Hello all. Long time follower, First time poster. Read through tons of threads on here, R&D's awesome IDI build(s). I have searched for hours on end looking for someone with a similar problem to my own and the one thread I did find was a dead end thread. My truck is a 94 CC dually, factory turbo turned up to 12 psi, pump turned up 3 flats. engine runs beautifully thanks to the things i have learned from this board. has 158k on it. Initially when I purchased this truck I ran the trans low on fluid and scored the input gear and matching countershaft gear. Fault of my own, i should have checked. anyhow, i purchased a new input shaft and the matching countershaft gear and a basic bearing service kit (mains, counter pocket) with the associated seals. all caged bearings on the mainshaft all spun smoothly and had no play. Checked preload and adjusted shims accordingly. I have read through several threads debating the use of fluids for this trans. I am running full synthetic 5w30 motor oil. extra quart added to combat rollover noise (has unknown SMF and clutch). Trans shifts great all the time, no grinding. has no issues getting into reverse. The issue I am having is under decel, mostly in 3rd and 5th I will get a squealing/chirping noise. sounds like a bearing but i have no idea where to start. It doesn't do it cold at all. once the trans warms up it will be sporadic. If i downshift from fourth into third i can almost make it squeal/chirp on demand. I know it's not the throw out or pilot as it makes the noise without me even touching the clutch. Trans is completely quiet under acceleration, even full throttle pulling a trailer. I have stopped driving it because i can't diagnose the issue any further and do not wanna tear back into it blindly. It will be getting a new clutch in the next few months, i will crack it open again at that time to have a look at the bearings i replaced. Thanks for all the good info over the years!

 

When it was ran low on fluid and you rebuilt it, did you remove all the gears and check the needle bearing under them? My best guess here is that being 3rd and 5th are the smallest gears their the first to loose contact with the oil and run dry. When you put a new seal in for the pocket bearing, did you make sure it was ALL the way in? If not, the seal end gets shredded off and the bearing could be starved of oil, though I would expect it to make noise in every gear.

Couple things from the service manual:

Condition:
Noise is present in all or several gears. Noise occurs at high and low engine speeds and may vary with engine speed.

Possible source:

Worn or rough output shaft rear bearing.

Needle bearing under mainshaft gears damaged

Wrong preload on main or cluster shaft bearings.

Condition:
"Whinning" Noise at high engine rpm in 3rd and 5th Gear

Possible Source:

Worn input shaft gear AND countershaft drive gear.

I'm assuming your truck being a dually is NOT 4x4 and you don't have a PTO on the trans.

 

sorry, should have mentioned it was a 2wd. no PTO. It doesn't really whine, its more of a chirping/squealing sound and only under deceleration. i read through the troubleshooting guide multiple times. I did make sure to get the oil scoop/baffle installed correctly and even dimpled the surface so it could not come back out as it seemed awfully easy to slide in. It did make this same noise before the rebuild but afterward it was gone for about 4k miles and just resurfaced recently. I intend to check the bearing pockets for signs of the races spinning within. I can also hear a faint squeal when downshifting from 3rd to second occasionally. When i did tear everything down to replace the bearings the first time is when i noticed the input and the counter scored/blued. however, the bearings looked fantastic. i replaced them anyway for good measure and piece of mind. I think i will order the caged mainshaft bearings and another basic service kit since I destroyed the cages pulling the old ones off. Strange thing is that under acceleration it is as quiet as a church mouse. normally a bearing makes noise under all circumstances, at least from my experience. I have honestly thought about getting another ZF as i have already dumped quite a bit into this one. hopefully when i pull everything back down it will be more obvious. Thanks for the input.

 

Verify that you don't have a driveshaft or differential issue. U-joints can make all kinds of strange noises, and the yokes on the 10.25" rear end are known for occasionally working loose. If you don't deal with it and the yoke is loose it WILL break the ring and/or pinion eventually.

If it's a loose yoke, the reason it makes the noise during deceleration is that the thrust during acceleration pushes the pinion gear mostly into place, but during deceleration or reverse, the gear is pulled out of place. A loose yoke will tend to wreck the crush sleeve, but a simple replacement and recrush will yield the same pattern without pulling the gear side bearing and shim(s). If it's been dinged up the nut will tighten on the bearings instead of on the sleeve which will either destroy the bearings, or leave the nut to work loose again.

Thrust issues in transmissions generally are more limited since linear thrust is only generated by the angle of the helical cuts on the gears, which ride on gear oil at the ends. The reason I reference linear thrust is since it does it on deceleration specifically. Where it may be an issue is on main and counter bearings, but this an issue generally specific to ball bearing supported shafts- IIRC the ZF uses tapered rollers, so this issue may be moot.

 

I will definetly check the the yoke on the rear end. When i got the truck it had the famed ring gear bolt backing out issue and the guy gave me a rear en from a 92. however i had to swap the yoke to the 94 style because of the difference in u joints. I did tighten everything back down then and this was before the trans was rebuilt and the noise was present. I will still double check everything from front to back as it does have some driveline vibration that i blame on old u-joints and or carrier bearing. you have got me thinking about the helical cut on the gears now.. under acceleration would they want to pull themselves together and the opposite under decel? This thing really has me stumped. especially since it shifts so well and makes no noise until you left off the gas. i may pull the shift boot off and take it for another ride, let some more sound in the cab.

 

some pics of the damaged gears



new hard parts

new bearing kit

and here it is getting ready to be buttoned back up. didn't take any pics during the rebuild. I will tell you that pressing the countershaft gear off and then back on took very precise usage of cursing, two crappy propane/mapp torches, about 6 beers and the longer jack handle from my engine hoist on my harbor freight 12 ton press. it was sketchy at best. that sucker is on there.

 

Block the tires and release the parking brake to check the u-joints. If it's a single chirp/squeak then check your motor mounts as well. I have had a few universals go bad and chirp too, changing loading on them can make some funny noises.

 

Why are you running motor oil in a transmission that specifies synthetic ATF?

 

Not trying to start a debate or anything by any means but I have seen several threads on the subject and I decided thats what i wanted to run. I have a SMF and was trying to quiet down rollover noise a little. I have seen where many people have used it successfully. I have also thought about switching back to full synth atf when i drop it again just to rule out that as being an issue. however the noise has been there both before and sometime after the rebuild. I did notice improved shifting with the motor oil over the ATF. very smooth, not notchy at all. slides right into every gear.

 

Were you running SYNTHETIC ATF?

Have you tried it with synthetic ATF after the rebuild?

 

initially it did have synthetic in it, yes. I almost feel like a race is spinning in the pocket on the trans. it has a very distinct bearing-like squeal. I will be dumping fluid next week if it warms up to inspect for anything unusual. as said before i only found the scorched gears previously, all the bearings looked new. I will try the full synthetic ATF again but from what i have read on here and what i have seen the most important item for lubrication of these transmissions is the viscosity. I certainly believe the current oil I am running would have no problems in that dept. I have read on here that people use straight ND30, 5w-30, 15w-30 (albeit problems with that weight) 30 weight atf and 50 weight atf. lots of gray areas there.

 

Don't let me get you too far off track with the axle/u-joint thing, just wanted to point it out in case it's something unrelated to the trans.

The cut on the rear end gears is easier to envision if you think about the pinion pushing on the ring gear since it's "low pinion" This push shoves it back into place. But in reverse it "pulls" against the ring gear, so if the nut is loose the force sucks the pinion toward the ring gear where it can flop around and interchange poorly with the ring gear or even rub on the carrier.

Very easy to check though. Give the yoke a wiggle. If it's got any play it's a problem and may be *the* problem.

If you have something funky going on in the transmission, you almost certainly will have some odd wear material. I'd drop the oil and pull the pto cover to take a look. I'm sort of suspicious that it might just be a u-joint, but I haven't heard the squeak.

I might wonder about something goofy in the clutch disc itself, but I'm grasping at straws with that one.

 

I've been wondering if a Blackstone analysis might shed some light (just spitballin').

 

I will see if i can get a video today. not sure of the quality as all i have is a cell phone for a camera.