtful) then the re-wiring will be easier.
As far as I know, the transmission end of all speedometer cables (GM) are the same, so you will just want to grab one that is long enough and mates to the cluster you end up with.
nerraw117
1/2 ton status
so then dyeager535 i have no clue what you think i should do then. i thought you wanted me to find a 87-89 wiring and guages? how would click me this not work? i do not know if i have vss now from the swap, a buffer or drac. all i know is the PO put 90 wiring in it, engine runs fine i guess, all i need to get working is my speedo. i would have thought something this small would not be so damn hard.
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Yes, the problem is you don't know what you have. 
If your truck was bone stock, I could say for certainty what you have. But since a PO installed it, and you currently have no VSS, (no cable OR VSS on t-case) I have no idea WHAT you have under the dash anymore. YOU have to be the one to find that out. If the '90 wiring is INTACT, then it has a DRAC, which REQUIRES the 40 pulse VSS setup.
An '82-89 cluster will get you a speedometer that works. Ignoring everything else I've posted, if you get a speedometer cable the right length, that mates to that speedometer, and install it in your truck (not even connecting the gauge wires back up at this point) you will have a working speedometer.
If you grab the VSS buffer that comes attached to (most of) the '82-89 trucks with that cluster, and wire it up as I said, your ECM will now know how fast your vehicle is traveling.
After that, you can worry about how to make the cluster connector work for your oil pressure, lights, etc.
The eastwood thing might work, but I'd never pay that much for a speed sensor, when a complete '82-89 cluster should be about $25.
If your truck was bone stock, I could say for certainty what you have. But since a PO installed it, and you currently have no VSS, (no cable OR VSS on t-case) I have no idea WHAT you have under the dash anymore. YOU have to be the one to find that out. If the '90 wiring is INTACT, then it has a DRAC, which REQUIRES the 40 pulse VSS setup.
An '82-89 cluster will get you a speedometer that works. Ignoring everything else I've posted, if you get a speedometer cable the right length, that mates to that speedometer, and install it in your truck (not even connecting the gauge wires back up at this point) you will have a working speedometer.
If you grab the VSS buffer that comes attached to (most of) the '82-89 trucks with that cluster, and wire it up as I said, your ECM will now know how fast your vehicle is traveling.
After that, you can worry about how to make the cluster connector work for your oil pressure, lights, etc.
The eastwood thing might work, but I'd never pay that much for a speed sensor, when a complete '82-89 cluster should be about $25.
