Can't identfy vibration

mhjo · Sep 11, 2011

After AOD swap (from c4) I experince vibration at a certain rpm. It is noticable at 50 mph in 3d and 80 mph in OD. Wheels have been balanced, axle too. Vibration can be felt in the shifter stick.

What can this be?

2+2GT · Sep 11, 2011

mhjo said:
Wheels have been balanced, axle too. Vibration can be felt in the shifter stick.

Driveshaft?

rbohm · Sep 11, 2011

2+2GT said:
Driveshaft?

seconded, check the front U joint specifically for excess wear and proper installation. the next thing to deal with the in output shaft bushing that keeps the yoke in proper alignment. if it is worn or the output yoke is worn, then you will also have a vibration.

Slobin3d · Sep 11, 2011

is your driveshaft a slip yoke style or a 2 piece?

if it is a 2 piece have you checked that your driveshaft is in phase? its very common to get the driveshaft 180* rotated and that will cause vibration and the more the angle of the drive shaft the worse it gets

or since your trans is new, does your pinion angle and trans output angle angle match, if not that will cause vibration too, a cvd driveshaft or axle shims can fix this

96 DOHC Cobra · Sep 11, 2011

What flexplate did you use? The swap requires a conversion type flexplate because the 5.0 that the AOD came from and your 289 are not balanced the same. The C4 flexplate won't bolt up to the AOD converter. The AOD flexplate will bolt right up to your 289 crank, BUT will cause vibration due to the balance differnce.

mhjo · Sep 12, 2011

Thanks so far. This will be my check list.

rbohm · Sep 12, 2011

96 DOHC Cobra said:
What flexplate did you use? The swap requires a conversion type flexplate because the 5.0 that the AOD came from and your 289 are not balanced the same. The C4 flexplate won't bolt up to the AOD converter. The AOD flexplate will bolt right up to your 289 crank, BUT will cause vibration due to the balance differnce.

that was my first thought, until i realized that he had the vibration at a couple of rpm points rather than through the whole rpm range.

mhjo · Sep 12, 2011

I only have vibration at a certain rpm

GTA6t7 · Sep 13, 2011

I'm having the exact same problem with my 67 aod conversion. Your post said you had your axles balanced. I didn't know that was possible. Who did you take it to?

Hack · Sep 13, 2011

GTA6t7 said:
I'm having the exact same problem with my 67 aod conversion. Your post said you had your axles balanced. I didn't know that was possible. Who did you take it to?

Don't balance your axles unless you're sure that's the problem. Did you swap axles right before you got the vibration? If you changed the trans and then got the vibration, why not start at the trans when looking to cure the vibration problem?

horseballz · Sep 13, 2011

mhjo,
You haven't answered the implied question about whether/how you dealt with the flex plate imbalance issue. If it is a stock flex plate from a late model 5.0 it will be balanced incorrectly for your 289 and WILL cause a vibration that may be worse at different RPM's.
HTH,
Gene

mhjo · Sep 14, 2011

Sorry for "lost in translation" When I say axle I mean drive shaft.
The people that sold me the flex plate insist it is the right one (they are a specialized Classic Mustang supplier i Norway who get their stock from NPD and Summit).
However, I will call the today and ask for product name/number and post here.

rbohm · Sep 14, 2011

horseballz said:
mhjo,
You haven't answered the implied question about whether/how you dealt with the flex plate imbalance issue. If it is a stock flex plate from a late model 5.0 it will be balanced incorrectly for your 289 and WILL cause a vibration that may be worse at different RPM's.
HTH,
Gene

actually yes he did.

mhjo said:
I only have vibration at a certain rpm

if the flexplate was the wrong one it would have a bad vibration through out the rpm range, and not just a couple of specific rpm points, which is why i think that he has a bad output yoke bushing, or the U-joint was improperly assembled.

mhjo · Sep 14, 2011

I called my Mustang supplier today (largest i Scandinavia), and he told me that I have a 28 oz AOD flex plate made for old model 289/302.

Slobin3d · Sep 14, 2011

FORDMUSCLE.com webmagazine - Vibration Diagnosis Guide

i'm still betting on the driveline angle or phase

mhjo · Sep 14, 2011

Thanks for link.

Driveline angle will be checked by pro's tomorrow. Can you please explain "phase"?

Slobin3d · Sep 14, 2011

mhjo said:
Thanks for link.

Driveline angle will be checked by pro's tomorrow. Can you please explain "phase"?

if you have a 2 piece driveshaft or custom built one that was made wrong, if the ends of the yokes are rotated the wrong phase the U joints will fight each other and cause vibrations

View attachment 173127

mhjo · Sep 14, 2011

Thanks! Great - I'll add it on the check list.

BTW: The guy who changed one of the U-joints and Yoke said that one is '65 and the other is '67 (larger). Any impact?

Slobin3d · Sep 14, 2011

mhjo said:
Thanks! Great - I'll add it on the check list.

BTW: The guy who changed one of the U-joints and Yoke said that one is '65 and the other is '67 (larger). Any impact?

As long as the appropriate hardware and yokes were used you shouldn't have an issue.

mhjo · Sep 15, 2011

They called today and reported that they found some issues. I shall report the findings and results tomorrow when I get the car back. Thanks again for tips!

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