Monthly Archives: December 2011

4L80E Transmission Facts

Rather than do an end to end anal exam with this transmission, i have to be honest…..compared to servicing a 4L60E this thing is not bad at all. if you can do a Th400, you can do this thing. for the most part it even shares the same gear ratio’s as the th400, reverse being a slightly lower ratio over the 400 though due to the overdrive unit.

first gear: 2.48:1

second gear: 1.48:1

third gear: 1:1

fourth gear: 1 :.75 – overdrive

Reverse: 2.08:1

 i am going to go over some of the things to look for and be aware of durning your build. most of these are outlined in your ATSG book. the first thing is that the later model transmissions were a different bell housing to accomodate the LS engine bell housing. the easy way to tell is it has the extra bolt hole at the top of the housing that older bell housing pattern housings did not have.

Starting at the front,S3700038 the overrun clutch assembly on earlier model trannys was known to be a problem area. in 2001 they changed the design of the overrun roller clutch assembly due to wear issues with the sprag. the new design set up can be retro fitted into older transmissions, however when they changed the sprag, they pretty much changed damn near everything you see in this picture to accomodate the change, including the input turbine shaft.



here S3700040you can get a good lookat the older style sprag to the right of the picture. it has a thick lip of plastic on one side. is this a real critical thing to have to retro fit into these, i don’t feel it is unless there is a wear issue when you do your tear down and inspection. that would be the time to consider the retro fit to the 01 and newer design.



moving to the rear, the front planetarydrum and clutch used a lip seal type piston up to 1996 or so, then they switched to a molded style piston. the direct drum and intermediate clutch pack is standard with a 4 disc clutch, 34 element sprag, and spiro clip retaining the sprag. like the forward clutch, somewhere around 96 they went to a molded…..or what is also called bonded piston where the seal is bonded to the piston and cannot be serviced separately.

when we move back to the center support, although it looks just like one from a th400 it is not. it fits into the housing a lot more snug than a 400 center support. in 1999 there was some what of an overhaul to the rear planetary design to beef up the rear planetary gearset. to do this….like the front overrun clutch assembly, several components also changed. the rear of the center support was changed at the torrington bearing.

the sun gear shaft changed 3 times. 91-96, 97-98, and 99 on up. they also changed the sun gear shell in 1997…..ironically reducing lubricating oil flow to the rear planetary.S3700030 the part that absolutely baffles me is that they made the rear mainshaft solid in 1997. between 97 and 99 they changed the torrington bearing set up a few times but to be honest, here you can see the bearing exploded out of this 99 unit due to lack of lubrication. basically, like in a demo car, if this is in a plow truck where 1st/reverse is held for long periods of time, this thing has no direct lubricating oil and fails……this is what failed in this particular 1999 unit. it trashed the rear planetary. for shits and giggles though i stuck some th400 parts from an old bop tranny in it to re-assemble it cause these were so trashed…..and they almost fit perfect. all i have to say is someone bought a gem of a core off me!


the S3700031rear output shaft is about an inch shorter than that of a th400, but has over 2 inches more of spline area. here you can see a side by side photograph as a comparison.





down S3700046to the valve body the first thing to be aware of is that there are two different force motors. my index finger is pointing to the force motor, the other is a solenoid. 91-93 models were different. the 94 and newer ones are different….and the electrical/case connectors also changed in 93. there are two shift solenoids to the rear of the valve body that also need to be checked out. like the 4L60E there is also a switch manifold that needs to be checked .



oneS3700045 thing not to overlook is the the shift solenoid feed filter found beneath this plug to the rear of the valve body. you can also see the two shift valves in this picture. like the 4L60E, there are concerns for valve wear in the aluminum valve body. be aware of it. if you have a clutch pack failure or a driveability problem, you need to look into your valve body if there is no other obvious signs of damage. for me, in this tranny the damage was pretty damn obvious and the valve body looked great. i would still clean it out and change the force motor.



the frontS3700044 pump is a cast iron pump with a pump gear set up similar to a th400. the regulator is in a similar mannor as a th400 and can be accessed from the bottom through the oil pan. in the picture i am pointing to your TCC valves that are, unlike the 4L60e or 700R4, located in the pump as well. the valve to the right can be seen like the regulator valve through the oil pan area with the pan off….the other valve i am pointing to is a converter limit valve. during pump service these should be removed and cleaned to insure proper function. also i should note that the drive gear does not have teeth on it like a th400 pump. it is driven by two flats on the converter hub. so if you look down the pump with a flashlight and don’t see any teeth to drive the pump…..don’t panic!