'95 3500 HD speedometer

[scott_1553]

Ok, I just want to say thanks in advance for any feedback because I am stuck!! I have a Chevy 3500 HD that I have turned into a nice dump truck. I bought it used with 160,000 miles and changed the utility bed into a dump bed. The 6.5L deisel was taken out and rebuilt. It runs strong and starts right up..
This is my issue. The speedometer only will read up to 50mph. I took it to the lovely local Chevy dealer for the $80 computer analysis of what the issue may be. They concluded that the instrument cluster was bad and needed to be sent out for repair. I pulled it out and off it went. $250+ it came back looking nice and clean. I popped it back in and off I went. Go figure, it is doing the exact samething! Back to the dealership I went. I was told that because they did not do the work, there was nothing they could do about it. They are now saying the fix will be to replace the speed buffer. They described it as the computer part that links all the speed sensors together.
I did some research into it and this is my question... I know that the ABS sensor on the passenger side front wheel is bad. I repalaced the brakes and noticed that the wires have corroded off the sensor. I called a local Delco parts deaer and they told me that the speed sensor and the ABS sensor is all the same unit. If the ABS sensor is bad, will it affect the speedometer? I would rather spend the $262 to fix the ABS sensor and solve my issues then spend who knows how much on the buffer and still not fix it!