4L80E Rebuild questions (that have not been covered)!


Nov 22, 2020
Hello, I am in the middle of a 4l80e rebuild. Parts spread all over the place at this point. Needs to get back together in a few days so I don't have time to order a bunch of parts. I already purchased everything I need, more or less (tools and rebuild components).
Vehicle is 3000-3200lbs, 700-800flywheel HP. Daily Driver, shifts 6300~ usually but at the track it might see 6800rpm or even 7k in 3rd gear to make the trap speed.
9.5" Yank 2800 converter

3 years ago I sent the transmission to a shop to install an HD2 kit. They "did" and sent it back to me.
Well, now that I am tearing down, I do not see any shift kit separator plate, nor holes drilled in the stock plate. So typical of trans shops to do stuff like that.

I assume its a stock plate trans, maybe there is a spring or two from the kit, hard to tell. The Low band spring did have some orange on it.

So I am working with what I believe is a stock 4l80e 2002 transmission with approx 130,000 miles. The pump was a reman unit they said already has a sonnax boost valve, which I believe (good rep seller from Ebay)

The Trans failure was clutch slipping - not enough shift pressure. Maybe partially due to the tiny holes in the separator plate, however my setting was also bad (65psi~ like stock). I raised the pressure to max (90psi~) and the trans came back to life and held from then on, but the damage was already done. Clutch materials spread all over it (grey goop) and clogged some orifices I guess, it lost reverse and started shifting weird, late, and 4th didn't feel like 4th anymore. Threw a EPC code even though the EPC is good ( I changed the EPC and it still had issues).

So here is my first question which I have never seen asked or answered on any website:
1. When programming the shift pressure in the ECU, I see the most popular setting is to go 100% (90 or 96psi torque signal) after, say, 50% throttle. Which kind of makes sense from the TV cable perspective (pull the cable all the way out).
How does this affect or interplay with the size of the hole in the valve body separator plate? In other words, is it possible to command TOO MUCH shift pressure, if the hole is very large? What is the common setting for 1-2, 2-3, 3-4 shifting in terms of how much pressure? For example should 3-4 and 2-3 always use more pressure than 1-2?
Would it be better to use a large hole with less than MAX pressure commanded?
Is there an easier way to deal with this: I think I should install a pressure gauge and adjust the shift pressure to meet some criterion like 200psi or something? My main concern is breaking something with too much pressure, and I would love to NOT have to install a gauge to check that (its a tight fit... most likely cutting involved).

Sorry that is my more difficult question. I can't find any resource, not a video or explanation of how to use the shift pressure properly in a computer, other than to just 'turn it all the way up'.

Question #2 (it gets easy)
I see for the dual feed we remove 2 seals and plug the center support. However, many people only plug the case, which allows the center support to leak fluid between the case and support. I was going to do this also because I don't have the right part to plug the center support itself. I was wondering what the draw back of this is, how bad is it for the trans? Negative consequences of not plugging the center support itself, of ONLY plugging the case.

Question #3
Since I don't have the HD2 kit's direct springs I was going to drill a hole .030 ish into the direct's corner to help prevent centrifugal apply with stock direct return springs. I hope that is fine with the dual fed.

4. I was also planning to leave the seal on inside the direct housing/inner seal. I heard this can improve 3-2 downshift which I frequently do. So basically I was only going to remove the 2nd center support ring and plug the reverse passage in the case to dual fed. Sounds good...?

5. The direct drum got a little water on it yesterday because it rained like crazy and it was in the trunk of my car, and it started to rust ever so slightly. Immediately I took some ATF and without thinking started sanding out the rust with a 600grit sand paper. The rust came right off- however that is when I realized OMG I just sanded a critical surface. So this is question #5: What grit sand paper should I " finish" the direct drum (Where I believe the Low/reverse band rides) with? I think this is the later band (shiny smooth surface) but I have to double check. I am hoping 600 or 1000grit is fine?

6. I see where it was said:
"If you don't want to mess with setting the bushing height to index the bearing....Use the 34006-SP, Knock it all the way down from the BACK of the case using Loctite. Roughing up the OD of the bushing with some emery or scotchbrite will aid the loctite in holding the bushing from walking."

Now, I have this sonnax bushing, and I am tempted to use it. However there appear to be two lube/oil passage which will become blocked if I press this sonnax no walk case bushing in backwards. So... what should I do about that. I've seen people cutting grooves into the bushing but I am not sure this is adequate. Personally I feel like the entire lip between those two passages would need to be removed. I'd love some feedback here.

7. I did manage to get the thick intermediate snap ring, and BW clutches. Plan to re-use the factory steels. Can I re-condition them somehow? Maybe some specific grit sand paper? Speaking of which, Some rebuild manuals suggest using 320grit to in some places of the trans. While other well known rebuilders say to use 600-1000-1500grit to polish some surfaces. So I am not sure which way to go with that, nor what to polished/sand on. Any direction would be helpful.

8. When I removed my pump, I did not find any thrust washer behind it. I don't know if I lost it, misplaced it when I changed the pump last year, or what. What sort of damage could this cause? I don't see any obvious signs of wear on the bushings or inside the bore where the input shaft rides. theres no way that it was never there in the first place, right? All pumps should have a thrust washer back there right?

Other notes:
did the AFL large valve reamer/fix already.
Plan to remove #9 checkball , curious about removing 3rd gear #8? Probably won't but, I don't plan to block my 3rd accumulator so... maybe I should?

Thanks for readin
Welcome, F4k.

I can't answer any of your questions, but you said they "have not been covered."

If you haven't already, I suggest reading posts by BITOG member clinebarger. He's been on a few 4L80 posts in the last year. I think there's still one going about a high-horsepower application.

Good luck.
I definitely read all or almost all of his posts, and Jake's posts, and probuilt automatics posts, and many others. They are probably the only individuals on the entire internet, maybe the world, that are willing to share so many details freely.
I do not believe that my questions have been addressed before, thus the title. And if I discover any answers I will be sure to come back and update the thread, Thanks
1. If you stay under 96 psi, Unlikely you'll break anything assuming no adjustments were made to the EPC solenoid itself. I don't modify the pressure tables, When built correctly.....You don't need to, It all starts with a GOOD pump! If your pump is worn out, It will shift soft on a factory calibration.
Factory clutch feed orifices will certainly make for slow-soft shifts & when making big power can distress frictions.

2. Simply plugging the Reverse Feed in the Case is a tried & true method & doesn't cause much more leakage than what was there from the factory. I just like to reduce leakage as much as possible.
*TIP.....The gold ball included in the SK-4L60E shift kit also works for plugging the reverse feed on the Center Support. You can also tap the feed & plug it with a set screw.

3. I'd Prefer to do both, Not only does both help with centrifugal apply, It also helps with knocking the Direct clutch off faster on a 3-2 downshift. Will just a bleed hole work?.....Most likely.

4. Never found any validity in that.....How would leaving the seal in the drum help exhaust the 3rd apply fluid any faster?? It's going to be slower than stock because you're exhausting 200% more fluid.

5. The Intermediate Brake Band rides on the Direct Drum, Not going to work too hard on such a light car. It just gives you engine braking in manual 2nd. Pictures??

6. I assure you that it doesn't adversely affect adequate lubrication of the Case Bushing, Output Bearing , Or the Extension Housing Bushing! You can file some notches if it makes you feel better. Don't drive the seal to bottom.....Just enough to install the snap ring. Picture below of a notched Sonnax Bushing.

7. If the steels have Hot Spots....Replace them. I no longer sand steels after attending a seminar sponsored by Raybestos.

8. Yes....All have a Thrust Washer! I've seen them get left out with no obvious damage to the Overrun Clutch Housing.....But did burn the Forward Clutches down because the Input Shaft would come out of the Forward Drum.

*Block the 3rd & 4th Accumulators with set screws or 700R4 TV Cxhaust Check Ball/Gold Balls out of a SK-4L60E shift kit. Or use a aftermarket block off plate. Then you can omit #5 & #6 Check Balls from the case. Leave #9 in place.....You're not backing trailers or anything (Are you?) or otherwise need a faster Reverse Apply? You could always enlarge the Reverse Feed in the Plate.

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Thank you for posting! So happy to get help!

Today I tried setting the end play rear. The output shaft was very difficult to slide through the new sonnax case bushing. I sanded the bushing lightly with 1000grit and put the output shaft in and out a few times and it loosened up just a little bit.

But now i have a serious problem (maybe). I have NO end play. I tried with the bearing, without the bearing, with all the shims, 1 shim, 2 shims, every possible combination yields me absolutely no end play. I can't get the output shaft to move up or down at all once the center support is stacked up and installed on top.
Another issue is the output shaft thrust surface will not ride on or turn the bearing unless I use at least 2 shims under the bearing, the thin .008" and .018"~ shims. The output shaft becomes a bit easier to turn with the two shims under the bearing. But I am not sure how much support the bearing is giving to the output shaft, just because the bearing turns doesn't mean its really supporting.

This is how I am checking end play. I pull up on the shaft by hand, hard.

Here I am trying to show the output shaft doesnt reach low enough to reach where the bearing sits unless I add two shims

you honor me with your time.
Is the bushing contacting the Output Shaft (Thrust surface radius)? Is it proud of the bearing with the just the bearing placed over the bushing?

Most TH350 bearings measure out at .141" thick & Original/Factory Thrust Washer & Selectable measure out at 146" (Give or take) & The rear Unit endplay will be .@020"-.040" on a "Good" running unit.

I always start with measuring the the original Washer & Selectable....Add .015" to that to get my starting thickness for the Bearing & Shims.

**I've never had an issue using the Sonnax bushing backward, However.......As it's being used incorrectly, The bushing could have ill regularities in actual under the head length.
If the Bushing is Proud of the bearing...Let me know!
I have taken every measurement,

New Roller Bearing is about .137"
Bushing sticking into the case about 0.112"
Shims measure 0.008", 0.016", 0.018"

Original bottom selective washer: 0.083"
Thrust washer above the selective washer: 0.057"

By the measurements, the bearing is over the bushing. However it is difficult to tell by feel.

In order for rear thrust to rotating the bearing when I rotate output shaft, I must use:
Bearing .137"
Shim 0.008"
Shim 0.016"


Also is it okay to drill lube to line bypass to .063" Instead of .055".... I read that it would be fine if I dont have a aftermarket "LUBE to line bypass regulator valve" In one of your previous posts. However I am not sure what kind of regulator valve i have... here is a picture maybe you can ID it. The place I bought the pump from said it would be a sonnax boost valve but didnt mention what kind of regulator valve.

I think the lube regulator has some holes in it. So I guess mine is just a normal regulator valve (OEM). But I wonder if I can tell the boost is sonnax or OEM (they said it was sonnax but...? Who knows? )

It is important to note that even if I remove the Bearing and shims, and then install the output shaft, the rear thrust surface still doesn't even come close to the bottom of the case. Its like something is holding the output shaft up from reaching the bottom of the case. Rear thrust can't touch the bearing... or the bushing.
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Here is a better picture with just the output shaft installed, NO BEARING,
You can see the output shaft stops way before it can reach the bushing. Something else stops the shaft from getting to the bottom of the case.
this could be totally normal. I assume it is. So I simply installed the bearing back with both shims like before and the output shaft turns with the bearing and kind of easy to turn now.


I pressed a new bushing into extension housing, lined up the lube hole. I hope the little notches go upwards. I pressed it just below flush, like the original bushing, but it looks like it could have went lower.

Drilled a bleed hole 0.035" around that in the direct drum because I dont have HD kit Direct springs so I figure this will help prevent centrifugal apply at 7k rpm. hopefully.

My forward clutches were shredding apart, and the directs were almost down to the metal.

My biggest concern is the transmission shop that had this trans for a minute may have done something BAD to the valve body or case passages.
So I'd really like to know, is there anything in particular that a trans shop could do on purpose to cause a transmission to burn its clutches/slip? I'd like to look very closely at specific areas to make sure nothing was modified with the intention of destroying the transmission.
The bushing might be tight or there's a high spot on the Output Shaft itself.....About the only thing can cause that.

Extension bushing install looks fine!

Looks to be a Sonnax Boost Valve, But the Pressure Regulator Spring looks stock.
The bushing might be tight or there's a high spot on the Output Shaft itself.....About the only thing can cause that.

Extension bushing install looks fine!

Looks to be a Sonnax Boost Valve, But the Pressure Regulator Spring looks stock.

Should I sand the output shaft? How do I get an end play? If it spins fine, turns the bearing, but has no up and down movement, can I just run it like that?
I would suspect the bushing first.....Should be able to see any damage to the Output Shaft.

You MUST have endplay.....You'll wipe the geartrain bearings out in short order. You'd be better off putting the stock Washer & Selectable back in than running with Zero endplay or even worse.....Pressure on the bearings!
So just to be clear. the output shaft thrust surface should be able to touch the bushing, it should go all the way down into the case.
Ill check the output shaft for marks. Ill play with the original selective and see how it feels.

Would you be able to tell me how the bearing should behave? Like, With the output shaft installed, should the bearing spin? When should the bearing be able to spin, when I push down on the output shaft? I never got a chance to rotate the output shaft with the original bearing, I SHOULD HAVE

My next random questions:
1. I lubricated the pump halves with ATF before torqueing the pump halves together. I wasn't sure if they should be dry or lubed up, it seems like ATF would prevent them from sealing properly, but I was afraid to dry them with brake cleaner (RUST)
2. Is it normal for the over run clutch housing to slide down off the input shaft enough to disengage a clutch? Like when I have the snap ring on the input shaft, and everything is assembled... the over run housing can move far enough away from the snap ring to fall out of a single clutch disc.

Thanks, im a poor college student, trying to do this in dirt and mud in the backyard. Its very hard to keep everything clean and any small mistake will ruin the whole thing, I know
Yes....The Thrust surface should touch the bushing, Albeit there's a Radius on the Output Shaft.....There's also a Chamfer on the Bushings edge.

With just the Bearing installed over the Bushing & just the Output Shaft installed.....The Output Shaft should spin VERY freely.

How to size the bushing without removing the bushing & buying a new one......
*Install the original 3-Tang Selectable Washer in the case.
*Install the original 4-Tab Thrust on the Output Shaft with some assembly lube to adhere it to the shaft
*Install the Shaft (By itself/Bare) in the case with the Bellhousing pointing up.
*Locate a long Drift (A long 1/2" drive extension will work).
*Strike the Output Shaft in 4 alternating locations. (Picture, Red Dots)
*If it doesn't loosen up....Rotate the Output Shaft a few degrees & repeat.


That worked! I was able to finally measure endplay with the original thrust washer/selective. I got .019-.022"

I put the bearing back into the case with .021" Shim And the endplay measured around .010" - .011"
So I took that shim out and put in the .010" + .019 shim and now my end play is .003 - .004"
I have no other shims to use so that was the only option.

NEW question,
I assembled the lower half, up to center support. Install low band, new sprag, and put in the center support snap ring.
Sun gear bevel is down, lube holes are aligned in gear and shaft. Everything got lubed.
Now when I turn output shaft it can turn very easily. Smooth, does not bind. No issues.

However, when I turn the shafts sticking out of the center support, The center shaft AND sun gear shaft, They turn freely a little but then there is a slight binding spot. I can turn it by hand through the bind spot back to the smooth spot. I am wondering if this is normal, what is that slight bind?
Nevermind , I think my hand was just raw and sore and full of cuts from turning the parts so many times. I let it rest a few hours and came back and it seems normal now.

I put the rest of assemblies in tonight and about to put pump in and move on to the valve body. I am having a bit of trouble (lack of tools) getting the front end play clearance using a micrometer and level... ATSG manual says to use a "H-micrometer" or something like that. I keep getting readings between .082" and .100" So I am not sure whether to use plastic .075" or plastic .090" Thrust washer behind pump yet. I'll check again in the morning.
Right now Im leaning towards the 75 since the pump gasket should eat a couple thousandths,
at .100" - .075 - .004 = .021" End play
.100 - .090 - .004 = .006" Too little

So .075" is winning because even on the large end of my measurements the .090 is still too thick.
But will the front be okay at .021" or .018" Range? I know I should be shooting for .008-.011"
.021" isn't the end of the world & will work fine, I guarantee it's an improvement over what it was!

But you won't know actual 'till you get the washer installed, The washers have a "range" of thickness. I have a Pump to Case gasket I use just for checking front endplay.
Another question, I just remembered, There is this weird silver cap shield thing that goes onto the output shaft, inside the extension housing. It has a seal on it also. I can get a picture of it if necessary. But I was wondering, what it is, what it does, do I need it? I had to knock it off with a rubber hammer originally.

I ask because the ATSG manual has no picture of it nor mentions what it does.
The OD Roller Clutch turns & locks onto the Overrun Clutch Housing/Hub, You have the old one in the OD Carrier.....Just making sure it didn't get assembled that way (If that's even possible).

Lot's of work ain't it!! ;)
The OD Roller Clutch turns & locks onto the Overrun Clutch Housing/Hub, You have the old one in the OD Carrier.....Just making sure it didn't get assembled that way (If that's even possible).

Lot's of work ain't it!! ;)

What do you mean by old one? Are you referring to the picture where I am showing the original OD roller clutch next to the brand new unit in the box? If so yes I put the new one in before I assembled it.

However your words could be taken another way. You could mean "OLD MODEL" Like I used the wrong model of OD roller clutch. Are you saying I used the wrong model (old model?) Or just making sure I took the new one out of the box and installed it