Who has felt a rumble in the rear?

[jray3]

My car developed a faint drivetrain rumble around 20k miles when I tried on lowering springs, which resulted in a 4 degree angle on the axles, and the experiment was quickly ended with a return to stock springs, but the rumble has gradually worsened, now at 59k miles. The Norwegian member with a black car who also tried the H&R lowering springs experienced this problem as well, but is no longer active on the forum. PV1 says he feels it too, and IIRC, he's never lowered his car.

The rumble becomes noticeable under heavy acceleration and full regen around 35 MPH, and now mine is stronger at around 60 mph, while previously it 'smoothed out' at higher speed. On my car it is noticeable with or without a heavy load. Of course it's still less vibration than most any gas car, so both i-MiEV certified technicians that have evaluated the car claim they can't feel it after making miniscule adjustments to the tire balance. BS! :roll:

I think this is an issue of the CV joints being unsuitable for the suspension angles that our car is capable of. I've run much more extreme angles on aircooled Volkswagens with the IRS suspension and no problems (dune buggies, anyone?). The car should be able to run on the bump stops without the CVs being the weakest link... shouldn't it? Likewise, the CV joints are primarily affected by torque and axle angles, not like wheel bearings, shocks, or suspension joints. Even if the car was pulling against a stump at full throttle, the CV should not be the weakest link. An electronic component should shut off or cut back due to thermal overload long before a mechanical driveline component fails if the drivetrain is only receiving stock power levels. We ain't drag racing here.

Maybe I'll cruise by the Sonic tonight and ask some kid in a lowered Honda Civic with his hat on backwards......

 

[Aerowhatt]

It doesn't seem surprising to me to see "premature" CV joint wear on these cars. If you think about it they get significantly more (and more dramatic) torque changes (if you will) than any ICE. The regen does most of the job of the brakes. If you are in stop and go traffic torque goes from high forward to high reverse and vice versa, relentlessly. Conversely, a CV joint on machinery with a constant (reasonable) torque load in a single direction will wear much longer than one would expect.

Similarly, the various electric motorcycles that I have more than a decade of experience with. Those with strong regen wore out belt drive components more than twice as fast as those without regen. Unless there is something special about the iMiEV CV joints, it's likely not the angles causing the issues.

The description of "rumble" certainly is consistent with wearing CV joints IME.

Aerowhatt

 

[mdbuilder]

Sounds like a good theory to me

 

[mdbuilder]

BTW, hasn't Tesla had problems with differentials? Similar issue I would think.

 

[jray3]

It doesn't seem surprising to me to see "premature" CV joint wear on these cars. If you think about it they get significantly more (and more dramatic) torque changes (if you will) than any ICE. .......
The description of "rumble" certainly is consistent with wearing CV joints IME.

Aerowhatt

Thanks Aerowhatt,
I'll buy that theory, especially as one who drives hard in B mode in hilly country EVery day, so if the CVs are seeing twice as many torque peaks as an automatic gasser, you could think of their effective mileage as being near 120,000 miles, but I'm inclined to think the torque cycles are more like 4x or 5x those on an automatic gasser! Under this logic, JoeS oughtta be feeling the rumble too, but I dunno if any of his i's have accrued enough miles.

Whatta ya know, Joe?

I'll also inspect the boots for tears or grease escaping. Moisture is a killer of cv joints, and though MR BEAN has never forded a stream, he spends about 9 months of each year soaking wet!

 

[JoeS]

I would agree with Aerowhatt that our CV joints are subjected to greater repetitive stresses than an ordinary car - not only that, but isn't our torque higher than a kei car's? My perspective is that the CV joints experience least stress when they are perfectly aligned and that the stresses on some of the load-bearing components rise inordinately the further off-center the drivetrain goes.

Ever since we got our second and third i-MiEV, we've stopped racking up the miles on our original Mitsi - it is now only at 47K miles and is quiet, as are the other two.

Perhaps CV longevity might be enhanced by driving around in Eco and not leadfootin'? Easy on the battery and easy on the CV joints. In our case, it averages out - my wife is very gentle with the car whereas I enjoy its sprightliness.

jray3, just turn up the radio volume and you won't hear the rumble... :roll:

 

[siai47]

A "rumble" sound seems more like it would be tire noise or a wheel bearing. However, application of power or regeneration might change it a little but even when coasting at the speed you hear it under load or acceleration it would still be there when coasting. If the CV joint boots look intact and there isn't any obvious noise (like clicking) if you rotate each tire while up on a jack I would lean away from the CV joints. When you have the car on a jack and the suspension is in full rebound this should be the maximum angle the CV joint sees and the angle where you might hear something. If it was my car, I would start looking at the reduction gear. Check the oil level and even if OK I would drain the oil and inspect it for anything metallic in the bottom of the drain pan. I would refill the gear with new oil and then recheck if there is any change in the noise you are hearing. Even though the gears and bearings in the reduction gear are robust something could be going on and loading and unloading gears and bearings could be a cause of the noise you are hearing. Just a thought.

 

[justind]

I have noticed this too. But for me it's when accelerating with alot of weight in the trunk( few hundred pounds) or 4 passengers. The extra weight is to the driveline like lowering the springs. Based on this and your (jray) "spring-lowering" test I don't think the car can handle too much variation in driveline angles. This is just a theory but there is a chance that it isn't your cv joints yet but the springs are a little weaker so the car is running lower in the back. I don't know how to test this though.

 

[Aerowhatt]

I have noticed this too. But for me it's when accelerating with alot of weight in the trunk( few hundred pounds) or 4 passengers. The extra weight is to the driveline like lowering the springs. Based on this and your (jray) "spring-lowering" test I don't think the car can handle too much variation in driveline angles. This is just a theory but there is a chance that it isn't your cv joints yet but the springs are a little weaker so the car is running lower in the back. I don't know how to test this though.

If it were shaft angles I should have trouble by now too.

http://myimiev.com/forum/viewtopic.php?f=9&t=1428&hilit=workhorse&start=80

Aerowhatt