Bang in reverse

[Bill W]

OK
I haven't done much with my 5 ton since I bought it other then starting to buy "must have " parts ( ie windshields,tires,WINCH!)
anyway I do move it around the property and twice now when going from forward to reverse and backing up I have gotten a Butt clutching "BANG" from underneath., I'm assuming this is something to do with the frt sprag???

 

[BKubu]

Try jacking the front wheels off of the ground. If the sprag is wound up, the front wheels should spin releasing the tension on the sprag. If the tension is not released, the sprag might fail (or might have already failed). I've never had this problem, but this is what I was told previously.

 

[gimpyrobb]

does it bang when you shift, or when you are moving backwards? Is it while going straight back or turning?

 

[Bill W]

No it doesn't do it when I'm shifting from first to reverse, it happens after I've bee backing up for about 30',both times I've been on a down angle and turning slowly while backing

 

[benni72]

i had the same problem. well i mite still have the same problem! my m52a2 is completely torn down for a resto but prior to tear down the transfer sprag was banging just like yours. the sprag was all wound up when i jacked up the front end. check the poppet valves on top of transmission, i found that one had a slight leak and the ball on the other was all rusty and worn. gonna take a spanking from memphis if you need to replace it, i think i paid around 200.00 or so. well anyway i tested the air cylinder by disconnecting the lines to the valves and blowing air through them with a compressor and i heard the familiar thump you should hear when shifting from forward to reverse. so i just assuming that my problem was with the poppet. hope this helps, adam

 

[DDoyle]

Definately a problem with the sprag - either the air valve is not functioning (do you hear a "hiss-whump" when you shift directions?) - or the sprag itself is stuck (which sometimes happens with thick grease or corrosion).

BEWARE, if you keep driving it, something expensive WILL break - I've seen transfer outputs twisted in two due to this precise problem.

HTH,
David Doyle

 

[m139h2otruck]

Same problem we were having with our truck. Make sure all air lines and valves are tight and not leaking air. I flushed out the case with a mixture of fuel oil, ATF and motor oil. As DDoyle said, bad things can happen quick and you will be installing a new transfer case.

Ours does not do this now (fingers crossed) and I think that the sprag unit was sludged up bad, from the condition of the oil when I first drained it (looked like crude oil). Oil and a flush job (or two) is way easier and cheaper than changing out a case.

 

[Bill W]

Thanks guys
I figured it had something to do with the sprag. I do hear the hiss when I shift from reverse to first but no thump. I will start by checking the the valves on top of the tranny and will definitly flush the transfer. How come only in reverse?
Again thanks for the input.

P.S. D.Doyle, it's good to see/read you on this site.

 

[DDoyle]

Hi Bill,
I now know who you are! (and I am still after a water purificatiion truck).

There are two sprags - one for forward, one for reverse. The forward sprag is staying engaged (hence, no noise going forward), but when in reverse the forward sprag is STILL engaged. These are overrunning clutches, and detect the rear wheel spin to engage the front axle drive (just like on an early deuce - but the five-ton uses air to select the sprag, while the deuce uses a linkage to do this - funny how folks that cuss the sprag ignore their presence in five-tons). When the forward sprag is engage, but the truck is moving backwards, the sprag is "confused' and essentially thinks the tires are slipping, and wants the front axle to pull to help - but the sprag thinks the truck is going FORWARD.

An oversimiplification - but you get the idea.

Good to see you back at it.

Sincerely,
David

 

[Bill W]

Thanks David
Hey guys can I take off the frt driveshaft for now until I have time to dig into this project ,she not on the road and only being moved around the property

 

[m139h2otruck]

Should cause no problems, but be aware, it is real heavy.

 

[Bill W]

Maybe I should have worded it better
Would taking off the frt driveshaft stop the binding on the sprags when I'm in reverse?
Thanks