Vibration

[Beekeeper]

So maybe I'm still missing something....how did it run smooth one day and extremely rough after a Trans mount change? If that is all that has been changed, I would put a rubber mount back in first before any other changes. It seems hard to imagine that the engine suddenly went out of balance the moment you changed the Trans mount.

What brought about the need to change the Trans mount? Did it start vibrating badly before you made the swap? In other words, did you change the Trans mount believing it would cure a bad vibration problem that just started up? If that is the case, something else went wrong that caused your vibration and the Trans mount is not a factor.

You say the engine idled smooth but I assume that was before. How does it idle now? Are you able to determine that it still idles smooth at a low rpm even with all the vibrations?

I would take everything one step at a time as you diagnose this. If you do several things at once, one thing can fix the issue while another change creates a new problem.

[crash340]

I believe the engine has not been re built, I will pull the insp cover today and check how many weights there are etc

[Chryco Psycho]

I have seen this before , the engine runs well & "seems" smooth but the rubber mounts are beat so the vibration is not transmitted to the frame , change to the semi solid Poly mount & there is a lot less give & now the vibration is noticeable , the solution is not to return to the rubber mount though , you need to figure out what is wrong , something has to be mismatched .

[crash340]

I wish I could video it, its not that the engine is running rough Beekeeper, its more a harmonic buzz/ high frequency low res vibration, very similar to a tailshaft vibration only when parked running up through the rpm.

[crash340]

Ok, the dampner is definitely a cast crank dampner, for now lets say the engine has not been pulled down. I checked the converter, it has two weights, one either side of the drain plug. the motor was assembled on the 12th Dec 1972. as best I can tell and assume, the converter was changed out with the trans and as indicated earlier it is a 77 HD truck trans by number, no history on the trans apart from it has a 'transgo' sticker on the top of the bell housing, I had the valve body off to check it and it had lets say, half a shift kit in it. thats all i have on the trans. it seems to shift ok, no slipping, a little noisy in second gear at low speed but from memory they are like that.
So, are we any closer???

[Chryco Psycho]

not really , just guessing but the converter was probably with the trans so it would be balance for the 360 with heavier weights

[crash340]

So CP. the heavier weights are not the issue or wont make any difference?

[Chryco Psycho]

yes , the wrong weights will affect the balance & are probably the cause of the vibration

[crash340]

Where are the weights located on the 73 340 converter? are they near the drain plug? if so which side? and by removing one of them whe should be good? OR if the weight is not near the drain plug, given the converter is clocked to the balancer via the crank and flex plate, where is it in relation to the balancer counter weight.

[Chryco Psycho]

there are near the edge of the converter body near the ring gear , a lot of converters do not have a drain plug , you could cut 1 off & see how it changes the vibration , it won't be right but it might be closer / better .

[Beekeeper]

Been thinking on your problem....if you are 100% sure the engine is running nice and smooth (idles at 700, never been rebuilt, has correct harmonic balancer and flex plate on it), then your vibration must be coming from the torque converter or the transmission.

I am not a tranny guy by any means but it seems to me vibrations come from things that spin. The torque converter is bolted to the flex plate and therefore spins. The torque converter is also spinning the something inside the transmission. This happens whether it is in park, neutral, or in gear.

Perhaps something has failed in your torque converter like vanes which have broken off inside and cause it to be out of balance internally. Or maybe something inside your tranny has failed. It might be helpful to throw a post in the tranny section to see what those guys think. I would ask if you could get heavy vibrations even in park from a converter or tranny failure.

Maybe you said this and I missed it but is this transmission from another vehicle originally? Do you know if the transmission and torque converter are in good shape?

If you had access to another converter and tranny, it would be interesting to know if switching them out makes your problem disappear. Perhaps the rubber tranny bushing masked the vibration and the bushing failed because of it.

You need to determine if your vibration issue is in the motor, the torque converter, or the tranny. I would be very hesitant to just start adding or removing rotational weight in the hopes that it gets better. Even if it gets better, you could still have balancing issues which will cause damage in your engine over time.

I am never one to suggest throwing money at a problem but if you got the motor and drivetrain from someone who didn't tell you everything, it could come down to a point where you have to pull the motor, disassemble it and have it rebalanced just so you can be 100% sure it is okay. And of course have the converter and tranny gone through as well.

If i starting working on this car without knowing its history, I'd find another converter and tranny from somewhere and test it out. Yeah it's big work but I doubt some magic solution is going to appear if it hasn't already. You could drive yourself insane by trying one little thing after another and still not get anywhere plus waste time and money. It might be less money and work to try some big trouble shooting ideas.

Just my two cents on your problem. I'll keep my fingers crossed for you.

[crash340]

The car is how I purchaed it, so past history is not there, that said, yes the motor runs well, I had the pan and valve body off the trans, no crap in the pan, things looked ok. For now, I'll put a rubber mount in it, new Uni joints (these where replaced by the previous owner but I noticed the rear joint had a tight spot in it when I had the diff out so I'll change them both for Sh#ts and giggles. I plan on ordering a motor 408 from MRL later this year so once it gets here, I'll pull the trans, have it rebuilt, I want an internally ballanced motor so I will buy a converter to suit the motor then etc.
I noticed yesterday, while sitting as I moved the rpm's up at one point the steering wheel shakes a little (dont know the rpm as I dont have a tacho yet) guessing around 1500 rpm then goes smooth again etc.

anyhow, I thank everyone for their suggestions and input, I always welcome it and more if you come up with anything.
Greg

[crash340]

So, out with the poly trans mount and in with a new rubber mount, the engine vibration is still present but not transferred into the cab so much now, even getting hold of a spare 727 out here is a nightmare, they are just not around anymore.

[burdar]

An option is to buy an aftermarket "weighted" flex plate for your 340.  Then you can run any convertor you want.  Replace the flex plate, knock the weights off the convertor and you'd be good to go.