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GM 4-Speed Auto Can't Get 3rd Gear

Discussion in 'Chevy Trucks' started by tvpierce, Sep 24, 2005.

  1. tvpierce

    tvpierce Senior Member
    from Maine
    Messages: 209

    My brother in-law is in a tight spot with his ’96 GMC Jimmy (S-15) 4WD/4.3 liter. It’s a daily driver, and his wife just got laid off, so they don’t have much (read: none) money to spend on it. I know you guys have a lot of General Motors knowledge -- especially with transmissions, and my experience with GM products is pretty limited, so I was hoping someone here could offer some expertise.

    The tranny is a 4-speed auto, and it’s acting up… here’s the problem: The tranny shifts fine into gear with no delay, and shifts fine into second gear while driving. But when it goes to shift into 3rd gear, he says it's as if it’s “popping/slipping out of gear”. He can drive the truck fine if he puts the gear selector into 2nd gear (thus keeping the tranny from shifting past 2nd). Obviously, driving with only 2 gears is not a long term solution, but at least he can limp around town.

    Any thoughts on this? Is this a common failure with these transmissions? Is it something that a simple drain/flush will correct, or are we looking at a rebuild/replace?

    If it requires a rebuild/replace, would the 4-speed auto box from a '91 Chevy Astro (2WD) be a direct swap? (I have access to one that's headed to the salvage yard.)

    Thanks in advance for your help on this.

  2. GetMore

    GetMore Senior Member
    Messages: 179

    2WD transmissions have a different tailshaft than the 4WD transmissions, so unless you swap the tailshaft (which includes one of the drums, if I remember correctly) it is not a direct swap.
  3. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Also, not sure if a '91 uses the electronic controlled valve body or not (4L60 vs 4L60e)......
  4. welded wrenches

    welded wrenches Senior Member
    Messages: 177

    4l60 A.k.a. 700r4 Yukk

    Hi all.Ok toss that tranny give to someone you dont like.And put a older trusty turbo 350.Too do the trans swap is a good th350 and special trans voutput shaft and a adapter plated.And you will need a kickdown cable and a modulator line.Everthing else bolts up normally.No hole to drill.I did this recently took out a smoked 700R4 and put a th350 connected to a 208 transfercase this was in a k-5 jimmy.General motors never perfectected those type of trannys.In 1987 to 1993 they made 23 different valve body designs,go figure.Who needs a computer to make a tranny work anyhow. welded wrenched. *I use type F (ford) trans fluid in all my chevys.
  5. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    And lose the overdrive on a daily driver? Ehhyeccccchh! I'd never go back to a TH350 again. I figure if a 700R4 can live happily behind the 350hp small block in my '68 Beaumont then it should be just fine behind a 4.3....

    Also, what transfer case would you be using then? The 208 from a K5 drops to the passenger side, while the S trucks drop to the driver's side... not sure if the shift pattern/shifter is the same either. He likely won't have bracketry for the kickdown cable either, on a Vortec style intake.

    Taking it out will also trigger Check Engine trouble codes.

    I was also under the impression that Type F fluid expands the seals (ones that are properly designed for it) so a bottle or so doesn't hurt, but I was told that a full pan of it will eat the GM seals. Not true?

    I really think he should fix the existing tranny and save a lot of headaches. I've asked my brother to read this thread, as he knows (at least the older ones) inside and out... maybe he'll know where to start. We'll find out in a day or two once he gets my email.
  6. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    OK I have gotten not one but two emails back from my brother, so I will just post them here in their entirety... Don't yell at me if you don't like the answers, they are direct quotes and I am just a messenger. Also remember that diagnosing thru the internet isn't the most accurate thing either, so consider it just information.

    Eml. #1.

    Well, his 96 is almost certainly a 4L60-E. But in 91 there were both 4L60's and 4L60-E's around, so he needs to check and see what the tanny in the Astro really is, since both were offered in the 91 Astro for some reason.

    Here's a couple ways to tell what the trans is, since the E version is pretty similar in appearance to the old ver.

    1. Look on the passenger side for a large round plug with around 15 wires in it - if it has 15 or so wires & a round plug it is definately a 4L60E.
    2. Drop the pan & have a look. If all you see is metal valvebody, then it's the TH700R4/4L60, but if you can see a number of black plastic bodied solenoids you have a 4L60E.

    Lots of internal parts interchange including 3-4 clutch packs. In fact the 3-4 Hi-Energy packs are the "hot ticket" for 700R4/4L60 3-4 longevity, along with the thicker steels (not the thin ones people put in to fit extra plates in, they warp easy, whereas the thick steels not only don't warp but also absorb and dissipate more heat from the frictions. The 3-4 clutch pack is almost certainly the component that failed (I know the symptom well). Only a rebuild will fix the problem. The nice thing about the 4L60-E is that much more info is available to the tech for diagnosing what went wrong. The bad part is you need the right tool/computer to interface with it.

    Since $$$ is the big issue the best solution is to try and find another 4l60-E out of something. Even buying a whole vehicle for the (working) tranny will be cheaper than a rebuild.

    Eml. #2

    BTW, yes, you can use the Type F fluid. That’s what all my sources say now but I prefer Dextron III because the seals are supposed to last longer.

    Also yes, 4wd is different tailshaft extension housing and shorter output shaft, so it would bolt right in if it's from a 2wd Astro. Not even sure if the AWD Astros are the same a 4wd or are they the same as Typhoon/Syclone. Need to measure the length before he pulls it.

    Pretty funny how you get "experts" with the TH350 solution. Especially buying custom adaptor plates etc is likely more $ than finding a donor vehicle. GM did not make 23 valve body designs, they made 3 (obviously the new ones were an improvement), I believe, although quite naturally there are many different CALIBRATIONS depending on the application. No reason 700R4's can't be built to last up to about 600hp reliably, or about an 11-12sec car. Beyond that and the input shaft is the weakest link, and will eventually fail, either the shaft itself or it will pull apart the aluminum to steel joint where it interfaces the input housing. No one makes a billet steel shaft and housing assembly yet (or ever will, likely) because there isn't a market for it. Because of the Buick GN guys the 200-4R got more attention, and there are many aftermarket parts, and a 200-4R, although weaker in stock form, can be made stronger (and more expensive) than the best 700R4. GM never "perfected" the TH350 either, it just has more margin than the 700R4. Yes, TH350's are most definitely stronger than the average "built" 700, unless lots of bucks are thrown at the 700, but so what? We are talking a 4.3L truck…

    Best bet is a wrecked Jimmy to pull the trans out of. Or maybe he has a buddy close by who has some experience on trannies who can help him rebuild, even a bandaid job (3-4 clutches only).

    If he got really lucky maybe the TH350 could be scabbed together but better plan the whole swap out first and budget for adaptor plates, driveshaft mods, finding a 4wd trans, etc. Then deal with the computer codes and no overdrive and no lockup. And lose money every time you drive it because of fuel consumption.

    Before I did that I'd put a regular 4L60/700R4 which is readily available in 4wd but there will be some changes, like with the lockup converter (700 is either on or off, 4L60E is pulse width modulated), and you'll still have computer trouble codes to deal with.

    So there you have it, folks, an independant unbiased opinion... based on many years of building 700R4's....
  7. neetchracer

    neetchracer Junior Member
    Messages: 26

    I am the trans guy at a GM dealership. Although I am not familiar with your problem, finding a used trans in the best bet.

    I'm not saying it can't be done, but a TH-350 in a 96 OBDII truck is just plain gay. There are inputs and outputs to make the vehicle run and drive properly from any electronic GM trans that need to be there. It may work OK in a 95 or older, but not in a 96 on up........whole different ball game.

    A 2wd trans will not work unless the outputshaft is changed.........basically taking most of the trans apart. Go with a used one.
  8. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    3rd email....

    I made a typo where I said :" Also yes, 4wd is different tailshaft extension housing and shorter output shaft, so it would bolt right in if it's from a 2wd Astro."

    Should read: "Also yes, 4wd is different tailshaft extension housing and shorter output shaft, so it wouldn't bolt right in if it's from a 2wd Astro."

    wouldn't vs would…makes a bit of a difference!