Recalibrating Speedometer

[Olds W31]

I have read thru some of the topics on this and I am wondering one thing.....Some of you who have stripped these cars out might know this....is there a seperate box (GM called it a DRAC or Digital Ratio Adapter Controller, or a Vehicle Speed Sensor (VSS) Buffer) located under the dash with the input from the VSS going to it and then output to the computer for speedometer, cruise, and antilock functions?

 

The reason I ask is that my speedo is off over 15%, and its off the wrong way. So I guess I have the FASTEST W body on the planet....unless somebody on the forum is off 20%.

 

Here is a link to an article I used to "fix" the speedo in my Suburban....any help in finding this "DRAC" or "VSS Buffer" would be appreciated.

http://www.614streets.com/drac.html

[Crazy K]

year/make/model?

 

I do not think that any W has this VSS Buffer.

 

I have seen our cars have speedo and other guage issues due to bad grounds, or damaged computers/prom chips.

 

 

tell us what you have and we'll start there.

[GnatGoSplat]

We don't have any such thing. On my Grand Prix, the speedo being off was caused by the calibration resistor in the cluster going bad. Jumping a ~1megohm resistor across the existing one in parallel fixed it.

 

[Drummer]

that happened in my Z34, all i did was unplug it and plug it back in and it went from 120 right to 0.

[Olds W31]

Sorry,

 

Year 1994

Make Olds

Model Cutlass Supreme S

Engine 3100.

 

Where is/was the resistor referred to...on the back of the instrument cluster or?

 

Thanks again.

[GnatGoSplat]

My Grand Prix is a '90 so it may be different, but the resistor is soldered to the main circuit board inside the cluster. It's a white DIP package device (looks like a chip), but it has black paint across the top of it. That is the resistor. If you look carefully, you will see a line cut into the black paint. That's how they fine-tuned the speedometer, the length of the cut determines the calibration resistance.

 

It might be different in a '94 though.

 

[Drummer]

didn't they change the cluster in 95? i thought i saw a 94 vert with the same dash as pre 95 dash, the only difference was the steering wheel cause it had an air bag.

[Drummer]

i think the 94 is realitively close to ours.

[Crazy K]

Sorry,

 

Year 1994

Make Olds

Model Cutlass Supreme S

Engine 3100.

 

Where is/was the resistor referred to...on the back of the instrument cluster or?

 

Thanks again.

EXCELLENT!!! I have the best answer... since this is the exact car I beat on mercilessly for a Daily driver.

 

I have gone 80mph at 1200 RPM.... if you were to believe the speedo and tach.

 

 

The issue in the car is a combination of loose grounds, and a loose aux post nut.

get some die-electric/silcone grease

1 make sure the aux post nut is tight. remove, clean, grease, and reinstall. Get new used or wherever, an EXTRA nut for your battery AUX post and crank it down on the first nut. (same nut as used on top of the tranny shifter post, or the grounds on the engine-to-tranny bolts)

2 remove the black plastic dash kick panel over your feet. there is a ground with several wires going to it about over the gas pedal. remove, clean, grease, and reinstall.

3 underhood, at the radiator support there are grounds. remove, clean, grease, and reinstall.

4 underhood there are engine grounds. one or two of the engine to tranny bolts on the front side of the engine/tranny have grounds. make sure those are tight.

 

report back if you still have a problem.

[Olds W31]

Thank you for the input. I will plan my Saturday accordingly, weather permitting.

If I understood one of the above posts, though, if you wanted/needed to recalibrate the speedo, say for larger/smaller tires...sounds like all you need is to solder a potentiometer to that resistor, or ohm it, put in a lower value, then do the pot trick to allow for accuracy.

 

I may be a little anal about all this, as I used to have a 9C1 caprice, and REALLY liked the "Certified" speedometer. It was good to 120 mph....well, after the mods, it was good for more than that, but that is as far as the factory would show.

[GnatGoSplat]

Actually, no, recalibrating the speedo is just to get it accurate to what the ECM is putting out on the VSS. It should always be 4000 pulses per mile.

Tire size calibration is actually in the MEMCAL (PROM).

 

[Crazy K]

If I understood one of the above posts, though, if you wanted/needed to recalibrate the speedo, say for larger/smaller tires...sounds like all you need is to solder a potentiometer to that resistor, or ohm it, put in a lower value, then do the pot trick to allow for accuracy.

 

doubtful. start with what I have said, let us know the outcome.

[Olds W31]

let us know the outcome.

 

Ok, spent about 30 minutes cleaning posts and grounds, etc. Drove the car Sunday and figured out that the issue is not linear...that is to say that only between about 40-55, is there an issue, IF it is going to happen. I am checking this against a GPS, by the way, and I can only assume it is more accurate...I have 11 satellites on a clear day

 

Anyway, it is MUCH better now....the only issue I see is getting the converter to lock up consistantly, as if the speedo is off, due to the VSS, then the computer isn't getting the right info to get the converter to lock, therefore my mileage suffers. Anybody ever do a manual converter lock on these? I have done so in my Suburban, but can tell you from experience that you can frag the clutch lining in the converter if you lock it up too early

[Venom]

Sorry,

 

Year 1994

Make Olds

Model Cutlass Supreme S

Engine 3100.

 

Where is/was the resistor referred to...on the back of the instrument cluster or?

 

Thanks again.

EXCELLENT!!! I have the best answer... since this is the exact car I beat on mercilessly for a Daily driver.

 

I have gone 80mph at 1200 RPM.... if you were to believe the speedo and tach.

 

 

The issue in the car is a combination of loose grounds, and a loose aux post nut.

get some die-electric/silcone grease

1 make sure the aux post nut is tight. remove, clean, grease, and reinstall. Get new used or wherever, an EXTRA nut for your battery AUX post and crank it down on the first nut. (same nut as used on top of the tranny shifter post, or the grounds on the engine-to-tranny bolts)

2 remove the black plastic dash kick panel over your feet. there is a ground with several wires going to it about over the gas pedal. remove, clean, grease, and reinstall.

3 underhood, at the radiator support there are grounds. remove, clean, grease, and reinstall.

4 underhood there are engine grounds. one or two of the engine to tranny bolts on the front side of the engine/tranny have grounds. make sure those are tight.

 

report back if you still have a problem.

 

I wonder if this would be the same as a 95 or should be pretty close anyways. My speedo seems to be off about 3mph right now.

[Crazy K]

always a possiblity.

 

You may wish to replace the VSS sensor, and see if that makes things more reliable. also, inspect the wiring to and from the vss too.