Vibrations at 4000 rpm and up

jrod92 · Jun 7, 2007

I did a search on this but it is really unclear as to what i need to do to fix it. I just bought an 87 gt and it has solid motor mounts. could this be causing the problem?? otherwise how do i check to see if the angle of the driveshaft is too much? should i replace the transmission mount? or get the driveshaft balanced first?? thanks

BK_CAULEY · Jun 7, 2007

the solid motor mounts will deffinatly cause a harsh vibration. and i dont think you have to worry about driveshaft angle on these cars. even if they are lowered its not enough to make it bind. (like a highly lifted/lowered truck) the driveshaft could be out of balance or warped though. and i dont think transmision mounts are your problem either. most of the time if they get worn or broke there will be a loud clunk when engauged or disengauged but from my experience with them going bad hasnt caused a harsh vibration.

93tealcobra · Jun 7, 2007

I agree about the mounts

Unless you are racing a moderate HP motor, solid mounts will make the whole care twist just slightly and really aren't streetable (from my experience). I did find recently that a warped, out of balance shaft or a junk u-joint, can cause experience, or cantasrophic failure. Take the mounts and change them. Not too hard. Then listen for a clank in reverse or forward, that's a u-joint.

As for the shaft, you would have to hit something like a tall speed bump or road debris to bend the shaft.

Just my .02

Chris

jrod92 · Jun 14, 2007

Shaking even when car in neutral

The car is still shaking i noticed it even shakes when the car is in neutral and is revved. Im afraid to even take it past 3000 rpm.

93 LX · Jun 14, 2007

harmonic balancer

jrod92 · Jun 15, 2007

have i potentially hurt the engine with driving it with a bad harmonic balancer?? the engine was recently rebuilt with 700 miles on it. i have not revved it past 3000 rpms more than 5 times since the rebuild.. thanks guys

BlownFiveLiter · Jun 15, 2007

It's possible that you hurt the engine, but considering the low mileage on it, I'd hope it'd be fine as long as you put a new balancer on and change the oil + filter. The only true way to know for sure if the engine is damaged is to pull the pan and pull the main and rod bearing caps to look for excessive wear.

93 LX · Jun 15, 2007

I drove my 86 with a bad balancer a few hundred miles before figuring it out. As log as you are doing 6 grand runs over a long period of time yhou should be fine. How I figured out mine was bad was when I went to set the timing. I set it at 10 and it pinged bad. I moved it bad until it stopped pinging which caused the idle to smooth out as well and checked where it was on the balancer. Well imagine my shock when I saw the timing light the back side of the balancer. I also crawled under the car and could see that the ring was pushed right against the crank pulley. Got a new one and when I compared the 2 side by side it became obvious that my stocker was bad!

The engine has survived I assume 161000 so far and after I replaced the balancer it has nearly 1000 miles more so your engine shoud be fine.

You mentioned rebuilt engine, that would have been a good time to change the balancer. No one thinks of that unless your building a high performance engine but it is a wear part os it should be replaced too.

Good luck.

Allen

jrod92 · Jun 16, 2007

Found the problem, where the torque box is located in the rear next to the lower control arm the metal has split. the rearend has a considerable amount of play. got a torque box kit to beef it up, gonna weld the split back and install the wild rides torque box kit. thanks for all the help

93 LX · Jun 17, 2007

jrod92 said:
The car is still shaking i noticed it even shakes when the car is in neutral and is revved. Im afraid to even take it past 3000 rpm.

So how does this equate to a cracked torque box?

jrod92 · Jun 17, 2007

well i guess this is the first thing i need to fix, but also i am going to change to ES motor mounts instead of the solids, then my crank looks a little marked up so im looking for an aluminum one, hoping this will solve all vibrations. with the car on the lift and running in 2nd gear you can see the flex on the torque box. should i still keep the harmonic balancer in mind??

89five.o · Jun 18, 2007

See what trannie you have in the car. I have a tremec 3550 and it vibrates at about that rpm range. I've heard of a lot of guys with this problem.

jrod92 · Jun 22, 2007

Its a borg-warner t-5 but i guess that still doesnt solve the vibration in nuetral parked the car for now until i get the money for a new balancer goes in tuesday for the battle boxes to be welded

TenorPlayinGuy · Jun 22, 2007

Yep if its happening while in neutral you can rule out the driveshaft and anything after.

- I would check, Visually even the damper,
- Flywheel damage (missing teeth)
- Flywheel dowels missing for the pressure plate, etc

Remember even an ounce of weight can throw things off when spinning at 4k. I believe 1 oz turns into about 40 lbs difference at that speed, I can't remember

But I remember it being bad. I would for sure think it to be clutch area related.

93 LX · Jun 23, 2007

harmonic balancer.. I thought I said it somewhere in the begining! LOL

Allen

Vibrations at 4000 rpm and up

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