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1970 Datsun 240Z — vibration under acceleration but not while coasting

ShopHunterCommunity StarterMay 3, 20261970 Datsun 240ZBaltimore
The car is smooth at the same road speed when I lift off, but under moderate acceleration I can feel a vibration through the floor. What would you inspect first to separate axle/driveline issues from an engine mount? Mileage is about 24,000.
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11 replies

BatteryDriverCommunity StarterCommunity StarterMay 3, 2026permalink
Intermittent stuff lies if you only catch it once. Loaded-suspension checks on the 1970 Datsun 240Z catch play that a wheels-hanging inspection misses. Don't erase codes until someone who can help has seen them. On “vibration under acceleration but not while coasting,” that was the fork that mattered for me. This is from a 1970 Datsun 240Z in Baltimore. If they can't show the line item, I assume it's hiding. If your situation is the opposite, ignore me. Happens in gear, not in park, for what that's worth.
CamberOwnerCommunity StarterCommunity StarterMay 4, 2026permalink
I wouldn't throw parts yet. Two 1970 Datsun 240Zs can feel identical and have different causes, so measure before you copy someone else's repair. Save the big job until that test fails. Happy to compare notes if your setup is different. This is the version I'd tell a friend.
WeekendPilot706Community StarterCommunity StarterMay 4, 2026permalink
This is usually cheaper to test than to guess. Two 1970 Datsun 240Zs can feel identical and have different causes, so measure before you copy someone else's repair. Don't erase codes until someone who can help has seen them. Time, temperature, and whether it's in gear are the notes that actually help a shop. This is me being the wet blanket on purpose.
ShopHunterCommunity StarterCommunity StarterMay 4, 2026permalink
Checked the easy stuff on the 1970 Datsun 240Z and found one clue worth chasing before I book a shop. No warning lights, which is why I'm documenting it.
HybridLearnerCommunity StarterCommunity StarterMay 4, 2026permalink
Intermittent stuff lies if you only catch it once. Swap the cheap/easy piece first on the 1970 Datsun 240Z and see if the fault moves. You'll know quickly if you're on the wrong tree. On “vibration under acceleration but not while coasting,” that was the fork that mattered for me. A shop burned me once by skipping that step. If your situation is the opposite, ignore me. Heat soak after errands is the other window.
BatteryDriverCommunity StarterCommunity StarterMay 4, 2026permalink
Start with the test that can prove you wrong. Get a real battery/charging test on the 1970 Datsun 240Z, not just resting voltage, before blaming a module. You'll know quickly if you're on the wrong tree. Verbal 'we'll take care of it' is not a plan. I've seen both outcomes, which is why I'd test instead of assume. If that fails I'll eat the diagnostic fee.
BoostCamper418Community StarterCommunity StarterMay 4, 2026permalink
Fair point. Counterpoint: Capture voltage while the 1970 Datsun 240Z is actually failing — after it restarts you've lost the clue. Don't erase codes until someone who can help has seen them. Run the total, not the monthly, before you commit. That's coming from doing this as an owner, not a shop. I'd rather pay for diagnosis than a second guess-repair.
HybridLearnerCommunity StarterCommunity StarterMay 5, 2026permalink
I hear you, though I'd still want a second check. If a shop can't duplicate it on the 1970 Datsun 240Z, bring a video plus freeze-frame data, not just a story. You'll know quickly if you're on the wrong tree. Had a similar mess a couple years ago and that's what finally sorted it. I'd rather look cautious in this thread than stuck later.
ShopHunterCommunity StarterCommunity StarterMay 6, 2026permalink
OP update: scanned the 1970 Datsun 240Z again and still only have the one pending code, no new lights. Trying not to diagnose from the couch.
ShopHunterCommunity StarterCommunity StarterMay 5, 2026permalink
Cleared nothing. I want service to see the alert on the 1970 Datsun 240Z first. I'm keeping receipts and dates in one folder.
TrackEnthusiastCommunity StarterCommunity StarterMay 6, 2026permalink
Fair point. Counterpoint: A pressure test beats staring at a dry driveway if the 1970 Datsun 240Z is losing coolant with no puddle. Don't erase codes until someone who can help has seen them. Learned this the expensive way on a previous car. Doing the boring step first on purpose.
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