Chasing a Vibration - Flex Plate?

[rwcstang 201]

3 hours ago, bigmal said:

Both the flex plate and harmonic balancer are new. When I told the company that internally balanced my engine that I had then replaced the flex plate afterwards, they said it should be balanced again. The engine vibration is not that significant, but something I would like to tackle at some point. Thanks.

Im Slightly confused here, so they did or did they not Internally balanced the motor? you're previous posts mentions it was externally balanced and now you're saying here, its internally balanced, which is it?

if internally balanced both Harmonic Balancer and Flexplate should be 0, not 28oz. I have a 427w that is internally balanced, and both balancer and fly wheel are neutral, no weights needed.

If your engine is really internally balanced, replace the balancer/flywheel with neutral balance, summitracing sells the replacement parts and no weights attached. no need to tear the motor apart unless the crank shaft is out of wack now since you installed the 28oz and that is the source of your vibration.

I would re-verify with your engine builder and have him show you documentation on what they exactly did with your engine. Engine builders should have and share all documentation about your motor.

at this point, it could be that crankshaft is too twisted no matter what you do to try to resolve it and the vibration will not go away with just replacing parts.

[RPM 1,190]

Just for info, internal parts have weight removed and added to them on an external balanced motor. 

[bigmal 225]

1 hour ago, rwcstang said:

Im Slightly confused here, so they did or did they not Internally balanced the motor? you're previous posts mentions it was externally balanced and now you're saying here, its internally balanced, which is it?

if internally balanced both Harmonic Balancer and Flexplate should be 0, not 28oz. I have a 427w that is internally balanced, and both balancer and fly wheel are neutral, no weights needed.

If your engine is really internally balanced, replace the balancer/flywheel with neutral balance, summitracing sells the replacement parts and no weights attached. no need to tear the motor apart unless the crank shaft is out of wack now since you installed the 28oz and that is the source of your vibration.

I would re-verify with your engine builder and have him show you documentation on what they exactly did with your engine. Engine builders should have and share all documentation about your motor.

at this point, it could be that crankshaft is too twisted no matter what you do to try to resolve it and the vibration will not go away with just replacing parts.

You are getting a little out of my area of knowledge here. The internals were supplied including harmonic balancer and flex plate. Pistons and rod were balanced separately. I understand the crank was balanced with the flex plate and harmonic balancer in place. The old flex plate had some metal remover during the process. Not a lot.

[bigmal 225]

I've just jacked the car and confirmed that there is up and down play in the yoke going into the rear of the transmision. On the weekend I will get the rear out and have the bushing replaced. I'll report back once I have an outcome.

Thanks for all your help

[jjstang 51]

The difference here is when you internally balance the entire rotating assembly, it includes the flex plate too. If you replace the flex plate you’ll probably have to disassemble and start over. That’s why I went external. Internal stuff can still be pseudo balanced (think blue printed). That’s the way it was explained to me. 

[RPM 1,190]

21 hours ago, bigmal said:

The old flex plate had some metal remover during the process. Not a lot.

I had a motor balanced where they added weight to the flex plate. When I swapped to a 4 speed, the machine shop said they could balance the flywheel to the flex plate. It sounds like you need the new FP matched to the old one. 

[bigmal 225]

17 minutes ago, RPM said:

I had a motor balanced where they added weight to the flex plate. When I swapped to a 4 speed, the machine shop said they could balance the flywheel to the flex plate. It sounds like you need the new FP matched to the old one. 

When I replaced the flex plate that I had damaged I told the engine shop bloke that I had replaced it. He said If I bring the old and new flex plates he can balance against the old. I had already thrown it out. Still kicking myself.

[bigmal 225]

Well, an update. I had a new bushing fitted to the rear of the transmission, as suggested. There was a little play, and I was happy to eliminate this.

Not only did it not fix it, it's now worse. This is doing my head in.

It's not an issue with how I mounted the rear uni, as I triple checked it.

I have to be close, as it's something I've disturbed. 

Both uni's are new and fitted by a reputable company. I'm thinking of taking the tail shaft back and getting them to check the balance and uni's.

[det0326 179]

Sorry to hear that Bigmal. when u found play there I just knew u had found your problem. I do feel your pain. When you mention tail shaft I assume you are talking about the drive shaft. Is the drive shaft the original or did u have a new one made? The reason I ask is I have heard that some older drive shafts had rubber internally that sometimes broke loose and caused a vibration. Never experienced it myself just heard of other people having a problem with it. The only thing that could of upset the vibration to make it worse by removing the drive shaft is it can be mounted  back to the pinion yoke  180 degrees from where it is now. I don't think that's your problem tho.  

[bigmal 225]

2 hours ago, det0326 said:

Sorry to hear that Bigmal. when u found play there I just knew u had found your problem. I do feel your pain. When you mention tail shaft I assume you are talking about the drive shaft. Is the drive shaft the original or did u have a new one made? The reason I ask is I have heard that some older drive shafts had rubber internally that sometimes broke loose and caused a vibration. Never experienced it myself just heard of other people having a problem with it. The only thing that could of upset the vibration to make it worse by removing the drive shaft is it can be mounted  back to the pinion yoke  180 degrees from where it is now. I drought very seriously that's your problem tho.  

Hi mate, yes a new tailshaft/driveshaft. I had the same problem with the previous driveshaft which is why I've replaced it with new good quality uni's. I must be close because what ever I did has affected the vibration (worse). Actually to the point where I am afraid to sit at that speed for fear of throwing the driveshaft.

As I have disturbed the rear shock mount I will check the pinion angles again just to make sure nothing has changed. Juts need to be away from it for a few days.

[RPM 1,190]

I feel your pain bro. As you've checked and changed everything I would, I have no advice for you. Stepping away for a bit helps the mind. I've got a buddy with a 66 who has changed everything but the body shell, and still has a vibration. 

 

[buening 63]

Vibrations are narrowed down to engine (vibration is RPM dependent) or drivetrain (speed dependent with no impact from change in RPM).  From what I'm reading, this is drivetrain related so I wouldn't focus on the new flexplate and engine balance.  A couple questions:

 

Is the driveshaft original or aftermarket, and has it been balanced with the new u-joints? 

What is the condition of the 3rd member/differential and has it been messed with? I don't forsee this being a potential for vibration but its in the mix.

What rear brakes does the car have? If disc brakes, make sure the rotor is centered on the axle hub

Have you removed the wheels and ran the car on jackstands to make sure its not the rear wheels? Install the 5 lug nuts to keep the drums attached, or better yet remove drums/rotors to eliminate those from the list.

[bigmal 225]

28 minutes ago, buening said:

Vibrations are narrowed down to engine (vibration is RPM dependent) or drivetrain (speed dependent with no impact from change in RPM).  From what I'm reading, this is drivetrain related so I wouldn't focus on the new flexplate and engine balance.  A couple questions:

 

Is the driveshaft original or aftermarket, and has it been balanced with the new u-joints? 

What is the condition of the 3rd member/differential and has it been messed with? I don't forsee this being a potential for vibration but its in the mix.

What rear brakes does the car have? If disc brakes, make sure the rotor is centered on the axle hub

Have you removed the wheels and ran the car on jackstands to make sure its not the rear wheels? Install the 5 lug nuts to keep the drums attached, or better yet remove drums/rotors to eliminate those from the list.

Hi mate, thanks for the response

The driveshaft is custom made by Hardy Spicer with new universals. The previous shaft was a replacement and turned out to be bent and out of balance. Changing made no differnce.

As far as I know the diff is in good condition. No noises and traction lock function well.

Rear brakes are drum. 

I haven't run with the wheels off yet but will try that on the weekend.

For some reason removing and replacing the drive shaft has made it worse. I did remove the cross member and rear shock mount to remove the FMX extension housing but there is only one way to replace it. I will check that the pinion angles are still matched.

[Midlife 814]

How is the rubber on the transmission mount?  You might want to check motor mounts as well.

[bigmal 225]

Just now, Midlife said:

How is the rubber on the transmission mount?  You might want to check motor mounts as well.

Hi mate, all mounts have been replaced. No noticeable difference

[RPM 1,190]

I'd flip the driveshaft 180°. The last vibration thread I read that had a fix, the axle flanges were bent and wobbled some. Might throw a dial indicator on them.

[bigmal 225]

2 minutes ago, RPM said:

I'd flip the driveshaft 180°. The last vibration thread I read that had a fix, the axle flanges were bent and wobbled some. Might throw a dial indicator on them.

Thanks Bob, will give it a go

[Brian Conway 264]

While the driveshaft is down start the moter and check for vibration.  In all the forward/reverse gears.  Run it up to the usual vibration rpm's.  Brian

[det0326 179]

I wouldn't run engine and trans with the drive shaft out because the transmission tail shaft would not have any support with the yoke out. May not hurt a thing but it really wouldn't tell you munch with the transmission tail shaft wobbling. 

[bigmal 225]

I would be concerned running it without the drive shaft yoke in place. While I like the idea I don't know enough about any damage it could cause or fluid loss.

Thanks

[bigmal 225]

Update: I took the drive shaft back to the company that made it and they found a thrust washer missing from inside the rear uni cap. This will make the uni offset about 1mm. I saw a washer on the floor of the garage and didn't recognise it so added to the washer box. This explains why the vibration got worse after changing the transmission bushing. Extremely happytto find that. They have put the shaft on their balancer and said it is slightly out of true. They are repairing it today and I am getting a new yoke and two new uni's just to be sure. I'll report back as soon as I have driven it again. Fingers crossed!!!

[smh00n 87]

The guys that did my shaft (I dropped you a PM) made sure I knew about that little issue of losing the washers.

Hopefully this fixes it for you.

[bigmal 225]

I got the repaired tailshaft back and went to fit it. The new yoke is longer than the old yoke so it wouldn't fit. I took it back to them yesterday to have it shortened 3/4". Starting to lose confidence with this company. Next will be the argument of paying for all of this. Fingers crossed the vibration is gone at the end.

[bigmal 225]

Bugger me. It's one thing after another. Refitted the driveshaft and test dive. A definite improvement, but still some vibration.

Back on the stands and ran it again, with and without wheels as suggested above. Definitely less vibration without the wheels. I've taken the axles to a shop and they are both bent. Surely this is the last possible thing. I'll report back once they're straightened and refitted. 

[smh00n 87]

It might be worthwhile pulling the housing and having it checked for straightness? More of a make sure nothing else is going to stuff you up step.