I always wondered why that sticker was there. Is it just too big a jump or do the synchronizers not work correctly in the opposite direction or something? I have done a lot of high range backing but not going to say any more about the title of this post to protect the innocent/guilty parties. The transmissions never failed and the trucks have since been sold on down the road.
I have done my fair share of high range backing as well. I suspect it's due to the significant difference in ratio, I can't shift it without the clutch so I wonder if it's to keep a gorilla driver from breaking stuff trying to make it change ranges while moving without the clutch.....? Truck Shop will chime in I'm sure
I am with Junkyard on that one. Worked for a couple of companies that made bridge beams. Sometimes they had to back long distances to the bridge site for cranes to unload them. Never saw high in reverse hurt a ranger but drivers preferred the Macks with 5 reverses.
I don't think the sticker prohibits using high reverse but I think they don't want you to shift from low to high while moving. That is what my question was about.
If you look at the syncrhonizer assembly for low/high range it's spring loaded to keep tension on the three slider pins and it's basically ment to operate in one direction when shifted. I have seen two over the years damaged from shifting low to high in reverse. It can break the pins or loosen them on the synchronizer hub. But I believe it was done with out clutching. It's one of those {it will work if done right things}. Another old trick or the hidden gear that can go upside down if done wrong is powering out in fifth with a 13sp and flipping the splitter to overdrive and shifting into granny or low. It would give you a split between 4th on the low side and 5th on the high side. I know some loggers that did it all the time and never a problem. Them loggers are gutsy buggers. Truck Shop
Hey, hey, hey!!!! I resemble that remark!!
I was wondering if it was something like that, some part loaded in one direction only. If that is the case then I wonder how it's possible to do it without damage. If I had ever "seen" it done it was only on 10 speeds and then it would only work by running totally against the governor, then shifting to neutral and waiting for the engine to come all the way back to low idle and then declutching and somewhat grinding back into high reverse. The engine speed drop takes a long time from high idle to low idle and the truck could easily stop from its very slow speed in that time. Jake brake helped. But anything to prevent having to back up half a mile in 12:1 reverse or whatever it is. 10 speed probably has a wider range box than a 9/13 speed. It never occurred to me to use it for splitting purposes but that makes sense. I only ever did this with a 9 speed and then by mistake because I was used to driving a 10 speed. On a 9 speed I did not see much difference between lo/high range and 4th/low range.
My old 91 F800 service truck was an ex Union Pacific rail welding truck with a 6610 roadranger and originally equipped as a Hi rail truck. I'm sure it saw plenty of hi range reverse time with shifts from lo to hi on the fly. The syncro springs were totally demolished when I got the truck and range shifts were very rough.
The three springs act as a damper on low/high range shift. To answer Birken Vogt's question it needs a total release from torque so clutching helps dampen the load on the synchronizer for low to high range shift in reverse. Here are two pics of a high torque model rear section and synchronizer friction hubs minus the fork hub and springs. Shift fork hub slides on the pins. Truck Shop
Nothing of note to add here aside from I never could (smoothly) shift from high to low in reverse on my 18 speed with the clutch. To make the shift easier I would turn the engine brake on, run it up in low, split, run up let off/shift range and split, and roll back on smooth like.... same idea on the 8LL, minus the split.