1996 GMC Suburban C2500

Tiny
DUALLYDAVE
  • MEMBER
  • 1996 GMC SUBURBAN
  • 7.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
I have a rumble, but when I hit 55 mph, it gets very noticeable.
Its not felt in the steering wheel. It doesn't matter if I'm coasting, excellerating or put the tranny in natural. Its still there and doesn't seem to change for better or worst except at the 55 mph mark.
I have new tires. Replaced the Joints. Serviced the tranny. And inspected the rear end then installed new oil with limited slip additive.
Any ideas on what is causing this?
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Saturday, April 12th, 2014 AT 11:41 AM

3 Replies

Tiny
CARADIODOC
  • EXPERT
I can offer two suggestions that may provide some clues. First, GM trucks have a natural drone in the drive line, but this can be aggravated by changes in ride height. That changes the drive shaft angle. Raised vehicles have a whole bunch of new problems, but if the truck is at the original height, sagged springs will reduce the drive shaft angle which can intensify the normal drone. You will usually notice a change in the sound and feel when the truck goes up and down over bumps in the road.

For noises with locations that are hard to identify, there is a tool called the "Chassis Ear". It's a set of six microphones, a switch box, and headphones. You clip the microphones to suspect parts, then drive around while switching between them and listening in the head phones. Be aware that many mechanics have never heard of this tool. Suspension and alignment specialists use it to find squeaks and rattles.
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Monday, April 14th, 2014 AT 10:39 AM
Tiny
DUALLYDAVE
  • MEMBER
I know of the tool you are talking about.

I recently had my driveshaft balanced. Apparently there was a carbon fiber wrap which is missing. I also replaced the bushing and seal in the tailshaft housing. The rumble is still there but not as bad.

Does someone make shims or wedges to put in the spring hungers to adjust pinion angle?

Thanks for your help
Dave
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Monday, April 28th, 2014 AT 3:24 PM
Tiny
CARADIODOC
  • EXPERT
Yes, there are inserts made for adjusting the pinion angle with leaf springs, but if you can't find them at an auto parts store, I only know to look at an alignment specialty shop. They will also have the tool for measuring the angle of the drive shaft to the pinion gear.
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Monday, April 28th, 2014 AT 3:58 PM

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