9LL issues

[Wasteaway]

Everyone I asked is stumped.

I bought a 2001 RD688 Western Contractor with a 350 Mack engine and 9LL Fuller transmission. With the truck came every service record since day one. Having seen three times where the previous owner had to retighten a set screw in the transmission (once fishing it out of the bottom) I decided that while the truck was idle to remove the top plate of the tranny and take a look. Upon seeing safety wire in the set screws that hold the shift dogs in place I assumed that the problem was addressed and fixed once and for all. I now believe those set screws come safety wired from the factory....but that "issue" is not the problem right now.

When the cover was "up", only high enough to look under because the floor doesn't allow for removal of the plate, I did ABSOLUTELY NOTHING to the inside of the tranny. I set the cover down and buttoned it up. Months later I went to drive the truck out of the garage and it will not shift into any gear except reverse if I hold the shifter tight to the gear as if it is going to slip out. So reverse, first, and third will chatter against the gears with the clutch in. Second and fourth will pull hard but never contact a gear. The shifter moves freely. I have removed the tower several times. The detent balls and springs are all in place. The high/low range selector does not always "click" with the normal loud thud. There is a light on the dash that flashes "electrical malfunction" that I don't recall being on before. The throttle pedal is now grounded with no change. The truck drove and shifted perfectly when brought in. I'm not familiar with any transmissions beyond understanding their basic internal function. I have contacted several "experts" to no avail. Many suggestions but none have born fruit. Anyone here have an idea?

 

Thanks for your efforts in advance. I haven't been on here in a while but I know from lurking before that there are some her who know their snit.

[Mack Technician]

Drop the oil, pull the side covers and take a look up inside to get some real-time information on who is and who is not doing what they are suppose to. 

[carlotpilot]

most likely this has been said by someone else but it sounds as if when you sat the top back in place one of the shift forks missed the slider that it fits in either in front or back of it

[Wasteaway]

Its possible for a shift fork to miss its correct location and not affect the cover setting down smoothly? The three "blocks" in the top plate that slide on the rails are all centered creating a clean "square" for the shifter "tail" to set into. I assumed that a shift fork out of place would cause one of these three blocks to be misaligned when the transmission is in the neutral position. It sure feels like a shift fork is not in its proper location.

[carlotpilot]

i`m not real familiar with a 9 ll  but a fuller 10 or 13 will miss its mark very easily. the collars on the main shaft will slide enough to cause a fork to miss   mack tech has a good idea check his out first  if that don`t answer the ques. then i suggest pulling the floor panel out take the top off and make sure whats happening from there

Edited December 7, 2017 by carlotpilot

[Wasteaway]

Thanks Carlot. The floor pan is up but restricts the plate from being removed more than about 7" high. My next move was to jack the cab from the rear for more clearance but even with that you can't look inside while setting the plate down. Thanks for letting me know that it is possible to be misaligned and have the plate sit properly. I will take mack tech's advice (thanks) and see what I can find.

[carlotpilot]

ok your watching   good  if you do find that one or more is not right the top will still have to come off to fix it. the sliders i`m refering to are free to move once the shift forks are lifted out of their slots is why i say its possible

[Wasteaway]

I think I know exactly what you're talking about. I can see down inside when the plate is up, but not to the rear of the transmission. I suspect the rear fork is not in place in the slider gear, which  cannot see. I'll try it once more by feel and if I can't get it I will open a side plate or jack the cab to remove the plate altogether. Just didn't think the fork could miss and the plate fit down smooth and all three rail blocks in the neutral position. To me that indicated that the forks were all home. Gotta be something stupid because I didn't take a thing apart when I was in there.

[carlotpilot]

2 minutes ago, Wasteaway said:

I think I know exactly what you're talking about. I can see down inside when the plate is up, but not to the rear of the transmission. I suspect the rear fork is not in place in the slider gear, which  cannot see. I'll try it once more by feel and if I can't get it I will open a side plate or jack the cab to remove the plate altogether. Just didn't think the fork could miss and the plate fit down smooth and all three rail blocks in the neutral position. To me that indicated that the forks were all home. Gotta be something stupid because I didn't take a thing apart when I was in there.

if the top was NOT lifted straight up or not straight back down  just a small tilt in front or back could have caused a slider to move enough to miss

[Wasteaway]

The saga continues. I finally got some time today to take a close look and I removed the top plate for the 20th time and this time was able to determine that the shift forks are all in the groove of their designated selector gears. i positioned the cover so I could peek inside just before dropping it completely down and determined that the forks are aligned. Nothing has changed. Shifting is impossible, yet nothing was removed internally. Again, there is an "Electrical malfunction" light flashing on the dash, the throttle pedal is grounded, and the clutch does disengage when depressed. I, along with everyone I have spoken to is stumped. Any more suggestions?