LOUD bang in drive train....M813

[texas-5-ton]

Today while out fighting fire in the 813, we were in reverse, backing up to get thru a gate. After backing about 25 feet, we hear this huge bang (just one) that came from under the truck. It sounded like we had plowed over something but this is the second time that this has happened. We were on pavement and not in mud or soft dirt. Any idea what might be going on. Maybe something binding up???

Chad

 

[Ferroequinologist]

I'm no 5ton expert, but sounds like the sprang(sp?) for the front axle is not disengaging.

 

[clinto]

Something unhappy is going on in the transfer. Tested the sprags to make sure they are engaging correctly? Air poppet valves..can you hear them going into reverse and first?

 

[texas-5-ton]

Re: RE: LOUD bang in drive train....M813

Something unhappy is going on in the transfer. Tested the sprags to make sure they are engaging correctly? Air poppet valves..can you hear them going into reverse and first?

Yes, I have heard it air shifting before, but today, the two-way radio was jabberin' and i wasn't paying attention to the air shift. You think thats what it might be?? Where should i start looking and what should i look for?? Thanks

 

[steelsoldiers]

That's what my 818 did when I first tried to drive it. It was fine in reverse, but forward gears it would bang all of a sudden. I took the front drive-shaft out to get it home. If you pull the drive-shaft, make sure you jack one wheel off the ground first to relieve any wind-up in the drive-line. It's either my selector valve or the actuator in the t-case.

Shift your truck from R to 1st and you should here a hiss and a clunk as the sprag actuator moves in the t-case. If you don't here that, then something is gummed up in the system. It's possible the actuator is just a little sticky in your t-case since it only did it a couple of times.

Have you tried R since it happened last?

 

[texas-5-ton]

Re: RE: LOUD bang in drive train....M813

That's what my 818 did when I first tried to drive it. It was fine in reverse, but forward gears it would bang all of a sudden. I took the front drive-shaft out to get it home. If you pull the drive-shaft, make sure you jack one wheel off the ground first to relieve any wind-up in the drive-line. It's either my selector valve or the actuator in the t-case.

Shift your truck from R to 1st and you should here a hiss and a clunk as the sprag actuator moves in the t-case. If you don't here that, then something is gummed up in the system. It's possible the actuator is just a little sticky in your t-case since it only did it a couple of times.

Have you tried R since it happened last?

Yes Chris, we did go into reverse easily several times after the occurance. We didn't have any other problems the rest of the day. I believe that this ol' truck probably sat for awhile before we bought it.

 

[steelsoldiers]

RE: Re: RE: LOUD bang in drive train....M813

Could just be a gummy actuator or valve then. I need to take mine apart and clean all the junk out of them. I will post pics.

 

[ARMYMAN30YearsPlus]

RE: Re: RE: LOUD bang in drive train....M813

Chri:
Do you recommend disconnecting and removing the front drive shaft for me to bring my truck home on the long drive? I now may be headed west to the DFW area to pick up a trailer if what my son told me is true so we would be making a near 2,000 mile trip.

 

[steelsoldiers]

RE: Re: RE: LOUD bang in drive train....M813

I only removed it because my sprag was stuck. If the sprag is working correctly, then it's not going to help you. If you jack one one front wheel off the ground and put the transmission in 1st with full air pressure, you should hear a clunk and the wheel should spin easily in the forward direction and not in the reverse direction. If it does this, then you should be fine for your drive. You never want to have the truck in a forward gear and let it coast backward or vice versa as this will produce wind-up in the t-case. When going from R to F, you always have to go through 1st gear to select the F sprag. You can put a valve in-line with the air supply line to the tranny valve to keep the sprag in neutral. This has been covered at length in other posts. For a 2000 mile trip, you could also pick up a pair of used hub flanges and de-spline/bush them for the trip.

 

[m139h2otruck]

I strongly suggest that you drain and flush your TC at least once with fuel oil and atf or something like this to clean out any sludge that may be in the case. Just drive it around slow for a few minutes to flush out the crud, shifting forward to reverse as many times as you can. Had the same problem with ours and after a couple of these loud bangs, decided I didn't want to risk blowing the case. No problems since. Also make sure all air lines are tight and valves are not leaking on top of the transmission shifter. Sometimes they can leak into the transmission and cause leaks there too.