This has been discussed before (the resonance/vibration from the middle of a GMT400 frame) though I can't remember the proper name for it. My C2500 Suburban had it mild at around 60-65mph - but it's got much worse and now occurs at 70mph - a useful cruise speed.
What has changed is that I rotated the tyres (as per handbook for four - spare not included) and a change of tyre pressures from 45/50psi F/R to 40/45psi F/R. I'm pretty certain it is the frame resonance thing - it is at a frequency much higher than wheel related. There's a remote chance that I got some underseal on the propshaft but I don't think I did. The vibration now is quite intrusive and I'd like to be shot of it.
Which if either of the above two changes has most likely caused the changes (in speed that it occurs and severity?
If tyre rotation - will it right itself as the tyre bed into their new positions?
If tyre pressures - is front or rear the bigger contributor? (If the fronts then I have scope to raise the pressure there but not at the rear (psi limit is 44psi on sidewall)).
All advice welcome! TIA.
What has changed is that I rotated the tyres (as per handbook for four - spare not included) and a change of tyre pressures from 45/50psi F/R to 40/45psi F/R. I'm pretty certain it is the frame resonance thing - it is at a frequency much higher than wheel related. There's a remote chance that I got some underseal on the propshaft but I don't think I did. The vibration now is quite intrusive and I'd like to be shot of it.
Which if either of the above two changes has most likely caused the changes (in speed that it occurs and severity?
If tyre rotation - will it right itself as the tyre bed into their new positions?
If tyre pressures - is front or rear the bigger contributor? (If the fronts then I have scope to raise the pressure there but not at the rear (psi limit is 44psi on sidewall)).
All advice welcome! TIA.