Broken flexplate or convertor?

Knebel

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My Fury has started with a decent rattle sound at idle that has been getting a little more consistent today after some WOT tests from stop in a parkinglot.. I have had some starter kickbacks after installing a multispark and it now makes the same rattle sound when cranking. Happens more in N and P but I can make it go away sometimes by shifting into Drive or reverse. How would I go about diagnosing a bad flexplate and torq convertor? Id rule out any valvetrain noise based on where its coming from, my vacuum is stable and the engine runs otherwise smooth ( at first though it was fuel igniting in the downpipe).

I also had the valvecovers off and all valves move and all plugs look fine. Noise there when cranking but not starting.

Video coming soon!

 
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fury fan

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I see you have gauges - presumably OP is good, you're savvy enough to have checked that.

You mentioned detonation in your video - I doubt it's that, detonation seems to require a variety of factors, which nobody ever talks about occurring at idle.

Walk around with a long screwdriver and place it on solid mounting for a listen (boltheads are good, avoid sheetmetal parts). If you listen to that with a timing light flash, that will tell you if in valve train or bottom end (which includes torque converter).

Then engine is also shaking a bit in neutral, but not in drive. Chase that down. Is potentially something hitting when the engine shakes?

See if a noticeable difference in N or P - one is allowing cooler flow (I think) so it is possibly loading the trans pump differently (but I'm stretching on that one).

Years ago a buddy had a cracked flexplate, and it made a rod-knock sound. (I don't remember the sound much, it was 25 years ago, but I distinctly remember it fooled several folks into saying he needed a new engine)
 
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65sporty

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Take the dust cover off the trans and look at the flexplate, look for cracks close to the bolt holes. Make sure the converter bolts are tight also
 

Knebel

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Sounds like rocks in a dryer. Nothing is different on the motor, only thing was disc brake install. The noise started today. OP not super high but not any different than it was before the sound started. Rockers all had a good amount of oil on them!
 
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CBODY67

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A flex plate crack can sound like some other things. Removing the dust cover and looking for lines of rust on the flex plate can be an indication of a crack. "Tight bolts" are good to investigate, BUT if the bolts are a thread too long for the hole, they will tighten down firmly (as normal) to the correct torque, but still allow the flex plate to move a bit under the bolt head, leading to a crack situation.

Please keep us posted on what you find,
CBODY67
 

Knebel

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Louder in Park than in N. Very loud when just cranking with the starter! Im doing this in a 1 car garage so i will need to lift the car tomorrow to do some inspection. I just banged on the teeth a little from some reach to see if anything there obviously moves but it did not appear that way
 
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fury fan

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As I think about this again -

You mentioned doing some WOT from a stop in a parking lot. Were you doing these in Drive, shifter in 1, or?

The fact that the noise goes away in Drive, but is present in P and N, and occurs when starting also are likely good glues.

I am wondering if your sprag might've failed, and if its rollers are what you are hearing bouncing around?
 

Knebel

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I did some in first and some in drive. I had to adjust my accel pump after installing a spacer.

What is a sprag?
 

HWYCRZR

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I am thinking a new flex plate is in your future. I bet you will find the flex plate holes are egg shaped or distorted. If you tighten you will buy a few more miles but with that much slop they will likely come loose again.
I could be wrong, but seems like an awful lot of movement even with loose bolts.
 

Knebel

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Yeah thats what im thinking BUT... could one simply put a spotweld on the bolt and flexplate? This is gonna have to be a keep it driveable situation until I can get a new flexplate and converter (need a little higher stall than stock anyway)
 

Big_John

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Suggestions on some quality Bolts for this?
The stock bolts are very good quality.

What you need to do is clean the threads and apply some blue Lock-Tite to the bolts.

I agree, you should figure on replacing the flex plate as the holes are now worn. Probably the bolts too.
 

fury fan

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Agreed, stock bolts are sufficient, and you need a new flexplate. Make sure whatever bolts you get are short enough, so they don't bottom out and give a false sense of proper clamping (somebody already mentioned that). Good that you found the issue, that it's readily repairable, but sucks that the trans needs to come out.
I did some in first and some in drive. I had to adjust my accel pump after installing a spacer.

What is a sprag?

The sprag is a 1-way clutch in the rear of the trans. It is sometimes the Achilles heel of a Torqueflite and can get damaged if doing an 'improper' burnout, esp one where the tires spin and then quickly grab (or in the case of full-throttle driveline failure). Depends on whether the trans has low-band-apply configured in the valve body, and what position the shift lever is in during the burnout. But a damaged sprag can go undetected and then cause another component in the trans to overspeed, resulting in the transmission exploding. It's scary stuff, and it's real, but as I said, has a lot of factors involved.

I've read about it and still don't know all the ins/outs. But I haven't done a burnout in 15 years so not a concern for me.

Your car and mine are cousins! Is that EZ-EFI or one of the Holley/MSD units?
 

MONC440

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Yeah thats what im thinking BUT... could one simply put a spotweld on the bolt and flexplate? This is gonna have to be a keep it driveable situation until I can get a new flexplate and converter (need a little higher stall than stock anyway)
Lol. Years ago dad and I were on a road trip in our 76 Dodge truck about 450 miles from home and a torque converter bolt broke off and we couldn’t get it out. We limped it to a small mom and pop shop and my dad mig welded the flex plate to the converter. Made it home and drove it for farm work for about 3 months before the flex plate broke at the weld. Then we fixed it correctly.
 

Knebel

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Agreed, stock bolts are sufficient, and you need a new flexplate. Make sure whatever bolts you get are short enough, so they don't bottom out and give a false sense of proper clamping (somebody already mentioned that). Good that you found the issue, that it's readily repairable, but sucks that the trans needs to come out.


The sprag is a 1-way clutch in the rear of the trans. It is sometimes the Achilles heel of a Torqueflite and can get damaged if doing an 'improper' burnout, esp one where the tires spin and then quickly grab (or in the case of full-throttle driveline failure). Depends on whether the trans has low-band-apply configured in the valve body, and what position the shift lever is in during the burnout. But a damaged sprag can go undetected and then cause another component in the trans to overspeed, resulting in the transmission exploding. It's scary stuff, and it's real, but as I said, has a lot of factors involved.

I've read about it and still don't know all the ins/outs. But I haven't done a burnout in 15 years so not a concern for me.

Your car and mine are cousins! Is that EZ-EFI or one of the Holley/MSD units?
I have a fitech. Got that one when they first came out. I dont think its the sprag then...

Could one get the trans off under the car and replace the flexplate? How much ground clearance should I factor in? But to be real, i will probably just tighten it up now with a small spotweld on the bolt to flexplate and then do it right next winter. Meanwhile signing up for AAA haha
 

fury fan

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You need to be able tighten the bolts into the crankshaft hub.
You could do the tightening with a small-offset box-end wrench, I suppose - IF you are super-practiced at recognizing a torque value by feel. Or you could just make super-tight and would probably be OK?
But - you need enough clearance to insert the bolts first!

Overall, I think you are basically doing a near-total trans R&R due to all the items that must be unhooked (linkage, trans cooler lines, driveshaft, trans mount, etc).
The only difference is that you can keep the trans in the trans tunnel on the jack, which does significantly reduce the amount the car must be raised (vs completely removing the trans from underneath the car). The amount might need to be iterative based on where the trans hits in the tunnel. If 727, whether SB or BB doesn't matter much (splitline is in same location) but a 904 trans would sure be easier.

A different-yet-same story:
25 years ago I did a clutch job on my Merkur XR4Ti (RWD, 2.3 Ford engine) - my first time doing a clutch job, and first time doing 'heavy' work on a foreign car.
The trans-to-bellhousing bolts went from INSIDE the bellhousing rearward into the trans. :confused:
Can't remember if the lower bolts were accessible around the clutch, but the uppers sure weren't. :rolleyes:
So the trans needed to be removed with the bell. Unorthodox, but ok.
The upper bell-to-engine bolts were a PITA to reach, and couldn't back out very far before the socket/ratchet hit the firewall. :(
Then, once loose enough, some cramped 1/8-turn by hand was required. BUT then the bolts hit the firewall before they could exit from the bell. :BangHead:
So I jacked it up, loosened motor mounts, and let it slowly sag tail-down to the floor. IIRC I did this 2-3 times before there was enough clearance to get those bell-bolts out.
Would've been simpler to take the whole engine out and do the clutch on the floor.
 

detmatt

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Those screws actually don’t look right to me. are they too long? If so you could just replace them with the right screws until you have time to take the whole thing apart to replace the flex plate.
 

Knebel

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Those bolts were fingertight, I could get them all out without a wrench. Not a drip of threadlocker on either. Of course the holes arent quite round anymore in the flexplate but they appeared too large for the bolt to begin with. Like its for a 7/16 or 3/8 bolt... anyway, I used loctite and made them nice and tight and the noise is 100% gone. I guess I'll start saving for a B&M plate and a higher stall. It flashes to 1500rpm off a stop and thats too low. I need at least 2000rpm flash.
 

65CopCar

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I didn't read the whole thread, but being the recipient of the same issue several times, I will share my experience. My experience is on my drag cars with 7/16 bolts.

You have incorrect bolts. Those are not flex plate bolts. It matters - a lot. Get correct bolts.

I use ARP bolts and with red loctite torque to 50 lb-ft. This has always solved my problem. I had to shorten a socket to be able to torque them.
 

fury fan

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From an engineering perspective:

The flexplate bolts are fully-threaded - there is no shank to act as a pin.
Besides, there is some clearance between bolt threads and the hole in the flexplate. This is mandatory for the bolt to slip thru, and also to allow all 4 bolts to hit the threads in the blocks welded onto the converter.

Ergo - the flexplate is held to the converter totally by clamp load. The converter is driven by the static friction of the converter blocks against the flexplate. Due to stamping (flexplate) and machining-welding tolerances (converter lugs) there may be 1-2 bolts that happen to be acting as pins on 180deg of their diameter - but this is not included in the engineer's calculations because that pinning is on threads and that is not a rugged interface).
The flexplate is driven the same way, by the clamp load in the area of the ring-pattern of bolts that hold it to the crankshaft.

A caveat:
Underneath the bolthead there is a semi-precision flattened ring for a clamp-load surface when a washer is not used. If the obrounding in the flexplate is sufficient that the bolt is tightening against its hex points instead of that flattened ring, then some clamp load is being compromised.


The point of all of that - if you still have sufficient clamp load to the converter lugs, some egg-shaping of the holes might not matter and the new bolts/fastening might last longer than we might expect.
 
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