2000 blazer with 122,000 miles, at 102,000 transmission lost 3rd and 4th gear and reverse. I put in a used transmission and about 15,000 miles later it started the P1870 code hard shifting problem. I changed valve body and then lost 3 and 4th gear again. This Time I bought fresh rebuild transmission and I now have a surging/ miss feel at 50 MPH and above plus I keep losing tranny fluid. Today it finally showed fluid all around the transfer case at tailshaft and extension piece but when I pulled the top plug on the case to check for a gush of fluid, the case was right at level and only has the blue auto trak fluid. This is the newer style transfer case with the three electronic plugs and not the vacuum lines. Is there a chance the fluid is separated in this case from any possible overflow from the transmission due to a bad seal? I also installed a new O2 sensor and fully tuned up this week as well.

 

Did you replace the torque converter through any of this? A surge/shudder feeling at around 50MPH sounds like the converter clutch chattering.

If the input seal on the front of the t-case were to go bad, it would fill the transfer case. The inside of the t-case is one large cavity. If the fluid didn't pour out the fill port, then the transmission fluid isn't entering the t-case.

 

Yes brand new convertor as well. trying to figure out where fluid is coming out of if it is not entering the transfer case.

 

We put 3 qts in new torque converter before installing and made sure it felt fully engaged before installing the transmission.