Yet another problem: bad vibration between 1700 and 1900 rpm

[Pentroof]

This build is a fresh 390 in a 1970 F100 with a new TCI C-6 and street converter.
Motor mounts are not stock, but have rubber isolators (front crossmember is from a late model Crown Victoria)
Stock transmission mount.
New flexplate, zero balance. No issues with starter engagement.
New Pro Products balancer, nice and tight.

I have a vibration that starts around 1700 rpm, is worst at around 1750, and then diminishes as rpm is increased. Above 1900, it's not really noticeable. If I rev the motor quickly, it revs right through that zone freely and you would never know. While driving, I feel it on the way up and down.

Vibration exists while driving, as well as parked or coasting in neutral and revving the motor. No connection whatsoever to vehicle speed.

[Pentroof]

The only accessory I question is the power steering because of the age of the pump, even though I went through it and had no concern.

I just pulled that belt and had no change in vibration.

The fan is an original steely and had no issues before this build. Alternator is a brand new 3G.

Next move is to pull the inspection cover and, well...inspect. Maybe a flexplate/converter issue?

Any other suggestions?

[machoneman]

Make sure # 7 and #8 plug wires are widely separated (not parallel) to avoid cross-fire.

[BruceS]

I had a stock aftermarket converter installed that was out of balance on my Fairlane SBF with C4.  Vibration was most noticeable in the 1500 rpm range and higher.  Had the tranny shop change to a different converter and problem went away.  From then on, I've only used "name brand" converters.  Btw I have had an ATI Street Fighter in there now for a number of years with no issues. 

[Pentroof]

Make sure # 7 and #8 plug wires are widely separated (not parallel) to avoid cross-fire.

Yep, well aware. That's why the wires look like this...
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7 and 8 divert immediately at the distributor and are furthest apart in the wire separator on that bank.
Coming off the plugs, 8 goes to the rear and 7 is routed forward, under 5 and 6.

[WConley]

I agree with Bruce.  At that kind of rpm, it's something big and heavy that's out of whack.  I would suspect the converter...

You mentioned that idle quality is OK.  If anything was wrong at idle, especially switching in and out of gear, I'd look hard at the engine mounts.  Seems like you've got that covered though!

[Pentroof]

I agree with Bruce.  At that kind of rpm, it's something big and heavy that's out of whack.  I would suspect the converter...

Yeah, that's what I'm suspecting. Just looking for some other potential low hanging fruit. I guess I'll crank up the A/C in the garage. If it is the converter, I'm screwed. I bought this TCI tranny package almost a year ago and it sat in a crate in my garage. I've only had the truck running and driving for a month or so, but have been focused on ironing out the little details and don't have any real miles on it.

[My427stang]

Make sure all the bellhousing bolts and converter nuts are tight first, amazing the odd feeling you can get if things loosen up.

[HvyFt4spd]

 The inertia ring or crank hole itself can be off center on the balancer.

[Pentroof]

I removed the inspection cover and checked the TC bolts. All good.

Then I started the motor and took a few seconds of video. It looks like there is a wobble, but you can't tell until you look at it frame by frame. Some guys suggest using a timing light, but I found reviewing the video on my phone in edit mode was quite revealing. Simply dragging the slider at the bottom of my iPhone from one frame to the next shows the flexplate is moving position.

Here's the good news! It's not possible to lower a C6 out of a 67-72 F100 because of a crossmember that's riveted in. So, I either have to move the motor as far forward as possible, remove the motor altogether, or cut the crossmember and fab some brackets to bolt it back in.

Since the tranny came from TCI, I should probably plan for it coming out on a regular basis, so I'm leaning toward modifying the crossmember.

[Barry_R]

Can you unbolt and push the transmission back an inch or so to disengage it from the flexplate.  Just enough to start it up without the converter spinning?

[blykins]

Any chance it’s a fuel related issue causing an imbalance or stumble?  I’ve had some jacked up carbs that have created imbalance issues that would shake the engine.

[Pentroof]

Can you unbolt and push the transmission back an inch or so to disengage it from the flexplate.  Just enough to start it up without the converter spinning?

Barry, I think that's my next move.

[Pentroof]

Any chance it’s a fuel related issue causing an imbalance or stumble?  I’ve had some jacked up carbs that have created imbalance issues that would shake the engine.

This motor has a Holley Sniper TBI. I suppose it could be a bad transition area or gap in the mapping, but I don't see a discontinuity in the AFR.

I can't rule out fuel at this point. I do have the timing issue (different thread) and need to dive into the tables.

Have you experienced a TBI unit causing a seat of the paints vibration?

[C6AE]

I have a '67 F250 with a C-6 (yes, I did that!)
Just grind off the rivet heads, punch the rivets through and you can move the cross member diagonally enough to remove it. I use nuts and bolts to reassemble...

[Pentroof]

Can you unbolt and push the transmission back an inch or so to disengage it from the flexplate.  Just enough to start it up without the converter spinning?

How does one go about starting an FE once the transmission (and starter bolted to the bellhousing) is pushed back?

The guy in charge of answering the phone at TCI suggested I back out the studs from the converter. If I were to entertain this idea, how much can the converter push back into the pump? I think 1/2 AN inch would do.

[Barry_R]

creativity, some longer bolts and a stack of flat washers...this is only a one time try it sort of deal

[My427stang]

The issue with the Ford design is that the studs will hit the flywheel, I have never had to pull a converter stud out of a Ford, but in theory, if you could, you shouldn't have to back the tranny up.  The pilot would be close, but I think it would work.  The issue would be keeping it from sliding forward again as you revved the engine.  If it did, it would spin up and being unbolted likely make scary noises as you are listening for less scary noises LOL Not to mention, you still won't really know the cause, just maybe the location.

I would have to guess, unbalanced converter, wrong converter pilot size, or bent/broken/wrong/poorly seated flexplate. Although I do agree you could fire it, I am not sure you are going to get anywhere with the test

I'd likely slide the tranny back and drop the flywheel and pull the converter and see what you can see.

[Pentroof]

Thanks Ross. I did end up pulling all 4 converter bolts today. The converter would only push back enough to prove the drain plug would still be an issue, even if I did pull the studs.

I also removed the fan to rule out itself and the water pump...I know, but I was hoping for an easy way out.

I’ve decided to pull the transmission. I just haven’t decided if today is the day. This brand new POS from TCI just has me in a bad mood. The drops of ATF at the Bell mouth are telling me I’m at least adding a seal to the list as well. Probably getting abused by the TC.

Well, it’s on the lift and I have a tranny lift too, so no excuses. It’s a beautiful day here too. I should be out in the Cyclone, not cursing TCI. I’ll just crank the tunes and grab a beer.

[Pentroof]

Well, no obvious defects. The converter has a slight wear mark around half of the hub, but nothing that can be felt with a fingernail.
The hub measures 1.995". Not sure what it should be, but there was quite a bit of fluid inside the bell.

I'm not a slushbox guy, so how much should the converter move back and forth once it's bottomed out into the pump? What I mean is if you were rocking it With both hands as if checking for bad wheel bearings.

The flexplate is correct, but it looks really cheap to me. It's a stamped piece purchased from Mac's. The stamping markings aren't completely even. I haven't pulled it yet, but will likely replace it even if it's flat.

I'm also going to buy a new converter. I've called every transmission shop within 80 miles and none of them have the ability to balance a converter.

[Barry_R]

I'm also going to buy a new converter. I've called every transmission shop within 80 miles and none of them have the ability to balance a converter.

Try an engine shop.  I've never done a converter, but our balancer will accommodate all kinds of stuff and we have balanced flywheels, clutch discs, pulleys, and machine parts.

[temarey]

Check that the converter hub is centered with the pump hub.
I have seen them not match and it causes odd vibrations.

[Pentroof]

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I took a quick pic this morning of the flexplate quality. I had forgotten that the holes for the bolts had to be deburred. All of the holes on this were die punched, not milled or drilled.

You can also see that the stamping dies are a 2 piece configuration and the 2 pieces didn't produce equal forces. I can feel a ridge at these locations. I'm beginning to think the flexplate may be forcing the converter to walk around, but I'll need to pull it and check it for runout.

In any event, I have a Hughes converter, PA flexplate and Timken seal ordered and they'll be here tomorrow.