Model 246 Transfer Case Problems

odieundun67 · January 31, 2009

My 1999 Silverado 1500 4WD with a model 246 Transfer Case. When I stop, transmission in drive, foot on the brake, push "4 High" button, pretty good 'clunk' noise thump in drivetrain, let foot off the brake, truck sits still (on snow or gravel), have to push accelerator pedal to get it to move, fairly loud whining noise from truck similar to other trucks sound I've heard in 4WD low. If I take my foot off the gas, it's like putting on the brake. When you switch from 4 High to 2 High, there's a clunk & a big relief like letting it release from the bind & the truck will roll forward at idle in drive. Selecting 'Auto' 4WD mode results in that same behavior only it rolls in drive & only does the behavior when the rear wheels slip. I have always used the dealer-recommended fluid (expensive stuff) & it doesn't leak. The truck DOES get used in 2WD about 99% of the time though.

The transfer case had these symptoms, I took it to the dealer who checked out all the sensors, front & rear diff's, tire size, ran code reader on it with no codes present, switch checked out OK, no fault messages on dash center, etc. Dealer diagnosed it as a problem in the t-case itself.

THEN I bought & installed a professionally rebuilt t-case with a 3 yr warranty & guess what..... the SAME symptoms. I took it to the dealer who ran through all the diagnostics, etc. & came to the same conclusion that there is a problem in the t-case itself.

I bought the rebuilt unit through a national chain auto parts store. They say pull the unit & bring it back in. They will return it to the rebuilder to exchange for a replacement. I'm hesitant to do that, especially since the symptoms are identical. I'm wondering weather something like a problem in the Control Module might cause a t-case clutch problem & NOT throw an error code, or maybe a problem in the encoder motor where it turns the shift lever too far or not far enough, but still doesn't throw a code, etc.

Thanks for reading this long post.

Any suggestions or ideas that you all might have are appreciated.

Odie

Spurshot · February 1, 2009

Tom,

I've gone thru some problems with my 246 TC as well. Just not like these. Anyway, did you use the old encoder (shift servo) from the original TC?

odieundun67 · February 1, 2009

Tom,
I've gone thru some problems with my 246 TC as well. Just not like these. Anyway, did you use the old encoder (shift servo) from the original TC?

Chuck,

Thanks for the reply. Yes, I transferred the encoder from the old unit to the rebuilt one.

Spurshot · February 1, 2009

That may be the culprit.

odieundun67 · February 2, 2009

That may be the culprit.

Might be. I did a test run this afternoon with the transfer case in Auto & when I got up to about 30 mph (on relatively dry pavement), it went into what felt like 4 Low automatically (tires chirping, etc. all the way until I slowed the truck down). When I slowed down & turned into a parking lot it went back into 2 wheels driving on its own (t-case still in Auto). I then repeated that a couple of more times. I pulled the ATC fuse after it did one of those "going into 4WD on its own in Auto on dry pavement" occurances & pulling the fuse just gets zero 4WD working & no lights on the dash control switch.

I also tested it in the deep snow behind my house. In Auto it seems to kick in the front axle fine when the rear is slipping, as long as I keep my speed low (under 10 mph), & it will pull itself through deep snow.

Maybe the encoder can only put it in Low when the module calls for it to go into 4WD. I don't know why the module would call for it to go into 4WD without wheel slip (as it did on dry pavement tests). The tires are all the same dia., etc.

I guess the thing to do next is buy a new encoder to see if that cures the problem. If that doesn't work, I guess the last thing to buy would be a control module.

Thanks for your replies........Tom

Spurshot · February 2, 2009

Tom,

Take me thru what happened exactly again? If you have it in Auto, then accelerate to about 30mph, it drops down into 4 Lo???? 4Lo will only go a bit fast than that wide open in my truck. That would make some horrendous screaching tires and reving engine noise?

If you give me specifics, I'll try the same test in my 99 2500 nbs.

odieundun67 · February 2, 2009

Tom,
Take me thru what happened exactly again? If you have it in Auto, then accelerate to about 30mph, it drops down into 4 Lo???? 4Lo will only go a bit fast than that wide open in my truck. That would make some horrendous screaching tires and reving engine noise?

If you give me specifics, I'll try the same test in my 99 2500 nbs.

If I have it in Auto, accelerate to approaching 30 mph on dry pavement in a straight line, the 4WD will activate causing screaching tires, reving engine noise & puts a heavy drag on the front wheels, especially the left front (would the front diff be an open one with just the drivers front wheel pulling?). It's pretty violent when it happens. It's like in Auto when it sees a certain speed regardless of whether there's a difference between the front & back wheel speed (lack of rear slip), it engages the front.

It does the same thing if I drive forward in a straight line around 20+ mph in 2 High & push the 4 High button- violent engagement of the front wheels/tires, screaching tires, etc. My reaction is usually to take my foot off the accelerator & the drag on the front usually brings my speed down quickly like its in low (without much if any braking by me).

If I'm stopped or barely moving in snow with it in Auto, it seems to work properly- when the rear wheels start spinning, the front kicks in & pulls me out as it should. I think the difference in that situation is that I'm stopped with the truck & gradually accelerating when the slipping in the snow occurs in the back & the front kicks in almost as a 'creeper' feel.

I when I get home from work tonight I think I'll test it by putting it in 4 Low & drive it for a few truck lengths on dry pavement, recording the speed & rpm, then put it in 4 High & do the same thing to see how they compare to see if there's a difference.

Spurshot · February 2, 2009

If you can do it in the dirt, it'll be less likely to break something in the driveline.

You should be able to drive it in Auto pretty much as you would in 2 Hi.

Spurshot · February 2, 2009

Tom,

Based on your description, I'm starting to think you may be correct about the Transfer Case Shift Control Module or a signal input to it.

I read thru all the troubleshooting section of my Helms manual. Nothing jumped out at me as similar or related to your problem. My guess is it's signal/sensor related.

Has the Transfer Case Shift Control Module ever been changed? The reason I ask is that it requires the correct VIN to be programmed into it.

odieundun67 · February 2, 2009

Tom,
Based on your description, I'm starting to think you may be correct about the Transfer Case Shift Control Module or a signal input to it.

I read thru all the troubleshooting section of my Helms manual. Nothing jumped out at me as similar or related to your problem. My guess is it's signal/sensor related.

Has the Transfer Case Shift Control Module ever been changed? The reason I ask is that it requires the correct VIN to be programmed into it.

I've had the truck for a year & a half haven't changed the shift control module, but it's had this problem ever since I've owned it. Then, after putting the rebuilt T-case in it & still having the same symptoms, I took it to the local Chevy dealer who plugged it in & found NO error codes being thrown. If someone before me replaced the control module & didn't program it to the VIN number on the truck, I don't know if the result would be error/fault codes being thrown or NO error codes being thrown. It is food for thought though. Do you know from personal experience that the VIN MUST be programmed into a replacement/new module for it to work?

Spurshot · February 2, 2009

"Do you know from personal experience that the VIN MUST be programmed into a replacement/new module for it to work? "

No, I just read about it in my Helms manual. There's about 100 pages on the 246 in my manual. I thought about scanning them for you, but it'd be a fair sized task. I'll see if I can come up with a way to get you the manual section. But, it's pretty involved to do the troubleshooting and you may not have the tools or inclination. Where are you located?

odieundun67 · February 3, 2009

"Do you know from personal experience that the VIN MUST be programmed into a replacement/new module for it to work? "

No, I just read about it in my Helms manual. There's about 100 pages on the 246 in my manual. I thought about scanning them for you, but it'd be a fair sized task. I'll see if I can come up with a way to get you the manual section. But, it's pretty involved to do the troubleshooting and you may not have the tools or inclination. Where are you located?

Sorry about the 'personal experience' question. What I meant was did you have it on good authority & you definitely do! I've run into a couple of people on the internet selling the control modules at a greatly reduced cost claiming that you don't need to program in the VIN, saying that they are better somehow because of that & ready to use out of the box. With what your manual says, it sounds like a that's just a sales method since their modules are non-refundable, non-returnable since they "have no idea what's wrong with your transfer case" & can't guarantee them to even work for you.

I'm located in a small town near Muncie, Indiana. I hate for you to go to the trouble to get me the manual section in some fashion. I've pulled bits & pieces of test routines off others' posts on the internet & tried a few, including pulling the fuse, which just resulted in no transfer case function at all. I saw one where you measure the torque in the clutch (in LB-In) with the unit in 2 High to see if the clutch pack is shimmed properly, etc. When I spoke to the rebuilder the other day over the phone (he's in Minnesota), he suspected the front diff, but my local Chevy dealer checked & eliminated that.

The dealer thought the problem was in the t-case itself, partly since it took 2 hands to rotate the t-case front yoke with the unit in 2 High. However the rebuilder says when properly shimmed the clutch pack should always have some load on it to keep it from rattling & making noise when running in 2 High (said the front driveshaft even rotates in some units when in 2 High, but without the front axle actuated/engaged, that's no problem).

I found some interesting things when I tested tonight in 4 High compared to 4 Low & Auto. I found that at a common speed, approx. 15 mph, that all (3) settings are at approx. 1800 to 2000 rpm. I had a feeling that was the case, but I had to prove it to myself. Maybe some combination of what the encoder is doing &/or being told to do by the module?

If you could help me with your Helms Manual identity, I'm thinking about buying one for my truck, especially since it would probably cover other systems on the truck & be very handy.

Thanks for all of your help.

Spurshot · February 3, 2009

The Helms manuals are available online here. This link should take you to the specific manual you need, which is listed under Shop/Service Information and is $135. I know it's a lot, but you'll save that much using it the first one or two times.

http://www.helminc.com/helm/Result.asp?Sty...RF4QSGT3BPCC514

Your TC rebuilder is correct about the drag on the front output/driveshaft. It takes about two hands to rotate it when it's in 2wd due to clutchpack drag.

I'd double check that front diff as well, just to be sure. Once you get the manuals (4 on my truck), you can see how it works and possibly test/troubleshoot it as well.

odieundun67 · February 3, 2009

"Do you know from personal experience that the VIN MUST be programmed into a replacement/new module for it to work? "

No, I just read about it in my Helms manual. There's about 100 pages on the 246 in my manual. I thought about scanning them for you, but it'd be a fair sized task. I'll see if I can come up with a way to get you the manual section. But, it's pretty involved to do the troubleshooting and you may not have the tools or inclination. Where are you located?

Sorry about the 'personal experience' question. What I meant was did you have it on good authority & you definitely do! I've run into a couple of people on the internet selling the control modules at a greatly reduced cost claiming that you don't need to program in the VIN, saying that they are better somehow because of that & ready to use out of the box. With what your manual says, it sounds like a that's just a sales method since their modules are non-refundable, non-returnable since they "have no idea what's wrong with your transfer case" & can't guarantee them to even work for you.

I'm located in a small town near Muncie, Indiana. I hate for you to go to the trouble to get me the manual section in some fashion. I've pulled bits & pieces of test routines off others' posts on the internet & tried a few, including pulling the fuse, which just resulted in no transfer case function at all. I saw one where you measure the torque in the clutch (in LB-In) with the unit in 2 High to see if the clutch pack is shimmed properly, etc. When I spoke to the rebuilder the other day over the phone (he's in Minnesota), he suspected the front diff, but my local Chevy dealer checked & eliminated that.

The dealer thought the problem was in the t-case itself, partly since it took 2 hands to rotate the t-case front yoke with the unit in 2 High. However the rebuilder says when properly shimmed the clutch pack should always have some load on it to keep it from rattling & making noise when running in 2 High (said the front driveshaft even rotates in some units when in 2 High, but without the front axle actuated/engaged, that's no problem).

I found some interesting things when I tested tonight in 4 High compared to 4 Low & Auto. I found that at a common speed, approx. 15 mph, that all (3) settings are at approx. 1800 to 2000 rpm. I had a feeling that was the case, but I had to prove it to myself. Maybe some combination of what the encoder is doing &/or being told to do by the module?

If you could help me with your Helms Manual identity, I'm thinking about buying one for my truck, especially since it would probably cover other systems on the truck & be very handy.

Thanks for all of your help.

Will do. Thanks for the link & your help Chuck. Take Care......Tom