Harmonic pulsation / Vibration?????????

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ken5124

ken5124

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Need your help guys.. at 1700 or so rpm My 318 feels like it has a harmonic "rolling" pulsation. If i increase rpm's or decrease them it goes away... Does not matter what gear I am in..

My engine was professionally built,mild cam, edelbrock 600( I think, it's the small one) thunder avs carb, hooker long tube headers 2 1/2 inch pipes to the bumper H pipe, Magnaflow xl mufflers.

Have replaced Harmonic Damper, torque convertor.. Wheels/tires and driveshaft just balanced.. new spark plug wires.

Timing is 16 initial , 34 total.. Occurs with Vacuum advance connected or not connected. Vacuum advance is on ported vacuum.

Runs strong and smooth under acceleration.

Is this just something I have to live with?? Anyone else experience the same situation?

I am thinking of changing out the distributor or spending more time with rotor phasing??

Help!!!!
 
Can you also feel it while in park? If yes, that would eliminate drive shaft, rearend, tires, wheels, etc..........

Any chance the exhaust is touching somewhere?
 
Did it just start that? or been there the whole time, If just started, check the mounts
 
You could maybe check your driveshaf for the balance weight?It may have fallen off without you knowing?U-joints?Just trying to pinpoint.:clock:Oops just reread,sorry.
 
motor mounts... When I had my golf car shop, I had 2 main parts suppliers for a certain motor mount. They both looked identical but, one had a lot harder rubber, the thing would shake and vibrate something fierce... other vendor's mounts, no issues. After a couple golf cars like that, I only bought mounts from the one vendor! I"d go get a pair of regular black motor rubber mounts and try that.
 
69B-Cuda said:
motor mounts... When I had my golf car shop, I had 2 main parts suppliers for a certain motor mount. They both looked identical but, one had a lot harder rubber, the thing would shake and vibrate something fierce... other vendor's mounts, no issues. After a couple golf cars like that, I only bought mounts from the one vendor! I"d go get a pair of regular black motor rubber mounts and try that.
Click to expand...

Thanks, Will put that on my list to try
 
my personal experience with any old mopar I've ever driven in - they all (almost all) do it. that seat of the pants vibration that oscillates whether you're driving, sitting in park and varying engine rpm's, etc. that kind of feels like bad u-joints.
Because my AAR does the same thing (and i'm sick of that cheap, vibrating, resonating that never goes away) I've asked the same question on other forums - and it's usually a brainstorming session of engine mounts, tranny mounts, tailshaft bushings, driveshafts out of balance, the need to change to an aluminum driveshaft, correct torque converter, etc. discussion that never ends in a concrete answer.
I've just accepted the fact that mopars have that quirk. Not sure why, maybe the R&D didn't do their NVH homework.
 
kielbasa said:
my personal experience with any old mopar I've ever driven in - they all (almost all) do it. that seat of the pants vibration that oscillates whether you're driving, sitting in park and varying engine rpm's, etc. that kind of feels like bad u-joints.
Because my AAR does the same thing (and i'm sick of that cheap, vibrating, resonating that never goes away) I've asked the same question on other forums - and it's usually a brainstorming session of engine mounts, tranny mounts, tailshaft bushings, driveshafts out of balance, the need to change to an aluminum driveshaft, correct torque converter, etc. discussion that never ends in a concrete answer.
I've just accepted the fact that mopars have that quirk. Not sure why, maybe the R&D didn't do their NVH homework.
Click to expand...

I appreciate that... I am doing probably what you already did, trying to make sure there is nothing else I can try or afford to try.. before I just accept it for what it is..
 
So, from your answers the vibration is present whether the car is moving or parked and only at 1700 RPM. When does it disappear, 1600 and lower and 1800 and higher. Also is there a vibration, maybe a little lower in strength at 3400 RPM.
 
..............I know this sounds weird, but i had a ford with a vibration while cruising, changed u joints helped some...........changed 2 the factory ford joints, problem solved.............kim..........
 
It's the exhaust. dynomax flowmaster etc = rythmic vibe at certain rpm.
The crossover h pipe helps and an x pipe would be even better but, really, Dr Gas has the answer. Call them and talk to them after reading the info on their site.
http://www.spintechmufflers.com/
 
I have a similar vibe myself...almost a carbon copy of what the OP said.

It was REALLY bad with the stock torque convertor....I went to a higher stall convertor (2400) and it was radically reduced but I still have "some" ...

Now, I have a magnaflow exhaust with an X pipe and I still have it, so the X pipe wont guarantee a cure I dont think....but worth a try I guess.
 
I know it has been asked but I can't find the reply.

Does it do this only when driving? Does it do the it when holding the engine at that RPM with the car parked?
 
I had the same noise in my AAR cuda. I went for a ride in another one and it made the same noise. I have a friend that has a Challenger T/A that makes the same noise also. I was told but never tried it. Change the angle of the rear end similar to when you lift a truck you would shim the rear so the drive shaft is not at such a steep angle. I never tried it but if anybody has let us know.
 
mopar340dave said:
I have a flomaster 3 chamber dual exhaust in 2.5".

I have had the same bs regrdless of different headers, engine, wheels, driveshaft, clutch, flywheel, balancer and anything else. Stock 85 318 w/340 intake and headers or built solid cam 340 w same headers or hyd 340 w tti headers...IT'S THE MUFFS!

http://www.spintechmufflers.com/index.php?_a=viewDoc&docId=1[/QUO

Based on all the things I have changed/ altered etc.. I think You may be dead on..

Thanks

btw can't say for sure it does it when parked... Will verify when I am back home April 1st... On a trip into Calgary/Edmonton right now..

Thanks for all the replies.. and keep the ideas coming if you think you got a solution!!

Ken
Click to expand...
 
You say the engine was professionally built. My question is, was it balanced?
 
This is one thread I want to hear the end of! Be sure to let us know if & when you have it corrected.
C
 
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