Who Can Answer This?

[LaDyInReD]

ok... I have 95 240sx automatic and I've been having this problem where the car vibrates (or shudders) at 1800rpms. It doesn't do it all the time but 90% of the time I'm driving it happens.. I was worried it would be the transmission ( which I just recently replaced), but when I brought it to the dealer they said my rear tires were "out of round" and I needed to replace them. What the hell does "out of round" mean?! Cuz when I asked them, they couldn't really desribe it. I brought my car back to the place I bought my tires ( by the way they are practically brand new only 4,000 miles on them!), they checked it out and said that the tires have nothing to do with the problem. And even they couldn't tell me what "out of round" means!!

Has anyone else experienced this vibration problem with their 240? Because it seems like nobody knows what's wrong with my car! I need your help!

Thanks

[rb25det 240sx]

welll i had a problem but it was with my car before i had the sr rebtop but also it was a turbo car but all i cant thinck of anything.......umm how long has it done this for???

[LaDyInReD]

about 4 months now... i know i waited a while before getting it checked out...

[mynismo]

you can try cleaning your air intake sensor. all you need is a philips head screwdriver.

the big plastic pipe going across the front of the bay... right where it ends under that and pull the black thing with the rectangular shaped thing off. just clean the inside of it (its prolly dirty). DON'T touch the lil thing inside, just wipe off the inside of the piping.

i tried to put it in the best of lamen's terms that i can

let me know if ya need help. thats prolly the prob, just a lil dirty in the air flow.

[vsiev]

I am thinking he is talking about your rotors....not really sure but found out if your rotors have any "dips" or "dents". That is might what he meant by out of round...if not, it might be the fact you have different tire size in the front and back, that is if you have it that way....had a old car that vibrated ever time i breaked because of the tires.

[LaDyInReD]

Originally Posted by vsiev

I am thinking he is talking about your rotors....not really sure but found out if your rotors have any "dips" or "dents". That is might what he meant by out of round...if not, it might be the fact you have different tire size in the front and back, that is if you have it that way....had a old car that vibrated ever time i breaked because of the tires.

yeah i know about the rotors, but the vibration doesn't happen while i'm braking... it's usually while I'm accelerating... as the rpm rises and passes 1800rpms.. thanks tho

--> someone suggested i check my motor mounts (which could be loose or cracked) and that the vibration may be the motor resonating at that rpm.. what do you think?

[LaDyInReD]

Originally Posted by mynismo

you can try cleaning your air intake sensor. all you need is a philips head screwdriver.

the big plastic pipe going across the front of the bay... right where it ends under that and pull the black thing with the rectangular shaped thing off. just clean the inside of it (its prolly dirty). DON'T touch the lil thing inside, just wipe off the inside of the piping.

i tried to put it in the best of lamen's terms that i can

let me know if ya need help. thats prolly the prob, just a lil dirty in the air flow.

Thanks, I'll try it and see if it helps

[mxd6]

Out of round tires usually happen when they are NOT rotated and balanced on a regular basis (every 7-9K). This is caused by uneven wear. With 4k on your tires this is NOT the problem.

The vibration:
1) Check to see if they (tires) were balanced correctly.
2) Alignment could be out?

These are the primary cause to have looked at first.

[vsiev]

wonder if it is an idling problem...maybe the spark plugs are cracked or something....happened to my car like it was going to die and it vibrated....it would make sense if it was the mounts, but why wouldn't it shake on higher rpms....

[zmanss]

You mention that the problem occurs around 1,800 rpms...does it occur in every gear at 1,800 or just first? If you notice the problem every time the tach passes the 1,800 rpm line, you are not dealing with a tire problem. Having an unbalanced or "out of round" tire would be apparant through certain vehicle speeds, not engine speeds.

Is the whole car vibrating or do you notice it through just the steering wheel? Also, are there any noises that become apparant during the vibrations?

[LaDyInReD]

hi, thanks for all your help!

1) I just had all four tires balanced last week when i brought my car back in to the tire shop and told them the problem; and they were aligned when i bought the tires last july, so I agree that the tires are NOT the problem

2) I also just got a tune-up last week so the spark plugs are brand new now, however i still feel the vibration

3) Yes, it occurs when it passes 1800rpms while I'm accelerating, but i have an automatic so i guess it's only on first gear? Also, it doesnt happen EVERY time it passes 1800, i don't know what makes it vibrate at certain times, but it IS always at 1800..

As far as the vibration, I would say that i can feel it through the whole car, and for any sounds, all i hear is the vibration sound. If I could describe how it feels, it's like the kind of vibration you feel when you drive on those small reflective bumps on the road.. or like running over a wire laid across the road. It only lasts like 2 secs..

My boyfriend also suggests that maybe there is a problem with the differential... Would that cause something like this?

Again, thanks for all your help, I'm trying my best to describe this whole situation to you guys.. I really appreciate it!

[civicsedannonvtec]

maybe the tranny
maybe the previous owner was launching the car which is a big no no for an AT.... though usually that just affects the shifting not just a particular area in the powerband....

[RWD Maniac]

out of round is self explanitory to my understanding, basically what they are saying is the wheel is not round... haha dents and nicks on a disc brake would be lateral runout if i am not wrong...

i would put money on your transmission, like most people said..

the reason why the dealer mentioned out of round is because they probably believe that you meant wheel tramping which is because of an unbalanced tire...

[mrflip69]

Hey so it only shakes at 1800 in first? So at a certain speed it always does that?.... You might want to try having your rotors inspected. Stock rotors on a 240sx are notorious for being shitty and warping under little stress. If resurfacing exceeds the cost of replacing, get some new aftermarket rotors so you don't have to deal with that again... If it's not the rotors, try the bushings too. My car use to vibrate exactly around 75mph and 35mph and it turned out to be cracked bushings in the front suspension. Good luck

[1viadrft]

It's not the Tranny, boys... the car does not have a problem accelerating, right?

Motor-Mounts or Trans mounts... that's the prob.