[RESOLVED] Vibration under acceleration from 3000 to 3500 rpm

[phill]

I drive a 1998 Eclipse RS, nonturbo 420A. Recently under acceleration my whole car shakes, enough to shake the rearview mirror off. The harder i accelerate the more violent the shaking is. It only shakes from the rpm range of 3000 to 3500 rpm, no matter what gear. I do not know if this is an engine, transmission, or suspension problem. Help would be greatly appreciated.

-Phill

 

[dsmulla]

There a lot of reasons the car could shake. Are your tires inflated properly? If the car is lowered has their been an alignment done? Have you checked your motor mounts? Also I don't have much experience with 420A motors and whether they have balance shafts or not? If they do has there been a timming belt job done recently as the B.S could not be timed properly.

Osman

 

[phill]

Motor mounts are all good I just bought them maybe a month ago. Alignment is good, brand new tires too. The shaking was still there before I bought new tires. My suspension is all stock. And yes I have balance shafts, how would I go about checking if they are in correct timing?

 

[Defiant]

And yes I have balance shafts, how would I go about checking if they are in correct timing?

Have you, now. Well, we may be on to something here.

 

[jeking]

countless post like this have lead to balance belts being installed incorrectly, give it a good look, it certanly fixed my vibration problem.

 

[TunaTalon]

With the balance shafts out of phase the engine will shake left and right as well as up and down which we consider "normal". When the harmonic imbalance frequency matches the natural frequency of your car's chassis/suspension the vibrations will be amplified.

See page 41 of http://www.kidzuku.com/StrokeOrNot.pdf. For more details.

 

[phill]

Well the left side of the motor doesn't shake. Only under the transmission mount is where is shakes. If you put a little pressure on the clutch pedal you feel the pedal shaking too. I checked the mount and it's good, so is the transmission mount braket as well. this is what is confusing me. i thought it might be an axle or something along those lines or in the actual transmission.

 

[phill]

Ok after reading only the 4g63 and the V6 have balance shafts. So that rules out the balance shaft out of timing. Anybody else, any ideas?

 

[TunaTalon]

Ok after reading only the 4g63 and the V6 have balance shafts. So that rules out the balance shaft out of timing. Anybody else, any ideas?

Your logic eludes me. If balance shafts phasing is ruled out because the 4G63 is the only in line four with balance shafts then does the long list of other similar fours in the Wikipedia article http://en.wikipedia.org/wiki/Balance_shaft rule them back in?


laserspeeddemon beat this dead horse to a pulp in this thread:
http://www.dsmtuners.com/forums/showthread.php?t=256735&highlight=balance+shaft+phase+rpm

Also see these two of the many similar threads.
http://www.dsmtuners.com/forums/showthread.php?t=243086&highlight=balance+rpm+vibrate

http://www.dsmtuners.com/forums/showthread.php?t=171747&highlight=balance+rpm+vibrate

 

[phill]

No other inline fours have them but the 420A, which I have, doesn't

 

[TunaTalon]

Sorry your logic is fine; I just misunderstood the phrasing, and was thrown off by:

And yes I have balance shafts, how would I go about checking if they are in correct timing?

FWIW 3500RPM is pretty close to the third harmonic of the natural frequency of your chassis.

 

[Defiant]

Aw, damn. Cat's outta the bag.

Check the motor and transmission mounts, and the axles for integrity.

 

[iziegsx]

Ok, check your driveshaft just a heads up my car did the same thing and i found out my driveshaft was damaged. Eventually is will get worst. Wont hurt to check

 

[peypey's ride]

It only shakes from the rpm range of 3000 to 3500 rpm, no matter what gear.

-Phill

If your only feeling it from the drivers side(tranmission on driverside), I would check your wheel bearing on that side. What you described is exactly the same problem I had 2 yrs ago on my passenger side(transmission side).I had no BS on my motor and new urethan mounts. After checking every possible thing I could think of sure enough it was a bad wheel bearing.

Try jacking up that one side of your car, then grab your tire at the 9 and 3 o'clock postions and try to lightly move it in and out. try the same at 12 and 6 0'clock too. Try not to turn the wheel or spin the tire. If you feel some play or maybe a lil shifting then I would replace. If you have any doubts check it aginst the other side to see if that side has the same amount if any play.

 

[phill]

The transmission mount is just fine, I checked again because I had to replace a shift linkage clip this morning so i figured why not. What am I looking for in the axle? This is my first car so I'm not 100% sure

 

[Defiant]

Ok, check your driveshaft just a heads up my car did the same thing and i found out my driveshaft was damaged. Eventually is will get worst. Wont hurt to check

He probably doesn't have any more driveshaft than he did balance shafts in his mighty 420A stallion.

But yeah, if you find one, check it.

Phill, with your inexperience, it sounds like you'll be ahead to pay a shop to find the vibration for you.

 

[GST with PSI]

Ok, check your driveshaft just a heads up my car did the same thing and i found out my driveshaft was damaged. Eventually is will get worst. Wont hurt to check

Yep....can only get worst . You bought new tires but how about new rims? How about dynamic wheel imbalance? Bent rim+new or old tire= car with Parkinson's. Rotate your tires and see if that make a difference.

 

[TunaTalon]

Yep....can only get worst . You bought new tires but how about new rims? How about dynamic wheel imbalance? Bent rim+new or old tire= car with Parkinson's. Rotate your tires and see if that make a difference.

Out of balance tires or out of round wheels will have a sympathetic vibrations at a constant MPH not RPM. The vibrations will be pronounced at the same speed in any gear. As I understood the OP the vibrations were at a given RPM in any gear.

A slightly damaged wheel in my Talon causes a noticeable vibration at about 90MPH.
With a less stiff chassis the speed would be lower.

If indeed the vibration is at a constant RPM in any gear then the problem must be before the transmission.

 

[EclipseGSX012]

try putting it on neutral and rev up to 3000-3500 and if the car shake you know it's engine related, about the tire balance part i had that problem before while i was doing 60 and up. so try neutral rev up and if it still shake you have engine related problem.

 

[GST with PSI]

Out of balance tires or out of round wheels will have a sympathetic vibrations at a constant MPH not RPM. The vibrations will be pronounced at the same speed in any gear. As I understood the OP the vibrations were at a given RPM in any gear.

A slightly damaged wheel in my Talon causes a noticeable vibration at about 90MPH.
With a less stiff chassis the speed would be lower.

If indeed the vibration is at a constant RPM in any gear then the problem must be before the transmission.

I stand corrected; failed to read the original post clearly.

 

[phill]

I think I discovered the culprit. A cracked transmission mount bracket. I just bought a new one, when it gets here I'll throw it in and see if the shaking goes away.

and would anybody know a trick to keep the shift linkage clips from falling out? It's really getting annoying having to replace them.

 

[peypey's ride]

Thought you said you checked the tranny mounts??? Its all good, glad to hear you found the problem!

 

[phill]

Well I checked the mounts...but it didn't occur to me to check the brackets too haha

 

[phill]

Phill, with your inexperience, it sounds like you'll be ahead to pay a shop to find the vibration for you.

Now how am I supposed to get experienced if I have somebody else do all the work for me?

The vibration is still there too guys

 

[Defiant]

Are you looking at this as a career path? It's a five-year apprenticeship. Since you've "found" the cause, but now it's "still there", cut your losses. There's not much more we can do by email.