Vibration & lack of power on acceleration - help troubleshooting

vibration
maserati
quattroporte

#1

I just bought a used 1980 Quattroporte III in good shape, with a documented history of extensive maintenance and restoration. It’s a 4.9l V8, rear wheel drive 4 door sedan.



However there are two things that bother me, firstly there is a huge amount of vibration (almost like the car/engine find a resonant frequency) at approx 2400rpm in third (top) gear (this is an automatic with a Chrysler Torqueflight 727 tranny). I don’t notice it in first or second gears at the same rpm, so my best guess is that it’s not the transmission, but maybe one or more unbalanced wheels. The documentation indicates that the motor, propshaft and diff have all been rebuilt/replaced and balanced, otherwise I would suspect something there. Any other suggestions as to what might be causing excessive vibration at certain speeds? Am I correct in starting at the wheels?



The second issue is when accelerating in 3rd gear. The jump from 1st to 2nd feels a bit hard, like the car lurches, but it seems to accelerate fine. When in 3rd however, if I hit the accelerator the engine revs but the car doesn’t feel like it’s moving at all. 60-90 seconds later it slowly catches up to the engine, or so it seems. From what I’ve seen of other models, the car should fly at those speeds/gears. I don’t think the transmission has been rebuilt, and although they are said to be bulletproof, I’m sure at some point something inside there will wear out. Does this sound like a typical transmission problem?



At this point I’d love hearing any further tests I can do in order to pinpoint the problem and have it fixed.



Thanks!


#2

Your vibration involves RPM and not speed. Speed usually is the common demoninator for worn or under-inflated tires. RPM vibration indicates a problem with the transmission or axles.


#3

I’d say that you do have a transmission problem.


#4

Thanks for the replies!

I’ll have the transmission checked out asap.