Transfer case grind chatter while engaging pto

[Kbussey]

I have a question regarding a 1990 m936A2 wrecker I have while engaging the pto. This is my second m936A2 wrecker I’ve owned and didn’t have this issue with the first one. I first had problems with the transfer case interlock solenoid couldn’t shift the transfer case. I disabled that solenoid by plugging the line going to interlock solenoid to allow me to shift the transfer case. Prior to this I would bleed down air pressure to shift . The problem I am having was with both scenarios. I place transfer case in neutral , engage pto, shift transmission to 1-5 (doesn’t make a difference going to 1-1) and once engine loads up telling me pto is engaged I would slowly increase rpm , in doing so the transfer case would make a chatter, grinding noise and engine would struggle some to increase rpm . What do you think the cause for this is? To me seems as if the gears are clashing or there is something causing strain on the gears .

 

[Kbussey]

I have a question regarding a 1990 m936A2 wrecker I have while engaging the pto. This is my second m936A2 wrecker I’ve owned and didn’t have this issue with the first one. I first had problems with the transfer case interlock solenoid couldn’t shift the transfer case. I disabled that solenoid by plugging the line going to interlock solenoid to allow me to shift the transfer case. Prior to this I would bleed down air pressure to shift . The problem I am having was with both scenarios. I place transfer case in neutral , engage pto, shift transmission to 1-5 (doesn’t make a difference going to 1-1) and once engine loads up telling me pto is engaged I would slowly increase rpm , in doing so the transfer case would make a chatter, grinding noise and engine would struggle some to increase rpm . What do you think the cause for this is? To me seems as if the gears are clashing or there is something causing strain on the gears .

Once the rpm gets past 700-800 rpm the noise would stop and everything would work smoothly.

 

[simp5782]

Does it do the chatter if you engage the front winch pto? Just trying to localize if it's a transmission or a transfer case. The noises radiate on these trucks.

 

[Kbussey]

Does it do the chatter if you engage the front winch pto? Just trying to localize if it's a transmission or a transfer case. The noises radiate on these trucks.

I crawled under it while engaged and noticed it was coming from the transfer case .

 

[simp5782]

I crawled under it while engaged and noticed it was coming from the transfer case .

Use a stethoscope or drive extension. High by the pto and pump or down medium lower? Could be a rattling shift fork in neutral

If it was a truck under that a wrecker you could atleast get the inspection plate off the top and try to pinpoint it

 

[Kbussey]

Use a stethoscope or drive extension. High by the pto and pump or down medium lower? Could be a rattling shift fork in neutral

If it was a truck under that a wrecker you could atleast get the inspection plate off the top and try to pinpoint it

Good point, could very well be since the interlock cylinder has been disengaged and previous owner could have gotten rough with high/low shifter to get it to go in gear . It also has air leaking out of the breather while In pto not sure if that’s connected some how and wonder how that could be fixed?

 

[simp5782]

Good point, could very well be since the interlock cylinder has been disengaged and previous owner could have gotten rough with high/low shifter to get it to go in gear . It also has air leaking out of the breather while In pto not sure if that’s connected some how and wonder how that could be fixed?

You do the line union connection to bypass the solenoid or just capped the line going to the solenoid?

 

[Kbussey]

You do the line union connection to bypass the solenoid or just capped the line going to the solenoid?

Plugged the electric solenoid line going to the actuator and plugged the interlock actuator. should I plug the pressure inlet line going to the electric solenoid instead of the outlet line going to the actuator ?

 

[simp5782]

Plugged the electric solenoid line going to the actuator and plugged the interlock actuator. should I plug the pressure inlet line going to the electric solenoid instead of the outlet line going to the actuator ?

You just need to connect two lines together to bypass the whole solenoid and auto 6x6 in low range..

 

[Kbussey]

You just need to connect two lines together to bypass the whole solenoid and auto 6x6 in low range..

Thank you so much!! I’ve been looking for that information for longest time. I was studying it under the truck but wasn’t sure. I just took off the switch mechanism off the low gear front wheel lock switch but this would be the best way to do it. Hopefully it fixes my two issues . Post video once I get it done

 

[Kbussey]

Thank you so much!! I’ve been looking for that information for longest time. I was studying it under the truck but wasn’t sure. I just took off the switch mechanism off the low gear front wheel lock switch but this would be the best way to do it. Hopefully it fixes my two issues . Post video once I get it done

Sorry got another question maybe you can help… can I disable the pto air switch just behind the cab? What function does it provide, does it just actuate the brakes or does it do something inside the transfer case?

 

[simp5782]

Sorry got another question maybe you can help… can I disable the pto air switch just behind the cab? What function does it provide, does it just actuate the brakes or does it do something inside the transfer case?

It engages the spring brakes override the parking brake handle linear valve that dumps the air to the brakes. This also overrides the Spring brake override button on the dash. However Some trucks were equipped with a brake override switch under the steering wheel. That was used for self recovery with the rear winch so that the Spring brakes would release.

Picture below of the override switch for rear recovery.

 

[Kbussey]

It engages the spring brakes override the parking brake handle linear valve that dumps the air to the brakes. This also overrides the Spring brake override button on the dash. However Some trucks were equipped with a brake override switch under the steering wheel. That was used for self recovery with the rear winch so that the Spring brakes would release.

Picture below of the override switch for rear recovery.
[/QUOTE both m936 I owned had that Valve under the dash to override the brakes. I disabled that valve behind the cab that someone on here called it a power divider air valve and it caused my hydraulics to work really slow didn’t seem like there was full pressure there. Hooked it back up and worked fine but caused bad air Leak in the breather . I still can’t figure that out..

 

[simp5782]

Under the truck. Drivers side. Right behind the air filter on the inside of the frame. There is a 4 or 6 way block there that has 1 large line going going the intake pipe. This is the vent connection block.

Remove 1 line at a time from the one side or the other to see which one is dumping that air out of it and we can chase it from there. Forward facing lines are for front brakes and for the brake pedal vent. The rears it depends on what size the line is as to what it's function does.

Take a picture of which line is dumping the air when you remove it.

 

[simp5782]

The button should not kill your hydraulics at all. The truck running at rpm gives the wrecker its 2200 to 2500psi which is the power of the crane. Rpm speed increases flow gpm and gives you speed of the unit.