front wheel drive doesn't work

[73m819]

ALL help is appreciated, every thought helps because it gets the OP thinking, all I can say is if someone has a idea about a problem post it, if it works great, if it does not work, then great we know that is not the answer. So when someone ealse reads the tread , thay will know what/what not worked

 

[817dumper]

Hey there,
Mine gives a loud pshhhh from the air valves at the transmission when shifted into reverse or out of (meaning neutral or any forward gear). Basicly it either applies air pressure to one air hose OR the other going to the air actuator on the transfer case. The psshhh... is the air venting from the opposite side.
its of course common for the air hoses to leak. One or the other Always has pressure on it.
hope this helps i'm still learing too

Mine only does the air noise from N to R and from R back to N. Like your mine also has the same issues and I have spent the better part of the day trying to figure it out. I have 6x6 in revese but no front drive in forward.

 

[wdbtchr]

Mine only does the air noise from N to R and from R back to N. Like your mine also has the same issues and I have spent the better part of the day trying to figure it out. I have 6x6 in revese but no front drive in forward.

Most likely in this situation it's the duplex valve on the the top of the transmission. The rubber seat for the forward half of the valve gets so worn it can't open the air to the Xfer case, but because the truck spends relatively less time in reverse over the years it doesn't wear as bad so still works. You can get a kit to rebuild the valve. I got mine from Memphis Equipment. My cylinder leaks too but still works so far, I have a kit for it, just haven't gotten around to putting it in.

The reason you didn't get any hits in search is because you have to insert "and" between each word in your search to make it work.

Afterthought: Next time try pulling with a load in the bed, you'll have much better luck.

 

[sterlun]

YES, with the air bypassing, it wont push the piston

Cool, thanks man. I'm gonna look into this stuff and see if it fixes it. Thanks a lot everyone for all your help. Wish me luck.

 

[Bob USNR]

I would use this procedure to check the front drive system.

Run the truck until you have highest air pressure.
Stop engine.
Place trans in reverse.
Jack up one end of the front axel and try to rotate the tire. It should rotate in both directions and make no noises. Look to see if the driveshaft is turning while you are doing this. It should always turn when the wheels are turning.
Then place the trans in any forward gear and try to rotate the tire again. If the sprage is working, correctly, the tire will rotate forward but not backwards. It may turn backwards just a tiny bit and then it should lock almost immediately.
If the sprage is not working the tire will rotate in both directions.

If the air cyl that controls the front drive engagement is stuck you should be able to free it up again. Air systems that sit for long periods of time sometimes develop stuck controllers. Stuff rusts. It is sticking 1/2 way out the front of the transfer case near the top.

Hopefully you won't be check'n your wallet and look'n for a good deal on a transfer case.


I'm pulling for ya'... we're all in this together. (Quote from The Red Green show)
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[817dumper]

Thank You I will give it a try

 

[sterlun]

Ok I pulled the tunnel cover and aired up. With the truck turned off and in 1st the continuous hissing came from the item pictured below. Same for reverse. At first it felt like it was leaking through the threads but after taping them up it still does it. So it seems the air is escaping out the top but, on the other hand, it almost appears to me that it's intended to. It's also where my "PSSSSHHHT" comes from. I don't know if I just need to replace this, repair it, or if I have other problems.

 

[73m819]

that is the trans vent,If air is comming from there, then one or both trans air valves are leaking into the trans though the end of the valve, thay need to be rebuilt.
the tm has some good stuff and there some really great threads on just this (rebuilding)

 

[jwaller]

ron thats not the trans vent, I mean it is but it's installed in his valve where it shouldn't be.

Where that vent was installed is the spot where you valve dumps when you change gears. NOTHING should be installed in that fitting.

take that valve out and leave it out, it no business installed where it was. the vent blocking the line could be an issue but I doubt it.

You should only feel/hear air coming out of that center hole when you change from 1 to R or go thru N.

if the valve is hissing when you have it in 1 or R or anytime, it is leaking. that valve should never hiss, only should blow off when you change from R to anything else.

 

[doghead]

Do an advanced search for "sprag piston seal" in the 5 ton forum. There are about 3 good threads that will help you understand this system and understand your problem.

 

[sterlun]

Yeah I was just looking in the TM blow-up and it doesn't show that hickey there at all. And when I looked up the tranny vent it shows it to be directly in front of the shifter boot. Ron was definately right in identifying it but it looks as though one of Uncle Sam's techs stuck it in the wrong hole..?? If so it looks like they fitted it into an adapter to make it thread into the top of the poppet valves.

So I take it from you guys that I need to rebuild/replace the poppet valves as the TM calls them. And hopefully this will get my front wheel drive going and I assume make it easier for me to get it in 1st gear? It has been stubborn.

 

[73m819]

ron thats not the trans vent, I mean it is but it's installed in his valve where it shouldn't be.

Where that vent was installed is the spot where you valve dumps when you change gears. NOTHING should be installed in that fitting.

take that valve out and leave it out, it no business installed where it was. the vent blocking the line could be an issue but I doubt it.

You should only feel/hear air coming out of that center hole when you change from 1 to R or go thru N.

if the valve is hissing when you have it in 1 or R or anytime, it is leaking. that valve should never hiss, only should blow off when you change from R to anything else.

Thank you for catching that
you are right, that is what I get for looking at a pic, quick, then start pounding on the key board, so now back to the transfer shift cylinder leaking past the seals

 

[doghead]

My best guess is, your sprag piston seal(2 way lipped seal) is bad, allowing air to escape out the exhaust port, while in gear. This also would cause you to not have front drive(the piston is not moving/holding the sprag engaged) because the seal is bad. That's my guess(seen it before a few times)

The seal is very easy to replace, and can be bought at Memphis equipment.

 

[sterlun]

My best guess is, your sprag piston seal(2 way lipped seal) is bad, allowing air to escape out the exhaust port, while in gear. This also would cause you to not have front drive(the piston is not moving/holding the sprag engaged) because the seal is bad. That's my guess(seen it before a few times)

The seal is very easy to replace, and can be bought at Memphis equipment.

Are you talking about the transfer air cylinder on the t-case or am I in the wrong place?

 

[73m819]

right place

 

[doghead]

Yes, if you get under the truck, looking toward the rear. Look at the T case front, just above the front drive shaft flange, there is an air cylinder. It had 4 bolts holding it together. Thats the sprag air cyl. It can be disassembled on the truck. No need to remove the drive shaft.

I think all this is covered in those threads, if you do the search I suggested.

 

[sterlun]

Wow. Reading the Admin's post about his sprag whoas that Doghead referred me to. Chris mentions that this repair eliminated "drive-line windup and lurching". Could I be so lucky that this is what's causing my truck to shake violently on the highway? (please please please)

You guys have all been extremely helpful. I'm gonna see if Memphis Equipment still carries the rebuild kit for the transfer air cylinder and I'll try to go ahead and rebuild the poppet valves too while I'm there.

 

[Floridianson]

Memphis kit might have the wrong brass washer that is on both ends of the transfer case air cylinder. Check to see if it is a perfect match. Also if you don't do anything to the popet valves make shure to tighten all eight if the 7/16 bolt that hold the valves to the trans. Every truck I have worked they were a little loose. While you doing the transfer case cyl. do the transfer case air seal that is behind the peened washer. If you have any problems feel free to call. 352-262-0398

Was just thinking your truck does not have a fording kit. I have never seen a one way vent put on the exhaust port of the poppet but I don't think it would hurt it. Seems like if you did do some deep water fording that might be a nice thing to have. You would think that if the water went in to the cylinder it would be forced out but it might be hard on the seals if it could not get out fast enough??????????

Also don't bend the locking tabs back on the air cylinder till after you conferm that it hold air as said Memphis had wrong size copper rings.

 

[jasonjc]

Wow. Reading the Admin's post about his sprag whoas that Doghead referred me to. Chris mentions that this repair eliminated "drive-line windup and lurching". Could I be so lucky that this is what's causing my truck to shake violently on the highway? (please please please)QUOTE]

If the tires are not the same size on the front and back of the truck , it could cause "drive-line windup and lurching"and the truck to shake violently on the highway. The front end could be trying to out pull the rear end. This would destory the sprag.

 

[sterlun]

Thanks Floridianson. I'll be holding on to that number and very well may use it. I appreciate that. Ron PM'ed me his too. It's really awesome that you two are so willing to help.

Jasonjc the tires are the same size numerically but might be hard to tell if they measure the same until I find a flat level surface. I know the fronts are a different brand and tread pattern than the rears. I thought maybe it was flat spots from it sitting on the base so long.