Hi everybody,

I have a 79 F-250 4x4 with a mid 80s 460 and a C6 in it and when the truck is idling it makes a pretty loud knocking noise but as soon as the RPMs are raised up off idle it goes away, it does it in park and also in gear but it ONLY does it when idling, it seems to be coming from around the torque converter, I thought the converter bolts were loose but I checked them and they are ok, The engine runs strong and has very good oil pressure so I don't think its a bottom end problem??

I have owned the truck for a few months and it has done it ever since I got it but I have not been able to track it down but it is embarrasing to be sitting at a redlight and having the thing rattling like crazy


thanks alot for any advice

 

The main bearings are going bad.

 

Can I replace these with the engine still in the truck? Is there anyway to verify this is the problem before ripping it apart?

How much longer do you think it will last before it blows up?

 

check and make sure the exhaust isnt hitting the frame. also i have seen flex plates crack around the bolts that hold it to the crank and sound exactally like a bad main bearing and it did it at idle .
just a few more ideas

 

your fly wheel or stress plate is cracked
do you have excessive end play in crank? if not bearings may not be bad? what is your oil pressure?

 

two of us agree in one minute flex plate co incidences never cease to amaze me good job drzman

 

I've already checked the exhaust to make sure it isn't rubbing anywhere and its not, I wouldnt be able to find out if the flexplates cracked without taking out the transmission would I? My oil pressure is about 75 at start up and 45-55 while driving
how do i check crankshaft end play??

 

to check the end play you would have to put a dial indicator on the front pully and measure the amount of end play movement of the crank shaft in the engine block, too much is usually an indication of excessive wear on the thrust bearing.
heres what I would do on the flex plate, take the torque converter nuts loose and push the converter back into the trans , it wont slide much, this will allow you to grab and try to move the flex plate, hopefuly you will notice it make noise or this could determin nothing and more than likely your going to have to pull the engine or trans its just your call , which one you`ll think will be easier.
hope this helped some

 

The oilpan was leaking pretty bad so I thought I would replace the gasket and then also see if I could see anything in there with it off, there was a few tiny metal shavings in the oil pan, I put them up to a magnet and they stuck to it.. shavings from the main bearings wouldn't stick to a magnet would they? If I had bad mains wouldn't it cause my oil pressure to drop alot? The truck runs great and has alot of power so that would really suck if the mains were going out, I don't feel like pulling it all apart

I had been running 10w40 so I filled it back up with 20w50 and a jug of Lucas to see if that would quite it down at all but it didn't

I guess I will just keep running it til it blows, lol

 

Definately a cracked flywheel. I pull the trans or engine and you will see it. With oil psi numbers like that I don't think your bearings are bad. Check with a flashlight through the hole where you tighten the torque conv bolts for any visable cracks. The fact that the Lucas and 20W50 didn't assist the noise tells me its external from the engine. Take all the belts off the front to eliminate any accessories.

 

my money is on the flex plate, if cracked pull the tranny back enough to drop flex plat and change it out they dont cost much and probably get a used one here on the site!

 

Ok I will have to check that out then, another one is about $55 at autozone, I had already ran it without the accesory hooked up to make sure it wasn't that either and it really does sound to me like its coming from flexplate/torque converter area... Do I need to take off transfer case or you guys think I can unbolt tranny, take out driveshaft and just slide it all back??

thanks alot for all the help guys!

 

My money is on the flex plate as well, Ive had it happen to another brand vehicle.
Good luck.

 

if you have a good jack and a solid surface just remove drive shafts after marking for balance un bolt crossmember and slide it back far enough to remove flex plate, remember to block torque converter so it dont fall off and make a mess.