Leaky tcase adapter on 97 2dr Tahoe + 6.0 Iron Block + 04 4L60e + OE NP243 + 0411

[MazingerZ]

The truck is lifted 2” (cranked and aal) running 295/75/16s and 4.88 gears (I know a bit of an over kill, previously it was on 315s which ran better but those where too big and the tires would easily catch the fenders during offroad suspension cycles and get damaged as a result) this truck doesn’t get much use, it is an offroad rig, must have done 20k miles in the last 10 years.

Anyways, I did a LS swap on my truck and at the time I kept the OE 4L60e 1 piece case trans, everything works good, from cruise control to AC to shifting in 4low. Unfortunately due to a bent rear drive shaft, it thew a u-joint cap on the slip joke and very quickly cracked the transmission’s case.

Given the circumstances at the time, I could only find a 4L60e from a 2004 Tahoe, it was taken apart, then rebuilt and installed on my truck, it went in fine and after some tuning got it to shift nicely.

Unfortunately at the time I didn’t know about the bent drive shaft so I continued to use the same bent one, which caused to crack the np243 transfer case twice, the tcase got fixed and a brand new balanced rear drive shaft was fitted to the truck.

The problem I am facing now is that the tcase adapter keeps leaking where it meets the tcase, I have taken the tcase down several times, resealed, new GM gasket with a dab of rtv etc and works for some time, after 100 miles or so it starts leaking again, this is becoming very annoying.

Since fitting the LS engine, the trans brace struts/rods were removed as those would interfere with the oil sump, following the installation of the 04 trans, the bell housing doesn’t even have the bosses to attach the rods. As I understand these are structural and got me thinking could these be the root of the problem?

The engine rests on energy suspension polyurethane mounts, these have been there for 10 years, since the time when the SBC was on the truck, the mounts got inspected and seemed fine and were re-used on the current setup. The transmission is sitting on a good GM rubber mount. This setup was never a problem, but could it be an issue now?

Did something inside the transfer case get bent with the old bad drive shaft? I am considering replacing the tcase.

So what’s your take/experience on the topic? Any help would certainly be appreciated

Many Thanks

 

[stutaeng]

This is an interesting case of yours. Sorry for your troubles.

Yes, those rods got eliminated that go from the bottom bell housing to the engine mounts on the NBS.

I believe I saw somewhere that how they managed to do it was with the bottom bell housing cover and a different transmission mount. I saw a guy talking about that on a YT video but I can't find that video. However, your transmission has the bell housing that goes all the way around already, well the 04 transmission at least.

Was your transmission cross member modified? I wonder what the difference is in that crossmember between the OBS and NBS.

We had a thread a while back on a guy that kept breaking transmission cases, but his truck was stock. I can't recall at the moment if the issue was resolved or not.

 

[Schurkey]

Fluid level overfull?

A dial indicator should tell you if the output shaft is bent.

Do the bolt threads that hold the transfer case adapter assembly together go into blind holes, or are the bolt holes open to fluid? Could the leak be from fluid seeping around the bolt threads?

 

[MazingerZ]

This is an interesting case of yours. Sorry for your troubles.

Yes, those rods got eliminated that go from the bottom bell housing to the engine mounts on the NBS.

I believe I saw somewhere that how they managed to do it was with the bottom bell housing cover and a different transmission mount. I saw a guy talking about that on a YT video but I can't find that video. However, your transmission has the bell housing that goes all the way around already, well the 04 transmission at least.

Was your transmission cross member modified? I wonder what the difference is in that crossmember between the OBS and NBS.

We had a thread a while back on a guy that kept breaking transmission cases, but his truck was stock. I can't recall at the moment if the issue was resolved or not.

Thanks, yes the 04 trans bolts to the engine all the way around, no modification was done to the cross member, in fact everything went in easily, the engine mount on the truck is PN 15113134 which is also used on the gmt800.

 

[Supercharged111]

Does it have the aluminum t-case adapter? Has the adapter itself cracked? Can you get an iron adapter for the 4L60?

 

[MazingerZ]

Fluid level overfull?

A dial indicator should tell you if the output shaft is bent.

Do the bolt threads that hold the transfer case adapter assembly together go into blind holes, or are the bolt holes open to fluid? Could the leak be from fluid seeping around the bolt threads?

The trans oil Level is just under the full mark, have done the resealing job several times (taken the oil out, taken down the tcase, reseal, tcase back on and pouring the oil back in) it is a PITA.

I believe the bolts go into blind holes, I've never seen any evidence of fluid leaking from those holes. Thinking to source some studs and try that too, I believe the stud's setup has stronger holding power.

Might struggle to find a dial indicator in the area, so I may have to order one.

 

[MazingerZ]

Does it have the aluminum t-case adapter? Has the adapter itself cracked? Can you get an iron adapter for the 4L60?

No cracks on the adapter, that would have been an easy find, I saw the iron adapter but cracks are not the issue.

My mechanic has actually suggested to use a double gasket to reseal the adapter, I am not sure if that would work.

 

[stutaeng]

Where are you OP? A dial indicator should be easy and cheap to source. I've used the $17 Harbor Freight ones and have had good success with them.

That was a great suggestion to check the run-out. I suppose you can also check end play since you are there.

 

[MazingerZ]

I believe I saw somewhere that how they managed to do it was with the bottom bell housing cover and a different transmission mount. I saw a guy talking about that on a YT video but I can't find that video. However, your transmission has the bell housing that goes all the way around already, well the 04 transmission at least.

Was thinking about the OBS 98-99 Bell housing, which has the holes for the rods, however I am not sure if the 300mm torque converter would fit that bell housing.

 

[stutaeng]

Was thinking about the OBS 98-99 Bell housing, which has the holes for the rods, however I am not sure if the 300mm torque converter would fit that bell housing.

I'm not sure I'm following you. 98-99 OBS bell housing... you'd have to swap transmission, right?

Can you just drill/tap your 04 Bell housing for the rods?

I could of sworn I saw somewhere that the poly transmission mounts cause issues like this... don't recall where though.