4L85E Front Seal Leak

L31MaxExpress said:

Thanks for the information, figured as much. It just started doing it.

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Youre welcome..If all those solenoids, psma and wiring harness are the originals that came with the unit, Id replace them all with new OEM and/or Rostra parts when you drop the pan.

I burned a test chip to force the unit into lockup and upshift early to test the gears at lower vehicle speeds. Re-ran it again, Drive, at 2,000 rpm, speedo was showing 40 mp and 4th had been commanded since 25 mph, lockup since 12 mph. Dropped to 3rd, 38 mph, dropped to 2nd it dropped to about 35 mph. I could feel a very slight and destint clunk shifting down manually 4-3 and 3-2 and placing it back in 4th resulted in it still holding 35 mph. If the clutch packs were smoked wouldn't the fluid smell terrible and be burnt? I used my vacuum oil sucker to extract some fluid, it is pink as can be not burnt. Driving it down the road shifter in Drive or 3rd and PCM commanding 3rd or 4th it also pulls instantly when the throttle is opened. I just find it odd that if the solenoid or shift valve were holding it 2nd gear, why does it have a distinct clunk shifting down with a corresponding change in output speed. I also noticed with the brake switch disconnected TCC slip is reading negative value in 2nd gear and increases to a positive value in 3rd and 4th. I have seen negative slip in park but never in gear, but never run one on jack stands either watching all the data. Converter locks in 2nd but releases in 3rd and 4th. PCM is commanding it to release for some reason even though the lockup is enabled in 3rd and 4th at the same speed the upshifts are set. Could the shift valves letting just enough fluid through to provide a change moving the shifter to around and not enough to actually upshift it? Just weird all around.

L31MaxExpress said:

I burned a test chip to force the unit into lockup and upshift early to test the gears at lower vehicle speeds. Re-ran it again, Drive, at 2,000 rpm, speedo was showing 40 mp and 4th had been commanded since 25 mph, lockup since 12 mph. Dropped to 3rd, 38 mph, dropped to 2nd it dropped to about 35 mph. I could feel a very slight and destint clunk shifting down manually 4-3 and 3-2 and placing it back in 4th resulted in it still holding 35 mph. If the clutch packs were smoked wouldn't the fluid smell terrible and be burnt? I used my vacuum oil sucker to extract some fluid, it is pink as can be not burnt. Driving it down the road in commanded 3rd or 4th it also pulls instantly when the throttle is opened. I just find it odd that if the solenoid or shift valve were holding it 2nd gear, why does it have a distinct clunk shifting down with a corresponding change in output speed. I also noticed with the brake switch disconnected TCC slip is reading negative value in 2nd gear and increases to a positive value in 3rd and 4th. I have seen negative slip in park but never in gear, but never run one on jack stands either watching all the data. Converter locks in 2nd but releases in 3rd and 4th. PCM is commanding it even though the lockup is enabled in 3rd and 4th at the same speed the upshifts are set. Could the shift valves letting just enough fluid through to provide a change moving the shifter to around and not enough to actually upshift it? Just weird all around.

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I have never done a simulated road test on jack stands so cant comment on those results but if it's not upshifting out of 2nd gear when on the road, 1-2 shift happens normally then the problem is either Sol B mechanical, 2-3 shift valve/spring or some electrical anomaly/fault somewhere.

Ive seen units come in with burnt clutches where fluid wasnt overly discolored but smells burnt. The smell is always the common denominator, in my experience. But your symptoms dont indicate burnt applied elements, they are being caused by a command/control issue.

Double Check all grounds, electrical, pcm. Yank the pan off, replace the solenoid (everything electrical if that stuff is all orginal), check the valve/spring then go from there.

L31MaxExpress said:

@NickTransmissions

Off the top of your head, any ideas what would make a 4L80E have a good 1-2 shift then not even try to shift to 3rd or 4th? It does not neutral when it commands 3rd or 4th, just hangs in 2nd, let off the throttle and coasts, pull it down to 3rd and it will engine brake so I am fairly certain nothing is slipping clutch wise. No codes either after multiple short drives. Hard to drive it much because even at 40-45 mph it is screaming in 2nd with a 4.10 gear. I can see the PCM call for 3rd and nothing happens, just stays in 2nd. It has both an accurate VSS and ISS signal. The unit in question only has the internal manifold pressure switch and the PCM is seeing the shifter positions accurately. If the shifter is moved from Drive or 3rd to 2nd you can feel a slight bump and it engine brakes in 1st as well. Has me at a bit of a loss. 2-3 shift solenoid or valve issue? I would think it would set an invalid ratio code fairly quickly or a stuck solenoid code but it does not. I checked and the unit has a 4L80E operating system in the PCM via reading the Memcal in it and the harness pinout seems correct as well. FWIW this is a 1994 TBI truck. FWIW I also back probed the connector with the truck on stands, accelerated it to 50 mph showing on the speedo and the 2-3 shift solenoid wire from the PCM pulls low so fairly certain it is not a wiring issue in the unit or to the PCM. The shift solenoid Yel/Blk wire has 12V on it before the PCM pulls it to ground.

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My friend Jenna in PA has a ton of great connections in the Buick world along with Gary Paine of Ohio who worked with me to have the custom Buick 350 block girdle designed, manufactured and re-produced.

Jenna’s channel:

If it is starting to feel like braking going in to 3rd would it not be a sign of cross leak applying multiple clutches? Sorry if misread. Had 4l60e that blew a seal internally have similar symptoms.

yevgenievich said:

If it is starting to feel like braking going in to 3rd would it not be a sign of cross leak applying multiple clutches? Sorry if misread. Had 4l60e that blew a seal internally have similar symptoms.

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He can can confirm/deny but I'm understanding L31MaxExpress' issue to be no 2-3 upshift.

NickTransmissions said:

He can can confirm/deny but I'm understanding L31MaxExpress' issue to be no 2-3 upshift.

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At first sounded like it was acting odd or possibly dragging when it should shift and then shift not happening. Sorry if turning this in wrong direction. I just remember chasing for a month thinking I have failure to shift when it turned out to be a blown seal. I actually did not find the answer until long after, as I just swapped to t56 as my solution(t56 was the end goal regardless). Just eventually did a tear down as it was bothering me on what was the actual issue.

yevgenievich said:

At first sounded like it was acting odd or possibly dragging when it should shift and then shift not happening. Sorry if turning this in wrong direction. I just remember chasing for a month thinking I have failure to shift when it turned out to be a blown seal. I actually did not find the answer until long after, as I just swapped to t56 as my solution. Just eventually did a tear down as it was bothering me on what was the actual issue.

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It could certainly end up with him pulling the unit but I'd rather him replace the 2-3 solenoid (at least); preferably all transmission electrical/electronic components should be replaced if they're original. As you know, 4L80Es are bad about harnesses shorting/leaking through the connector, solenoids literally falling apart, etc.

Then he should check the 2-3 shift valve movement in the bore, confirming/denying it will move relative to spring tension, etc...If there's nothing pushing back against the valve when you push it in, may be due to the spring being broken or compromised in some way (I've not actually seen this but anything's possible). It's also a good idea to install Sonnax parts into the valve body, should he discover that valve/spring is the problem.

If he does all that, valve and spring show movement/appear to be fine and he still has no upshift then (and all non-trans causes have been ruled out), I'd be pulling the trans and taking it down. To your point, symptoms that don't initially appear to be caused by internal-case mechanical problems can turn out to be exactly that.

yevgenievich said:

If it is starting to feel like braking going in to 3rd would it not be a sign of cross leak applying multiple clutches? Sorry if misread. Had 4l60e that blew a seal internally have similar symptoms.

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Moving out of drive applies the over-run clutch and I believe there is manual 2nd gear brake band as well. Need to look at a bit more.

NickTransmissions said:

It could certainly end up with him pulling the unit but I'd rather him replace the 2-3 solenoid (at least); preferably all transmission electrical/electronic components should be replaced if they're original. As you know, 4L80Es are bad about harnesses shorting/leaking through the connector, solenoids literally falling apart, etc.

Then he should check the 2-3 shift valve movement in the bore, confirming/denying it will move relative to spring tension, etc...If there's nothing pushing back against the valve when you push it in, may be due to the spring being broken or compromised in some way (I've not actually seen this but anything's possible). It's also a good idea to install Sonnax parts into the valve body, should he discover that valve/spring is the problem.

If he does all that, valve and spring show movement/appear to be fine and he still has no upshift then (and all non-trans causes have been ruled out), I'd be pulling the trans and taking it down. To your point, symptoms that don't initially appear to be caused by internal-case mechanical problems can turn out to be exactly that.

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That is where I am going to start. Will not get to tear into it until next week.

It is definitely a no 2-3 condition. Does not even try to engage 3rd. I drove it around the block with the revised shifting calibration forcing to upshift amd lockup at X MPH regardless of TPS. I can feel the destinct converter lockup right after 1-2 and it just hangs in 2nd.