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4l80e no reverse

97gmc2500

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97gmc2500 New Member

97gmc2500

Posted
Posted

i have a 97 gmc 2500 hd with 6.5. at 86,589 i replaced trans that lost reverse. at 87,101 trans lost rev. again. brought back to dealer they found reverse band and drum brunt up. they replaced trans under warr. a few hundred miles later trans would delay going into foward or reverse after it was hot. dealer replaced pump assembly under warr. now a few months later reverse is blown again. dealer says it is same parts as first time. i was a gm tech for 11 yrs i've got no idea. any help would be great. scott

Haulin' 8.1 Enthusiast

Haulin' 8.1

Posted
Posted

After 3 1/2 trannies in such a short period I would be looking hard at factors exterior to the tranny that can kill it. I've only been a NAPA autocare tech for just over 2 years but I've got plenty of ideas.

 

Check trans cooler and lines for restrictions, kinks, touching exhaust, over corroded radiator, leaks. Keep in mind drivetrain movement can make close parts touch under load and rubber sections can collapse from movement or internal suction but look fine when on the lift.

 

Driveshaft length too long or being pushed into tailshaft when truck weighted down. Seen this after driveshaft replacements. Excesive u-joint angles and or binding at ride height. Frozen U-joints usually come in as a complaint of lurching off the start and warped brake rotors on the same truck.

 

Engine crankshaft thrust. Excessive fore and aft play in the crankshaft playing hell on the front pump of the tranny.

 

Transmission shifter linkage adjustment and operation. Linkage wear that causes inprecise gear selection on the tranny itself.

 

Miscommunication with the powertrain control module or it's wireing harness. A possible failure in the PCM causing incorrect operation of the transmission valve body. Check out the trans harness for corrosion at all connectors. Examine the pins and sockets for break offs or push outs. Go down the entire harness looking for overheating, chaffing, or splits especially when in close proximitiy to aftermarket equipment or after misrouting. I've seen a K&N filter kit rub through an emmissions harness that normally is covered by the box and cause me a whole day of work to find out why the EVAP system on the fuel tank wasn't working half the time.

 

Incorrect filter being used, sometimes trannys come with deep sump pans that require a different filter that reaches lower. If the regular filter is used it will suck air at times.

 

Incorrect dipstick? Had to be replaced in the past but got the wrong length, wasn't an issue until slow leakage brought level low enough to cause failure, now new trannies are underfilled from the start. Beleive me you never know what has happened to things unless you know, LOL.

 

Good luck,

Vernon

robsawatsky Enthusiast

robsawatsky

Posted
Posted

If there was internal damage to the tranny from this or previous failures, it is absolutely essential that the tranny cooler and lines are flushed and clean. I'd go as far as to change the tranny cooler completely. If crud from the cooler gets back into the rebuilt tranny it can kill it in no time.

Friz Enthusiast

Friz

Posted
Posted

This may sound dumb, but check your radiator level. One of my buddies had an older truck with the 6.2 and it would eat a couple of trannys a year. He finally figured out that he had a real slow water leak and the coolant level would drop enough to leave the tranny cooler dry. The truck never got hot so he never looked in there.

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