94 3500 doesn't seem to shift when 4 low is engaged

Krash

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So finally got around to picking the truck that I wanted after looking for a month and a half. It's a 94 GMC 3500 crew cab 4x4 with a 454 and 4L80E transmission. Everything seems to work fine except for when four low is engaged. When four low is engaged it doesn't seem to shift through the gears on the transmission as it normally would. And on one occasion it shifted only when it got to a high RPM and hit kind of hard. I've never seen anything like this any suggestions?
 

Krash

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I've had quite a few four-wheel drives and I could have sworn they shifted in four-wheel drive low. But after just doing some reading, I read that the wheels aren't going fast enough to trigger the transmission to shift. Which could be a good point. And please correct me if I'm wrong I just thought in the past putting it in for a low it goes through the gears normally as it would in four high or two wheel drive.
 

454cid

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It should still shift, you'll just be turning more rpms and going slower.

I dont believe wheel speed has any bearing on the transmision shifting.
 

Krash

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It's a 94 and it has the 4l80e, on the column there's 2 D's like you would see for the 700r4 transmissions. I've never seen that on a 3500 with 4l80e. Usually it only has the one D. I think maybe I didn't have it in the overdrive option when this happened.
 

Nad_Yvalhosert

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I've had quite a few four-wheel drives and I could have sworn they shifted in four-wheel drive low. But after just doing some reading, I read that the wheels aren't going fast enough to trigger the transmission to shift. Which could be a good point. And please correct me if I'm wrong I just thought in the past putting it in for a low it goes through the gears normally as it would in four high or two wheel drive.
Tire speed doesnt trigger transmission shift, engine RPM, throttle input, and driveshaft output speed makes the combined decisions.
Low range has a max speed of about 45 MPH, so itll shift every 7-9 mph. You wont feel it.
 

Krash

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Tire speed doesnt trigger transmission shift, engine RPM, throttle input, and driveshaft output speed makes the combined decisions.
Low range has a max speed of about 45 MPH, so itll shift every 7-9 mph. You wont feel it.
Considering the truck has 456 gears wouldn't it shift even faster or at a even a lower Mph per gear with a lower top speed?
 

dave s

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4:56 gears! Yes it would shift quicker and at lower speed than say 3:73's. I have no idea why it would wind out and not shifht though. The 4:56 brings back old memories. Mid 70's I just got out of basic training and saw this Nova for sale. Took a spin and said wow! I'll take it. Drove it from Texas to PA with 4:56 gears, lol. I was only 17.
 
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4:56 gears! Yes it would shift quicker and at lower speed than say 3:73's. I have no idea why it would wind out and not shifht though. The 4:56 brings back old memories. Mid 70's I just got out of basic training and saw this Nova for sale. Took a spin and said wow! I'll take it. Drove it from Texas to PA with 4:56 gears, lol. I was only 17.
You'll be pleased to know it's still a standard joke amongs all branches that fresh boots IMMEDIATELY all go purchase dream machines (stereotypically, a mustang at 33%APR) lol
 
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