4l80e rebuild gone wrong...

Bextreme04 said:

Round pattern 205? Or did you modify a figure 8 to have the long input? I have a stock 205 Figure 8 with the short input as it originally had a TH400 in front of it. I'm using the stock adapter with a Northwest Fab adapter plate and cut down a 2wd output shaft to fit the required 4-7/8" length. I don't think I've ever seen a 205 input shaft go that for onto a 4L80 output shaft to have stripped it that close to the trans.

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NickTransmissions said:

Yep, plug that VB with a set screw.

When was that picture of the stripped output shaft taken? Is that it's current state or was that taken prior to you rebuilding the unit?

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TubeTruck said:

Prior to rebuilding. See post above

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NickTransmissions said:

Sorry, lots of addl posts since my last, didn't read them all.

That said, I'm assuming you still have no movement in any range, reverse, drive, D3, 2 or 1 - correct?

If so, think a couple folks mentioned checking the T-case and/or rear end, which makes sense to do. Rule them in our out first then start trouble shooting the trans...

Normal pressures at idle in P-1 are as follows:

P, N, D, D3: 55-80 PSI
R: 95-120 PSI
2/1: 135-175 PSI

This assumes as stock pressure regulator spring and otherwise unmodified pump assembly.

No movement in 4L80Es is typically OD roller clutch assembly failure as the pumps are pretty resilient and not prone to failure like transmissions with vane style pumps (700R4, 4L60E, 6Ls, etc).

Let us know what you find once you start digging back into it.

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TubeTruck said:

Ok. I want you all to know I am a moron

@Bextreme04 had it correct. It was the t-case. Or rather operator error. I had it in fwd with no front driveshaft. Swapped sticks and it lights the rear tires up.

But now a new problem. It doesn't shift lol

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NickTransmissions said:

No upshift from first gear? Plug the speed sensor back in.

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TubeTruck said:

Bought a new factory separator plate since mine had some major check ball wear. Should be in tomorrow. Plugged the hole I drilled for the HD2 relief.

Here's what's going on. Anything else I should check while the valve body is out?

Put the truck in drive, first gear wouldn't shift until high rpm (I didn't check what rpm, I could just hear it), when shifting into second it feels like the brakes are on. Not sure if something is binding or if a band isn't releasing. Taking my foot off the gas, the truck would basically nose dive and chirp the tires downshifting to first. Then the tranny would start smoking.

Reverse works fine.

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NickTransmissions said:

When you say, "first gear wouldn't shift until high RPM" are you meaning to say that it's not upshifting into 2nd gear until very high RPM or it doesn't begin to move forward until you have to really put your foot in it to get it moving?

Binding in 2nd gear may be caused by a problem with the low-roller one way clutch holding beyond first gear or 1-2 accumulator...

Based on everything you've written thus far, I suspect that thing has to come back out, gone through with a fine tooth comb and then reassembled properly. I'd remove the Transgo HD2 spacer plate, replace it with either a factory plate or Transgo's factory replacement separator plate for your vintage of 4L80E. Dual feed the direct clutch internally and perform these lube mods (don't drill the pump cover if you installed Sonnax's pressure regulator valve)

I asked you a whole bunch of questions further upthread, you never responded to any of them but here they are again so you don't miss them this time:

During assembly, did you:

> Replace the boost valve with a Sonnax 4L80E-LB1 (I don't like Transgo's valves either for these or the TH400s)
> Perform a case air check prior to bolting on the valve body
> Vacuum test the valve body and pump stator support
> Check the forward drum for sealing ring groove wear (very common in these units)
> Check one-way clutch rotation to confirm they were installed correctly

Let us know...

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TubeTruck said:

It moves instantly. It won't shift into second until high rpm.

I answered the questions in post #6, but probably got skipped over because they were in paragraph form. Here they are again:


> Replace the boost valve with a Sonnax 4L80E-LB1 (I don't like Transgo's valves either for these or the TH400s).
* I didn't know much about the Sonnax stuff when I got to rebuilding it. The majority of my research was around how to take it apart and put it back together, if special tools were needed, etc., rather than upgrades. Since I installed the Transgo HD2 kit, I installed the Transgo boost valve and drilled the hole in the pump.

> Perform a case air check prior to bolting on the valve body
*didn't have a way to air check stuff at time of assembly (I know, my own fault), but I do now. I have to go through your videos to find all the spots to test, but I did test the rear band and I can see that activate and release, and I applied air to the bolt closest to the converter (center support?). I can see the clutches activate, then hear it leaking inside the case, not sure if it's supposed to do that.

> Vacuum test the valve body and pump stator support
* I did not. I have no way to do this.

> Check the forward drum for sealing ring groove wear (very common in these units)
*I did check it. I did not see or feel any bad spots.

> Check one-way clutch rotation to confirm they were installed correctly
*yes. It only spins in 1 direction


If it does have to come back out. I'll buy a new pump and the Sonnax boost valve and dual feed it.

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NickTransmissions said:

The Transgo boost valve is fine but I prefer the Sonnax version given it has O-rings which completely seal off any leakage between the sleeve and casting in the boost circuit.

One way clutches can be installed backwards so make sure you check that whichever OWC you're checking that it spins in the correct direction. Sounds like yours are installed correctly because you'd not move or have 2nd gear otherwise.

I don't think you need a new pump, as the existing pump isn't the source of your problems (at least not what you've stated thus far)...The caveat here is that your line pressures are normal and not either low or excessively high, both at idle and at stall.

Addl Questions:

> Did you purchase and install a new 34-element sprag?

> Did you double check the intermediate sprag assembly snap ring was fully installed; there should have a spiral-lock snap ring if it's a 97+ unit

A slight amount of hissing is normal when air checking on the bench, especially if checking a circuit sealed off by teflon sealing rings, which is the case with the center support, unless you used the stock plastic interlock rings (they air check a bit better). But teflon sealing rings seal better given they expand and fully conform to the inner diameter of their respective bore locations where as cast steel and plastic rings don't do that as effectively.

Check the intermediate clutch apply via the 3/8 12-point feed bolt in the center support, the hole left of the center support feed for direct clutch apply, the hole to the right of the center support feed bolt for high-reverse apply (this is plugged when dual feeding, 2nd sealing from top on center support left off and direct drum center seal left out when dual feeding) and T40 Torx feed bolt for Overdrive clutch apply.

I'd yank the valve body off and do a case air check to see what, if any anomalies, you observe (keep the low reverse servo cover on at this time). Then check the 1-2 accumulator to see if anything's wrong with it that could explain the binding feeling when in 2nd gear. You can also check l/r band clearance/servo travel at this time...You want between .125-.175 total inboard low reverse servo travel to ensure the band doesn't bind while keeping clearance within spec.

Let us know what you find...

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TubeTruck said:

Yes, new sprag was purchased and installed. I remember checking to make sure they spun in one direction and in the correct direction.

The spiral snap ring was installed correctly. I remember checking to make sure it was seated properly and fully.

Air checked the T40 bolt. I can see the clutches apply and it holds air until I pull the air gun off.

The 3/8 bolt has the air leaking by. In my head it's worse than it might be. The hole to the left and right... blowing air into one hole it blows out the other side. Is it supposed to do this? If I plug the opposite hole with a rag I can hear the clutches apply. It does the same thing when I switch holes.

The l/r band servo. I couldn't find anything skimming your videos on how to measure this. After a quick Google search I found a video using a special tool to determine pin length, and an article on making your own tool to measure travel. Do you have another way to measure travel? Or is this what I need to do?

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Thank you so much for your help in all of this!

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