Allison 4th gear lock up issues

[Gflanagan]

Pump is air shift. One light in cab for ok to pump. This light comes on when placed in pump gear. Have not checked the trans' shifter switch. Is this a neutral saftey switch or a 4th gear switch, I don't know how this switch is suposed to work if it has one. I'm going to work on it on monday, hopefully I can answer more detailed questions. Any advise on things to look for would be helpful. I've read that all these swiches and safty devices go to a relay, then to the transmission solinoids. I dont know what this relay looks like, where it is lokated or how to test it.

[Tom Gaines]

Originally Posted by Gflanagan

Pump is air shift. One light in cab for ok to pump. This light comes on when placed in pump gear. Have not checked the trans' shifter switch. Is this a neutral saftey switch or a 4th gear switch, I don't know how this switch is suposed to work if it has one. I'm going to work on it on monday, hopefully I can answer more detailed questions. Any advise on things to look for would be helpful. I've read that all these swiches and safty devices go to a relay, then to the transmission solinoids. I dont know what this relay looks like, where it is lokated or how to test it.

Gflanagan:
Some Builder use different methods to wire their pump shift circuit. I am assuming you have checked the builders Service Manuals for electrical drawing and diagrams. If no drawing are available, the objective is to send an electrical signal to the lock-up solenoids “only” when the fire pump is in pump gear. If your truck is an older vintage say the 80’s or early 90’s it may not have the newer Interlock features with several relays especially to inhibit electronic throttle on the pump panel until the fire pump is engaged and the parking brake is set. On the back left side of the Hale Pump Transmission there should be one or two switches. After April of 1995 Hale pumps had two switches. The lower switch was use for Interlocks to Relays to the throttle and transmission lock-up solenoids. The upper switch was use for the pump shift lights. These switches are not rated for high amp loads and builders were not supposed to use these switches to carry the entire load of the shift circuit, that is why relays were to be added. However I have found several older pumps to be completely wired through the pump transmission switch and have worked that way for many years with no apparent problem. I have also seen air switches, such as a stop light switch, mounted in the air line to the air pump shift circuit to achieve 4th gear lock-up. So you see there several ways 4th gear lock-up can be achieved.

If your transmission goes into 4th gear lock-up and the pump engaged light is on, when in pump gear, the pump and transmission should operate properly. The only other concern I would have is if there was some kind of circuit protection such as a fuse or circuit breaker.

Hang in there and share more information when you can.

Hope this helps, Tom Gaines.

[Elmhurstevt]

Originally Posted by Tom Gaines

Gflanagan:
. I have also seen air switches, such as a stop light switch, mounted in the air line to the air pump shift circuit to achieve 4th gear lock-up. So you see there several ways 4th gear lock-up can be achieved.

Hang in there and share more information when you can.

Hope this helps, Tom Gaines.

Just to add to what Tom said about the brake light switch. I had what appeared to be an oil pressure switch plumbed into the park brake circut that was used as a ground circut for an interlock. when the pump was engaged, it used the ground from that park brake switch to trip a relay to allow "OK to Pump". I found it to be defective and replaced it. I goofed when installing it. To insure there would be no air leaks, I used teflon tape on the threads. This kept the switch from grounding through the threads. It did not take nearly as long to troubleshoot it the second time!

[MGS207]

Like Steve and Tom have written, I have seen the same. Keep us posted on what you find or not.

Mike

Steve did you recieve your e-mail from IFAMA ?

[Gflanagan]

Fixed!! finally, It was the relay that opperates off the neutral switch. This relay kills power to 4th gear lockup when it is in neutral and when you swich it into 4th it sends power to the transmission solinoids. Man am I glad that problem is solved. Thanks for all the help in diagnosing it.