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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3320
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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I have an 1996 Isuzu NPR with a recently rebuilt

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I have an 1996 Isuzu NPR with a recently rebuilt transmission. First and second gear work fine. When going down a hill it will even shift to overdrive. However third gear is not engaging. Pinned out the shift solenoids. They are all within spec. Fluid and filter are spotlesa. Could it be a valve body problem?

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If the solenoid for sure is good on fresh plates in the transmission, I would check the valve body as you suspect. There may be a gouge in it, a piece of gasket leaking by one of the valleys, or something else that is causing the pressure to drop away for that particular gear. With you getting the other gears, I doubt it is a clutch issue in the transmission from the disk flipped for you would lose all forward gears. This sounds more like a pressure issue with either a defective solenoid by having debris in it (even if it ohms good, could still have something blocking the port) or a valve body concern.


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Customer: replied 7 months ago.
Sorry didn't get to check it today. Is there a specific valve body to check for third gear only problems?

There is only 1 valve body. The mapping is hard to understand. If you are good on transmissions, pull it and look at the seal. You can see if it is cracked. I am hoping there is no issue with the front band and it is in the valve body. On new parts, there shouldn't be a front band issue...

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