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copb8

Need Your Opinion on Recent Repair Issue

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In December I brought my car into a reputable transmission shop in Dallas that's been in business over 50 years and has people very familiar with FMX transmissions. I wanted the following done to my transmission:

  • Seal all leaks
  • Fix issue with hard shifts
  • Fix issue with always starting out in 2nd
  • Clean up the entire unit

When I picked up the car there was a very obvious vibration at around 3000-3200 rpms which cause a cycling drone as your drove down the highway. VERY obvious and irritating. All of the other items on my list were fixed and the transmission shifted beautifully for the first time I'd owned the car and didn't leak a drop on my garage floor. 

I called and talked to my contact and we agreed to return the car to the shop. Once there they seemed to be looking for outside reasons this was happening. There was a lot of talk about the rear-end, suspension rubbing, etc., etc. While I waited they put it on the rack and said there were some rubbing issues with the exhaust and body, that rear suspension components were to close to the exhaust, etc. etc. All these items were very minor and adjusted right then and there. As I suspected while driving home the vibration was unchanged. All the items they mentioned were in place when I got there and the car didn't vibrate before then. 

Again I returned the car and again there still seemed to be some talk of outside interference and possibly the engine had a vibration. I told them that there was never any vibrations prior to the rebuild and that it had to be something to do with the transmission. Also, you could clearly feel the vibration when the car was in neutral and revved to 3000+ Rpms.

They took the car for another week. They pulled the transmission and said that they found that the flexplate was installed incorrectly from a previous repair and that they put in a 'new' flexplate and another rebuilt torque-converter in.  They also said that while the transmission was out they installed a bell housing and ran the car with no transmission installed. It ran 100% smooth with zero vibration from the motor! However when I went to pick up the car and rev'ed it in neutral there was still a very clear vibration from just off idle all the way to 4000+ where it smoothed out a little.  It was a bit different but obvious and they recognized this as well. I left the car there.

So, after my long story, I have these questions:

  • Since they ran the car with the original flexplate and bell-housing doesn't that 100% eliminate either of those as any source of vibration?
  • Since the vibration happens with the transmission mounted and while the car is stationary and in neutral doesn't that 100% mean it's either the torque converter or the transmission pump? Is there anything else spinning in the transmission when in neutral?
  • Doesn't all of this 100% indicate that there's an issue with the transmission and nothing else on the car?

I like the guys at the shop and I believe they're trying to do the right thing but I also believe they'd like to see this car gone and that the issue not be theirs.

Thoughts?

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54 minutes ago, copb8 said:

In December I brought my car into a reputable transmission shop in Dallas that's been in business over 50 years and has people very familiar with FMX transmissions. I wanted the following done to my transmission:

  • Seal all leaks
  • Fix issue with hard shifts
  • Fix issue with always starting out in 2nd
  • Clean up the entire unit

When I picked up the car there was a very obvious vibration at around 3000-3200 rpms which cause a cycling drone as your drove down the highway. VERY obvious and irritating. All of the other items on my list were fixed and the transmission shifted beautifully for the first time I'd owned the car and didn't leak a drop on my garage floor. 

I called and talked to my contact and we agreed to return the car to the shop. Once there they seemed to be looking for outside reasons this was happening. There was a lot of talk about the rear-end, suspension rubbing, etc., etc. While I waited they put it on the rack and said there were some rubbing issues with the exhaust and body, that rear suspension components were to close to the exhaust, etc. etc. All these items were very minor and adjusted right then and there. As I suspected while driving home the vibration was unchanged. All the items they mentioned were in place when I got there and the car didn't vibrate before then. 

Again I returned the car and again there still seemed to be some talk of outside interference and possibly the engine had a vibration. I told them that there was never any vibrations prior to the rebuild and that it had to be something to do with the transmission. Also, you could clearly feel the vibration when the car was in neutral and revved to 3000+ Rpms.

They took the car for another week. They pulled the transmission and said that they found that the flexplate was installed incorrectly from a previous repair and that they put in a 'new' flexplate and another rebuilt torque-converter in.  They also said that while the transmission was out they installed a bell housing and ran the car with no transmission installed. It ran 100% smooth with zero vibration from the motor! However when I went to pick up the car and rev'ed it in neutral there was still a very clear vibration from just off idle all the way to 4000+ where it smoothed out a little.  It was a bit different but obvious and they recognized this as well. I left the car there.

So, after my long story, I have these questions:

  • Since they ran the car with the original flexplate and bell-housing doesn't that 100% eliminate either of those as any source of vibration?
  • Since the vibration happens with the transmission mounted and while the car is stationary and in neutral doesn't that 100% mean it's either the torque converter or the transmission pump? Is there anything else spinning in the transmission when in neutral?
  • Doesn't all of this 100% indicate that there's an issue with the transmission and nothing else on the car?

I like the guys at the shop and I believe they're trying to do the right thing but I also believe they'd like to see this car gone and that the issue not be theirs.

Thoughts?

im not sure the flexplate can be installed incorrectly. even though the holes look evenly spaced it actually only lines up correctly in one position. 

I had a similar problem recently with a vibration, it turns out i was using a flexplate for older mustang (28oz) when being i installed a 5.0 HO engine it requires a 50oz. I replaced the flexplate and vibration is gone. You may want to make sure your new flexplate is a 28oz which i believe is what is required. 

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Thanks Newstang.

Follow up on your response. Since the current flexplate was installed when they had the empty bell bousing installed and the engine ran 100% smooth, wouldn't that eliminate the flexplate from consideration?

 

 

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12 minutes ago, copb8 said:

Thanks Newstang.

Follow up on your response. Since the current flexplate was installed when they had the empty bell bousing installed and the engine ran 100% smooth, wouldn't that eliminate the flexplate from consideration?

 

 

so the engine was running with flexplate on and transmission disconnected?

If so, im not sure, you mentioned that it was put on wrong ( which i dont think can be done) and they put on another one. I really dont know if the balancing is strictly for the engine or if it requires it to be connected to tranny.

 

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When I say I'm no expert in this please know that I'm even less than that.

My understanding is the flexplate weight is to counterbalance the engine only. That is you upgrade your engine to be internally balanced, no weight is necessary at all on the flexplate.

They showed me the old flexplate and torque converter and laid the plate on the converter clocked where they said they found it. You could see a small dent/dimple where the drain bolt dented the plate. Now I can't say if they did that on the first install or not. Maybe that's why the vibration changed after the second go-around? 

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9 minutes ago, copb8 said:

When I say I'm no expert in this please know that I'm even less than that.

My understanding is the flexplate weight is to counterbalance the engine only. That is you upgrade your engine to be internally balanced, no weight is necessary at all on the flexplate.

They showed me the old flexplate and torque converter and laid the plate on the converter clocked where they said they found it. You could see a small dent/dimple where the drain bolt dented the plate. Now I can't say if they did that on the first install or not. Maybe that's why the vibration changed after the second go-around? 

oh, so the flex pate installed on the engine correctly, they didnt line up the converter to the hole for the drain plug. not sure if a dimple would make it shake though.

 

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The flexplate has unevenly space bolts and can only be installed in one orientation.  A vintage Mustang with a FMX has what is called a 28oz imbalance. The flexplate has a weight welded to it.  

A bad torque converter could cause vibrations.

A bad harmonic balancer, also a 28oz imbalance, could also cause vibrations.

If the car did not vibrate when you turned it into the shop, then, it is something they did.

If it does it in neutral, then that eliminates the downstream drivetrain (driveshaft, universals, rear end, tires/wheels)

I would make sure they have a 28oz 164 tooth flexplate that is made for an early Mustang.   If you still have the old flexplate post a picture.

 

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This is a tough one.  Starting to seem likes it's the torque converter.  But they've tried two with the same results.  Were they both from the same rebuilder?  Has anybody tried a new harmonic balancer?  I know it doesn't seem like that's the source.

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22 minutes ago, Vicfreg said:

The flexplate has unevenly space bolts and can only be installed in one orientation.  A vintage Mustang with a FMX has what is called a 28oz imbalance. The flexplate has a weight welded to it.  

A bad torque converter could cause vibrations.

A bad harmonic balancer, also a 28oz imbalance, could also cause vibrations.

If the car did not vibrate when you turned it into the shop, then, it is something they did.

If it does it in neutral, then that eliminates the downstream drivetrain (driveshaft, universals, rear end, tires/wheels)

I would make sure they have a 28oz 164 tooth flexplate that is made for an early Mustang.   If you still have the old flexplate post a picture.

 

Thanks vicfreg.

 

You know, now that I think of it, they told me they noticed that the flexplate mounting was off on the SECOND time they pulled the transmission. Well it would've been impossible not to pull the transmission and converter the first time they rebuilt it so id HAD to be their tech who clocked it wrong putting it back the first time.

Only way that wouldn't be the case is if they somehow pulled the transmission off while leaving the converter in place. Not even sure if that's possible and even if it where it would mean they didn't rebuild the converter the first time when they said they did.

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3 hours ago, copb8 said:

When I say I'm no expert in this please know that I'm even less than that.

My understanding is the flexplate weight is to counterbalance the engine only. That is you upgrade your engine to be internally balanced, no weight is necessary at all on the flexplate.

They showed me the old flexplate and torque converter and laid the plate on the converter clocked where they said they found it. You could see a small dent/dimple where the drain bolt dented the plate. Now I can't say if they did that on the first install or not. Maybe that's why the vibration changed after the second go-around? 

This sounds like they have installed the converter incorrectly on the flex plate. As the vibration only occurred after they did the work it would be them. If the vibration is still there now the converter is in the correct position it could be an issue with the converter but I understand that this is not likely. When they said they ran the engine with a dummy bellhousing and no torque converter were you present? I would start doubting what they are telling you unless it is demonstrated in your presence. I’m suspecting it is related to the flex plate. Possibly the wrong counterweight 28/50 or a previously balanced engine that included the flex plate and the new one is not matched.

Ive been chasing a balance issue for two years. I’m about to start experimenting with small Tyre balance weights in various positions on the flex plate and see if I can improve it by trial and error. If I find the correct weight/location I will use a small bolt in that location. Could be something to consider if all else fails.

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The flexplates look the same, but can be very different.  I have a C-6, and that flexplate is different that the C-4 and FMX flexplate.  They look very similar.   So, the guys who rebuilt your transmission needed to get the correct flexplate.   the question today is if they have the correct flexplate, why is there any vibration at all?   They did it, so it is their problem.   If the engine and flexplate don't vibrate on their own, then the problem is in the transmission, which they rebuilt.   

There are many resources on line.    Here is an example:    

 

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Before I talk to these guys again today can someone answer whether you can physically remove the transmission from the car without unbolting the torque converter?


It seems that if space wasn't an issue you could pull the transmission and bell housing straight back far enough to clear the input shaft of the transmission from the converter and drop the gearbox BUT is practical terms I believe the bell housing would hit the transmission hump well before you'd be able to clear the units? Am I right?

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I can say back in 1980 I watched my oldest brother install a 351W in a 1969 Mach 1 with the torque converter attached to the flex plate.  It was an FMX trans as well.  I guess he was careful enough aligning everything and just rotated the crank at the balancer a little to engage the splines.

To answer your question, I don't think that's what happened, but, I since the motor and trans can lean downward when removing the trans, it can be removed with the torque converter attached to the flex plate.

Maybe the shop should try a torque converter from another manufacturer?

Most of us work on our own classic cars.  These day's I think reputable repair shops that can work on older cars are far and few between.

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Thank you. That was the answer I was looking for.

I actually did remove the transmission last year and replace all of the seals but it still leaked a bit and shifted poorly so I figured I go to someone who was expert and had experience in old transmissions. The the shops credit the transmission is dry as a bone and shifts and operates beautifully now, with the obvious exception of the vibration.

 

 

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On ‎2‎/‎4‎/‎2020 at 11:17 AM, 1969_Mach1 said:

I can say back in 1980 I watched my oldest brother install a 351W in a 1969 Mach 1 with the torque converter attached to the flex plate.  It was an FMX trans as well.  I guess he was careful enough aligning everything and just rotated the crank at the balancer a little to engage the splines.

To answer your question, I don't think that's what happened, but, I since the motor and trans can lean downward when removing the trans, it can be removed with the torque converter attached to the flex plate.

Maybe the shop should try a torque converter from another manufacturer?

Most of us work on our own classic cars.  These day's I think reputable repair shops that can work on older cars are far and few between.

Yes you can... Have done it with my 4R70W a few times LOL, just a matter of making the motor tilt back far enough in the rear...Don't even ask how I made that happen LOL

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Here's a different thought.  I believe the vibration could be a drive train alignment issue.  If the transmission was removed and replaced, did they put in a new mount and if so was it the correct one?  If possible, I would start looking at the alignment of the components. If you get the transmission misplaced when mounted, the drive shaft angles (relative to transmission on one end and differential on the other) change slightly, and it's possible that the different configuration can have harmonic frequencies that set-up vibrations.  with a situation like this, you can have all the right parts in there, but still have an unacceptable performance due to the physical alignment of the parts.  I would search this forum for "drive shaft misalignments" and see what you can find.

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2 questions.

Would alignment still be considered a possible issue if the vibration happens while standing still and revving in neutral?

Should the transmission rest firmly on the frame cross-member?

 

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The trans should rest on the rear mount and not compress the rubber.

Removing the trans with the converter connected to the flex plate is easy, You should not install it that way.

damage can occur to the seal, pump, convertor so installing it into the trans first is the proper way to avoid this.

From your postings on this problem, I have not seen any that say they balanced the convertor after it was rebuilt.

If there is no shaking when they had it all off and the shaking returned when installed the only rotating mass is the convertor/pump when in neutral so that's where I would look.

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On 2/6/2020 at 7:06 AM, copb8 said:

2 questions.

Would alignment still be considered a possible issue if the vibration happens while standing still and revving in neutral?

Should the transmission rest firmly on the frame cross-member?

 

In neutral, only the torque convertor in the transmission is rotating, so a vibration could theoretically be setup by having the torque converter out of balance, or improperly bolted up to the flex plate.  Bottom line, look for replaced or repaired parts that are rotating while in neutral as these items could be causing an out of balance rotation, and hence vibration.

I would say yes, the trans should mount solidly.  If it is not solidly in it base, the engine is sitting on two mounts on the sides and could tend to oscillate without the 3rd hard point of the transmission mount. I agree with Mach1 above.

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Follow-up question. I don't believe the shop has done this and was wondering if doing so would eliminate the torque converter as the issue.

Couldn't they mount the flex-plate and torque converter, and bell-housing, but not the transmission, and then run the engine to see if there's a vibration? Or would the torque converter be too unstable without the one end inserted into the transmission case and therefore not a reliable or feasible test?

 

 

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Not feasible as there is fluid in convertor. a test run with flex plate is a normal test.

Has the trans shop done a bench test of the completed trans? some shops have a dyno type set up just for this and testing operation of rebuilds.

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I don't think they have any ability to bench test the transmission. They do rebuild a LOT of torque converters and have the equipment for it.

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