Hey, I have suddenly developed an extreme driveline vibration in my 86 GN. Everything was perfect when I parked it in my shop last weekend. I say driveline because of no engine vibration while in park and vibration is not engine RPM related. It literally feels like it is going to shake the car apart starting at 50 mph (3.42 gears 26” tall tires).
I always go back to what has changed since I last drove it. The one thing that I did was I welded in a GNX crossbrace behind rear seat but I don’t see how that would cause vibration to start.
So...to make a long story short it seems the vibration is at 50+mph and only under load (no vibration on my lift or with rearend tubes on jack stands) Is there a chance that my lock-up torque converter has suddenly developed an issue? What makes it even stranger is that if I drive it up to 50 mph holding it in second gear the vibration is present. If I understand the design correctly, the TCC shouldn’t be able to lock in second gear. I’m thinking it’s TC shudder, but I may be way off.
My car mods:
BRF trans with the re-stalled “orange stripe” converter
stage-rite trans brake.
All stock internals on the 8.5 rear.
Stock long block
Bison built TE-60
CAS V4 SLIC
TT 5.7 alky chip
60 lb injectors
Julio’s ALKYCONTROL single nozzle kit.
Bailey 2-step, scanmaster-G, and powerlogger w/WB, fuel pressure, and boost as Aux inputs.
stock location control arm mounts
Lower control arms are UMI tubular. Uppers are stock.
rear sway bar with the linkage to the frame (HR style)
QA1 rear adjustable shocks
Poly body mounts including GNX bushing (been installed for a while)
GNX rear seat brace
Things I have checked:
I changed all 4 wheels/tires to a known good spare set and no change.
Doesn’t seem to be RPM related. It starts at 50 mph whether I’m in 2nd, 3rd, or 4th
I didn’t sling a weight off stock driveshaft and the u-joints appear (centered etc) and feel in good condition (no slack or squeaking).
I ran it at the same MPH on my lift and I can’t feel the vibration; however if I run it up to 65 mph I can feel it, just not as severe as when driving.
The rear wheels don’t appear to have any runout while running on the lift (attempting to rule out a bent axle).
I always go back to what has changed since I last drove it. The one thing that I did was I welded in a GNX crossbrace behind rear seat but I don’t see how that would cause vibration to start.
So...to make a long story short it seems the vibration is at 50+mph and only under load (no vibration on my lift or with rearend tubes on jack stands) Is there a chance that my lock-up torque converter has suddenly developed an issue? What makes it even stranger is that if I drive it up to 50 mph holding it in second gear the vibration is present. If I understand the design correctly, the TCC shouldn’t be able to lock in second gear. I’m thinking it’s TC shudder, but I may be way off.
My car mods:
BRF trans with the re-stalled “orange stripe” converter
stage-rite trans brake.
All stock internals on the 8.5 rear.
Stock long block
Bison built TE-60
CAS V4 SLIC
TT 5.7 alky chip
60 lb injectors
Julio’s ALKYCONTROL single nozzle kit.
Bailey 2-step, scanmaster-G, and powerlogger w/WB, fuel pressure, and boost as Aux inputs.
stock location control arm mounts
Lower control arms are UMI tubular. Uppers are stock.
rear sway bar with the linkage to the frame (HR style)
QA1 rear adjustable shocks
Poly body mounts including GNX bushing (been installed for a while)
GNX rear seat brace
Things I have checked:
I changed all 4 wheels/tires to a known good spare set and no change.
Doesn’t seem to be RPM related. It starts at 50 mph whether I’m in 2nd, 3rd, or 4th
I didn’t sling a weight off stock driveshaft and the u-joints appear (centered etc) and feel in good condition (no slack or squeaking).
I ran it at the same MPH on my lift and I can’t feel the vibration; however if I run it up to 65 mph I can feel it, just not as severe as when driving.
The rear wheels don’t appear to have any runout while running on the lift (attempting to rule out a bent axle).
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