M35A3 Neutral Safety Switch?

[BHaas35]

Not seeing such a thing on the TM's under Figure 80 and 81. However, TNJ and Osh have it listed: SWITCH,SAFETY,NEUTRAL TRANS M923/A1/A2 M35A3. Does the A3 have a safety switch?

Reason I am asking, turned the truck on this am, tried making a 30 point turn around a 5th wheel trailer in the driveway and the third time I put her in reverse...nada...nothing. Put it in drive, pulled forward, back to reverse...nothing. Could it be this possible switch? Read all the bad stuff about the AT1545 but I don't run her hard. Could something on the AT1545 fail that easily? I do have to admit, the temp wasn't fully at operational but I literally was going so slow speed didn't register. Can't get her back into reverse. Shut her down for a bit and turned it back on...lost all air pressure 2 minutes in. Turned her off and back on. Turned off CTIS, air pressure back, still no reverse. I turned the lights on, parking brake set and put her into reverse, jumped out and looked at the reverse lights...not on like they usually are. Turned off...sat for awhile...click, truck won't turn on. Tried a few times, click, nothing. Charged each battery (low 12s) to 13+v on each, nothing. Tried a dozen times, tapped on the starter and solenoid...nope. Happy Monday to me. Oh and it's been pouring nonstop here in TX and after trying to get her in reverse I only managed to roll it forward off the driveway and encroaching into the grass, now mud pit. Too heavy to roll her back. When does it end? Thanks in advance for any help. If you are local please bring your deuce to drag me off the lawn.

 

[HDN]

I'm sorry to read about your bad luck!

I don't think there's a neutral safety switch on the truck. IIRC the manual makes it very clear that the truck must be in neutral for startup and shutdown otherwise death or injury to personnel may result (their words!). Did you check the ignition switch for continuity? Do you get any power when you throw the battery switch?

From the Operator's Manual pg. 3-4:



And there's more in the Direct Support Troubleshooting up to replacing the engine to fix the problem, which wouldn't do you any good if the problem is electrical anyway

Once you get the truck started, check the shifter linkage. It might've gotten loose. Typically these transmissions have a 4th and reverse failure at the same time due to a blown piston or seal in the transmission. Losing all the gears because of a transmission problem isn't common at all from what I've read.

Do you have any of the TMs? They have a lot of troubleshooting instructions that may be helpful for anything that might go wrong with the truck. The A2 manuals are also helpful in this regard since a lot of A2 parts are reused.

 

[BHaas35]

Thanks HDN,

I do have all the TMs in a nice organized binder with tabs for every issue and went through it all and all the searching on the forums prior to posting. Contact unit maintenance in my next step.... Truck is always in N when starting or stopping. Tested the starter switch, relay and starter along with the batteries. All look good. I am thinking the truck thinks it is in Drive. Can't be R since the backup lights do not engage and I lost R previously and was only able to engage D. I crawled under the truck while our Nanny went through the gears with the truck off (because it won't start). Link seems to be okay? There is a little shake in the bracket but nothing concerning. There has to be some sort of safety switch to have the truck not start in gear. I Even when my shift lever is in N the truck still thinks it's in D. All I can find in the parts manual is the reverse switch. Found it strange TNJ and Osh have a neutral switch listed for A3s...

 

[HDN]

I Even when my shift lever is in N the truck still thinks it's in D. All I can find in the parts manual is the reverse switch. Found it strange TNJ and Osh have a neutral switch listed for A3s...

Ok, I stand corrected. The truck does have a neutral safety switch just like you found. I never tested it so I didn't know it existed, especially based on my reading of the operator's manual. But my memory can be a little fuzzy

The safety switch is #8 on the diagram for both transmission models pictured:



Here's a detail including the switch leads:



Here's the part info in case you didn't find it all:



As for the manuals, I have the operator's manual printed out in a binder as well as the original book. I keep all copies of manuals in PDF form that way I can use Ctrl+F to quickly search for part numbers or terms like "neutral safety switch". That only works if the text is readable by the PDF reader, though. The manuals I have came from @jatonka 's website, and my Adobe reader can search them all for words and part numbers.

 

[BHaas35]

Perfect! That’s it. Thanks for this can’t say I’ve seen this page before. I just downloaded the Allison manual to start my search there. When I crawled under to check the linkage I did see those two wires. They went through the linkage bracket. Looks like a pain to work on. Now I wonder if I unplug I’d be able to start her up if it is the issue? I’ll diagnose and share my outcome. Thanks again!

 

[HDN]

Perfect! That’s it. Thanks for this can’t say I’ve seen this page before. I just downloaded the Allison manual to start my search there. When I crawled under to check the linkage I did see those two wires. They went through the linkage bracket. Looks like a pain to work on. Now I wonder if I unplug I’d be able to start her up if it is the issue? I’ll diagnose and share my outcome. Thanks again!

You're welcome! When I just searched the part number in the parts and special tools book, the neutral safety switch showed up on a page with other miscellaneous items without showing its location. When I searched the general support manual it came up in the transmission replacement workflow.

I'm grateful for the guys at TACOM or where ever who put these manuals into a searchable PDF. I haven't spent enough time reading older truck manuals to appreciate how easy I've got it with the M35A3!

 

[BHaas35]

Update: Disconnected the neutral safety switch and attached an ohmmeter to it. I received the infamous (to me) OL so it is open in gear. Replaced connection and ran through each gear...OL. However, it is interesting, when unplugging the two connections, one of the crimps just fell right out, was not even crimped. New switch on the way. I'll post an update if the issue is fixed. Might mean I need a Tranny flush...Was going to do that but was hoping later down the road.

 

[BHaas35]

Update: replaced neutral switch. She fired right up. After all the research prior to purchasing an M35A3 I never knew these to fail.
However, I still don’t have reverse. Now I need to read how to adjust the shift linkage.

 

[BHaas35]

Update: Shift linkage was wayyyy off. Have everything dialed in and she works! Gear shift feels better than ever…nice and tight! Good to go!