# Banging noise in four wheel drive



## 2COR517 (Oct 23, 2008)

Towards the end of plowing season last year, the 97 was making significant noise in four wheel drive. Most noticeable when changing directions, especially with the wheel cut sharply. The noise seemed to be coming primarily from the front driveshaft area. I know, that's a little vague. While doing some maintenance last night, I thought I would measure the play at the wheel/rotor. I put the key on, put the truck in 4WD, and jacked up one side. Turned the rotor hard one way, and made a mark. Turned the rotor hard the other way and made another mark. Almost two inches of travel at the outside circumference of the rotor. That would be five inches at the tire tread.  The rotor is about 12 1/2 inches in diameter, so that works out to be about 5%, or 18 degrees. That seems like too much to me. Unfortunately, the slack isn't coming from just one spot. It's just about evenly split between the front axle itself, and the transfer case. The CV shafts don't seem to have any play. The front driveshaft u-joints are new, although the front one already has a little play in it :realmad: (The shop that did my transmission replaced them, and put the stupid greaseable joints in. I have not had any luck with those.) A very tiny tiny amount of play in the slip yoke. The banging noise itself really seems to come from the case. 

So my question is, do I need to tear down the case, front diff, or both? Do I rebuild, or put in some used stuff? Or can I keep running it as is? If anyone has had a similar problem, I would really appreciate your feedback and suggestions. 

Thanks, Palmer


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## B&B (Nov 4, 2006)

2 inches of radial play at the rotor is nothing to be concerned with. Thats completely normal on a used truck, it's the half turn ones that will scare you. 

A loud sharp bang is usually caused by one of two things. Either the CAD (central axle disconnect) isn't staying engaged (worn fork or engagement collar in the pass axle tube or a weak actuator) or a worn shift fork or 4X4 dog clutch in the T-case. Any one of these will cause the problem as more load is placed on it, such as in a sharp turn as in your example. A worn dog or fork in the T-case is usually due to low fluid level. They'll actually get to the point that they'll bang and skip even in 2WD. Wear in the CAD is just normal on the higher mileage trucks that spend more time in 4X$ than the average truck.

You really need to depend on your ears here to try and identify the component thats causing the sound. Having a helper crouch down along the truck and listen while you duplicate the sound helps greatly.


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## 2COR517 (Oct 23, 2008)

I knew I could count on you

I'll have my son help me. Are those cheap mechanic stethoscopes any help for something like this? The CAD has been very sloooooow since I bought the truck. Guess it's time for the Posi-lock kit. As for fluid in the case, seems like we put in maybe a quart in early winter last year. And I just drained about a quart and a half out of the fill plug the other night. You know what that means, I already called the shop that did the transmission.


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## 2COR517 (Oct 23, 2008)

A little update. Had my son crank the tire back and forth while I climbed around underneath. There is almost NO play in the front diff. The CV joints do have some play. The inners maybe a little more than the outers, but both sides seem about equal. I thought there should be zero play in them. I have never heard any clicking, and the boots are still good. Mileage is unknown on them, but I bought the truck with 75K, 135K now. The case has alot of play as I mentioned before. And the clanging noise really seems to be coming from it. But, the driveshaft makes it sound like it's coming from the front diff a little bit too. Probably should pull the driveshaft and make sure.

Is the case easy to repair/rebuild? And is a used unit likely to have the same problem.


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## B&B (Nov 4, 2006)

The 241's are a piece of cake to work with but unfortunately their internal hard parts are a bit expensive depending on what it needs once you have it open. At the very least you likely need a chain and sprocket set and probably the shift fork or dog clutch that I mentioned before. Those components alone will run you around 4 bills. Factor in a $180 seal and bearing kit since you have it that far.

Generally I like to open them up first to see whats up. And if it turns out that its going to need more than about 2/3 the cost of a used replacement case can be had for, then I go that route instead. Looking for one with the lowest mileage of course. I do normally pull the replacement T-case apart also before I install it, just to give it a clean bill of health before it goes in.

32 spline 241's are still plentiful in good used condition so they don't cost an arm or a leg. I can purchase them all day long around here for $500 for a low mileage unit. How many would you like?


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## 2COR517 (Oct 23, 2008)

So - how long can I run it like this? Will it just grenade on me at 2:00 am in a blizzard? If I go used, will I have to put in an electric shift case? I'd actually rather have the floor shift. Probably will have to wait till fall to tear it down. 

Thanks for all your help.


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## B&B (Nov 4, 2006)

So it's push button? Ok then it's a 243 not a 241. They're basically identical....except for the shift method of course.

How long it would live really shouldn't be an issue, I wouldn't recommend attempting to run it through another plowing season regardless when you know it already has issues. Fix it before you need it if you have customers depending on you. :waving:

It is possible to swap over the the 241 but it takes some electrical knowledge to get it to interface. Need to move some wiring around and eliminate a few things in order to continue to get 4X4 info/input to the engine ECM for it to work correctly. Not a major deal if your wiring savvy but it needs done correctly to work correctly and be reliable. Adding the manual shifter in the floor is the easy part and everything else will bolt right up, it's just the wiring that takes some effort. But if you want to tackle it I can walk you through it.


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## 2COR517 (Oct 23, 2008)

No, I definitely will fix it before winter. I'll start shopping around for a case, maybe I'll get a good deal. I presume I'll want to check for front output shaft play before I buy it. If I open it up to see what's going on in there, will I need to buy the seal kit? Would you bother to switch to the the 241, or do you feel the shift motor on the 243 is reliable enough?

Is this case still in use? It would be nice to find something with maybe 50K on it, or less.


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## 2COR517 (Oct 23, 2008)

Would a BW 4401 fit? Are they much stronger?


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## B&B (Nov 4, 2006)

No I wouldn't switch to a BW as there's nothing to gain except limited parts availability later when you need them. Nothing overly great to be gained with the 4401 over the 241/243 for your application anyway, the 241/243's are plenty strong and reliable enough, they just wear out with use like anything else. 

If it were me I'd leave the 243 in. They're no stronger or weaker than the 241 and the encoders have a good track record for being dependable and thats the only difference between the two. Plus if you replace the case entirely now you'll end up with a spare encoder too. 

Even in the worse case scenerio if it dies you can roll under the truck, pop it off and shift it manually with a cresent wrench.

If you open up the replacement case for inspection you won't require a seal kit as the case halves are just sealed with RTV. But I'd certainly install one while I had the chance. Seal kit only (no bearings) is cheap...less than $50. And although the 243's haven't been used for several years now if you look around you should be able to find one with decently low miles.


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## 2COR517 (Oct 23, 2008)

Did some calling around today. 200K for $300. 100K for $550. And JustChevyTrucks.com down in Lebanon Maine is getting $250 on average, mileage varies between 100K and 200K. I'll be keeping my out for a deal or someone parting out a truck. I'll go for the 243 unless I get a great deal on a 241. I saw a bearing and seal kit on Ebay for about $100. Proceed with caution, I guess.


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## 2COR517 (Oct 23, 2008)

Found an OK breakdown of the NP243. If anyone has anything better, please post it.

http://www.drivetrain.com/images/stories/product_imgs_large/np243_lg.jpg

Thanks, Palmer


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## B&B (Nov 4, 2006)

Here's a couple that are a little better that I happen to have lying around.


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## firewoodguy (Jan 21, 2013)

transmission mount is bad. driveshaft hits the bottom of 4x4 shifter


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