Hey everyone,
I thought I would add to this excellent thread, as it seems to be the definitive one for the torque converter clutch slip and code 1870 transmission issues.
Although my 1999 2WD van did not display the 1870 code, my van was shuddering/stuttering/hesitating when driving in Over Drive. Several other AstroSafari owners have this shudder and live with it, but I thought I would swap out the Valve Body with a rebuilt unit to eliminate any pressure issues with the PWM-TCC valve bore wear (an known issue on the 1998-1999 4L60E transmissions).
I purchased a rebuilt valve body from Ken Partin Transmissions for $105! it even came with a 1-2 shift ball repair kit and nice directions. Highly recommended.
http://www.kenpartintransmissionparts.com/4l60e-rebuilt-valve-b460.html
Now, as it turned out, changing the valve body did
not improve the shudder in OD, so my van's torque converter clutches are probably worn (at 115kmiles), so I may add some friction modifier in the short term, but certainly a new torque converter in the long term to avoid the eventual failure mode.
Here are some supplemental pictures for doing the Valve Body change out with the transmission still in the van.
The many great YouTube videos do the valve body change with the transmission belly up on a work bench.
Here are the notable differences with doing the job
"upside down."
The first issue is fluid drips... wear safety glasses, and allow for fluid to drip and drain.
The wire harness does need to be moved out of the way, but not removed. I zip tied it to the exhaust pipe.
Note: the lock-up solenoid is an integral part of the harness and you may want to put it in a plastic bag to keep dirt off of it.
The Switch Assembly does not have to be removed, only the three 10mm bolts need to be removed (keep the two 8mm bolts in the Switch Assembly)
Before removing the valve body, let the fluid drain for several minutes.... let it rain.
Note: when you do drop the valve body, the seven check balls may fall out.
The Valve Spacer Plate will stay in due to the Accumulator and the Retainer plate.
After the Spacer Plate is removed, this is where the Accumulator Spring, Filters, and #10 Check Ball go on the "case" side of the spacer plate. So you can see how it will be "reinstalled".
If you are going to make the 1-2 shift ball repair in the Valve Body Spacer Plate, then this is where you will find it.
The hole needs to be bored out with a 1/4 inch drill bit and the valve seat is then installed (with the seat pointing to the valve body side, not the case side).
Before you attempt to install the gaskets and valve body spacer plate, apply some fresh fluid to the surface to make the gasket "stick". The picture shows how the gasket fits snugly on the newly installed 1-2 check ball seat.
Before you install the valve body spacer plate and gaskets into the transmission, you will need to secure the number 10 check ball in place with some TransGel or Vasaline... it sits right next to the accumulator. Note: there are two other check balls in the case, but they are captive by some collars and you don't have to worry about.
Use two of the bolts to help align the far end of the gasket and spacer plate as you install the Accumulator and Retainer Plate finger tight (at the engine side of the transmission).
Before installing the valve body, figure out where all the bolts go. Here is a picture of how my bolts fit, and notice that the three bolts in the "upper left" of this photo have 8mm heads. Three long 10mm bolts go into the Switch Assembly. Most bolts are "medium" length 10mm bolts.
Diagram of bolt locations.
The last step is to install the wire harness, and the Lock-up Solenoid, and the PWM TCC solenoid.
Add about a gallon of fresh fluid and you are done.
Good luck,
Herminator