[pggto]

Originally Posted by HWYSTR455

Does it go away when you put it in N and coast?

.

I haven't tried that, but I will.Thanks

[HWYSTR455]

Originally Posted by pggto

I haven't tried that, but I will.Thanks

If you put it in N and it doesn't vibrate, it's before the trans. If it does, it's after the trans or chassis related.

Another thing to check is to rev it to the 2600-2800 RPM while parked, see if it vibrates. That will also tell you if it's engine or chassis related.

Usually, if it's RPM related, it's engine related, if it's speed related, it's a chassis issue.

I've seen people have pulleys and fans out of balance that they kept swapping for config to config, car to car, and it followed them.

.

[pggto]

Originally Posted by HWYSTR455

If you put it in N and it doesn't vibrate, it's before the trans. If it does, it's after the trans or chassis related.

Another thing to check is to rev it to the 2600-2800 RPM while parked, see if it vibrates. That will also tell you if it's engine or chassis related.

Usually, if it's RPM related, it's engine related, if it's speed related, it's a chassis issue.

I've seen people have pulleys and fans out of balance that they kept swapping for config to config, car to car, and it followed them.

.

New engine has new balancer, water pump, ps pump, and alt. I was just playing with the timing up to 3000 rpm and it runs smooth while setting the timing. But i did transfer over the pulleys, they were bead blasted and repainted, and look to run true on the engine, but I give them a closer look while running. Thanks

[HWYSTR455]

I had a vibration issue with the LeMans once, and it ended up being the yoke on the rear, the 'nubs' that center the u-joint caps were worn, and the u-joint would shift making it 'wobble'. It took a very close visual inspection to catch that.

Keith - What's the source of that diagnosis chart, etc? I'd like to have a copy on hand...

.

[Keith Seymore]

Originally Posted by HWYSTR455

Keith - What's the source of that diagnosis chart, etc? I'd like to have a copy on hand...

.

Looks like some things got packed away during my last office move; I believe it is from a Chevy S/T truck service manual.

I also have a (very interesting) Pontiac Vibration manual from the mid 60's but am hesitant to post that in case there are copyright issues.

K

[2002Z4CSS]

Since the vibration got worse after the new engine was installed, how good is the engine and trans mounts? Sounds like one may be grounding out or the exhaust is grounding out.

[pggto]

Originally Posted by 2002Z4CSS

Since the vibration got worse after the new engine was installed, how good is the engine and trans mounts? Sounds like one may be grounding out or the exhaust is grounding out.

The mounts are new, I put in the polyurethane motor mounts from Bulter and the trans mount was replaced a few years ago and is still in good shape. This vibration is definitely rotational due to the harmonics that I feel. I was an auto mechanic for 10 years and have fixed my share of vibrations, but this one has me stumped.

Maybe the reason its worse now with the new engine is because of the stiffer motor mounts, but that still doesn't explain the cause.

[Keith Seymore]

pggto -

Did you do this yet?

Originally Posted by HWYSTR455

If you put it in N and it doesn't vibrate, it's before the trans. If it does, it's after the trans or chassis related.

Another thing to check is to rev it to the 2600-2800 RPM while parked, see if it vibrates. That will also tell you if it's engine or chassis related.

Usually, if it's RPM related, it's engine related, if it's speed related, it's a chassis issue.

You've really got to "split the dictionary" to know where to start.

This first step will eliminate half the car, so you know you don't have to worry about that part of it and can begin homing in on where you need to focus.

K

[goatwgn]

Is the tranny crossmember bent in any way? Another thing to check is how close your engine sits to the engine crossmember. (Does the fan come real close to hitting the bottom of the shroud?) Sometimes (especially on cars that have been drove hard or have a lot of miles) the engine crossmember tends to "spread out" ever so slightly, letting the engine sag and throwing off the pinion angles. Just something else to check. Still comes back to the basic pinion angle deal.

[Nicks67GTO]

Heres a question for you vibration guys since we are on the topic. Could it be a slightly bent pulley? I have a bad vibration that comes in after 2500 RPM and gets much worse with vehicle speed but its never present before 2500rpm in any gear and it only shows up strong in 3rd 4th and 5th.....I think I have a crank pulley that has a small bend in the outer portion of the ring from when I put in in a tire to haul it. Its not messing with the fan belt but the bend is obvious. Im going to tap it back in place tomorrow and report back. I guess im thinking out loud since we are on the topic.

[HWYSTR455]

Originally Posted by Nicks67GTO

Heres a question for you vibration guys since we are on the topic. Could it be a slightly bent pulley? I have a bad vibration that comes in after 2500 RPM and gets much worse with vehicle speed but its never present before 2500rpm in any gear and it only shows up strong in 3rd 4th and 5th.....I think I have a crank pulley that has a small bend in the outer portion of the ring from when I put in in a tire to haul it. Its not messing with the fan belt but the bend is obvious. Im going to tap it back in place tomorrow and report back. I guess im thinking out loud since we are on the topic.

Nah, since it's gear related, my guess it's behind the trans. Do you have a spare slip yoke? If so, pull the shaft, slide the spare in, and see if it wiggles. First guess there is the tail housing bushing/bearing is bad.

With the car on the ground, how much remaining 'slip' area on the yoke is showing? Same question when it's on jack stands and the suspension is drooping?

When the shaft is out at this point, take a close up of the rear yoke and post it. Also, grab the rear yoke and wiggle it. A pinion bearing is also a possibility.

.

[Bobalong]

Originally Posted by goatwgn

Is the tranny crossmember bent in any way? Another thing to check is how close your engine sits to the engine crossmember. (Does the fan come real close to hitting the bottom of the shroud?) Sometimes (especially on cars that have been drove hard or have a lot of miles) the engine crossmember tends to "spread out" ever so slightly, letting the engine sag and throwing off the pinion angles. Just something else to check. Still comes back to the basic pinion angle deal.

--------------------------------------------------------------------------------------
Really ? I had to shim my engine mounts up slightly to get the fan to quit rubbing the bottom of the shroud. I tried everything trying to determine why after all these years it started rubbing. Shimming fixed the problem, but I never knew the cause.

[HWYSTR455]

Originally Posted by Bobalong

--------------------------------------------------------------------------------------
Really ? I had to shim my engine mounts up slightly to get the fan to quit rubbing the bottom of the shroud. I tried everything trying to determine why after all these years it started rubbing. Shimming fixed the problem, but I never knew the cause.

Are you sure you got the right engine mounts? Did this start after changing the engine mounts? Frame spread is somewhat common, but it takes a lot of like 'general lee' jumps and stuff to spread it that much. You can take measurements from the chassis service manual that will tell you if in fact it's frame spread.

Trans mounts too, seen where the wrong trans mount causes issues.

And now of course you need to verify your pinion angles.

.

[goatwgn]

Originally Posted by Bobalong

--------------------------------------------------------------------------------------
Really ? I had to shim my engine mounts up slightly to get the fan to quit rubbing the bottom of the shroud. I tried everything trying to determine why after all these years it started rubbing. Shimming fixed the problem, but I never knew the cause.

There is another thread here from about a year ago addressing this issue. A PY member actually manufactured spacers to put under the motor mount brackets. I purchased some myself but havent installed them yet. I corrected my problem (Milodon oil pan rubbing the crossmember) with modified motor mounts before I saw these spacers. I intend to install them the next time I need mounts. I only had to jack mine up about 1/4 of an inch at the mount. Made a bigger difference overall than you may realize. I beleive in my case it was due to high mileage. (395,000). Plus some hard driving. Your vibration is likely a combination of different things, but it is something to address.

[HWYSTR455]

I'm on engine # 8 in the driver, and get about 100k+ out of each, and if you look at my crossmember, and the current headers on the car, you would agree that I don't baby that thing. So don't think miles has much to do with it.

I'm not convinced it's frame spread some are experiencing, because it takes a considerable amount to show up like that. It would more show in an alignment than in shroud or oil pan clearnace.

On the shroud, my first thoughts would be the core support bushings are worn, and the bolts were tightened. That would raise the core support up to 1.5 inches or more, and cause shroud clearance issues.

Pan to crossmember clearance, my first thoughts would be due to the engine mounts. I've seen such variations in mounts that cause all kinds of problems, wrong part (box/part swap), poor manufacturing, and incorrect application (cross reference wrong). Think about it, if it spread that much, don't you think it would show up in an alignment? Those front upper control arm mounts would have to move like more than an inch, and that would need like a stack of shims to get right.

Second thought would be trans mount is too high, wrong app again. And that would show up as a vibration, since it would whack out the pinion angles.

Original Poster - Guess we're all still waiting for you to complete the diagnosis as suggested, before we can continue. Have you isolated the area the vibration is coming from yet?

.