Thank you Jeff.

No Problem. By the way Steve Shearer said to say Hi!

Jeff, I thank you for clearing up the murk surrounding the origins of the drain back hose modification. Roadway Express certainly presented it to the troops in the trenches as a bona fide Komatsu developement, or at least a KFI endorsement.
I now feel like I have spread some erroneous info around the world. My apologies to you and the folks at Komatsu Forklift USA.
You can just mention to Steve that Larry Walker in the Roadway Express shop in Nashville, TN was asking.
Steve paid us a visit sometime maybe around late 1999 and spent the day on our dock investigating an issue we (all of Roadway) were having on the -11 models. While he was there he noticed that some of our -12 models had the "economy seat" on them instead of the higher end Michigan anti-static seat that came on them as OEM customer specified option. I told him that came about because our parts department manager refused to pay the $550 cost of the seat and we had to put whatever he would buy on them.
Steve informed me and another forklift mechanic that OEM replacement seat CUSHIONS were available (for around $95) and gave us the Komatsu part numbers for both cushions on the spot.
That enabled me to go to our Shop Manager with an explanation as to what had taken place. After hearing the facts he revoked the decision made by the parts manager and from that point on we addressed worn seat cushions by replacing only the cushion.
Since that time Steve has helped me with a few other problems both directly and through our local Komatsu dealer (MHR).

L1ftmech, thanks. But we never gave them nor approved of the design. Yes Steve is still here, who should I say is asking? Our only manufacturing location back then was La Palma (the old KFM location). Manufacturing began in Covington in 1995 and now BX50 (-16) trucks are made in Newberry, SC.

Jeff, you are right on the money.....Roadway! But the company published that and stated in a company technical service bulletin that the procedure came from KFI.
And I do remember seeing on the data plate on the circa 1990 ZB units the words "City of Industry, California"
We received 6 FG20ST-11s that year at our facility with that stated that on the data plates.
About 1998 we received our first FG20ST-12s and the data plate reflected "Covington, Georgia" on those.
I do remember us receiving FG25ST-8 model that was transferred in (with 15,000 hrs) and it already had the drain back hose installed on it.
Do you know if Steve Shearer is still working for KFI or has he retired?

Thanks L1ftmech.
I edited/corrected my post below after sleeping on it. It was not the pinion seal that failed on the ZB Series, it was a retainer o-ring. Roadway did make a "home made" modification similar to what you described on XXB (-4/-8) Transmissions. The failure typically didn't happen until the truck reached >8k-10k hours. Roadway used trucks up to 40,000hours so they did this as a cost saver for them. Maybe someone out there applied this Roadway fix to ZB trucks?

FYI your a city or two off :-). Our plant was in La Palma, CA and the Product Support Facility was in Buena Park, CA.

Jeff, the "fix" may not have been an official Komatsu field repair procedure but the procedure paperwork distributed by my employer certainly described the entire corrective measure to have originated at Komatsu (which at the time built the ZB models in City of Industry, California).

Gentlemen,
Komatsu never published any such modification for "drain back". Maybe someone out in the field made it up and it was a cheap fix and passed it around, but it was never a Komatsu fix. Komatsu did have a retainer o-ring issue on early "ZB" Series forklifts FG(D)20/25/30T-11 trucks. The fix was to install the new style viton o-ring.

I agree L1ftmech- I saw many modified Kamatsu -11 trucks with this fix. Didn't know what it was at the time but never had a problem with the rear running in ATF.

Old thread but since nobody responded to danny k's skepticism...
That actually was a bona fide field fix to manage the problem of pinion seal failure in those FG--ST-11 models trucks without having to replace the pinion seal.
I installed the "drain back" hose field modification on more than a dozen FG20ST-11 trucks in our company shop back in the mid 1990's.
Most of the pinion seal failures occurred fairly early in the life of the truck and that fact is likely what inspired Komatsu and the transmission OEM to develop this radical approach to resolution of the issue. My guess is that there were enough failures occurred during the factory warranty period that the drain back hose mod was the easy way out for both corporate entities.
In our shop we would install the drain back hose and then put the truck back into service on the dock with Auto Trans Fluid in the differential. The truck would be used for 1 day and then return to our shop for a complete drain and fill of the transmission and the differential. Then after that the truck was just operated normally.
The only thing we had to do differently to the modified trucks was to drain and fill the differential along with the transmission when we did the 3,000 hour PM service so that we would not be diluting the new fluid with old fluid from the differential case. We also had a decal printed with the special instructions for maintenance which we applied to the lift cylinder hose guard plate where it could be seen when checking or servicing the truck.
Regarding the durability of the differential components being run in ATF vs. heavy gear oil: We never had a single failure of any differential components while those trucks were in use.
Some of the trucks remained in service accumulating well over 30,000 hours before the company began selling them off as newer model trucks were bought.
When Komatsu introduced the successor FG--ST-12 model truck it had a different transmission than was in the -11 trucks and pinion seal failure was no longer a problem.
Maybe somebody will find this fix helpful if they encounter one of these old trucks needing "the cure".

You are having a laugh arnt you!!!??? Sounds like a complete bodge to me!!!!!

I was just looking through some of the posts and saw this. I worked alot on the FG25ST-11. They had a problem blowing the pinion seals alot. Komatsu had a tech bulletin to correct the problem. It required installing a differntial bypass. You put a fitting in the side of the tranny down low at the point of the screen. then a fitting in the fill plug on the differntial and a hose between the two. You have to drain the gear oil out of the differential and refill it with tranny fluid. The fluid is pushed back into the tranny when the diff gets too full.

thanks that was the problem

If you are filling the transmission with oil and it is coming out of the diff case breather then you have a pinion seal failure.
This would require the transmission to be removed and striped to rectify this problem, which is a fairly big job.