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Flex plate or torque making noise?

8K views 70 replies 13 participants last post by  EVL SS 
#1 ·
I'm new to this so, take it easy on me :)


I have a bad clunking noise going on. At first I was concerned it was the motor but, I think it is the torque converter or in that area.


I put the car up on jack stands and I check the flex plate bolts. They were definitely not torque very high but, they were not falling off. I torqued them to 45lbs and re started the car. It seems less noisy but, it is still there.


I can grab the flex plate with my hand and I can rotate it back in forth about 1/4" and it seems to make the clunk I am hearing. It does not move front to back rather it rotates around the axis(as I assume it should).



Any ideas? I don't know how it bolts to the crank but that almost seems like the problem??


thanks,
Dave
 
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#2 ·
Flex plate should not move at all. It is bolted solid to the crank. If the crank isn’t moving the flex plate does move. Not even a 1/4”.

Imo time to pull the tranny and change the flex plate.
 
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#3 ·
Sounds like the holes in the flex plate got elongated because they were loose. Like John said... Needs replacing.
 
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#5 ·
Thanks guys everyone. The flex plate is brand new (500miles on it), I bought the car as is and I have e receipt where they had a transmission shop align the bellhousing and install everything so, I assume it was done correctly but, who knows.

I did look for cracks and I don't see anything. After I tightened everything, it seems to make a little less noise but, still makes noise. I will have to pull the transmission. This stinks, lol.. I have almost everything to do a T56 magnum swap but, I want this noise figured out before I introduce more issues.
 
#8 ·
More than just the driveshaft......you need to drop the crossmember, unbolt the tranny from the block, disconnect cooler lines and TVS cable. Unbolt the flexplate from the torque converter and remove the trans.
Make sure you support the rear of the engine so you don't break the distributor cap or motor mounts.
I've never seen it but I bet the flex plate bolts to crank are loose or its cracked really bad - somewhat doubtful.

I have had a cracked flexplate before. No noise at idle but when you rev'd it up it sounded like a rod knock. Took it to 3 different shops in San Diego and they all diagnosed as a rod knock or wrist pin. Oil pressure was unchanged at all so I was skeptical. The fourth shop was a general repair shop and the old black man sitting in a rocking chair out front said "son...you have a cracked flex plate" as I got out of the car.
Sure enough there was a small crack in the flexplate.
 
#9 ·
You need to unbolt the TC from the flex plate then pull trans & TC to be able to access the flexplate. whatever the noise source is, assuming its not from the motor, it is not involved with a T56 swap so if that where you are headed your current flexplate, TC, automatic trans will not be used
 
#10 ·
Thanks again everyone! Looks like I got some work to do. Thank god for the quarantine! If I do get it apart and it is just the flex plate, then I will go for the trans swap.

Can I unbolt the TC from the flex plate and push it way from the motor and start the motor to rule out the TC and trans?
 
#14 ·
It can be done. It mostly depends on how far your torque converter is already in the pump. I personally wouldn't be comfortable with less than a quarter inch gap. However this will take any stress off if your flex pate . That may make the flex plate sound go away if it is in deed the plate that is the problem. The flex plate can crack in many places. Most of the ones I have encountered have been cracked in the center where it bolts onto the crankshaft. Your problem sounds more like a bolt hole problem to me. I have been wrong before though. My wife reminds me of that often. Then I say , but I picked you. That usually changes the subject .
 
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#20 ·
OP

whatever you decide to do, fix or T56 swap, use loc-tite on FW/Flexplate bolts

If you had 1/4" movement of the flexplate the holes and or the bolts holding it on the crank are now enlarged and or the bolts have been worn into

If its about getting the car back on the road quick a new flexplate won't cost much...but if a T56 swap is the desired end goal...you now have incentive to do so

You can just start the motor once you get the 350 out to confirm motor is not "part" of the source of the noise although if the flexplate and bolts were compromised than you would have to put on a new one unless you happen to have a donor flexplate or FW to use
 
#21 ·
Ok, I am finally able to get in the garage and start taking it all apart. How much fluid comes out of the transmission lines gong to the radiator and I assume it is transmission fluid?

I am going to find the problem and regardless, put the T56 magnum in. I am hoping it is just the flex plate loose and bolt holes getting slotted or cracked. If it is the motor, I am going to jump off a cliff, lol..
 
#22 ·
It will look like alot of fluid, but it will be less than a quart. Good luck. I'm getting ready to wash the Z and go for a cruise. The 5 speed is definitely worth the effort.
 
#28 ·
I was going to offer a driveshaft yoke but the 69 yokes have a hole in them. You'll be hard pressed to find a spot of ground tall enough in Chicago to hurtyourself if you jumped off but tall buildings ..... Yeah plenty of those!

I'll bet you'll find the flex plate cracked around the bole holes.

Jeff
 
#30 ·
Thanks Jeff, yeah flat but very tall buildings for sure! I ordered a Sonnax 1350 forged slip yoke . Good for 700'ish HP which I will not be close to but, you never know, lol...


On a side note, My 68 has the 4 gauges on the center console. Do all 67-69 have low fuel lights? I can't see where mine would be. I just changed the sender and have zero gas in the tank and I saw no dash or console light??
 
#31 ·
EVL

If you don't have a lift, the Harbor Freight tranny jack works great. Have used it for a few swaps. You will need to get the car high up on cribbing but that also makes it way easier to work under the car.



You can buy the cheap plastic tail shaft plug for around $5 to keep tranny fluid from spilling when you pull the 350

I use the floor jack with padded block on jack to support engine and also be able to adjust it up/down slightly when stabbing the trans



The T56 is going to be a great swap, good luck
 
#32 ·
If you don't have a lift, the Harbor Freight tranny jack works great. Have used it for a few swaps. You will need to get the car high up on cribbing but that also makes it way easier to work under the car.

You can buy the cheap plastic tail shaft plug for around $5 to keep tranny fluid from spilling when you pull the 350.
The T56 is going to be a great swap, good luck
I don't have a lift yet but, I was thinking about a Harbor freight trans or motorcycle jack. I will have to buy one of those plugs, thanks for the tip. I have to figure a safe way to get the car high off the ground. otherwise, I work like a jackass about 20" off the ground, lol

As of right now, my neighbor interrupted my day and I just got the seats out, center console and shifter out. Tomorrow, I will get under the car and start taking it apart.

Prior to gutting the interior, I was able to make brackets and install black leather, heated Audi TT seats. They look decent but, not great. I also fitted a 6 gen center console that I got cheap but, I don't know if it will work without some work.. I have pictures if people are curious.. I don't know if I should start a build thread??

Dave
 
#39 ·
I have a Harbor Freight trans jack I've used a few times. I've not put my car or truck high enough to put jack and trans under car at the same time. I muscle the trans on to the jack under the car and then install the converter. The 4L60 was a pain. I've got a project coming soon that will require the car to be at least that high so we shall see.

As far as a low fuel light I'm not sure about a 68. The 69 has a spot in every car but no bulb or wiring if you have dash fuel gauge. Is the 68 in the Tach that replaces the in dash fuel gauge?

Jeff
 
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