Cruise speed rattle

SLittle

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1991 F350 2wd 7.3 n/a with E4OD

Coming home today I seem to have acquired a rattle.

It is most noticeable at 25-30 mph (around 1200 rpm). Pulled in the drive and I hear it at idle too.

It sounds like a rattling heat shield or a loose flex plate. Its loud. Of course, I don't see any heat shields and it definitely sounds like it is coming from the flex plate area or could be oil pan. If you've laid under an idling IDI you know it isn't the quietest environment.

I can easily check the flex plate to torque converter nuts. Not much else is EASY. If the torque converter nuts are tight, where do I go next?
 

IDIBRONCO

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It's not a bad idea to check the torque convertor nuts, but don't be surprised if they're not loose. I've heard that sound before and I (or probably anyone else) wouldn't call that sound a "rattle" That's a knock for sure. It's possible that the inspection cover itself is loose.
 

SLittle

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Knock as in main / rod bearings?

That is definitely a worst case possibility. Maybe I'll try to get audio of the noise to post here. I'm not accustomed to diesels but I've heard plenty of gassers with rod bearing and main bearing issues and it doesn't sound similar.
 

Kizer

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It's possible that the inspection cover itself is loose.

A loose inspection cover has made me think that my truck was COMING APART!
I seriously expected to be looking a rod hanging out of the block by the time I got shut down.
 

SLittle

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Inspection cover over the flex plate / torque converter bolts? When I crawled under yesterday I noticed that inspection cover is MIA.

After some google-foo I found this video which is exactly what my truck sounds like:

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What I will do this evening is see if I can get any movement at all out of the flex plate with the engine off using a pry bar. If I can confirm a cracked flex plate then it is just a matter of dropping the transmission and replacing the flexplate! Much better than pulling the motor and rebuilding. It'll also be an ideal time to install a Tugger kit in the transmission.

.....if I can find a flex plate...
 

IDIBRONCO

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inspection cover is MIA.
I guess that's not it. I didn't say that the rods were knocking. If the torque convertor nuts are loose, it sounds like a rod is knocking, not just a little "chuff" noise or a ticking noise. It will hammer pretty bad with loose nuts.
 

SLittle

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With a prybar on the flexplate teeth I can get a little play before the crank turns. Tells me the flexplate is broken.

Cold idle yesterday the truck sounded good. Soon as the high idle dropped out I put it in reverse and HOLY SHAMOLY it rattled for just a bit as it fell in to reverse.

I'm going to pull the transmission this weekend.

Previous owner only put 2k miles on the truck. PO states that the guy he bought it from had the transmission rebuild. I can't confirm, but it looks cleaner than the rest of the under side. Based on this, I plan to pull tranny, install Transgo tugger kit, replace flex plate. I also noticed my oil cooler is now leaking so I'll reseal that too.

Can you confirm my parts list is correct:

https://www.amazon.com/gp/product/B004K7FJJG

https://www.amazon.com/Transgo-4R100HD2-Reprogramming-Kit-4R100/dp/B072LT1VWS

https://www.amazon.com/Sonnax-3642501K-Front-Drainback-Valve/dp/B071SHS5X4

https://www.amazon.com/gp/product/B000C2GB0O

https://www.amazon.com/gp/product/B00H7Y3DH4

Are there any other tasks that I might want to consider while the transmission is out? Nothing seems in need of attention, but if its easier to do now...

U-jonts. Carrier bearing. Rear main seal. ????
 

IDIBRONCO

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Well, it will never be easier to change out the rear seal (with the engine still in the truck) like you suggested. Don't forget to put thread sealer on the threads of the flexplate bolts when installing them.
 
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