Bouncing VDO Speedometer ??? ***VIDEO***

[yullose]

I'm working on a buddy's GN...

I just connected a Casper's VSS signal conversion module to send VSS signal to ECM and a tach module to run the cruise control.
Electrically, that end of things seems fine. The Scanmaster is showing accurate and stable MPH, but the speedometer is bouncing up and down.

This is a VDO electrical speedometer, not cable-driven mechanical.

I already lubed the upper speedo cable, but not the lower yet.

Is it possible for a sticky cable to make the speedo jump, but yet the scanmaster and ECM see stable MPH ??? That's what confuses me... If the cable is making the speedo bouncy, why not the ECM signal too ???

 

[The_Six]

I hope you can figure it out I have the same trouble and can’t figure it out. Here is the post made about my car I have taken the dash out and reinstalled it and it made no difference. http://www.turbobuick.com/forums/ge...917-anyone-running-electronic-vdo-speedo.html

 

[TurboDave]

If the cable were the problem you wouldn't have a stable signal to the ECM (which feeds the scanmaster).

I'm guessing there's an issue with a faulty speedo, or connection between speedo and VSS.

The problem obviously lies somewhere BEYOND where the ECM receives its signal from.

 

[TurboBob]

the ecm 'filters' the speedo signal quite a lot. so its hard to say if the ecm signal is bouncy also.

one idea is to run the speedo pulser right at the transmission instead of in the middle of the cable.

what part number pulser are you running?

Bob

 

[yullose]

I think it's the cable after all...

I ran it again on the jackstands... At 60mph the speedo is rock-steady and the scanmaster shows the same.

Lower mph it gets bouncy.

I pulled the cable off at the transmission and tried to pull the core out, but it appears to be a sealed cable. The end in the engine compartment is a female end with no core showing, so I figured it must come out at the trans end.
I guess it's not servicable.

The cable feels a little tight if I turn it by hand... so I suggested to the owner that he buy a new lower cable and replace the entire thing. The symptoms seem to indicate a bad cable, so I'm going with that theory.

Bob... not sure what part number it is... as there were no numbers on it. It was already on the car when it got here.
From what I understand, it's a VDO 16-pulse dead head unit.

The fact that it smooths out at higher MPH makes me think it's got to be a bad speedo cable. Stock clusters will do the same thing apparently.

 

[The_Six]

Thats the same thing mine does bounces all over until around 60 65 and then it stops. I hope the cable idea works I may try it too.

 

[yullose]

Here's another video @ 60MPH...

 

[yullose]

You know... I was just thinking.

I wonder if it would be OK to mount the VDO VSS sender right off the transmission and eliminate the speedo cable completely ???

I guess my only concern would be a reduction in signal strength running through 6ft of wire... Either that, or it would work perfectly, since there would be zero cable flex involved and it would run directly off the gear in the trans.

The sender I have here looks like it would work in that application, as it has a 7/8 female nut and a little 1" stub of drive cable coming out of it.

Dammit... if I try that... it means I 'gotta open-up the dash cluster again...

 

[yullose]

Here's what the sender looks like...

 

[yullose]

the ecm 'filters' the speedo signal quite a lot. so its hard to say if the ecm signal is bouncy also.
one idea is to run the speedo pulser right at the transmission instead of in the middle of the cable.
Bob

Bob, you pegged it.

I moved the sender down to the trans and extended the wires to the speedo.

She's perfect now.

Initially I had a problem... in that it showed no signal at all. Turns out it wasn't an electrical problem, but instead, the short stub of cable wasn't long enough to engage the speedo gear.
I pulled the speedo gear adapter out of the trans and spent an hour with it and the sender on the workbench. All it needed was a short plastic sleeve as a spacer between the brass collar crimped on the cable, and the sender. It was just enough to do the trick... so it's all good now.

Here's a pic and video...

 

[Bruce Urie]

This is the thing I just love about this forum...group of fellas working together, analyzing the problem, throw out suggestions, follow through those suggestions, and Bingo!...the problem has been solved. Great group arriving at the solution. What a great group here!!! I'm honored just to TYPE on this site!:tongue:

Now, Bob, how much are you going to charge him for the correct solution you suggested?

Bruce '87 Grand National

 

[yullose]

This is the thing I just love about this forum...group of fellas working together, analyzing the problem, throw out suggestions, follow through those suggestions, and Bingo!...the problem has been solved. Great group arriving at the solution. What a great group here!!! I'm honored just to TYPE on this site!:tongue:

Now, Bob, how much are you going to charge him for the correct solution you suggested?

Bruce '87 Grand National

Now don't go giving him ALL the credit... I was already kicking around the idea... he just gave me enough of a nudge to actually follow through with it.

I also don't want to keep distracting him with these posts... he needs to stay busy developing that new 2-step gizmo. I need one of those pretty bad.

 

[The_Six]

Sweet now I have to get the engine back in to see if im haveing the same trouble I may pm you on this later my cruz doesnt work ther so I think Im going to start over and see if i can get it all to work.

 

[yullose]

Sweet now I have to get the engine back in to see if im haveing the same trouble I may pm you on this later my cruz doesnt work ther so I think Im going to start over and see if i can get it all to work.

It really wasn't that bad...

The best way to do it is to mount the sender on the trans to eliminate the cables. MAKE SURE you have positive engagement between the sender and the speedo gear. That was a setback for me... as I was looking for an electrical problem. It was a simple fix, but one that could have been avoided if I had known to look for it.

You will need the Caspers conversion module to convert the VDO 16-pulse signal to a 2-pulse signal. For the cruise to work, you will need a "tach" module also. (This would be #2 if you already run one for a VDO tach.)
Ignore the "Tach Module" name... it's needed to run the cruise control.

When you unplug the factory VSS buffer (little green box) you will see a white plug with 3 wires and a black plug with one wire.
The brown wire in the white plug goes directly to the A10 terminal on the ECM and gets connected to the signal output from the conversion module. The wire in the black plug goes to the cruise module and gets connected to the signal output from the tach module.
Both the signal converter and tach module each get 12V+ switched, a ground, and a signal (in) wire from the VSS sender. The only outputs from them are the brown wire from the signal converter (going to A10) and the yellow wire from the tach module (going to the cruise module).

I wiretied the two modules together and made a harness to keep it clean and the wires color coordinated.

Here's a couple pics:

 

[The_Six]

Thanks Ill have to get the Caspers conversion module and a 2nd tach module.

 

[yullose]

Thanks Ill have to get the Caspers conversion module and a 2nd tach module.

Don't forget to buy a bunch of wire too.

You'll need:
red (12V+)
black (ground)
brown (output to ECM)
yellow (output to cruise module)
white (VSS signal)

I also highly recommend soldering and heat-shrinking all your connections and terminals.

 

[The_Six]

Maybe I should get every thing together and bring you the car for an hour. So how often are you in Mooresville.

 

[yullose]

Maybe I should get every thing together and bring you the car for an hour. So how often are you in Mooresville.

It will take more than an hour... I'm pretty sure of that.
I spend alot of time on petty details like soldering, heatshrink, wire routing, cable ties, etc... I also spend alot of time being careful with someone else's car. I cover seats, floor mats, fenders, steering column, etc... anything I might lean against or scratch. When I'm done, the snibbles get vacuum'd up, and any fingerprints wiped off.

I've probably got 6-10hrs of labor just in wiring on this car... not including the time spent troubleshooting the VSS/speedo gear engagement problem... along with several other things I did to his car...
Luckily he wasn't in any hurry to get it back... because almost always, there are unforseen problems and setbacks.


I'm in my home town of Reading, PA right now... and get to Mooresville whenever I need to interview for a job. I was working on a Nascar team until being laid off in January... so I still have friends, family and contacts down there.
Eventually I will stay wherever I can find work and make money.

 

[aschulz261]

Interestingly, my car was originally a digital dash car that I put one of the ATR dashboards into. ATR attached the sending unit for the VDO to the transmission in that application. I don't know if the analog dash cars were installed that way though. Mine has been hooked up this way since 1988 with the only problem being where the little stub won't engage the speedo gear very well. I just shimmed it some and it has been fine ever since.

 

[yullose]

the only problem being where the little stub won't engage the speedo gear very well. I just shimmed it some and it has been fine ever since.

That's exactly the trouble I had when I moved it down to the trans. All it took was a little shimming and that squared it away.