GNX VDO speedo reads wrong speed

[viper8ol]

I have one of the aftermarket GNX type gauge clusters. For some reason the speedo has started display about 20% higher. The Odometer is reading correctly. The rear end gear is the stock 3:42 and the speedo gears in the tranny are still the stock ones. Nothing has changed with the gears but for some reason the speed reads higher now. But the mileage odometer is reading correct. Does anyone know how this VDO Speedo works is it electrical or mechanical? Any suggestions to trouble shoot?

 

[pacecarta]

the speedo is mecanical , the odometer is gear driven so no room for error if trans gears are correct and cable spins but the speedo head is a mechanical magnetic watch spring style like the stock gn speedo and they can go out of calibration

my 160 vdo cockpit read way high when i swapped to a th400 (had to use a .60 reducer) so i redid the speedo gears in trans and its still reading like yours , id say im atleast 15% off


i checked around and there are some repair places for porche gauges (they used VDO speedo) but for what they want going to a new VDO speedo would be a better option

 

[viper8ol]

Sounds like we have the same VDO speedo. My speedo is also a 160 with a tripodometer. From what you are saying it sounds like my Speedo went out of calibration. It was working fine for a long time and with not changes started to read high. So I guess it sound like I am going to replace the VDO speedo. I assume that the cables are all good being that my odometer works great. Did you ever fix yours or replace it?

 

[pacecarta]

nope , its on "the list" but not near the top

btw if you are still using a scanmaster the MPH reading on it should be accurate since the reading is from the ECM based off the in cable mounted vss pickup under the hood by the wiper motor

 

[viper8ol]

Sorry to sound stupid. But what is the scanmaster? I do have the connection under the hood that you talk about. My car is running A OK! It is just reading the wrong speed.
I just purchase this 86 GN about a month ago. I had a 87 GN back in 88 and was mad at myself for selling it.

 

[RI-Matt]

Viper8ol,
Unfortunately I don't think VDO makes the mechanical ones anymore
so sorry to say, if your speedo is the mechanical one you have two choices:

1. Send it out to be fixed. You can keep your mileage intact.

OR

2. Replace with an VDO electric speedo and either send it out to have it programmed with your mileage or start over.

A few guys have used a place out in California "North Hollywood Speedo" or something ???

Matt

 

[viper8ol]

Thanks Ri-Matt for the info.
I will try to contact North Hollywood Speedo.

 

[viper8ol]

Good News, Bad News The good news is the VDO speedometer can be fixed. If the odometer reads right and the speed is reading fast it can be fixed. This VDO Mechanical Speedometer is no longer sold be VDO. But North Hollywood Speedometer (North Hollywood Speedometer and Clock Company. Serving your gauge needs since 1955. VDO, Porsche, Mercedes, BMW, Volkswagen, Veigel, Veglia) has the part and can fix them. Now the bad news is that it will cost about $150. I spoke to Kevin at North Hollywood.

 

[pacecarta]

yeah i thought i mentiioned that in my first post

the new vdo with electronic odometer is cheaper than the repair

i never measure mine to see if its 3 3/8 or 3 1/8

$113 new 3 3/8 160mph VDO cockpit speedometer at summit

VDO Gauges 437053 - VDO Cockpit Series Speedometers - Overview - SummitRacing.com

and they still sell a 3 1/8 120mph at same price that the face design better matches the old one and the 8k tach but the 120 would be pinned alot for me
http://www.summitracing.com/parts/VDO-437050/ ,

 

[viper8ol]

Pacecarta, You are the right the new electronic VDO speedometer are cheaper. The only problem I have with them is that the location of the trip reset button is in a different location. The location does not agree with the clear cover over the gauges I currently have. Since I do not want to create a new cover I am going to either repair my speedo or find a used one. Thanks so much for your help and infomation.