GMC auto transmission squaks...

Discussion in 'The Garage' started by FlySniper, Nov 15, 2012.

  1. FlySniper

    FlySniper Bleh...

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    2001 GMC Sonoma pickup:

    About two years ago I replaced the valve bodies in the tranny. The kit had a bunch of "upgrade" stuff (Corvette bits) and has banged into second gear ever since.

    Now, instead of the bang it just sort of squaks/groans going into second, especially when hot or when under load. The fluid is still clean and clear (as was the original stuff), no metal flakes or burnt smell. It doesn't slip or misbehave, it just makes a nasty noise with the 1-2 shift and occasionally on the 3-4 or 4-3 shift.

    Could it be the bands are out of adjustment? Something more sinister? The super clean fluid is throwing me off....
    #1
  2. troidus

    troidus Long timer

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    Sounds like whatever is bypassing/defeating the 1-2 accumulator (assuming a 700R-4/4L60/4L60E has one) has failed.
    #2
  3. Camper292000

    Camper292000 Adventurer

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    bought a 99 silverado in 2001 used from ripoff Bill heard chevrolet. It would slam from 1 to 2. Went back and this NICE guy there said hold on....plugged some high tech thing into the tranny and put in a different program. Slamming gone.

    It still shifts are in towing mode, but that's probably normal.
    #3
  4. concours

    concours WFO for 41 years

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    Band adjustment went the way of contact breaker points. ( a few Mopar trans. excepted) Your transmission has long travel servos, no adjustment. The groan is slippage. It is headed out.
    #4
  5. Benesesso

    Benesesso Long timer

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    While we're on the subject of GM auto transes, my 1995 4T60E has a weird problem. It makes a funny noise whenever the shifter is in L. If I move the lever out of L the noise instantly stops, even tho the trans is still in L (like 5 -10 mph).

    I think there is a "Low band" that is applied when the lever is in L, but why the noise? It's been doing this for years, not getting any worse. Sometimes in heavy stop and go traffic I like to pull the lever down to L, but I don't want to screw anything up, so I don't.
    #5
  6. troidus

    troidus Long timer

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    It'll be in the valve body, most likely. Different passages are active in manual low than are in drive, even if all the clutch packs and whatnot are in the exact same operating position. Now that you mention it, I think I recall hearing some extra noise from my 700R-4 when I had it in manual low.
    #6
  7. FlySniper

    FlySniper Bleh...

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    I went back and looked at the paperwork that came with the kit. This transmission is a 4L60E, so no real band adjustments... but TransGo has a way of shimming the servo pins (or grinding them shorter). Sounds like a bad idea/band aid fix.

    Looks like it's time to shop for a manual transmission, ECU and gauge cluster (and pedals and console and.. and .. and... .... Hmmm, maybe I should just shop for a nice Nissan or Toyota.).
    #7
  8. FlySniper

    FlySniper Bleh...

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    Yep it has a 1-2 accumulator. The one I installed was for a C-4 (6?) Corvette and went in literally upside down from the stock unit. .... I wasn't comfortable with it then and am a little suspicious of it now, even though everything I found verified that I installed it correctly.
    #8
  9. Benesesso

    Benesesso Long timer

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    UPDATE

    Just checked the trans. fluid, ~2 qts. low. Added 2, noise is GONE! :clap
    #9
  10. fritzcoinc

    fritzcoinc Enjoying my last V8

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    2 quarts low!
    Good God, when was the last check? During the Nixon administration?
    Was it even on the stick?
    #10
  11. groop

    groop So much to ponder

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    Interesting. I have 2000 Silverado that does that only sometimes and only after driving at least 100 miles. Like yours, it only shifts hard between 1st and 2nd. I've been reluctant to take it in because it's almost impossible to duplicate without taking a tech on a long roadtrip.
    #11
  12. Benesesso

    Benesesso Long timer

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    Not Tricky Dick's, but Slick's. Yes the oil was on the DIPstick, at least until I wiped it off. But since you begged, you're going to hear the rest of the story (repost from a few years ago here).

    GM 4T60E Automatic Transmission Problem--Hot Trans. and No TCC/OD (Torque Converter Clutch/Overdrive-4th Gear)

    Cheap Fix for TCC/4th Gear Problem


    My 1995 Pontiac Transport with the 4T60E trans. developed the rather common problem of losing TCC/OD when the trans. fluid got hot. First I installed a small trans. cooler in front of the rad.&A/C cond. Tried piping it both ways-with and w/o the rad. cooler. It worked much better in series, with the fluid going thru the add-on last.

    But the problem remained-it just took longer to lose the TCC/OD. Did a LOT of research into the problem. Seems some moron trans. engineer in GM designed the TCC-apply valve such that the slightest leakage which got past the valve (steel valve sliding in the soft alum. valve body) would cause the TCC to disengage. The "stupid computer" would then sense the RPM mismatch. It had commanded the TCC to apply, and therefore didn't expect any RPM difference in/out. It then decides to prevent 4th gear (OD) from engaging, so you are supposed to drive home in 3rd gear and no TCC.

    I live in Phoenix and the trans. temp. sensor never got hot enough to set a code. The problem was the trans. fluid getting thinner as it got hot.

    I believe Trans-go or Sonnax makes a kit to replace this valve and add a steel bushing (what the trans. should have had originally), but it appears the trans. has to be removed to install it.

    Fortunately there is another answer.

    I decided to take a chance and use a thicker trans. fluid. I knew I was going to have to pull the trans. anyway if it didn't work, and then I'd have it rebuilt with the stronger heat-treated stuff etc. that also should have been used originally. I also wanted to re-gear it lower, because even with a good-running 3.8 the trans. was way overgeared, at least for me.

    So, after MANY phone calls, etc. I bought a 5 gal. pail of 50 wt. "Powershift" trans./hydraulic clutch fluid from a Caterpillar dealer. This fluid is used in earthmoving equip.that has wet clutch packs, and also comes in 30 and 10 weight. I dropped the pan and refilled the trans.-you can only get ~50-70% of the fluid out. Refilling with the 50 wt. gives about 30 wt. with the fluid that remains in the converter. What all this means is that I gained ~30-40 deg. F on the viscosity of the trans. fluid, and the problem disappeared. It has worked fine for ~9+ years and 50,000 miles so far.

    The fluid is not too expensive-I think I paid $85 (2011 price) for the 5 gal. They don't sell it in smaller amounts.

    Several cautions besides the "do this at your own risk". Because I live in Phoenix, the lowest temp. is ~30 F. That means the trans. fluid is about like reg. ATF at 0 or -10 F--no big deal. But if I lived where it got colder I'd have used the 30 wt. for ~15-20 F "advantage".

    I wonder how many millions of $$$ have been paid to trans. shops and GM dealers because of some moron "engineer's" blunder many years ago.
    #12