BRetty
Full Access Member
- Joined
- Jul 16, 2020
- Posts
- 948
- Reaction score
- 2,669
- Location
- Los Angeles
- First Name
- Franklin
- Truck Year
- 1973
- Truck Model
- c10
- Engine Size
- 350
All,
Per the title, my '73 C10 (350 sbc, th350c (but TCC not wired up)) has very recently started to vibrate severely on the highway. It seems to maybe start around 35mph, jumps up around 45 and is shaking/rattling through ~75.
It is only under throttle -- if I let off the throttle it coasts and vibration is gone, press the gas it is back. The freqency feels like RPM-driven. I have a secondary vibration also, the interference makes the sound surge and pulse. (This might actually be the 170 and 5 freeways natural bumpiness frequency.) Whatever it is, it keeps unscrewing and spinning out my air cleaner stud, all the way out.
A week or more ago, I thought I felt a low-freq thump at idle - felt like an out of balance condition, felt it while parked and also in motion. There was a distinct pulse in my exhaust I could both hear and feel at the tailpipe. That low-level thump is still faintly there, but sudden driveline vibration more pressing.
My first thought was U-joints. Sat, I took her to the shop on the corner with the U-Joints I had got months ago, but I had the wrong size. The mechanic, pretty lazy honestly, said the u-joints looked good. He suggested tires/wheels out of balance, although I don't feel it when coasting at 60. He (allegedly) checked the flywheel/TC bolt-up saw no cracks nothing alarming.
Last week I worked on carb/fuel line. I put a vacuum gauge on and it read perfect 19", rock steady. So steady it seemed suspicious. I also swapped out my alternator last week b/c voltage seemed to read low.
So reading other stores of similar vibration, I can think of these possibilities. Any input on probability of these will be appreciated.
-- Harmonic balancer
-- flywheel / torque converter interface
-- engine mounts suddenly crumped
-- transmission has shifted / trans mount
-- driveshaft may have lost a balancing weight
-- U joints are going suddenly
-- DIFFERENTIAL IS FAILING (GM 12-bolt)
-- wheels/tires/alignment/suspension (suspension needs a rebuild and all soft bits replaced, certainly)
-- misfire or preignition under load
-- timing is somehow farked.
Thanks for all the knowledge I have already gained,
BRetty
Per the title, my '73 C10 (350 sbc, th350c (but TCC not wired up)) has very recently started to vibrate severely on the highway. It seems to maybe start around 35mph, jumps up around 45 and is shaking/rattling through ~75.
It is only under throttle -- if I let off the throttle it coasts and vibration is gone, press the gas it is back. The freqency feels like RPM-driven. I have a secondary vibration also, the interference makes the sound surge and pulse. (This might actually be the 170 and 5 freeways natural bumpiness frequency.) Whatever it is, it keeps unscrewing and spinning out my air cleaner stud, all the way out.
A week or more ago, I thought I felt a low-freq thump at idle - felt like an out of balance condition, felt it while parked and also in motion. There was a distinct pulse in my exhaust I could both hear and feel at the tailpipe. That low-level thump is still faintly there, but sudden driveline vibration more pressing.
My first thought was U-joints. Sat, I took her to the shop on the corner with the U-Joints I had got months ago, but I had the wrong size. The mechanic, pretty lazy honestly, said the u-joints looked good. He suggested tires/wheels out of balance, although I don't feel it when coasting at 60. He (allegedly) checked the flywheel/TC bolt-up saw no cracks nothing alarming.
Last week I worked on carb/fuel line. I put a vacuum gauge on and it read perfect 19", rock steady. So steady it seemed suspicious. I also swapped out my alternator last week b/c voltage seemed to read low.
So reading other stores of similar vibration, I can think of these possibilities. Any input on probability of these will be appreciated.
-- Harmonic balancer
-- flywheel / torque converter interface
-- engine mounts suddenly crumped
-- transmission has shifted / trans mount
-- driveshaft may have lost a balancing weight
-- U joints are going suddenly
-- DIFFERENTIAL IS FAILING (GM 12-bolt)
-- wheels/tires/alignment/suspension (suspension needs a rebuild and all soft bits replaced, certainly)
-- misfire or preignition under load
-- timing is somehow farked.
Thanks for all the knowledge I have already gained,
BRetty