1900 rpm vibration

mxquattro · Oct 11, 2014

I have an interesting problem with my new build. 68 Coupe, 496, T56 6 speed, Strange engineering chromemoly drive shaft, Stange engineering Dana 60 rear end.

Car starts and runs like a dream, but at 1900 rpm or so, from inside the car, I get a vibration. It happens in neutral just sitting there too, so I completely rule out driveshaft, rear end, suspension, wheels, etc.

The strange part is, when under the hood the engine is as smooth as silk. It doesnt vibrate, or move in the least. On the inside, with my hand on the shifter, it is also smooth as silk and zero vibration. So it seems I can rule out tranny, clutch, etc.
It seems like Im just finding a harmonic of the motor to the chassis and it resonates. The million dollar question though is how the hell do I find it and fix it?

Should I start drinking now? Will my hair start falling out prematurely? I just have a sneaky suspicion that problems like this are almost impossible to find. Any tips appreciated!

I didnt know what forum to put this under since I really doubt its an engine or driveline issue... so I stuck it here.

scblucam · Oct 11, 2014

Should I start drinking now? Will my hair start falling out prematurely?

Umm, maybe, Umm mine did. Maybe an anomaly between your ignition timing advance and your cam timing?

mxquattro · Oct 11, 2014

I can check that again. Putting my hand on the motor at 1900 is smooth as can be though, but Illl definitely look.

cv2065 · Oct 11, 2014

Did you replace your water pump?

mxquattro · Oct 11, 2014

I did not. Feeling this vibration throughout the whole chassis...so if the water pump was THAT bad, Id feel it on the motor I would think, or at least at the pump

cv2065 · Oct 11, 2014

Not sure about your specific vibration, but mine resonated throughout the entire cab, vibrating the glove box and console, but did not feel it in the engine bay. Was barely noticeable visually unless you sat there and watched it for a moment. Worth a check anyway.

mxquattro · Oct 11, 2014

wow OK. Ill definitely check it out. Ill try to take a short video too

gwbutch · Oct 11, 2014

Did you check the body mount bolts and rear spring mounts?

bilodeaulynn · Oct 11, 2014

Diagnosing from a distance is a bit of a crap shoot... but it really sounds like a resonance issue with the exhaust. Not uncommon at all.

Do you have headers?
What mufflers you running.

First, eliminate any rotating assembly, i.e. water pump, ps pump, alt. etc.

Second, make sure the exhaust is hung properly, i.e. no metal on metal, and no rubber hangers in a bind. Neither of those will CAUSE the resonance problem, but will greatly magnify it.

Third, if it is in the exhaust, I wish there were an easier way, but you will have to add, subtract, or change your muffler system in some way to get rid of it. Easiest addition is resonators, which is a fancy word for small mufflers. That will change the harmonics.

mxquattro · Oct 11, 2014

I can help narrow things down a bit. Since this is a new install, I had basically nothing on the motor when I noticed it. No PS pump, no exhaust, no alternator or accessories at all. Not even a rear suspension or driveshaft. I did have open headers hanging though, and figured once I got exhaust it would quiet things down and be OK. When the exhaust went on it made no difference.

I triple checked motor mounts and everything underneath is tight as can be.

69ndpce · Oct 11, 2014

I had a 350 that did that. It was supposedly balanced and blue printed. I'll almost bet that yours, like mine was, is not balanced correctly. Balancing is a craft not just weighing some parts and sticking them together. A lot of "craftsmen" don't know how to balance them correctly. You might talk to someone that is more knowledgeable than me. I hope yours turns out to be an easy fix.

gwbutch · Oct 11, 2014

Transmission mount and crossmember?

bilodeaulynn · Oct 11, 2014

69ndpce said:
I had a 350 that did that. It was supposedly balanced and blue printed. I'll almost bet that yours, like mine was, is not balanced correctly. Balancing is a craft not just weighing some parts and sticking them together. A lot of "craftsmen" don't know how to balance them correctly. You might talk to someone that is more knowledgeable than me. I hope yours turns out to be an easy fix.

This would be my guess.
However, it is easy enough to check the water pump. You can run it for a very short time with the belt off. That will eliminate the wp.

mxquattro · Oct 11, 2014

I just did a little more troubleshooting with help this time. I took off the alternator/water pump belt, same thing.
Id like to point out that it didnt do this on the engine dyno at all, so Im hopefully ruling out a balance issue. The guy that built it is a place thats been in business forever building top end race engines (for paul newman etc) so I know hes good. I used to work there as a teenager and Im certain he did me right and put in the extra mile for me.
What I DID find today though was that it might be because my header is hitting my steering box. Pretty solidly too, theres no gap there at all that I can see. When I held the motor at 1900 to make it vibrate, he would feel the steering box, steering shaft, column etc and it was shaking pretty good. My dash shakes the most when this happens and that would make sense since thats what my steering is attached to.

Before I start the monumental job of removing the header from the drivers side and denting them in, do you guys think this is even a possibility or am I barking up the wrong tree? Id hate to go through all that and find out its probably not it.

cv2065 · Oct 11, 2014

Glad you started eliminating things like the water pump. If your vibration is only coming through the steering column, or anything attached to it, then you might be on to something, but if it's coming through the chassis, then I would suspect not. Either way, I'd still pull the box and grind on it a bit to make some clearance instead of dimpling the header if you can help it. I had the same thing happen on mine.I would assume that would have been something your builder would/should have noticed?

mxquattro · Oct 11, 2014

The box is mounted to the frame, so I can see how it would get transmitted to the whole car

PA Camaro Guy · Oct 12, 2014

My header touches my steering box just a little. I don't get vibration.

Headshake · Oct 12, 2014

Just my 2cents. You don't want the headers in contact with the steering box ever and if it is it will certainly transmit not only noise and vibration up the steering column but will induce a lot of excess heat into the steering box. Just a tip, when you pull the header to clearance it, buy yourself a pair of these new "Dead Soft Aluminum" gaskets from Percy's or MrGasket. They are the best sealing gaskets I have ever used in 40 years of running headers.

mxquattro · Oct 12, 2014

Thanks for all the tips guys. sure will.
Today I got the header of but not out. Im not seeing how that sucker is going to come out at all. I might have to unbolt that motor mount and jack up the engine to get it out. Its tight in there!

68SSlemans · Oct 13, 2014

mxquattro said:
Thanks for all the tips guys. sure will.
Today I got the header of but not out. Im not seeing how that sucker is going to come out at all. I might have to unbolt that motor mount and jack up the engine to get it out. Its tight in there!

Tight is good :thumbsup:

1900 rpm vibration

mxquattro

scblucam

mxquattro

cv2065

mxquattro

cv2065

mxquattro

gwbutch

bilodeaulynn

mxquattro

69ndpce

gwbutch

bilodeaulynn

mxquattro

cv2065

mxquattro

PA Camaro Guy

Headshake

mxquattro

68SSlemans

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