Allison 4th gear lock up issues

[Gflanagan]

helping a VFD with a tranny issue. Truck goes into pump gear but starts in first gear and you have to rev up engine to get it to fourth. Checked the switch on gearbox and it is working. tranny is Ht 740. wondering if there is anything on the web for troubleshooting the lockup activation. how to check the solinoids on the front of the tranny and what wires should be hot and when. Any help would be appreciated. Gflanagan@fortsmithar.gov

[Louis Marro]

Try looking here: Show Thread http://www.evta.info/forums/showthre...highlight=lock

[Mhenricks]

Is the pump a Hale or Waterous? If it's a waterous, check to make sure it is shifting completely. If the switch plate is worn it could actually make the shift to pump but might not come in contact with the switch. The skinner valves, one is normally open and the other is normally closed, if that helps. Also, check the wiring from the transfer case switch to the trans, and check for grounds. You should also be getting the "Ok To Pump" light, if your not getting the light check for power and ground.

Good luck

[FDMECH12]

One solenoid is normally open, the other is normally closed. When lockup request is made, the N.O. solenoid is closed and the N.C. solenoid is opened allowing main pressure into the govenor circuit and the shift assist circuit. By doing this you raise govenor pressure to engage 4th gear clutch. There should be a pipe plug at the top of the "T" fitting that can be removed to verify that your solenoid is opening and you are getting main pressure. If you are then the problem is "downstream". See if your Allison dealer can give you a copy of Service Information Letter: 10-TR-76, REV B. This lays out the whole set up! Was the pump/trans operating O.K. in the past? Did this happen all at once? Just curious.

[Gflanagan]

Thanks for all the input guys, it really is helping me wrap my head around this problem and help the transmission shop figure this out. The shop hot wired the solinoids and the trans went into 4th gear lock up. They just cant get it to go in on its own. The switch on the gearbox is sending power when in pump gear but does anyone have any wiring diagrams as what other wiring systems come into play when dealing with these solinoids. All help would be apreciated.

[Tom Gaines]

Gflanagan:

I would look for a Parking Brake Relay or a Parking Brake Switch not working. Some manufactures interlocked the wiring for “Pump Engaged” to the parking brake circuit. What kind of truck are you working on?

Tom Gaines.