ZF5 rollover noise with a twist

[LCAM-01XA]

So we all know the ZF5 behind a diesel with a SMF can be one noisy thing. Here's the twist tho, how loud are they behind a gas engine? Gas clutch is by default a SMF... This particular transmission growls/whines at idle, noise is coming from the middle of its body, pretty much right in front of the bulge on the driver side for the reverse gear idler. It is not a very loud growl/whine and cannot be heard from inside the cab, but it is quite pronounced when you're under the truck. Periodically there is a quick rattle from there as well, like a something is loose and free to sway back and forth and bang against other things, this noise now seems to come right from the reverse idler area - this also cannot be heard from inside cab, but standing outside next to the truck it is noticeable.
It pretty much goes like 10-15 seconds of growl/whine followed by a few quick bangs, and that is repeated for as long as the truck is idling in neutral. Oil temperature doesn't seem to affect this behavior, it is present both when she's cold and after a long drive. Warmed up temp hovers around 130F measured at the reverse idler gear section btw, so I doubt she's friction-overheating from a failing bearing. Functionally the transmission performs a it it should, shifts fine in all gears and engaging reverse is not a problem.

So I need some ideas as to *** is going on here. This is a junkyard transmission out of a 5.0 F250, with about 3 weeks left on its warranty. Zero play in the input shaft so I do not suspect worn main shaft bearings, she rolls over nice and smooth by hand. However, for some reason its factory shifter was bent to the right at the neck between the pivots and the rubber insulator (which I found out after trans was in its new home and shifter sat straight up instead of pointing at the driver) - running a non-damaged shifter now and I see no need for applying to it the excessive force that would result in the old shifter bending like that, maybe it was an accident with someone unintentionally leaning against it with their weight?

Any ideas? And yeah I know this is the IDI section, but I need a quick answer, and lots of you here seem to run ZF5s in everything you own so you may have run into this before...

 

[79jasper]

Haven't drained the fluid and looked at it?
I don't know what all the smf vs dmf fuss is about. My psd has a smf and I don't get these crazy noises.

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[LCAM-01XA]

Fresh fluid in it, and salvage yard had drained it before shelfing, so no indicator of how worn she is inside.

 

[Diesile]

I never heard rollover from a gas rig and attributed it to the lower (and less dynamic) compression/firing events which
smooth out with rpm increase.

 

[Dieselcrawler]

could it be missing a spring on the detent, allowing the shift fork to rattle?

 

[LCAM-01XA]

I never heard rollover from a gas rig and attributed it to the lower (and less dynamic) compression/firing events which
smooth out with rpm increase.

This one doesn't idle very smooth, but does get better as engine speed increases. Actually when she goes into high-idle mode for the A/C the transmission noise disappears completely. No tach tho, so we don't really know how high the high idle is, guesstimate would be 900-1000 RPMs.

could it be missing a spring on the detent, allowing the shift fork to rattle?

Thought of that, but those are sliding forks, so didn't think it was possible for them to rattle back and forth. Maybe a bit side to side tho, if their fingers are somewhat worn? As far as we can tell all the detents are there, but I suppose one can't go just by the feel of it. This noise only happens in neutral and only at low idle, engage any gear or bump up the engine speed and it completely goes away. Wouldn't a rattling fork rattle all the time when not used?

 

[oregon96psd]

This one doesn't idle very smooth, but does get better as engine speed increases. Actually when she goes into high-idle mode for the A/C the transmission noise disappears completely. No tach tho, so we don't really know how high the high idle is, guesstimate would be 900-1000 RPMs.

I think this is your problem. My 97 has had a smf in it for years and never had any rollover noise, when the throwout bearing went I decided to put a new clutch in it while i was in there. The new pressure plate wasnt balanced and made my engine kind of surge/idle choppy. This made my transmission sound like a blender with rocks in it at idle, but any increase in speed would make it completely disappear. Replaced the clutch with a balanced one...problem gone. I bet if you got your idle smoothed out yours would go away too.

 

[kawamatt]

My ZF behind a (tired) 351 has rollover when it is warmed up. Can't hear it in the cab but can hear it well standing beside the truck or with your head down there. Thing runs great though so I'm not concerned. I put all new shift forks in mine during the rebuild and everything went back together as per the manual. I think the rollover is from two things; 1) backlash between the helical gears and 2) the synchronizers rotating back and forth in the dog teeth of the synchronizer bodies on the mainshaft. The three openings in the synchronizer body below are what the synchronizer keys into and there is a lot of room for radial movement of the synchronizer in relation to the synchronizer body.

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Transmission-Rebuild

 

[LCAM-01XA]

Alright, so it sounds like there is no cause for alarm. Idle quality is something that will get worked on eventually, hopefully that will help quiet her down a bit. For now she gets run as is without mercy, truck needs to earn its keep Kawamatt, I've seen your article both on here and on FSB IIRC, great info there. Not sure this one will get that treatment any time soon tho, she shifts great so in all likelihood idle rollover noises will be ignored till something more major presents itself.

 

[Black dawg]

I have grown to dis like the zf because of the noise. They all make noise if you listen close enough.

 

[LCAM-01XA]

I could live with the noise no problem if the diesel gear ratios weren't so worthless. OD + 3.55s is solid a 20MPG combination, but damn is it pain to get going under load with that 4:1 first gear... 5.72 gasser first is much better.

 

[79jasper]

3.55 is when a ZF6 would shine over the 5.
But that's for another time. Lol

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[sjwelds]

I have grown to dis like the zf because of the noise. They all make noise if you listen close enough.

Dude its a diesel. If you want a quiet rig buy a Prius!

 

[Black dawg]

Dude its a diesel. If you want a quiet rig buy a Prius!

I was meaning the zf5 in general (dude).