Experience with 1996 Chevy Suburban 2500 7.4 Transmissions

[LiLNomad]

Hi,
I have some questions regarding my 96 Chevy Suburban 7.4l 2500 Transmission. I am not comfortable with info I have received from my mechanic and would like to run it by someone very familiar with this year transmission. Please PM me.
Thanks
LilNomad

[DanB]

4L80e? Great tranny, what's the issue? It's good to share issues on here for historical reference.

[nvestysly]

Yes, I'd like to hear the issue too. I'm not an expert on transmissions so I don't know that PMing you will help any. I have the same vehicle and a similar 2005 so I'd like to be aware of any concerns you have with your transmission.

I agree it's useful to have the information posted here for future use.

Thanks.

[LiLNomad]

Ok will try to summarize what happened..Had someone else who tows with a Suburban and has had the almost the same year etc as mine drive mine and give me his opinion. We determined mine wasnt going into 2nd gear properly. Took it in to mechanic & had transmission rebuilt. It came back, I took it & trailer on a trip towed fine. Next day no REVERSE or 1st gear. Back to mechanic. Was told the band which controls these gears was faulty..it was replaced. Picked up car and went on test drive, felt like now 2nd & 1st werent working..took back to mechanic .I was told that the Suburbans had an issue (especially when used for towing and downshifting to assist in slowing down vehicle and trailer) that too much pressure was going into the transmission so the fix was to install a TRANSCO valve SK-4L80E-B. According to the literature I was given and what I was told "prevents/corrects/reduces high pressure parts breakage." I just got back from a test drive and now it seems to be downshifting into 2nd and 1st fine. Anyone else heard of this? I have the literature. I asked my friend w/ the Suburban and hes never heard of this valve. Anyone familiar with this? Just wanted some other opinions as I tow solo. I love my Suburban and dont plan on replacing it as a tow vehicle, I keep up the maintenance, have never had any issues outside of this and it has only 61k original miles..YES ORIGINAL MILES. Just want to ensure this was the proper fix.
Thanks
LilNomad

[nvestysly]

I have not heard of that problem but that doesn't mean it's not legitimate. Both of our vehicles have the 4L80E transmission - the '96 with 190k miles and the '05 with 120k miles. In both cases they have towed significant numbers of miles, including mountains, and I've used the transmission to slow us when going down hills. Both vehicles have the heavy duty trailer towing package with secondary coolers but I would think all 2500's have that.

A quick search on the internet indicates several retailers sell the TransGo SK 4L80E valve (shift kit) you described. So in that respect it seems legitimate.

Did your Suburban ever illuminate the check engine light? It seems when the transmission was not working properly, prior to a failure, it would have "thrown a code" to indicate there was a problem. I've included a link to the OBD transmission codes. Might be interesting to ask your mechanic about this.

http://shop.ukrtrans.biz/wp-content/..._CODE_BOOK.pdf

Thanks for posting this. Sounds like your problem has been addressed - hopefully some other people with benefit. This transmission was used in vehicles from 1991 through 2007 so I'm sure there are lots of Air Forums members towing with this transmission.

[russelld]

I have a 1996 GMC with the 7.4 L with 120,000 miles and pull a 31 ft AS , no problems

[TomKirk]

Without doubt, the 4L80 is a bullet-proof tranny.....or at least it should be. And with 61K original miles, you shouldn't have any problems at all - provided, of course, your tranny's been serviced properly; which would be at 30-60-90K intervals.

I know there's a lotta after-market parts out there, but I've never heard of a magic "TRANSCO valve SK-4L80E-B" that'll fix the problem you describe. Frankly, I think your mechanic is leading you down the primrose path.

You need a second opinion. You need to find an old school tranny shop with a certified, old school tranny technician. Because the guy you've got now is nothing more than a certified "parts replacer."

Back in '96, I worked the back counter of a Chevy parts dept. Rather than tear into your tranny willie-nillie, my tranny guy would "start" with a transmission service and send you out the door. If the problem persisted, he'd hafta dig deeper. But more often than not, 9 times out of 10, the tranny service fixed the problem.

Bottom line- Your tranny guy is making rocket science out of this. Fancy part, fancy name, fancy part number; one size fits all, fixes all - sound's suspicious to me.

Tom

[LiLNomad]

Thanks for all the feedback. I definitely didnt have 2nd before they did whatever rebuild they did. Now I can hear & feel the difference in the engine & speed when I downshift from 3rd to 2nd to 1st. So it feels better...however I will still keep an eye on it as well as consider 2nd opinions if it acts up..but as of now seems fine. I dont know what was done prior to me purchasing the truck, but I am obsessive about keeping up with any maintenance.
Thanks
LilNomad

[mykytiukr]

Had sort of the same problem except I never lost reverse. Mine kept going into limp mode. That's where you lose 1st and 3rd and the pump goes to maximum line pressure. Now I am not a transmission mechanic. But I am an ASE certified heavy truck mechanic. So I generally know what makes sense. Took it to a tranny shop and they diagnosed it and replaced a couple of shift solenoids and a couple of sensors. Worked for a day. Took it back and they said one of the new sensors was bad and they fixed some loose wires. Worked for another day. More than $800 and I'd had enough. Started looking on some of the Chevy Truck forums. Ran across the usual stuff about solenoids and and ECMs. Then the throttle position sensor and a vacuum sensor was mentioned. I had a couple of used ones around from an engine swap so I changed them out and in was an instant fix. Now you'd think with numerous experienced mechanics there and all the up-to-date expensive diagnostic equipment they should have been able to figure it out. What do you think?

[cliffcharb]

They installed a shift kit which does include some upgraded parts. If this transmission was rebuilt it sounds like they only rebuilt what was broken at the time, not a full rebuild. If it's working go with it. You can generally get a lot of mileage out of those transmissions. Transgo is quality parts so that's a plus.

[bibbs]

I agree with mykytiukr, all that fancy diagnostic equipment, you would think they could get it first try. My 4l80e drops out of 4th when it needs to then won't shift back for 20 miles or a lot longer. Drives me nuts! New valve body? My transmission doesn't set codes.

[Tn Traveler]

My '97 K2500 Suburban has 207,000 miles on it. The transmission has been rebuilt one time.

[m.hony]

Sounds kinda sorta like the transmission re-builder only replaced what was obviously broken or worn or damaged several different times.
If he had completely rebuilt the tranny 1 time- every clutch, gear, solenoid, valve- it could have been 1 trip to the shop instead of 3.
How much money have you thrown at it?
You could have gotten a GM rebuilt 4L80E with a 3 year 100,000 mile warranty for about $2700.

[LiLNomad]

Everything was rebuilt. Its been driving& shifting fine. I might take it out this week with the trailer. Hoping to get back to my goal of putting 1 million miles on it hehe.
Thanks for all the help. See ya on the road!
***OOH now I'd like to move on to my next project of brighter headlights...can I just have LED bulbs put in?..then maybe we will talk about a roof rack!
Thanks
LilNomad