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Loud rattle at lower rpms and warmed up 80 Eldo diesel

Started by TJ Hopland, August 15, 2010, 11:57:07 PM

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TJ Hopland

Had my new toy for a 2 days now and one odd thing it does is once there is some heat in the engine there is a loud rattle at lower engine rpms.   I dont notice it on a cold start.   Its there in gear moving or not moving or neutral/park.  It seems only based on engine RPM and I would say its borderline at idle but gets strongest just below 1000 rpm then stays gone higher up.   It sounds just like a loose heat shield on a cat converter when you hit the right resonance.  I would say its more of a buzz than a rattle.  Its about as loud as the engine itself.  I cant tell where its coming from its about as strong underneath as it is up top.  It almost sounds like its in the trans like maybe the back cover where the chain is?   I have driven the thing almost 200 miles now and it has not changed and as loud as it is I would think it would have destroyed something if it was really a huge issue.  Trans fluid still has a red tinge to it and its not foaming at all.  I have talked to several people about common issues and none of them would have lasted 200 miles.  Its strong enough that it does seem to vibrate the whole car so sometimes sheet metal sort of rattles.  The starter looks fairly new.  I was thinking of trying to get a peek at the flex plate.  Anyone know if these had balance stuff on the flexplate or if it was all in other places?  Only thing that does not make sense there is why it does not seem to do it cold.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

bcroe

I can tell you that the diesel has an externally balanced flexplate.  The 79-85 THM325 trans requires a slightly smaller flexplate than a RWD car with the same engine.  Flexplates can fail, esp a diesel.  Out of 3 of these transmissions (gas engine) I drove, one failed to make high miles without a failure.  Diesels with a bad injector can make a sound like a bad rod, but it doesn't seem like that's your problem.  good luck, Bruce Roe

Bob Hoffmann CLC#96

Bruce,
  Sorry, but there's that word again.  Flexplate.  If it's got teeth on it it's a FLYWHEEL! They used "flexplates" on 1956 to 1964 Cadillacs with the jet-away trans and maybe other transmissions. They called it a flywheel drive plate. It did not have teeth on it.
HTH, Bob
1968 Eldorado slick top ,white/red interior
2015 Holden Ute HSV Maloo red/black interior.
             
Too much fun is more than you can have.

bcroe

Thanks for the explanation.  I always saw a plate used with a torque converter as a "flexplate".  I saw a rotating unit with gobs of metal (esp at the outer edge) for rotational inertia as a "flywheel".  Not much of that on V8s, they seem to have the minimum metal, partly because the flywheel function has been taken over by the hefty torque converter.  Then there are starter teeth, I don't see them related to this question.  Bruce Roe

TJ Hopland

Interesting about the rod knock.  Yesterday this accelerating on it own came up and then today I spent about 6 hours on an international 3 cyl diesel tractor.  Came home and started up the car and the self accelerating issues seems to have gone away but I think I hear a knock.   I wonder if I have some crud floating around that has now made its way to an injector?  Or if there is just crud in my ears?

I dont remember from being under there what sort of access is there to the 'flywheel'?  Can you see enough of it to tell anything?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

TJ Hopland

Just getting around to posting the solution to some of my posts so future people looking at the topic can actually find out what the fix was.  Dont you hate it when you do a search and find someone with your exact problem but there was never a solution posted?

The rattle (besides being a rattly old diesel) turned out to be the inspection cover.  Its supposed to have 3 bolts in it.  Mine had one sort of cross threaded into it, luckily the starter pretty much keeps it from falling off.    The bolts are a metric self threading lag looking thing.  I found some that were close on the rack at my local parts store.  In 2 locations I had to trim the tip off the bolt because the hole was not deep enough.

Side note the diesel starter is much heavier than the regular one so be ready for that when you get the bolts loose.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

bcroe

Seems like the people who work on that TH325 trans love to strip & cross thread those aluminum metric bolt holes.  I have spent some time running a tap a lot deeper than stock, and putting in a selected longest bolt possible, as a repair.  Yea all diesels have a much bigger starter, and a special flexplate with coarser teeth.  The starter is a lot easier to work on if it has only the 2 required wires, with disconnects on the fender so it can be dropped with the wires in place.  Bruce Roe