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Tranny won't shift right

S

sodfarmer

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utah
I have a 88 Suburban 3/4 ton 6.2 diesel with a 4l80 tranny I think. It's the only tranny the pan shape fit. Anyway I took the tranny out to replace the flexplate and after I got it back together it won't shift into overdrive and all the other shift are soft and quite random. I've checked all electrical connections and they are all in the right place. Have any of ya'll seen a problem like this and how did you fix it.

thanks

Breton
 
4L80s didnt come around until 1991. what does the pan look like? and how many bolts are there holding the pan on?
 
I also thought the 4l80 came later, but we had the transmission book from napa and the only pan that resembled it was the 4l80. The pan is rectangular longer front to back. 17 bolts. On the drivers side is has 3 electrical connectors. 1 large round one with several prongs 10 or so and 2- 2 prong connectors. The transmission has no kick down cable so I assume it is fully electronic controlled and probably where my problem lies.

Thanks
 
in 88 it wouldn't have been a fully electronic trans. at best it would have wires for tcc. All the 4l80s i've seen dont have rectangular pans but are shaped more like a bullet. are you sure some one hasn't done a retrofit job
 
I'm going to go out on a ledge here and say you have a 4L80E. Definitely not stock on your truck, but there wasn't a transmission made by GM with that amount/style of connectors when your truck was made.

As to exactly what your symptoms are pointing at, I don't have a clue. I would most definitely be looking for pinched/cut wires around the bellhousing area, since the trans was removed working and now doesn't, and pinched/stretched/broken wires are so common when pulling engines or transmissions. How about the VSS wires on the t-case?

Plus if the trans was never opened, internal problems are unlikely although of course never impossible.
 
Yeah, sounds like either a 60e or 80e to me too. Probally the 80e being behind the 6.2... There should be a stand alone diesel controller for the transmission somewhere on the truck. Maybe something got jarred loose on it?

Just don't drive it the way it is, short stacked shifts like you are describing are extremely tough on a transmission...
 
17 bolts, square pan, definitely a 4L80E. and there never was a "4L80" non-electric trans. i would almost bet on both the motor and trans both being swapped from a different truck.
 
i had my trans overhauled and it would not shift into overdrive and sometimes not out of first gear untill i reset the tv cable.also a tranny guy told me while running at idle pull the downshift cable so it goes to full pressure-it may blow out some crud in the valve body
 
KTEX said:
i had my trans overhauled and it would not shift into overdrive and sometimes not out of first gear untill i reset the tv cable.also a tranny guy told me while running at idle pull the downshift cable so it goes to full pressure-it may blow out some crud in the valve body
Click to expand...

2 things...

1. the 4L80E, like the 4L60E, has no TV cable to adjust.

and 2. if the trans was built by a reputable shop, there would be no "crud" to blow out of the valve body. i think the only thing being blown anywhere here, is smoke, directly up your butt.
 
Thanks for all the info. I too think it was retroed from another truck due to the fact the title says it was gas and my buddies scan tool wouldn't read it correctly. My mechanic buddy knows a transmission shop that will trouble shoot for him for free so I am going to haul it over there.

If someone retroed the tranny in, where would I find the controller?

thanks for all the help.

Breton
 
Controller is *probably* behind the glove box, as that was where the ECM's were mounted.

In a retrofit though, depending on harness, it probably got mounted wherever was easiest.
 
does anyone have a wiring diagram for the large connector. It may help along with what voltage each pin has.

thanks
 
I don't have a link to the 1991 wiring diagrams, sorry. You might get lucky searching the boards thoroughly for them though, someone might have posted them.
 
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