My 99 gmc yukon has started a shuddering or rumbling vibration when I am at 55-60 mph. As soon as I let my foot off the gas or acccelerate past 55-60mph it quits. I just had a new engine put in and the noise is still there. The shuddering is not enough to really notice if you are a passenger and not paying attention. When driving it feels like its could be coming from underneath the car. I am stumped - any ideas?
[b]GM trucks have had problems with the slip yoke on the driveshaft that goes into the transmission. But the usual complaint is that there’s a popping noise when accelerating from a stop.
What happens is the slip yoke gets dry and starts to bind. So the slip yoke isn’t able to slip back and forth to compensate for the rear axle moving up and down for road irregularities.
So, you might try removing the driveshaft and have the slip yoke lubed up with some moly disulfide grease.
Is the vibration dependent on road speed (55-60) or a particular range of engine speeds (say, 3200-3400 RPM)? You could check by driving 55-60 in a lower gear and seeing if you get the vibration. It’s possible that something is resonating at particular engine speeds or road speeds – maybe something in the exhaust was knocked loose or not properly reconnected when the new engine was put in (but you say this problem existed with the old engine too?). I’ve also heard of engine pinging (knocking) causing resonance at particular speeds, even if the original pinging wasn’t quite audible. Have you been careful to use the recommended octane gas?