2005 chevy 4L60E trans, i tore apart ailing trans. 1-2 shift is fine. rev is fine. fluid is black. when trans tries to shift to 3rd, it freewheels. or feels like it. does trans actually shift into 3rd but trans slips big time since clutches are not working? all 6 friction discs are coned and black. steels look ok which means they seem flat and not scorched. i was just wondering what trans does at 2-3 shift? stay in 2nd or go to 3rd and slip?
When that transmission makes the 2-3 shift, pump pressure is introduced to the 3/4 piston which clamps the 3/4 clutch pack. The turbine shaft drive is now driving the planetary gears. With the input sprag and 3/4 clutch holding the output is direct drive. When the 2/4 band engages the input sprag releases and the transmission goes into overdrive.
So when you get freewheeling (engine run away) in the 2-3 shift the most likely cause is the failure of the 3/4 clutch pack. I wish Transman628 was still around as he knew GM transmissions backward and forward. He would usually make recommendations to improve the durability of these transmssions (although a 4L60E should be plenty durable as is).
I guess my question was, is the trans actually in 3rd gear but slipping since clutches are wasted? I assume so since truck is not accelerating and motor rpm is rising
Yes the TCM is commanding third; the shift valve has moved to engage third; the pressure is there to apply the 3/4 apply piston and release the 2/4 band; but the 3/4 clutch pack is slipping, big time.
The black fluid indicates that the transmission got extremely hot. Did the fluid smell like burnt transformer oil? Can you scrape the friction material off the plate(s) with your finger nail? Have you miked the friction discs and how far off is the measurement?
When you rebuild this, in addition to replacing the 3/4 apply piston lip seals, replace the input shaft slip rings. When you reassemble the transmission, air check the 3/4 clutch application to make sure there are no leaks. Should be a solid ‘thud’ not ‘thud hiss’. If you don’t replace the steel plates (I would if I were rebuilding this), carefully measure the 3/4 clutch clearance all around the backing plate to make sure that there is the specified clearance everywhere.
New 3-4 clutches, steels, 3-4 apply piston, 2-4 band. Slips in 2-4 now. Pulls hard in 1-3. Little bit of a 2-3 shift flare. 2-4 drum looked good. The servo pin has 2 grooves in tip. Been told this is ID feature.
Stoveguyy … are you a DIY’er and repairing your automatic transmission yourself? If so, good on you.
i did not replace the input shaft sealing rings. the 4 white rings? yes, u need and expander tool and sizing tool. if those rings are bad, would 3rd gear pull good? it goes great in 3rd, slips in 4th
I assume when you had the 2/4 servo pin out, the servo piston, servo case surface, and seal ring were serviceable. The grooves on the servo pin are length IDs. There is a procedure using a special tool and a torque wrench for determining the required length. The length takes the place of band adjustment screws and lock nuts seen in other transmissions. On old school transmissions you could adjust the band according to the book and then deviate a little depending on the output of the engine. You might blindly go with the next longer pin but make an attempt to see if the band is dragging on the reverse shell.
The 2-3 flare is an indication that the 2/4 band is releasing a little too quick as the pressure rises on the 3/4 apply piston. If the 2/4 serve is at the limit of its travel, it would probably spring back quickly when the pressure starts to drops. Another indication that not everything is right in the 2/4 band apply department.
Also consider that if the servo piston is leaking that the resultant pressure drop may have affected the clamping ability of the 3/4 piston causing the 3/4 clutch pack to slip and burn previously. The initial failure probably occurred while pushing the transmission in overdrive. So do an air check on the 2/4 band servo to see it there is a leak somewhere.
Yes if 3rd gear is holding the slip rings are probably good.
Good luck on this. You might go back to the old 2/4 band and extant servo pin which were probably well matched. I bet you are getting tired of taking this transmission in/ out/in/out/in of the truck.
I will pull out servo and inspect o-rings and all parts for damage. Check pin tightness too. Pretty sure the pin is 2 groove. Which is middle length. No groove is longest. It’s not like I am going to put old band back.
The book I use as a reference has steps to make sure the 2/4 band is in the correct position. When the servo pin is inserted it says to make sure the pin engages the socket of the band. This is being done with the pump already installed. It seems likely that the pin can be engaged incorrectly.
In reviewing the assembly sequence, I wondered why it would not be possible to install the servo pin, return spring, and servo piston before the pump is installed. Then you could visualize the correct engagement; press the piston down; check the travel; and verify the band application.
Just some thoughts.
Went to the highest rated trans chain in town. They have 8 locations. They refuse to do carry out jobs. A typical job like mine with overheated clutches is $2800. They replace entire 3-4 clutch drum assy. They have 2 yr warranty. He basically said 50% of my trans internals were ruined. Almost zero chance of non-pro fixing it.