Auto trans slipping in 4th?

Hacksterbaby

New Member
Hey all,

92 LS automatic, 208K. Engine well maintained, purrs like a kitten. 100-mile daily round trip commute. It's recently started stumbling when it gets up to highway speeds (>60mph; usually run 75-80). At first I thought it was the engine missing, but that didn't seem to make sense since it idles fine, accelerates and shifts through all the gears fine, etc., so that seems to rule out fuel pump, fuel filter, timing, vacuum leaks, etc. Once it starts the stumble is fairly continuous and ranges from real light to real noticeable.

It appears that it may be confined to 4th gear. Trans fluid level is fine, nice bright red. The only tranny-related part covered in the Haynes book that I'm *not* sure that it's *not* is the vacuum modulator, and I'm not sure what that is, what it does, or what it looks like (no pics in the book). Is this something that *might* be the problem, and if so, any help on finding/replacing it? Or any other thoughts on what it might be, if not the tranny? Any and all ideas appreciated-- thanks.
 

Hacksterbaby

New Member
Okay, so it's NOT the tranny (whew!) Started missing at fast idle today after a cold crank, and missed a little in the lower gears. Seems to be getting worse at highway speeds.

check into your distributor mine just went out on me and would stumble like you are describing
Could be, but I just replaced the cap and rotor not 5K ago, and the plugs and wires are less than six months old. I'll go through all that stuff just to be sure, though.

Also gonna look again at FITV-- cleaned and tightened it five or six weeks ago, and it still had a little vacuum after the motor was warm (not supposed to) but had been running just fine since then, until this week (plus, I don't think it's supposed to have any real effect above idle speed). I'm also thinking maybe vacuum leak, fuel filter, or (shudder) fuel pump...:cry:
 

Hacksterbaby

New Member
check into your distributor mine just went out on me and would stumble like you are describing
You nailed it, pretty much. Haven't had time to work on it for a couple weeks, or else the weather's stunk.

Got to thinking about it and remembered- when I replaced the rotor, the head on the shaft screw was wrecked (somebody tried to change it before, and failed) and I had to drill it and use an extractor. Used another screw on the new rotor that was the right size, but not real snug. I had tightened it good but didn't use any loctite. Hmmmm....

Sure enough... pulled the cap off, and the screw had come *completely out*. Rotor's just sitting there, loose on the shaft (and even though it was stumbling a bit, the thing still got me back and forth on a 100-mile daily round trip commute for over a week before I switched over to my truck). Found a better screw and used loctite this time. Test drive... perfect. My daily driver's back.

Thanks for the suggestion.
 


JdmBoi

Edm_Bo
sometime the cold can cause this to. i remember when i was driving my friend car and out of no where the tranny would jerk or slip you may say real hard and i didnt know what it was but after driving his car i found out it only happen when weather cold so i geus that could be the problem
 

gotgohan

Apprentice Mechanic
This is totally off topic, but the weirdest thing happend to my Chevy Cav. When I put a turbo on the car, my check engine light came on with a temperature sensor for the air. I just let it go because of I just added turbo to it, BUT THEN as I let it sit my trans would really really shift super hard in every gear until I fixed the air sensor problem.. what a weird thing taht was
 
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