AOD SWAP PROBLEMS

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Ok, im new to the mustang world so your info would be great. I have a 72 mustang that I bought in pieces, so I found a cheap 351c stock 2v with a fmx trans attached. I never seen or heard it run, I installed and it run great, BUT it had a crazy vibration off idle.so I pulled trans and found it had a new flex plate on it.it turned out to be a 50oz, I replaced it with a 28oz and bam, its fixed. Now I have been driving this for a year and have decided to swap to an AOD, Now here is my issue, the AOD came with a 50oz so when I swapped it out I left the 28oz on because I thought it would vibrate again with a 50oz, now it vibrates again like it did with the 50 oz, So my question is does the engine dictate what weight you need or the trans? sorry about the novel but just wanted to tell everything that has happened.

 

scarpent1

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The counterweight on the flexplate is matched to the rotating assembly of the engine. Preferable the rotating assembly including the balancer and flexplate are balanced at a machine shop. So, if you engine originally used the 28 oz flex plate that is what should be used.

There could be many causes of the vibration. You need to look at whatever was changed and review each change for potential causes of the vibration. Good luck!

 
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The counterweight on the flexplate is matched to the rotating assembly of the engine.  Preferable the rotating assembly including the balancer and flexplate are balanced at a machine shop.  So, if you engine originally used the 28 oz flex plate that is what should be used.

There could be many causes of the vibration.  You need to look at whatever was changed and review each change for potential causes of the vibration.  Good luck!
it sound like I will pull trans and try both flexplates and see what one vibrates first. then go to next part like converter.

 

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If you haven't changed anything in the engine the flex plate would still be the 28 oz. A trans swap does not change the counter balance. Just trying to save you a step here. With the AOD swap did you have to shorten your driveshaft at all, if so did you get it rebalanced? Have to checked your pinion angles since the swap?

 

Mister 4x4

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With the AOD swap did you have to shorten your driveshaft at all, if so did you get it rebalanced? Have to checked your pinion angles since the swap?
I never changed the length of my driveshaft - no issues.  There also shouldn't be any issues with pinion angle as the FMX and AOD are generational, and pretty much the same casings (although the valve body and pan on the AOD is a bit larger).

 

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With the AOD swap did you have to shorten your driveshaft at all, if so did you get it rebalanced? Have to checked your pinion angles since the swap?
I never changed the length of my driveshaft - no issues.  There also shouldn't be any issues with pinion angle as the FMX and AOD are generational, and pretty much the same casings (although the valve body and pan on the AOD is a bit larger).
Not knowing what was done during his particular the swap, IE different trans mount, if other service items were replaced or other small upgrades done etc, I thought I would give him some things to check that might be causing the vibration.

 

Mister 4x4

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With the AOD swap did you have to shorten your driveshaft at all, if so did you get it rebalanced? Have to checked your pinion angles since the swap?
I never changed the length of my driveshaft - no issues.  There also shouldn't be any issues with pinion angle as the FMX and AOD are generational, and pretty much the same casings (although the valve body and pan on the AOD is a bit larger).
Not knowing what was done during his particular the swap, IE different trans mount, if other service items were replaced or other small upgrades done etc, I thought I would give him some things to check that might be causing the vibration.
Understood.  And good point on the balancing bit if he did shorten it. 

As for the pinion angle, I'm not seeing that as much of an issue - in order for the pinion angle to be affected much at all, there would need to be a lot of change in the tail-shaft location (upward/downward) which just isn't there to be had (spoken as someone who has owned lifted 4x4s my entire adult life).  

I'd be more suspect of a bad U-joint than the pinion angle itself, since the driveshaft would've needed to be adapted to an AOD output shaft with a special U-Joint.  FWIW, when I did my AOD swap, I'd forgotten to sufficiently tighten my axle-end U-joint and it unexpectedly dropped out of the car at slow speed in my neighborhood.

 

73pony

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Eric,

Pinion angle being out can easily cause vibration due to premature wear on u-joints etc and it is easy to check, you can download the Tremec app on your phone and check it with that. Better to find the cause of the wear than just replace parts, only to replace them again and it is easy to get the angle out of spec on these cars. Remember it is not just the angle of the transmission tail shaft, the rear end may have tilted slightly when the driveshaft was removed etc. You check pinion angle in 3 locations not just one! This is why I suggested checking it.

1. It will cause premature wear on parts that will cause this type of vibration.

2. It is easy to check

3. It is easy to get things out of alignment when you have a bunch of stuff torn out of the car.

Not trying to be a dick here but also not sure why you feel the need to argue or suggest that the advise given above should not be looked into. I'm just trying to give him some direction so he isn't just throwing parts at something.

 

Mister 4x4

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I'm not thinking that in the least, and I apologize if you feel that's how this conversation is going.

I'm also not arguing against checking any of those things out, but rather just explaining that pinion angle is an extremely unlikely issue, given the physical dimensions of both transmissions, my experience in making the swap myself, and having dealt with so many vehicles where no-kidding pinion angle changes have actually occurred.  

At the very worst possible scenario, the pinion angle between the FMX and AOD to the rear axle would only change maybe a degree, depending on how much lift (or droop) was introduced by the transmission mounting point - which would be precious little, given the restrictions of the transmission tunnel and the length of the driveshaft.  The pinion angle swing on either of the driveshaft when the suspension goes full cycle is less than 3 degrees.  That's hardly an issue of consequence.

I lifted my Jeep 4" with a spring kit that came with axle degree shims.  It also came with a 1" drop for the transfer case, and over the length of its 30" rear driveshaft (the front driveshaft is a LOT longer, of course), the whole installation changed the pinion angle on each end of the rear driveshaft a whole 4 degrees - well within the operating parameters of the U-joints at speed.  Never had an issue.  The front axle, however, is having issues because the shop that installed the lift kit, put the degree shims in because of being so worried about pinion angle, they screwed up the caster, causing all sorts of wandering issues (since been removed, and suffered no ill-effects on the drive line as a result).

The Mustang driveshaft is around 51" or so, so the amount of angle deflection is going to be even less at each end.

If the axle is changing its orientation simply from removing the driveshaft, there are much bigger issues to address. ;)

 

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You're sure making a lot of assumptions about the install. Just a point ask any good mechanic at an actual driveline shop and the first thing they check when there is driveline vibration is the driveline angles. Also anytime a trans is pulled, replaced, rear end pulled or replaced or when reinstalling the drive shaft after replacing u-joints this should ALWAYS be checked. My two cents.

 

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72mustang67gto,

What transmission was the car born with (trans code on the sticker) and what transmission crossmember are you using?

MY 71 fb came with a fmx and the po swapped in a c 4 transmission, there was a terrible mismatch.

So it could be possible there is a mismatch in your app as well.

The AOD is a very close match to the aod and not a c-4 at all.

In my case the trans was cocked to one side a fair bit (don't remember which side, but it vibrated pretty bad.

Perhaps you can find a number on your crossmember (if it is OEM and not aftermarket and we could verify which one you have.

Reports for this swap usually some trimming of the FMX crossmember may be needed.

Boilermaster

 

Mister 4x4

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You're sure making a lot of assumptions about the install. Just a point ask any good mechanic at an actual driveline shop and the first thing they check when there is driveline vibration is the driveline angles. Also anytime a trans is pulled, replaced, rear end pulled or replaced or when reinstalling the drive shaft after replacing u-joints this should ALWAYS be checked. My two cents.
Valid points.

However, based on the information he provided I'd be more interested to hear what happens when he swaps the flex plates around - they seem to be the lowest common denominator between the transmissions.  I know my FMX plate didn't fit the AOD's torque converter, and the AOD's flex plate didn't fit the 351C's output, so I had to buy yet another [correct] flex plate when it was time to mate up the AOD to the 351C.

 

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You're sure making a lot of assumptions about the install. Just a point ask any good mechanic at an actual driveline shop and the first thing they check when there is driveline vibration is the driveline angles. Also anytime a trans is pulled, replaced, rear end pulled or replaced or when reinstalling the drive shaft after replacing u-joints this should ALWAYS be checked. My two cents.
Valid points.

However, based on the information he provided I'd be more interested to hear what happens when he swaps the flex plates around - they seem to be the lowest common denominator between the transmissions.  I know my FMX plate didn't fit the AOD's torque converter, and the AOD's flex plate didn't fit the 351C's output, so I had to buy yet another [correct] flex plate when it was time to mate up the AOD to the 351C.
Swapping out the flex plates is a bad idea. If the engine is set up as a 28oz counter weight putting a 50 of counter weight on is not the thing to do.

 

Mister 4x4

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My AOD-to-351C conversion flex plate is a 28oz balanced unit as well.  It was necessary because the AOD's torque converter wouldn't bolt up to the factory 351C flex plate.  28 oz flywheel from mid-'80s Crown Victoria (P/N: FRA-205 Pioneer Inc - scored at O'Reilly Auto Parts)

Now who's assuming?  :whistling:  ;)

Here's the link to my AOD swap.  I'll work on fixing the pictures - I'd linked them from FB and they apparently don't like that.  https://www.7173mustangs.com/thread-aod-conversion

 

73pony

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My AOD-to-351C conversion flex plate is a 28oz balanced unit as well.  It was necessary because the AOD's torque converter wouldn't bolt up to the factory 351C flex plate.  28 oz flywheel from mid-'80s Crown Victoria (P/N: FRA-205 Pioneer Inc - scored at O'Reilly Auto Parts)

Now who's assuming?  :whistling:  ;)

Here's the link to my AOD swap.  I'll work on fixing the pictures - I'd linked them from FB and they apparently don't like that.  https://www.7173mustangs.com/thread-aod-conversion
I'm not assuming anything. Maybe you should try reading the first post by the person asking for help. And carefully reading. He was asking about putting a 50 oz flex plate on it that came with the AOD. Maybe you should check your ego at the door before posting.

 

Mister 4x4

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My AOD-to-351C conversion flex plate is a 28oz balanced unit as well.  It was necessary because the AOD's torque converter wouldn't bolt up to the factory 351C flex plate.  28 oz flywheel from mid-'80s Crown Victoria (P/N: FRA-205 Pioneer Inc - scored at O'Reilly Auto Parts)

Now who's assuming?  :whistling:  ;)

Here's the link to my AOD swap.  I'll work on fixing the pictures - I'd linked them from FB and they apparently don't like that.  https://www.7173mustangs.com/thread-aod-conversion
I'm not assuming anything. Maybe you should try reading the first post by the person asking for help. And carefully reading. He was asking about putting a 50 oz flex plate on it that came with the AOD. Maybe you should check your ego at the door before posting.
Maybe you should just learn to relax a little and remember this is just an internet forum where people are sharing ideas and opinions. 

Nobody has dismissed or disagreed with anything you've suggested checking on as to what could be the cause of the vibrations - I simply explained (rather well, I believe) that I thought the pinion angle is most likely not the issue, so you accused me of making assumptions and can't take a friendly poke back in return.  Now, you're suggesting I'm an egomaniac for posting up an actual part number and experience from having actually done my own AOD swap.  Sorry if I've hurt your feelings in daring to [apparently] disagree with you.

I read the initial post and obviously took something different from it than you did.  You're having him chase down things that are definitely valid concerns, but are more secondary issues than anything.  The lowest common denominator in this whole thing is the wrong flex plate, and the vibrations went away and came back when things were done directly involving the flex plate.  Knowing that he doesn't have the right flex plate for the AOD-to-351C conversion, I've made my suggestion and offered a viable part number.

Maybe now we just sit back and wait to find out what the resolution might turn out to be.

 

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Can we just Breathe.... now a deep cleansing breath....

 
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Thanks to everyone on there input, I did not mention one fact in my original post, I forgot to mention this vibration I had is with no drive shaft installed just sitting in one place. UPDATE: so what I did was pulled trans. installed bell housing off a fmx to mount starter. then ran engine with just flex plate, Ran Fine no vibration, Then installed converter and ran with just converter and flex plate and no vibration. then installed trans again and vibration is back. I have figured it is something in trans that is the issue. So im sending it to Monster Transmission to have it built.

 

Mister 4x4

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Well.  There it is.  Thanks for the update, and let us know the rebuild goes - Good luck with it.

We still good, Jason?   :imsorry:   ::beer::

 
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