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Who knows their stuff about Silverado trucks?

Lowrange2

NAXJA Forum User
Location
Abbeville, SC
Alright, so my truck is screwed up. It's a 99 Silverado 1500. New body style with a NP246 t-case, auto transmission. I've never fooled with working on these things.

Pulling off from a red light the other day I got a serious grinding sound and the driveline started binding and catching. I drove it 2 more miles, parked it and then towed it home on the trailer.

It felt a lot like the rear end was toast. The grinding certainly sounds like a bad bearing.

So, last night I pulled the diff cover and everything looks good. I got the rear wheels off the ground, started it up and put it in drive. When the driveline spinning the grinding is constant and clearly rotational.

The noise is obviously coming from the transfer case/transmission area. If I had pinpoint it I'd say that it's coming from between the two.

Now, since I've never had one of these apart I have no clue what sort of bearing is between the two.

This truck stays on pavement, no lift, no nothing, all stock.

Is this a common failure?

np246_part_ill_lg.jpg


np246_interanal_lg.jpg


I'm not seeing any sort of bearing that'd be between the t-case and the transmission.

Could this be something in the transmission?! The transmission still shifts perfectly.

I guess the next step is to pull the t-case and start looking for issues...

Anyways, any helpful information would be greatly appreciated.

Thanks, Andy
 
Yeah, I guess I'll find out when I pull it apart.

Used JY case costs 300 (Condition unknown)

Remaned case costs 825 (1 yr warranty)

Pull mine apart and rebuild it costs parts. Which will probably be close to 200.
 
i'm new to the Silverados myself, i find alot of good info on silveradosierra.com.
if you can filter thru the "whats the best air filter?", "how do i make my muffler louder?" , and "why is my mileage so bad?" there is some good searchable tech.
 
Cool, I'll give it a look.

My searching and research hasn't yielded me much at all yet.

I did good to find that diagram above.

I'm not 100% which input spline I'm going to need.

Pretty sure my truck has the 4l60e. That'd mean I need a 27 spline case.

I'm thinking that my best bet is going to be to pull the case apart and repair any parts since this case had a major factory defect with rubbing a hole in the housing. They make a part to fix that issue. Remaned cases come with it already fixed but the used JY case wouldn't have that done and who knows how long it'd last.
 
Did you already fix the pump rub issue? Did the t'case have fluid in it?

1/2ton Silverados had 4L60Es.

As far as I know the case hasn't been modified so the pump rub issue would still be present but I'm pretty sure that wasn't the cause. I don't see any major leakage but I also haven't had time to get in there and pull it out yet.

I wouldn't doubt that it leaked out.

I'm HOPING that just some bearings are trashed and I can rebuild the case I have with all new bearings, seals and add the case saver to solve the pump rub issue.

If not, I've got a line a used case for $300.
 
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I've seen a few encoder motors go bad and cause some strange noises, might be worth pulling the encoder first and see if you can shift it by hand to resolve the noises.
 
I finally got around to pulling the t-case.

Cleaned it up, threw it on the bench and spun it by hand and it feels nice and smooth.

Decided to drop the transmission fluid pan...

Found this:

20131023_175302_zps84777a05.jpg


20131023_173830_zps5a24a9aa.jpg
 
Sounds like the infamous 4L60E 2nd gear sprag/sun shell issue.

http://www.gmtruckhq.com/?q=node/93
7. Sudden grinding noise with no prior warning primarily in 2nd gear, behavior in reverse may be abnormal; sunshell is fractured. R&R. Try not to run or drive the car or further damage could result.
 
Yup, that sounds about right...

Got a used transmission being delivered to me Tuesday. It's got 80k on it so maybe it'll last for a while. 90 day warranty.
 
I thought those things had a snap ring issue on the transfer case output shaft. Only happens when you accelerate from a stop. Part should only cot a few bucks to replace.
 
Hmm, I haven't heard about that one. Only heard of the pump rub issue in the t-case.

This is a grinding noise at all speeds. 2mph or 60mph.
Yes,the pump rubbing a hole in the transfer case housing is common on 98-2006 and maybe newer.There's an after market kit to fix the pump....But the case might need replacement and all the labor.....
While the tranny is out make sure to check into the T/C pump..
 
Yeah, the t-case is sitting on my work bench. I was hoping I didn't have to pull it apart but I might as well since it's already sitting here.

It definitely hasn't rubbed all the way through yet but there's no telling how much longer before it does. I may pull it apart and add the plate to fix the issue.

The new/used transmission is laying in my shop floor now.

Now I just have to find time to swap them out.
 
... Swapped the transmission. Ran great for 6 months.

Now it's slipping in 2nd. No noises, still have reverse, Pulls great in 1st.

Getting a "Transmission component slipping" code.

I wonder if it's an electrical issue or it's fried.
 
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