ZF trans noise

Got another question on this 99 F250 sd with 7.3. It also has a ZF 6 spd. It has the gear rollup noise in neutral at idle and in 4, 5, and 6th when at 1 to 1800 rpm with it not accelerating or completely letting off. It is fairly loud, just wondering how long before I have to replace bngs. Just not sure how much is considered normal and too much. Im used to it in 10, 13 spd and such in big trucks not with these little trans.

I also have the gear "roll-over" noise(2000 F250 4x4 w/ 7.3), some will say it's normal for these ZF's to have this noise, I figure if it's noisy it is also has increased wear happening. I have replaced clutch in mine twice, 1st time the noise was almost completely gone by the use of a Southbend Kevlar pilot bushing that goes in the flywheel, once the bushing wore the noise returned. The second clutch replacement I installed a input shaft repair kit here: http://www.ebay.com/itm/NEW-Ford-Input-Shaft-Pilot-Bearing-Repair-Kit-ZF-5-6-Speed-Manual-Trans-/171550593342
which repairs the end of the input shaft due to the original Ford pilot bearing wearing/chewing up the end of the input shaft(the reason I installed the Kevlar bushing). Once installed the trans still made the noise, but I figured the shaft was properly supported with the new pilot bearing and sleeve installed. I changed the trans fluid(ATF fluid is used in the ZF) to Mobil 1 but removed 1 quart ATF from the total and added a quart of 85w-140 synthetic gear oil, the trans is quieter for sure with no shifting issues. I know eventually I will be rebuilding replacing the trans ($3K), but I figured with the reduced noise also comes reduced wear. Ford has changed their requirements for the ZF trans' fluid, from ATF to gear oil in the later F250-F350's, not sure what if any internal mods were done to the trans due to the fluid change. Sorry for the long reply, I hope this helps in some way. Todd

Todd, I was thinking of changing fluid to 75W90 syn gear oil as it is slightly thicker to "cushion " worn parts. We have used 50 wt syn gear oil in big truck trans for years with huge improvement over conventional 140. And 75w90 syn in rears which drastically cut our rear end power divider repairs.
But like you I cannot find any reliable info on its use in a ZF. I would trust this group as I have for many years.

I tried gear oil in my '92 F350 with 460/ZF 5 spd, it made gear shifts notchy and felt like it didn't allow the gears to slow down quickly enough for smooth/quick gear changes(that trans always had the gear "roll-over" noise, although ALOT less with the gear oil). I would try the 1 quart gear oil first to see if it helps, I have also tried 5w-40 Mobil 1 diesel truck engine oil in my ZF 6 spd and it seemed to quiet the trans down but the biggest impact was with adding the 1 qt of gear oil. I have removed the 5w-40 after 6k miles and saw no metal "glitter" in the oil, at least not any more than what was in the ATF(I used the 5w-40 due to it's low temp viscosity similar to ATF, but it's viscosity @ 100C was much more than ATF, less thinning) . The Ford ZF 6 spd has an internal oil pump, so be careful with adding too much gear oil, the GM ZF has gears that are said to be cut differently which does not require the oil pump. You will find a trans cooler for the manual trans, the internal pump circulates the ATF trans fluid, GM doesn't have the trans cooler due to having no internal pump. Good luck. Todd

Just a quick update as to results of what I tried so far. Add 1 qt of w140 gear lube to the trans fluid. Noise is reduced very slightly but shifting is a big improvement, lots smoother and less effort.

Try straight 30 weight no detergent motor oil the next time.