Chasing a Vibration - Flex Plate?

[bigmal 225]

Hi guys, I have an annoying vibration I've been trying to track down and suspect it's the flex plate. I have a 351 Cleveland with an FMX.

It has new universals and tail shaft. I tried measuring the angles of the front and rear universals on the weekend but with the tail shaft in place I couldn't get an accurate measurement. Also has new tyres and new rear wheels with a good balance.

The vibration occurs most significantly around 58 kmph. It's not severe but brings out the rattles that seem to be everywhere. Placing in neutral the vibration drops off but as the speed decreases quickly it very difficult to be positive that it's RPM related and not speed related, but I'm pretty sure. Interestingly it is silky smooth and quiet at 110 kmph.

When I had the engine out last year I recall the Flex plate was marked in felt pen as '351 Windsor'.

I have read that there are different counter weights for different engines. Would I be correct in thinking the 351 Windsor flex plate would have a different counter weights to a Cleveland? And would it cause the sort of vibration I have described.

If this is likely to be the cause what counter weight flex plate should I get?

Thanks.

 

Edited June 12, 2018 by bigmal
Incorrectly called the FDlex Plate the Flywheel. Oops.

[RPM 1,190]

The crankshaft and trans out put shaft are are on the same plane. Measure off the front pulley, It'll be the same, or 90* off.

[bigmal 225]

3 minutes ago, RPM said:

The crankshaft and trans out put shaft are are on the same plane. Measure off the front pulley, It'll be the same, or 90* off.

Thanks Bob, I hadn't considered that. I will do that on the weekend.

[barnett468 418]

also, sit in the car and rev the engine to around 2000 rpm for 10 seconds then to around 2500 or a little more for 10 seconds and see it if vibrates.

 

[bigmal 225]

4 minutes ago, barnett468 said:

also, sit in the car and rev the engine to around 2000 rpm for 10 seconds then to around 2500 or a little more for 10 seconds and see it if vibrates.

 

Will do. Thanks.

[larryc94 38]

Windsor or Cleveland same flex plate, both 28 oz imbalance

[bigmal 225]

8 hours ago, larryc94 said:

Windsor or Cleveland same flex plate, both 28 oz imbalance

Thanks for that. I thought they were different. Now pinning my hopes on universal alignment. Some checks to do this weekend

[bigmal 225]

So I put the rear axle on stands and ran it up to about 60mph. Between 25 and 35 is the worst vibration. Seemed even worse than on the road. I then put it in Park and ran up through the same RPM and nil vibration. Yep, not the engine.

I checked the alignment between the engine and diff and the front of the diff tilts down around 5deg. The engine mounts look to be in good condition and I have very little room to drop the front of the motor (Due steering rack clearance) or raise the rear of the transition. Looking at the diff it appears to be slightly tilted down sat the front but the leaves look strait

Any suggestions on where to go from here

[MAC390 327]

Hey Mal , get the tail shaft balanced, worked for me.

[larryc94 38]

I would loosen the rear u-joint and the see if there is any play between the locating tabs in the yoke. I had a slight annoying vibration also. I had 0.012" play by pushing and pulling the joint against the tabs

As a temporary fix I cut two pieces of 0.006"  feeler gauge to fit between the two tabs. 

Looks like you have a "long" yoke, very hard to find in a 1310 u-joint size.  You have to get new or you risk having the same problem.  I got one at Quick Performance, only thing it is a 1330 u-joint.  You have to use a conversion joint 1310 by 1330 

 

If the above is good I would have a driveshaft shop check the balance

[mwye0627 44]

12 hours ago, bigmal said:

So I put the rear axle on stands and ran it up to about 60mph. Between 25 and 35 is the worst vibration. Seemed even worse than on the road. I then put it in Park and ran up through the same RPM and nil vibration. Yep, not the engine.

I checked the alignment between the engine and diff and the front of the diff tilts down around 5deg. The engine mounts look to be in good condition and I have very little room to drop the front of the motor (Due steering rack clearance) or raise the rear of the transition. Looking at the diff it appears to be slightly tilted down sat the front but the leaves look strait

Any suggestions on where to go from here

I had the exact same symptoms on my truck two weeks ago...    I checked the u-joints for sloppiness but there was none... 

I then jacked the truck up and put the rear end on stands and I watched the driveshaft as it was rotating in gear.  I noticed significant runout behind the front u-joint.   I removed the driveshaft from the truck, and while there was no sloppiness, the front u-joint was stiff and bound up on one axis!!!   I replaced that U-joint and All Is WELL!!!

I'm glad I caught it early before that runout damaged the tailshaft bushing on the trans!!!

[bigmal 225]

10 hours ago, larryc94 said:

I would loosen the rear u-joint and the see if there is any play between the locating tabs in the yoke. I had a slight annoying vibration also. I had 0.012" play by pushing and pulling the joint against the tabs

As a temporary fix I cut two pieces of 0.006"  feeler gauge to fit between the two tabs. 

Looks like you have a "long" yoke, very hard to find in a 1310 u-joint size.  You have to get new or you risk having the same problem.  I got one at Quick Performance, only thing it is a 1330 u-joint.  You have to use a conversion joint 1310 by 1330 

 

If the above is good I would have a driveshaft shop check the balance

Thanks for the advice but I am not sure what you are suggesting. I am not familiar with the tabs you are talking about.

Also, I have new universals and the tailshaft has just been shortened and balanced. I hope the balance was OK.

[1969_Mach1 333]

I haven't had a lot of experience chasing down issues like you are having.  But in my experiences these are items that have contributed to it.  These might not all apply to your issue.

-  Out of balance wheels or driveline.

-  Motor mounts and/or trans mount.  This happens more often than you'd expect for odd vibration issues.  These are usually inexpensive and sometimes worth replacing if there is no other obvious cause.

-  Trans tailshaft bushing worn out.

-  Universal joints.

-  Bad tire(s).  More common with road noise than vibration issues.

-  Bent rear axle(s) or wheel(s) (uncommon).

I'm not saying rule out the driveline angle.  But unless you changed something in the suspension or drivetrain, I wouldn't think that would be off.

[larryc94 38]

the tabs I'm referring to are the locating tabs of the rear end yoke that the u-joint caps fit into

[bigmal 225]

56 minutes ago, larryc94 said:

the tabs I'm referring to are the locating tabs of the rear end yoke that the u-joint caps fit into

Thanks for that. Now I see what you mean. I will check the clearance later today.

[bigmal 225]

3 hours ago, 1969_Mach1 said:

I haven't had a lot of experience chasing down issues like you are having.  But in my experiences these are items that have contributed to it.  These might not all apply to your issue.

-  Out of balance wheels or driveline.

-  Motor mounts and/or trans mount.  This happens more often than you'd expect for odd vibration issues.  These are usually inexpensive and sometimes worth replacing if there is no other obvious cause.

-  Trans tailshaft bushing worn out.

-  Universal joints.

-  Bad tire(s).  More common with road noise than vibration issues.

-  Bent rear axle(s) or wheel(s) (uncommon).

I'm not saying rule out the driveline angle.  But unless you changed something in the suspension or drivetrain, I wouldn't think that would be off.

Thanks for these ideas. I will look at each one in order:

The vibration has existed since I got the car two years ago.

I have replaced the tyres, Replace the back wheels and had them balanced twice. Happy it's not wheels/tyres.

Motor and Transmission mounts look ok but that is definitely something I will need to consider

Bent axle, possible but I would expect to see that with the wheel rotating. I will double check that later today when on stands.

I will also have a look at exactly what is happening while on stands and running to see if it is something visible. (Thanks MAC390)

[bigmal 225]

I did some more trouble shooting and things are a little different to what I thought. I checked the clearance between the tabs and they are hard against both sides.

Had the car at the speed wit most vibration in 3rd gear, 50kmph. Wheels have about a 1/32" max out of true. I think that's OK.

Looking at the universals there is nothing obvious while it is vibrating. I jacked the front of the diff so it is more closely aligned with the angle of the front yoke. This made no difference to the vibration so it looks like the angle is not the issue.

I tried some more accurate checks of the vibration. In third rear (50kmph) it has a surging vibration which is around 1160 rpm. I changed to second and the vibration  was still most at 1160 rpm. Same in first although not as severe as in third.

In neutral I took the engine to 1160 rpm and the vibration is there. It rapidly disappears above this point.

This tells me it is not the universals, diff, axels. I am thinking transmission, torque converter or flex plate.

Any further thoughts?

[larryc94 38]

Disconnect drive belts to eliminate front accessories.

[1969_Mach1 333]

13 hours ago, bigmal said:

I did some more trouble shooting and things are a little different to what I thought. I checked the clearance between the tabs and they are hard against both sides.

Had the car at the speed wit most vibration in 3rd gear, 50kmph. Wheels have about a 1/32" max out of true. I think that's OK.

Looking at the universals there is nothing obvious while it is vibrating. I jacked the front of the diff so it is more closely aligned with the angle of the front yoke. This made no difference to the vibration so it looks like the angle is not the issue.

I tried some more accurate checks of the vibration. In third rear (50kmph) it has a surging vibration which is around 1160 rpm. I changed to second and the vibration  was still most at 1160 rpm. Same in first although not as severe as in third.

In neutral I took the engine to 1160 rpm and the vibration is there. It rapidly disappears above this point.

This tells me it is not the universals, diff, axels. I am thinking transmission, torque converter or flex plate.

Any further thoughts?

In an earlier post you mentioned in park and revving the engine you could not detect any vibration.  So now when in neutral and the vibration was there, was the car still rolling?

[bigmal 225]

1 hour ago, 1969_Mach1 said:

In an earlier post you mentioned in park and revving the engine you could not detect any vibration.  So now when in neutral and the vibration was there, was the car still rolling?

Thanks. As the vibration is in a reasonably narrow rev range and not as significant I missed that it is present when in neutral. And the wheels are stationary when in neutral.

I'm starting to think torque converter. I recently had the transmission looked at and was told it was making metal and on it's last legs. He cleaned the filters and said I'd get maybe 12 months from it. Seems OK at the moment but I am wondering if the torque converter has metal in it.

In case you haven't guessed this is an area I have almost no knowledge of.

[1969_Mach1 333]

Don't feel bad.  Your issue is more strange than anything I have encountered.  Since it is fine in park I wouldn't think it's the torque converter.  Almost seems isolated to the trans.  But I haven't seen an internal transmission issue cause a vibration.  That doesn't mean it can't be.  Might help If you knew what is going on inside the trans that is different between park and neutral when the car is stopped.

Since the trans is on it's last leg.  When you have the budget, it's probably worth rebuilding and replacing the torque convertor.  At least because of the wear and all the metal that was in the oil pan when it was serviced.

[bigmal 225]

4 hours ago, 1969_Mach1 said:

Don't feel bad.  Your issue is more strange than anything I have encountered.  Since it is fine in park I wouldn't think it's the torque converter.  Almost seems isolated to the trans.  But I haven't seen an internal transmission issue cause a vibration.  That doesn't mean it can't be.  Might help If you knew what is going on inside the trans that is different between park and neutral when the car is stopped.

Since the trans is on it's last leg.  When you have the budget, it's probably worth rebuilding and replacing the torque convertor.  At least because of the wear and all the metal that was in the oil pan when it was serviced.

It does also vibrate in neutral/Park at the same RPM but not as severe. I rang the transmission guy yesterday to ask about the torque converter and he said he has never seen one cause this sort of vibration. He suggested it could be the harmonic balancer. I am a little sceptical but will run it again and se if I can see it vibrating. Job for the weekend.

I will have the engine out in October to replace heads and cam so can look at the flex plate. Also considering a 2000 rpm stall converter so I can go a little lumpy on the can (just a little) but I will start another blog with questions about cam and lifter/rocker choice a little later.

[1969_Mach1 333]

All this time I thought it was fine in park.  With the new information your trans guy might very well be on the right track.  A harmonic balancer is simple to replace on these cars.  Might be worth replacing it.

I had a minor engine vibration through a specific RPM range on a Chrysler 360 far back in the late 1980's.  Lower RPM range like you are dealing with.  Not too bad but enough to be noticeable and sometimes annoying.  It was the harmonic balancer in that case.  The outer ring hadn't slipped so there was nothing obviously wrong with it.  The Chrysler 360 is also externally balanced.  So I guess the harmonic balancer just didn't have the correct imbalance.  The vibration was eliminated after I replaced the harmonic balancer.

Good luck with the future thread on cam choice.  Items like that can sometimes be subject to some personal preferences.

[bigmal 225]

2 minutes ago, 1969_Mach1 said:

All this time I thought it was fine in park.  With the new information your trans guy might very well be on the right track.  A harmonic balancer is simple to replace on these cars.

I had a minor engine vibration through a specific RPM range on a Chrysler 360 far back in the late 1980's.  Lower RPM range like you are dealing with.  Not too bad but enough to be noticeable and sometimes annoying.  It was the harmonic balancer in that case.  The outer ring hadn't slipped so there was nothing obviously wrong with it.  The Chrysler 360 is also externally balanced.  So I guess the harmonic balancer just didn't have quite the correct imbalance.  The vibration was eliminated after I replaced the harmonic balancer.

Good luck with the future thread on cam choice.  Items like that can sometimes be subject to some personal preferences.

Thanks for that. Interesting comment re the Chrysler 360. I also had a Chrysler 360 and could not track down a vibration in that. May have been the harmonic balancer for all those years.

[barnett468 418]

On 6/18/2018 at 2:11 PM, bigmal said:

It does also vibrate in neutral/Park at the same RPM but not as severe.

it can be a little worse/magnified when driving.

is the vibration cyclic or constant?