4L80E slipping bad

[ees]

My transmission has been slipping really bad the last week or so. It is worse when the truck is cold or climbing. It seems to be Ok in reverse, but not happy in forward gears until above maybe 40 mph. I have checked the fluid level and it looks fine. I know the transmission has issues, but I just want to string it along a little bit more until I get my quattro back on the road.

The last two days have been the worst, but I think my alternator is on the way out (trucks sounds like a piece huh?).

Will the 4L80E run like crap with low battery voltage?

One of the diesel mechanics at my local dealer told me last summer that unplugging the main connector on the drivers side of the tranny would put it into a limp home mode with max line pressures. Said it would be like a drag transmission. I could use that about now with all the slipping during gear changes, but don't want to grenade it the rest of the way.

Any thoughts or suggestions? Yes I have already started to prepare myself for dropping in a new transmission.

[AndyL]

If you unplug that connector I don't think it would even shift out of first. The only way this idea would work is to remove the pan and unplug the connector on the force motor. This would give you max line pressure.

I don't remember their functional order but it is very possible that one or both of your shift solenoids haved failed.

[ees]

Once it has been driven for about 10 minutes or has idled for a little longer it will drive normally. Since my commute to work is 15 minutes I get a good deal of the bad part. I have been trying to warm it up first, but don't always have the time. When it does finally decide to connect it generally shudders just a bit and then feels solid, so you are likely correct on troubles with the solenoids.

I have noticed that the point where wires enter the drivers side of the tranny has electrical on it. It makes me wonder if someone mucked with it in the past.

I know that I likely need to just yank the tranny, but I want to insure there are no other possible reasons for the problems.

[rjschoolcraft]

Several things can cause low line pressure when cold...resulting in the slippage you're experiencing. A plugged filter is one easy culprit to check. ;)

[ees]

I think the fluid is also kind of fried. I have heard stories of old transmissions that flat out stop working with a fluid change. Is their any basis in fact here? Should I try a oil and filter change to see if I can buy some more time? I rather loathe pumping a couple grand into this truck right now so I am willing to try a few things.

Thanks for the input so far.

[Steve O.]

Eric, I can't offer much help on the fluid question. I've heard the same theories but have no experience on that front.

However, just a note of caution about yanking the box yourself: When my 4l80E went bad this summer I yanked it with the invaluable help of Charlie P. I figured I'd have it rebuilt and then we'd reinastall it.

Brought it to a trusted tranny shop, where I was almost turned away becuase I'm sure they were unhappy about missing out on the labor. Of course, what they said was that they now had a) no way of testing it, and b) that they could not warranty their re-build unless they did the install. Caught between a rock and a hard place time-wise, and basically understanding the warranty issue, I had them do it. That said, they were very good to work with, and took care of me on the some of the price anyway where they could. But just a note of caution before you yank it and have the same issues.

Steve

[Tough Guy]

I'm with big Ron on this one, but first check for DTC's then drop the pan, replace the filter, add the proper amount and proper type ATF and look for excessive sludge in the pan around the magnet. Check all your electrical conectors/wires and such...


Cheers

[ees]

Thanks guys. I will pull the pan and take a gander, plus just clean everything up.

Steve thanks for the heads up. I ran into a similar problem when I painted my wifes car. I did all the prep work and then could not find anyone who wanted to shoot it. In the end I got it done, but it was harder. My plan is to buy a rebuilt unit and then pay a shop to pull it. I don't have a tranny lift and it is a little bigger than I would like to tackle by myself.

It will likely be a little bit before I can do the maintenance on this, but I will post what I find and how it behaves after.

Thanks again

BTW... side question. If I am going to drop the pan anyway I am going to put a drain plug it it. I was just going to buy a drain plug from the parts store and then find a nut that fits it and weld it into the pan. Is their a better way? The stamping for the pan already has a boss for the drain plug it just doesn't have one.

[arrowheadracing]

Two things. Yes changing the fluid on a high mileage transmission thats never been changed, or is very bad in color and smell , will almost guarantee a slipping useless trans. I can speak from first hand experience for myself and about 10 others I ve warned, but they still had me do the work anyways. The few trans I ve done for myself, I knew what was going to happen, I had another trans ready to install , but thought I would try changing the fluid first. It slipped so bad, that it sounded like it had a race torque convertor in it. It would rev to about 4500 rpm and then start to creep forward. So becareful when deciding to do that fluid change. As the old fluid holds the used clutch disc material and the new fluid is going to go through and clean all the out and leave slippery surfaces. Trans fluid is a detergent cleaner.

For the trans pan plug, weld the nut on the outside. That way you dont have to fight the trans fluid that is on the inside of the pan. Unless you throw the pan in the oven for about an hour ( 450-500 degrees ) to burn off an excess residue on the metal, you might have a hard time getting the plug to weld good on the inside. Beside putting it on the outside, gives you an area to put a wrench on it, if the drain plug ever gets cross threaded.

Good luck
Todd

[ees]

The plot thickens.

So I took the truck to the discount auto parts place to get the alternator checked. I have not had the hood up with the engine running in a while. It was immediately obvious what the problem was. The belt is loose.

It now appears that the belt was too long to begin with and has been slipping and machining itself down over time. It has only been about 4 months of driving. This would explain why I had to get Heath's boost controller since I had no vacuum. Didn't bother to check the belt.

I wonder if my low voltage is causing the problems with the tranny...please

[David Brady]

I had a problem with low voltage that was caused by battery connections and at one point it had the trans in some kind of limp mode, it ran in second gear only. It was very dependant on the voltage.

[ees]

Well I got the new belt on. Alternator is charging again, no change with the tranny.

Oh well.