Chasing a Vibration - Flex Plate?

[RPM 1,190]

[MAC390 327]

Well done mate, glad the is sorted out , now drive the ass off it.

[bigmal 225]

Well guys, I reported the vibration was gone after rebuilding the engine. Well, it seems that my vibrations have been from multiple sources and still not fixed., although it now appears to be driveline related.

351 Cleveland, FMX, 9" 3.25 Traction Lock.

Driving is relatively smooth up to about 55/60 mph. Then starts at 65. At 70 mph it is the worst. By 75/80 the vibration is gone.

Vibration starts as constant then as speed increases becomes a surging vibration.

When placed in neutral and engine reduced to idle, the vibration doesn't change.

Vibration is also visible with the shaker.

So far to date I've done the following:

• Replaced harmonic balancer,
• Rebuilt engine and balanced. I damaged the flex plate on installation and replaced with a new 28oz plate which has not been balanced with the engine (this troubles me),
• Run with belts off,
• Engine appears to be running well with no miss or roughness,
• Replaced torque converter,

There is still a slight engine vibration, but not unacceptable. This may be from replacing the flex plate after rebuilding. I will be stripping and balancing again.

• New wheels and tires. balanced to lugs (3 times).
• Tail shaft replaced in early trouble shooting. Took that one to get checked for balance and found bent 1/8", ends not strait and significantly out of balance. New shaft fitted. I really thought I had it this time. no noticeable change :(
• New front and rear universals fitted. Checked and installed correctly.
• Diff pinion had slight damage to universal mount. New pinion fitted.
• New front and rear engine mounts.
• Pinion angles adjusted with 3deg shims so 0deg split. Tested at 1, 2, 3 and 4 up and down. 3deg up has reduced the vibration to the best yet but still there.
• Axles appear straight. Wheels would wobble if bent.

I had the FMX serviced a few years ago and was told it was making metal and on its last legs. I have done about 2000 miles since then and appears to be shifting fine with no odd noises.

This is really doing my head in, and I need to get it sorted before I move to body and paint.

Has anyone experienced this sort of vibration and it was caused by the FMX? I know nothing about the internals of automatics, but I fear I am about to learn.

[det0326 179]

Well it is just my experience but I have never had an auto transmission to cause a vibration. Not saying it can't just saying it is rare.

I know u have probably stated in your thread somewhere your trans tailshaft and pinion angles but to keep me from rereading do u have that information.

[bigmal 225]

1 minute ago, det0326 said:

Well it is just my experience but I have never had an auto transmission to cause a vibration. Not saying it can't just saying it is rare.

I know u have probably stated in your thread somewhere your trans tailshaft and pinion angles but to keep me from rereading do u have that information.

Thanks mate. New tail shaft, universals and pinion angles adjusted to 0 deg.

[Brian Conway 264]

I think you are right to be troubled about the flex-plate.  That would be my first guess. Brian

[jjstang 51]

Is it internal or external balanced?

[det0326 179]

16 hours ago, bigmal said:

Thanks mate. New tail shaft, universals and pinion angles adjusted to 0 deg.

Not quite sure what u mean by 0 degrees.  If u put a inclinometer on the tailshaft of transmission or on the front pulley of the engine then what ever that angle is the pinion angle should be the same angle minus 1 in the opposite direction.

[rwcstang 201]

@bigmal Im sorting something similar with my SOT 3 link, but I have a TKO. I have yet to try it, but since I dont have a garage, the rain is keeping me at bay. 

but to piggy back of of Det, and Im sure you have done this, put the car on an even surface with jacks, so it can mimic the car is on full weight on tires, measure the transmission tailend with an inclinometer or app on your phone, measure how many degrees the transmission tail is, measure the drive shaft angle and finally pinion angle. 

at least for my set up, SOT recommended my car to be around, 3-4 degrees Transmission down and 3-4 degrees pinion up. of course have the transmission and pinion be centered at 0 degrees should cause no vibration. 

 

 

[bigmal 225]

On 3/13/2023 at 4:29 PM, jjstang said:

Is it internal or external balanced?

Standard 18oz external, but the internals were balanced on a machine while stripped. As I have replaced the flex plate since then, so I may be looking at another strip.

While laying awake in the middle of the night I've been trying to come up with a way to balance the flex plate in situ. I was thinking of placing small tire weights on the plate and repositioning them by trial and error. Unfortunately there is not enough room through the bottom plate. Another thought was to remove the transmission and attach the bell housing and use the same method. If I can get rid of the vibration with this method I could then drill holes opposite.

Anyone tried this? Or am I off the mark? Or just bite the bullet with another strip and balance?

Noting that the major vibration is not the engine, its somewhere rear of the torque converter.

[bigmal 225]

On 3/14/2023 at 3:38 AM, det0326 said:

Not quite sure what u mean by 0 degrees.  If u put a inclinometer on the tailshaft of transmission or on the front pulley of the engine then what ever that angle is the pinion angle should be the same angle minus 1 in the opposite direction.

Hi mate, by 0 deg I meant that the difference between the diff angle and the engine front pully is 0.

The Pinion angles are adjusted with 3deg shims so there is 0 deg split. I tried shims at 1, 2, 3 and 4 up and down. 3deg up has reduced the vibration to the best yet but still there.

[bigmal 225]

On 3/14/2023 at 5:24 AM, rwcstang said:

@bigmal Im sorting something similar with my SOT 3 link, but I have a TKO. I have yet to try it, but since I dont have a garage, the rain is keeping me at bay. 

but to piggy back of of Det, and Im sure you have done this, put the car on an even surface with jacks, so it can mimic the car is on full weight on tires, measure the transmission tailend with an inclinometer or app on your phone, measure how many degrees the transmission tail is, measure the drive shaft angle and finally pinion angle. 

at least for my set up, SOT recommended my car to be around, 3-4 degrees Transmission down and 3-4 degrees pinion up. of course have the transmission and pinion be centered at 0 degrees should cause no vibration. 

 

 

Hi mate, that's some very helpful information. I have tried shimming the pinion up and down 1, 2, 3 and 4 degrees. 3 deg up has the least vibration and a 0 degrees difference between the diff and transmission angle. The amount of pitch up with the engine under load is something I was wondering about. As I have shifted to neutral at the speed where the vibration is at its worst, the diff is not under load and the vibration is unchanged at that speed. It also shows that as the engine has dropped to idle, the major vibration is somewhere rear of the torque converter.

What troubles me most is that I may have eliminated parts as the cause by replacing them and the new parts may still be an issue. First replacement tailshaft was bodgy, so a new one fitted. I thought I'd found the culprit, but no noticeable difference.

[det0326 179]

24 minutes ago, bigmal said:

Hi mate, by 0 deg I meant that the difference between the diff angle and the engine front pully is 0.

The Pinion angles are adjusted with 3deg shims so there is 0 deg split. I tried shims at 1, 2, 3 and 4 up and down. 3deg up has reduced the vibration to the best yet but still there.

So Bigmal If I understand correctly when u check front pulley (for simplicity let say it is 3 degrees) meaning the top of the pulley is set back toward the rear by 3 degrees. When u check front of pinion it is set turned up by 3 degrees. If your answer is yes then that should work fine. are u using wedge shims between the leaf spring and spring perch to change pinion angle.   

[det0326 179]

I suppose u have checked drive shaft yoke at the transmission for excessive clearance between yoke outside dia. and the bushing in the transmission. 

[bigmal 225]

2 minutes ago, det0326 said:

So Bigmal If I understand correctly when u check front pulley (for simplicity let say it is 3 degrees) meaning the top of the pulley is set back toward the rear by 3 degrees. When u check front of pinion it is set turned up by 3 degrees. If your answer is yes then that should work fine. are u using wedge shims between the leaf spring and spring perch to change pinion angle.   

Hi mate, I am using a digital protractor and I set zero on the front pulley. Then when I take it to the rear pinion it is also zero. Makes it a little simpler then using maths :) 

Yes, using wedge shims. I have 4 sizes 1, 2, 3 and 4 deg. I didn't know what tolerance was acceptable so used trial and error.

[bigmal 225]

1 minute ago, det0326 said:

I suppose u have checked drive shaft yoke at the transmission for excessive clearance between yoke outside dia. and the bushing in the transmission. 

No, that's something I haven't checked. The yoke appears to be in good nick and I've replaced the seal so there are no leaks, but I haven't checked for a worn bushing.

That is new territory for me. Is it easily replaced? I'm getting a little excited....

[det0326 179]

1 minute ago, bigmal said:

Hi mate, I am using a digital protractor and I set zero on the front pulley. Then when I take it to the rear pinion it is also zero. Makes it a little simpler then using maths :) 

Yes, using wedge shims. I have 4 sizes 1, 2, 3 and 4 deg. I didn't know what tolerance was acceptable so used trial and error.

Is the 2 angles tilted in the same direction. Sorry for all the questions just trying to figure out if we are on the same page. 

[bigmal 225]

4 minutes ago, det0326 said:

Is the 2 angles tilted in the same direction. Sorry for all the questions just trying to figure out if we are on the same page. 

Don't be sorry. I'm really glad to have the input. The angles are parallel. Car on stands, digital protractor set to zero on the pulley and taken to the diff is also zero. As I haven't checked the car is level, I can't say what the true angles are, just that they both match. 

[det0326 179]

2 minutes ago, bigmal said:

No, that's something I haven't checked. The yoke appears to be in good nick and I've replaced the seal so there are no leaks, but I haven't checked for a worn bushing.

That is new territory for me. Is it easily replaced? I'm getting a little excited....

If it is worn u should be able to physically move it up and down and side to side also. Not that difficult to change. Tail shaft housing would have to come off. 

[bigmal 225]

1 minute ago, det0326 said:

If it is worn u should be able to physically move it up and down and side to side also. Not that difficult to change. Tail shaft housing would have to come off. 

I'll be checking that first thing on the weekend. As I'm not a transmission man, just confirming I need to drain the oil, remove the housing, and a press to change the bushing? Assuming its worn.

[det0326 179]

2 minutes ago, bigmal said:

I'll be checking that first thing on the weekend. As I'm not a transmission man, just confirming I need to drain the oil, remove the housing, and a press to change the bushing? Assuming its worn.

I have jacked rear of car up far enough that the rear of transmission is higher than the front and never lose but a few drops of fluid. There is a tool to do that but with right size tubes and etc u could do it with a press I am sure. Don't know about Australia but here some of our car parts stores has a tool loan program where u pay a deposit which u get back when the tool is returned. 

[bigmal 225]

2 minutes ago, det0326 said:

I have jacked rear of car up far enough that the rear of transmission is higher than the front and never lose but a few drops of fluid. There is a tool to do that but with right size tubes and etc u could do it with a press I am sure. Don't know about Australia but here some of our car parts stores has a tool loan program where u pay a deposit which u get back when the tool is returned. 

Sounds great. I will replace it regardless so at least its eliminated. I just need to source a bush.

[det0326 179]

2 minutes ago, bigmal said:

Sounds great. I will replace it regardless so at least its eliminated. I just need to source a bush.

I would get car up far enough to get under and make sure it can't roll and put in neutral so there is no pressure on driveshaft. Then see if you can move it around if not it is probably ok.

[jjstang 51]

1 hour ago, bigmal said:

Standard 18oz external, but the internals were balanced on a machine while stripped. As I have replaced the flex plate since then, so I may be looking at another strip.

While laying awake in the middle of the night I've been trying to come up with a way to balance the flex plate in situ. I was thinking of placing small tire weights on the plate and repositioning them by trial and error. Unfortunately there is not enough room through the bottom plate. Another thought was to remove the transmission and attach the bell housing and use the same method. If I can get rid of the vibration with this method I could then drill holes opposite.

Anyone tried this? Or am I off the mark? Or just bite the bullet with another strip and balance?

Noting that the major vibration is not the engine, its somewhere rear of the torque converter.

When my engine was rebuilt, I elected to keep external balance. (They still did some balancing on inside parts but I don't know how that works)  I should be able to change out the flywheel/flex plate & harmonic balancer to my hearts content and as long as they are the proper balance weight (and assuming they were made correctly)  it should not be a problem.  I assume your flex plate or harmonic could be defective?

[bigmal 225]

14 minutes ago, jjstang said:

When my engine was rebuilt, I elected to keep external balance. (They still did some balancing on inside parts but I don't know how that works)  I should be able to change out the flywheel/flex plate & harmonic balancer to my hearts content and as long as they are the proper balance weight (and assuming they were made correctly)  it should not be a problem.  I assume your flex plate or harmonic could be defective?

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.