Sherlock9c1 builds some 4L60Es

Let's build out the input housing. Thee are there clutchpacks in here, the overrun, forward, and 3-4. The pistons get installed in opposite order. First thing to do is replace the green o-ring that goes in a groove in the center area.


Next, install the 3-4 piston. These come in every 4L60E rebuild kit ever. In this pic, it's already installed, so I'm holding a second one for reference. These drop in easy with a little Assembly Goo.


The 3-4 clutch apply "basket" drops on top of it, followed by the return spring and snapring. I used my snapring compressor to secure it; not worth a pic.


Next up is the forward (outer, with tabs) and overrun (center) piston. I like to install these together into a big steel dish and then lower the whole assembly in. GM went to bonded steel pistons in place of aluminum in 1997; the aluminum forward pistons were prone to cracking if all five teeth weren't EXACTLY level, and the lip seals could blow out if you looked at them wrong (that's what happened on my Impala). Gently work it in and the bonded seals will behave.

Next up is the forward/overrun return spring. This is different than the old style, it has a lower metal retainer ring. GM P/N 24206085. Snapring goes on as normal. As of 2022, it's pretty hard to find original B-body 4L60Es in the junkyard, but if you do, these new pistons are yet another reason not to trust one that's still factory original.


The first thing to go in is one of the overrun steels. There's only 2 steels and 2 frictions in the overrun clutch on 4L60Es... if you manually downshift, this is all there is to bring the engine revs up, so do them a favor and add a little throttle when you downshift.


Don't forget to add the rubber seal to the end. This completes the lube circuit between the input shaft and output shaft.

Here are the rest of the overrun clutches and steels. Easy peasy. On this build I reused the steels since they were fine, with no evidence of heat damage or coning.


Needle bearing soaked and installed into the middle. This is the correct orientation. It rides between the input housing and the forward sprag (most people just call it "the sprag.")


Original sprag on left, updated "29-element, dual cage sprag" on right. Personally, I think the stock sprag is fine for stockish builds; I've only seen them fail in one of the 25 I've been in. The upgraded one is less than $50 as of 2022 so it's a cheap upgrade though. Sharp-eyed observers will notice I actually have the new one backwards in this picture.


Once you reassemble the sprag and reinstall it, insert the front sun gear and turn it counterclockwise. The sprag should freewheel that way but lock together if you turn it clockwise. If not, flip the sprag elements over, otherwise you won't have 1st and 2nd without manually downshifting to rely on the overrun clutches.


This is the correct orientation.

Next up is a thick plate with a dimple that separates the overruns from the forward clutches. Just drop it in.

Install the wavy plate.


Then, 5 steels and 5 frictions, starting with a steel. Always have a steel against a wavy plate or spring plate.


Forward clutches fully installed. I've circled two areas; the upper area shows the sprag assembly fully seated against the needle bearing. The lower area shows correct total height of the forward clutches. It just "looks right" - you can check with feeler gauges after the plate goes on, but I like to use my calibrated eyeball as a secondary QC as I go.

This is the top plate of the forward clutch. The snapring that goes in here is very tight; you really have to wrestle it into place. I seem to do it a different way each time. Get it in, fully supported on the housing lugs, and send it.


Here's the bottom of the 3-4 clutchpack; this sits on the five ends of the "basket" that reachs up to apply them. This one was pretty scored due to debris from the needle bearing failure, but the owner babies this truck and didn't care about replacing them. I would not have reused this for a 400hp B-body, but in his light truck, it'll be fine.


Looks like I did not take pictures of the rest of the 3-4 clutchpack or the load release springs. Those 10 little tiny springs were blamed for 3-4 clutchpack failure, which just makes no sense when you consider how little they really press against the basket. If you take those out, you might as well pull half of the springs out of the 3-4 piston return spring as well. Or, you could just fix all the hydraulic leaks in the 3rd gear apply circuit and make sure the transmission is putting out consistent line pressure.

You can also replace the backing plates with Sonnax 74140-01K HD backing plates which also allow you to run the 4L70E 7-disc clutch stackup. It's not cheap, but those are good parts. Very stiff and they resist coning far better than the factory plates.

Next time I get a few minutes, we'll get into the pump.

Maybe?