Trying to find the vsb (vehicle speed buffer).

[72timemachine]

Hello,

I have a 1990 GMC c2500 2 wheel drive with a 350 engine and 400th transmission. Speedometer and odometer are operating intermittently. They have a tendency to work once the truck has been driven for several miles.

I did test the vss at the tail shaft of the trans with my meter set on a/c volts to see if I was getting a pulse signal from the reluctor ring and the vss, seems to be in range when the driveshaft was rotated. The wires and connecting plug to the vss appear to look in good condition and is clean at the connecting points.

My question is, where the heck is the vsb (vehicle speed buffer module) I have been reading about? This is perhaps one of the most misunderstood topics I have read about. Seems to be a lot of misinformation or no information about the location of where it is on my year truck.

There is nothing in my dash cluster, I do not see it, even with a mirror and flashlight, behind the dash cluster and in front on the a/c ducting. It is not located left of the ecm behind the glove box or fastened on the backside of the dash left of the glove box.

Thank you ahead of time if you happen to know where this thing is hiding, burning up the internet for what it looks like and where it is seems to be a dead end.

[95 S_Trucker]

Its built into the instrument cluster on 88-90 models.

Its also referred to as the DRAC module.(digital ratio adapter controller)

91+ trucks have the DRAC separate from the cluster.

[Mr_Rich]

I have the same issue on my '89. I've mentioned it before; the speedo drops off to zero when I'm driving down the road and I hear the engine change tone since the speedo is tied in to the ECM and is in the process of going open loop. I give it the "Fonzie whack" on the face of the cluster and the speedo starts working. I've tried re-soldering micro-opens on the circuit board and that hasn't worked yet or I didn't find the right connection points. So in the meantime I use the cruder repair method.

[95 S_Trucker]

In the pm you sent me, it's part of number 15. It's
On the circuit board.

I like posting in the thread instead of a pm so other people can see the answer in the future. I would recommend posting your image here.

I was looking at some other stuff related to this at my work computer today. I will try to find it and post it this evening, but if I don't it will be tomorrow.

[95 S_Trucker]

Here's a thread with some good info:

http://67-72chevytrucks.com/vboard/s...d.php?t=313815

From the service manual:

[72timemachine]

Originally Posted by 95 S_Trucker

Here's a thread with some good info:

http://67-72chevytrucks.com/vboard/s...d.php?t=313815

From the service manual:

Attachment 1798111

Attachment 1798112

Well that explains why I was having a hard time finding it for my year truck, thank you for the information, I hope this helps others in the future.