Mechanics

WHILE DRIVING IN 2WD OR 4WD IT SEEMS TO SLIP INTO NEUTRAL, AND SPPEDOMETER KEEPS CLIMBING.

1996 Chevrolet Suburban • 217,000 miles

I have a 1996 Chevy Suburban K2500 7.4L 454 4X4 with 217000 miles. Originally, driving the truck to about 40 mph would appear to slip into neutral, while the speedometer kept climbing. Stepping on the gas made the speedo go faster, but the truck did not. Once you slowed down to about 20mph, it would make a very disturbing sound like it was slamming back into gear, and you could accelerate again. At first, you could engage 4WD and it would drive up to 70mph without slipping at all. It has deteriorated to a point that driving in 4WD does the same thing now. I didn't think it was the transmission, because it drove fine in 4WD for a long time, so I suspected the transfer case. I have inspected the transfer case, and the chain and gears seem to be in good condition. I was told it could be the TCCM or the transfer case mode fork or pads. The pads are a little worn and chipped, but is that sufficient wear to cause it to act like this? What is the function of the TCCM in this process? Where is the TCCM located? I was told in the door panel, and under the steering column, but haven't really located it yet.
What further steps can I take to troubleshoot this effectively?
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SantaFeBiker
October 12, 2011.




Your TCCM is under the dash on steering column bracket. Your speed sensor is on teh tcase so if it sppedsup and you don't go faster it may be teh trans screwing up as there is a speed sensor on the input shaft as well. The slamming in and out may be one of the clutches inside the trans going in and out either from an electrical problem or failure. It also could be the tcase slamming in and out due to the trans. The TCCM is more for shifting in and out of 2wd/4wd. We can't see how worn the pads are but if this is original you do have high mileage on it. I really think you should go to a trans shop so the guy there can scan it and give you a better perspective of this. The only other thing I can think of is that it doesn't engage the tcase correctly. But I wouldhave the trans checked first.

Hmac300
Oct 12, 2011.
Originally, the problem was ONLY in 2 wheel drive. I drove a thousand miles in 4WD without a problem ever. I was able to pull a 30ft. Trailer in 4WD for 80 miles at 60mph without the trans slipping once. Only until recently, does it do it in 4WD. Is it at all possible the transfer case is slipping into neutral? It has a shifter on the floor, not push button shift. 4WD low seems to be OK still.

Tiny
SantaFeBiker
Oct 12, 2011.
I think you have a new venture 243 t case. IF you get an intermittent grinding noise then check the shift linkage for binding and if that's ok, remove the rear output housing and check for a broken snap ringon the rear bearing. Again I don't know how worn your pads/forks are so I can't comment on that. But if it doesn't go into gear all the way then you could also have a bent shift fork or rod.

Hmac300
Oct 12, 2011.
Its a 241 C transfer case, and the mode fork and rod look fine. I want to think that putting it in 4WD affected the tranny in a way that it didn't slip at first, but has finally caught up with the 2WD problem. I would have a warm fuzzy feeling if I knew the tranny would act differently in 2WD then in 4WD. I believe I have a 4L80E tranny, and I would like to know if there would be a better choice for a tranny that might give me better mileage, since I don't really need the 10,000 lb towing capacity anymore. I read a Bowtie Overdrive 700R4 might be suitable.
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Tiny
SantaFeBiker
Oct 13, 2011.
The 4l80e is a lot better trans than teh 700r 4. It's an electronic version and has way fewer problems. Not much you can do about fuel mileage with a 454.

Hmac300
Oct 13, 2011.

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