VIBRATION AT 50 MPH,1200-1500RPM

VIBRATION AT 50 MPH,1200-1500RPM - 10/24/08 09:45 PM

71 Barracuda, stroker sb/727/8-3/4

Got a vibration going on that occurs with trans(727)in neutral or drive. Vibration feels like it's coming from the convertor/trans/exhaust. I had the car up on the rack and nothing is rubbing, loose, obviously vibrating.

In the past 2 months I've replaced the convertor with a new ring gear(checked the torque on the bolts...tight), replaced the stock ignition with a used MSD(great upgrade).

I'm at my witts end with this. When I replaced the convertor I changed fluid....I've talked to many convertor and trans shops and they are saying it is not a convertor balancing problem....

Could the harmonic balancer cause a vibration at a specific RPM only...it's an original peice on this stroker motor from a 71 340.....

Thanks!

dougcataline@cox.net
405-596-6513

Posted By: BradH

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/24/08 09:53 PM

Sorry, but your title made me laugh... Both my cars have 4.10 gears and turn about 3500 RPM at 65 MPH. My Challenger runs a biggish cam for a street car and IDLES at 1200+ RPM. I simply can't imagine either one of mine loafing down the highway at such a low RPM w/o falling on their faces from being so far under the torque curve.

Posted By: 71STROKERFISH

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 01:44 AM

yeah, I remember the 3.91 days in a BB Roadrunner I had....I could hear the years being shaved off the rings when I loped down the interstate:)

I'm running a 2.76:1 and I'm actually guestimating the RPM because I'm not running a tach....it may be closer to 1800ish. I know it's not much off idle(850)maybe closer to 1400 and definitely at 50 MPH..

any other ideas out there??

Posted By: MoparforLife

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 01:50 AM

Have disassembled and check the u/joints? Take the drive shaft out of the rear yoke and turn it 1/2 turn and put back in and try it and see if it changes any. Check tire and wheel balance.

Posted By: 71STROKERFISH

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 02:00 AM

The vibration is originating from the trans tunnel area, felt from the inside of the car. This vibration occurs in neutral and engine RPM reaches 1200-1800ish. I do also see it at 50mph, but I'm guessing its not the u-joints since this vibration occurs both at the curb and on the road. I won't rule this out though..

Posted By: Alaskan_TA

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 02:05 AM

There is a factory Technical Service Bulletin on "Vibration diagnosis procedure", it is 20 pages long, very thorough.

Go to this link;

http://www.hamtramck-historical.com/1974-Dodge-TSB-Index.shtml

Then drop down to Chapter 25, it is the fourth one down in this chapter. Click on each page number to read that page.

Barry

Posted By: 71STROKERFISH

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 02:14 AM

WOW that's a ton of very useful info I've never had access to....man! Thanks!!

Posted By: MoparforLife

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 02:16 AM

Sorry I missed the Neutral part. Sounds like a balance problem. did you have the engine balanced internally and put on a weighted or B&M flexplate. Or did it get balanced for standard cast shaft balance and you didn't use the weighted plate or damper. (Don't know exactly what you have so throwing things out at you)

Posted By: 71STROKERFISH

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 03:01 AM

I guess I left all the info out. The engine has been up and running for 5+yrs. Crank was internally balanced HD cast stroker crank. No problems until a recent 150 mile roadtrip. I started to feel the vibration once I depart the interstate....hasn't stopped since. As I mentioned above, the convertor needed a new ring gear because I unfortunately forgot to install the left engine dowel that aligns the trans belhousing. This unfortunate forgotten piece which I never notice was missing lead to a failed flexplate and the misalignment of the starter=starter grinding the flywheel.

I had a new gear welded onto the convertor, balanced etc. The convertor was a very high end piece from a convertor shop in Jax, Fl.

After speaking to them and other shops, seems I should be looking at other places for my problems.

Posted By: dmerc

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/25/08 12:52 PM

I had the same kind of problem and it turned out to be an out of balanced radiator fan, take your fan belts off and see if the vibration goes away. If it does, the problem is the fan blade, water pump or alternator. Something that the belts are driving. It's also possible to have an out of balance harmonic balancer but not likely.

Posted By: 71STROKERFISH

Re: VIBRATION AT 50 MPH,1200-1500RPM - 10/27/08 01:50 AM

Well, sounds like I've got something else to look at now.

Got the car outta the garage today, and did the following:

Loosened belhousing boltls, started the engine: still had the vibration

Loosened the transmount bolts, started the engine: still had the vibration

Swapped out the ignition coil: still had vibration

I put the timing light on it and had a closer look at the vibration RPM....it's more like 1900ish in park, neutral, in drive(power braking), on acceleration, and at 50MPH.

I guess I'm going crazy here, but I plan to yank the fan and belts off next....what a headache!

Thanks for the info so far folks!!!

--71STROKERFISH

Posted By: Exit1965

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 12:40 AM

Any update on this fish?? I have a very similar vibration at 1900 RPM, mine does not go away when I take the belt off. :|

Posted By: Triple Threat

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 02:01 AM

Engine, Trans, flexplate or converter. If it will do it in neutral its obviously not anything from the trans back.

Posted By: Quikshft

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 03:28 AM

Don't laugh, but it simply sounds like a bad transmission mount. You've done so much trying to chase this down, try removing the mount and see if the rubber has degraded. When it fails it allows a metal to metal contact which will create a harmonic at certain rpm levels, regardless whether the car is at cruise speed or sitting at the curb in neutral.

Posted By: Wagonmaster

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 04:58 AM

Quote:

Don't laugh, but it simply sounds like a bad transmission mount. You've done so much trying to chase this down, try removing the mount and see if the rubber has degraded. When it fails it allows a metal to metal contact which will create a harmonic at certain rpm levels, regardless whether the car is at cruise speed or sitting at the curb in neutral.

I chased a vibration in the same RPM range for a couple years in mine. Had the carrier replaced, u-joints, shaft balanced, balancer. Turned out to be an UNBROKEN, yet old and hard trans mount.

Posted By: RapidRobert

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 05:17 AM

I'm afraid to suggest it but I would pull the pan & see if any weight is laying in the pan/shake the rods & see if anything feels/looks amiss.

Posted By: Jwilli500

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 05:45 AM

Hey Doug. Just a thought but I've heard of the outer ring rotating on the hub on a factory style harmonic balancer causing some issues. Might be something to look at, Take care bud!
Jack

Posted By: Exit1965

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 01:19 PM

Quote:

Quote:

Don't laugh, but it simply sounds like a bad transmission mount. You've done so much trying to chase this down, try removing the mount and see if the rubber has degraded. When it fails it allows a metal to metal contact which will create a harmonic at certain rpm levels, regardless whether the car is at cruise speed or sitting at the curb in neutral.

I chased a vibration in the same RPM range for a couple years in mine. Had the carrier replaced, u-joints, shaft balanced, balancer. Turned out to be an UNBROKEN, yet old and hard trans mount.

I don't know about the original thread maker, but I am going to replace my trans mount today.

I'm using the red poly one, and I've done more searching and found that other people have the same symptoms with that stinking mount -- a pulsing vibration. I have a stock NAPA replacement I'm going to throw in there and will post back the results.

Posted By: CYACOP

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 02:53 PM

I replaced my tailshaft bushing and it made a world of difference.

Posted By: Exit1965

Re: VIBRATION AT 50 MPH,1200-1500RPM - 01/11/09 11:49 PM

I replaced the Energy Suspension red poly trans mount with a new stocker, and that seemed to fix the vibration.

I was hyper sensitive to vibrations when I took for a test drive and had it up to where it pulse-vibrated most noticeably (around 2200 RPM in 3rd) and it no longer does that. I think I am still feeling small "normal" vibrations of having a torque strap, but the pulsing vibration is gone.