Relays
for your 1986 GMC C3500
The purpose of the relays housed with trans components-automatic is to transmit and intercept data from the transmission and its components to the ECM of the GMC C3500. If the relays aren't processing the information clearly and the sensors are off, your transmission may lock into certain gears or start slipping out position.
If there are problems with the transmission, you GMC C3500 might show it several ways. You may have trouble downshifting in your vehicle, or it may not shift at all when the transmission should. You might hear grinding noises, and you may feel the car shudder when the transitioning between gears. Check StockWiseAuto.com for replacement parts.