'86 Crew Cab 4x4 with 7.3, ZF5, NP208. A while after changing my clutch to a South Bend "stage 2" I now have a horrible rattle at lower RPM when lightly accelerating or decelerating. Put more load on the gears tip into the pump for no load and there's no rattle. It's a terrible sound, not rollover noise. Never heard a ZF5+NP208 do this. ZF5 was rebuild maybe two years ago, input shaft had no slop when I replaced the clutch a few months ago so preload on the mainshaft at least is still good. Trans got all new needle bearings during rebuild. Transfer case is original 1986, only thing replaced while I've owned it the past 6 years are the yoke seals.

It seems like the rattling is quieter or less pronounced in 4hi than an in 2hi. I don't know if this noise is in the trans or the transfer case. It sounds almost like if it was in the trans it would be failed needle bearings between gears and mainshaft, allowing gears to rattle. The noise is more pronounced in lower gears, less in higher gears. I can slightly hear it if listening carefully and carefully reproducing the load in occurs under in 5th, and even in 4th which is direct (no load on countershaft or any of the gears with needle bearings). I have not been into a NP208 ever aside from peeking inside when my 460 truck split them wide open, so not sure what in there might make a noise like this. Any thoughts on what it could be or what to check?

 

that T case has a chain don't it ??


EDIT: I don't know if the Chain would move when not in 4WD ???
Just a thought

EDIT: I guess an easy check would be drain the T Case and inspect the fluid... IF ya find metal that might tell ya something.

 

208s are chain, chain moves all the time, dont seem to hold up as well as the borgs. They do make an awful noise when the chain starts digging into the case from too much slop, but its more of a grind.

 

I recall some Chevrolet transfer cases from 99-07? Had that problem. Would cut all the way through until it grenaded.

 

jeeps too, ive never been a fan of any of the newer / chain NP cases. Replaced a few np241s? in jeeps for the same reason, wears a hole in the case, oil goes out, kabang.

 

Single mass flywheels sometimes cause gear rattle, that is why they went to the expense to use dual mass in the first place.

 

I think the main reason was to have smooth take offs. My single mass with the t19 and its tall first gear along with 3.55 gears out back and 33" tires make for a jerky take off.

It got worse when I replaced the clutch because it grabs so good now. Never did break in any

 

Ford used the dual mass to absorb the firing spikes on these particular engines in order to prevent long range trans problems, not to hide gear rattle. I agree with what a full time IDI mechanic found some time back.