I ahve a 1988 Ford f250. It has a noise that sounds very similar to a loose rocker arm. The noise however is comming from the bottom end. I thought it might be a rod at first but after pulling off the dust cover for the flywheel it appears to be comming from there. I don’t see any cracks in the flex plate or loose nuts on the torque converter, no obvious scratches or dings where it might be bumping something. I am starting to wonder if it may be telegraphing from the crankshaft but I have heard plenty of rod knocks in my life and never heard one sound like it was comming for the front of the trans. Any theories? I am actually a mechanic myself ( diesel) and have had a few friends look at it and they don’t seem to have a clue either.
There may be looseness at the flex plate-to-crankshaft bolts, or possibly a crack in the flex plate that’s too close to center to see yet. While not terribly common, these are known to occur occasionally. Unless and until it gets worse, you’ll probably have to separate the engine and trans to verify these. First, though, I’d also check fore/aft crankshaft play for a faulty thrust bearing.
Thanks Gary, no thrust play at all. As you say seperating the two is likley ineveitable anyway. I don’t pick up any back and forth or fore and aft movement at the flywheel. I am not at all familiar with auto matic trans, is their anything in the torque converter or front pump that could produce a noise like this?
Not that I know of, but I’m not a tranny specialist. I have remembered, though, that flex plates often crack close to the center (google on cracked flex plate for more). You might be able to verify this before disassembly using a pry bar and a very skinny light (e.g., Bend-a-Light).
I found a video on line, sounded just like mine. It was a flex plate. Only difference was, it sounded the same as mine when idling after start up but his got a lot worse after reving engine and letting it return to idle. I think I will go with the flex plate.
A number of years ago I had a knock in my car that I would have bet money was from the Saginaw PS pump. I pulled the pump and rebuilt it. Same noise from the front of the engine. I pulled off all the belts and the noise was still there.
WTF?
So I went under the car and found I could also hear it at the bellhousing. Turns out the wavy washers on the torque converter had lost their spring and I was hearing the TC chattering against the flex plate. When I looked closely I could see rust in a star pattern from under the bolt heads.
Two lessons here. First the crankshaft can transmit sound like a speaker, and 2 it’s not always coming from where you think.
[QUOTETwo lessons here. First the crankshaft can transmit sound like a speaker, and 2 it’s not always coming from where you think.[/QUOTE]
Very true, I have found this out the hard way more than once!