700R4/241C leaking from vent?

[ballencd]

I have a 1991 V1500 Suburban with a 350/700R4/241C. It appeared that the trans was leaking ATF but cleaned it all up and looked like it was coming from the top of the trans in the area of the transfer case vent. None coming out the tiny drain hole in the bell housing at all. So I opened the fill plug on the transfer case and it was loaded with fluid.....(overfull). So....I decided that the transmission was leaking out the rear seal and overfilling the transfer case and blowing out the vent.
Today I pulled the transfer case and found no ATF between the transmission and transfer case as expected in the cavity of the adapter.

I'm not sure where to go from here. The transmission is losing fluid. The transfer case was over full but no ATF in the adapter....????

Any ideas where I should go with this?

Thanks

 

[ballencd]

Nobody's got any idea whats going on here?

I started the engine and put the trans in drive with the transfer case out. I got a fine stream of ATF squirting thru the seal at about 11:00 so I know that the cavity inside the adapter is getting excess ATF. My confusing now lies in the fact that I did not find any ATF in said cavity when I separated the transmission and transfer case. My plan at this time is to replace both seals and put it back together and see what happens but I sure would like to know whats going on with the missing fluid between the cases.

Any ideas on that?

 

[bucket]

It must have drained out of the adapter as it sat? I dunno, but it certainly has the symptoms of bad seals causing the transfer of fluid.

 

[ballencd]

OK...another question before I do more then needed. I am seeing on another thready (Diesel Page) that there is NO seal at the back of a 700R4 trans in a 4x4 vehicle with a transfer case behind it. The seal in the front of the transfer case is to keep trans fluid out of the transfer case and the oil that leaks from the transmission into the adapter drains back into the pan of the transmission when the vehicle sits. The seal in the front of the transfer case can get hard and stop working and that is when the transfer case gets overfilled.......ANYBODY know anything about this. This is the first I have heard of it....???????

 

[PrairieDrifter]

OK...another question before I do more then needed. I am seeing on another thready (Diesel Page) that there is NO seal at the back of a 700R4 trans in a 4x4 vehicle with a transfer case behind it. The seal in the front of the transfer case is to keep trans fluid out of the transfer case and the oil that leaks from the transmission into the adapter drains back into the pan of the transmission when the vehicle sits. The seal in the front of the transfer case can get hard and stop working and that is when the transfer case gets overfilled.......ANYBODY know anything about this. This is the first I have heard of it....???????

There’s no other path from the trans to the transfer case for fluid to get through, the adapter is the only way. There’s no secret oil passage or nothing like that, if you’ve got a transfer case overful and a trans that’s low, it’s definitely pushing fluid through.

I’ve had my 700r4 apart on all sides except between the adapter. I know on a th350 there’s drain back holes in the back of the case and fluid is constantly on the adapter.

You must be registered for see images attach

 

[PrairieDrifter]

Th350 has an o-ring between the trans and adapter

 

[ballencd]

Apparently the transmission does NOT have a rear seal in a 4x4 application and the cavity in the adapter is wet from a intended squirting of AFT into it which drains back into the transmission pan. This would explain why the adapter was clear when I pulled the transfer case off. IF the transfer case seal is bad then pressure pushes ATF into the transfer case overfilling it and it leaks out the vent as mine is doing.

 

[ballencd]

PrairieDrifter....It looks like the 700R4 is the same as the 350 as in no seal and intended drain back to transmission. I watched a small hole spew ATF while transmission was in gear which looks like it is intended to lube the speedo gear mechanism.
T
hanks for your update. It did not show on my PC before I responded a few minutes ago. I thought I had refreshed it be apparently not.

I have learned a lot in the last few days. It has been cold and wet in the drive but the sun is out now and the temp is mid 55's and comfortable enough to attempt the reinstallation. I was not leaking at the adapter at all so I did not go into see if there is an "O" ring between the trans and adapter but I suspect there is one like your 350. Maybe next time I will see it if this does not fix the issue. I was just talking to a mechanic at the auto parts store around noon and he said to check the trans fluid cooler because it will get worse if it is clogged then trans will still run fine but get hot causing thinner oil, more pressure and more leaks and of course eventually blowing it up. As soon as I get it back together I will look into that.

Thanks again for your response. The information was very helpful.

 

[PrairieDrifter]

PrairieDrifter....It looks like the 700R4 is the same as the 350 as in no seal and intended drain back to transmission. I watched a small hole spew ATF while transmission was in gear which looks like it is intended to lube the speedo gear mechanism.
T
hanks for your update. It did not show on my PC before I responded a few minutes ago. I thought I had refreshed it be apparently not.

I have learned a lot in the last few days. It has been cold and wet in the drive but the sun is out now and the temp is mid 55's and comfortable enough to attempt the reinstallation. I was not leaking at the adapter at all so I did not go into see if there is an "O" ring between the trans and adapter but I suspect there is one like your 350. Maybe next time I will see it if this does not fix the issue. I was just talking to a mechanic at the auto parts store around noon and he said to check the trans fluid cooler because it will get worse if it is clogged then trans will still run fine but get hot causing thinner oil, more pressure and more leaks and of course eventually blowing it up. As soon as I get it back together I will look into that.

Thanks again for your response. The information was very helpful.

I don’t believe it’ll be necessary to mess with the trans cooler much. Personally I would check it now while it’s apart just to verify it’s not clogged, but it wouldn’t pertain to your current problem.

The o-ring sits on a lip on the adapter and is basically just sealing the outside edge so nothing comes in from the outside and no fluid gets pushed out, nothing else(between trans and adapter)

Then there’s the seal around the input of the transfer case so no fluid gets pushed into the transfer case from the trans, THROUGH the adapter. Then you have your typical gasket around the bolt perimeter for the transfer case to adapter mounting.

 

[PrairieDrifter]

Unless of course if the trans had more line pressure it could push through the seal. But I’m sure the seal is just shot

 

[ballencd]

Thanks, I will find out soon. Headed out now to put it back in.

 

[ballencd]

Well it is back in. I replaced the seal on the input of the transfer case only. I did put some (small amount) silicone sealant around the outside edge of the input flange and another bigger bead on the outside flange of the adapter to transfer case seat. It's filled with ATF and seems to be running fine. I plan on draining the trans and putting in a new filter but didn't want to muddy the waters with my first issue. It was a messy job on a gravel drive but not terribly hard.
Thanks for all the help.

 

[PrairieDrifter]

Follow up once you’ve got some miles on it

 

[ballencd]

Will do. Thanks again for the help.

 

[WHEELMAN]

Sounds like a internal pressure problem.call a Chevy dealer find one that has their own transmission man.and run it by him.