Four Speed 8844A Transmission

[AJ]

MC8, four speed manual Spicer transmission, question.
On the reverse shift, as I engage the clutch on reverse(apply torque to the reverse gear), the reverse gear pops out to neutral. It doesn't stay in the reverse.
My reverse solenoid is in working order, draws about 30 amp on pull and 4 amp on hold.
My question is what could cause the gear pop out? And what can be the cure?
Thanks.

AJ

[Len Silva]

Assuming there is nothing actually wrong in the transmission, I would check all the linkages, particularly second gear to make sure it is fully engaged.  Just go by the book and adjust the shifter linkage to spec if you can.

With these old buses, there could be enough wear that you can't do it without some repairs.

Do you have any problem with it popping out of second when you coast?

[bevans6]

If you manually hold the shift lever in place, does it still pop out of gear?  Edit:  I apologize, this post is kinda pointlessly detailed about the innards of a 8844, but  there you go.  I am a transmission nerd. Sorry...

What the reverse solenoid does is move the 1/2 shift lever on top of the box cover over to engage the reverse shift rod that moves the reverse shift fork.  Once it's over there it will stay put until the reverse shift rod goes back to neutral.  The shift rod is held in place with a little spring and ball that fit into a little groove on the shift rod, it is not going to keep much in place against a force that is trying to get reverse to unengage.  You can move the shift forks past those detents  by hand with around 25 lbs of force.

Reverse gear inside the box is actually three gears, one on the layshaft, an idler gear, and the  1/2 sliding gear that engages those first and second gears.  It is huge, and has straight cut gears on it's outer circumference.  When you engage reverse what happens is that 1/2 sliding gear is locked in neutral, and the reverse shift finger moves the idler gear over to engage both the layshaft and the sliding gear, and power is transferred from the layshaft to the idler and up to the main shaft via the sliding gear.  Makes more sense if you can see  it.  What can happen is the bracket and the shift finger are pinned to the shift rod with set screws.  I can see one backing out and letting the bracket or the shift finger move along on the rod and the reverse idler gear will no longer be fully engaged into the other two gears, and it could pop out of engagement even though the shift rod is in the right place.  On the other hand if holding it in place with your hand on the shifter keeps it in gear, that detent spring may have given up.

Edit: you can see the shift levers on top of the box through the floor hatch.  If you look and the box is correctly engaging the gears, the adjustment is probably OK.  It's good to look because it's very possible the rod ends on the shift levers are worn out, and they are easy to change.  They are 1/2" thread, 1/2" bore rod ends.



Brian

[JohnEd]

 In the standard shift transmissions that I have worked on over the years, all automotive, the "pops out of gear" problem was due to the shifting linkage being worn and not pushing the trans lever FAR ENUFF into engagement.  The ball and detente spring wasn't engaged.

Test this by putting the trans in reverse....disconnect the shifter linkage....see if you can push the shifting lever on the trans further into the gear that pops out.  Usually this was second gear but any will do this on worn shifter linkage external to the trans.

If the linkage is pushing it far enuff then you simply have a worn trans.  Smart money is on the linkage being in need of adjust and/or needing rebuilt.  Lots of posts about how "the thing seems to shift itself after rebuilding the shifter linkage from the front to the back".

Good luck,


John

[AJ]

Thank you for all your valuable inputs and comments.
This is why this board is is so good.
Appreciated for your help.

AJ

[bevans6]

But - did it work?   

Brian