Shifting
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Junior User
Joined: Jun 2015
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Shifting
Hey guys curious if I have an issue with my tranny or if this is normal.. I have the NP435 4 speed behind my 390. Obviously 1st is a granny so I never use it but when I need to downshift from 3rd into 2nd to turn a corner slow or parking spot I damn near have to be at a stop to get her in second.. Is this normal, that slow of speed?? 3rd bogs my already limping motor when I go to accelerate out of a turn..
Thanks,
Thanks,
Fleet Owner
Joined: Dec 2009
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From: NorCal
First gear is not synchronized so avoid downshifting into it. Second gear is synchronized but ya gotta be slow... double clutching sometimes allows it to be downshifted into second seamlessly. Try it.
The NP 435 is more or less a three-speed unless getting off the line with a heavy load or ambling up a slope.
.. and with 37s the gear spacing sucks monkey nuts. 3.90s or 4.11s in the rear would help but the first gear ratio x the rear gear ratio will be even shorter.. you'll be able to walk faster beside the truck with it idling in first gear.
The NP 435 is more or less a three-speed unless getting off the line with a heavy load or ambling up a slope.
.. and with 37s the gear spacing sucks monkey nuts. 3.90s or 4.11s in the rear would help but the first gear ratio x the rear gear ratio will be even shorter.. you'll be able to walk faster beside the truck with it idling in first gear.
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Junior User
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Clutch isn't bad have no idea how old it is. Have never tried shifting without using it. Stock gears 4.10 with 37s should be fine, she has plenty of power. The lugging in 3rd is the low rpm the motor is at while in that gear. I've been in plenty of rigs where they didn't regear with bigger tires and the loss of power is across the board.
Lead Driver
Joined: Nov 2006
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From: Pa.
I've been in plenty of rigs where they didn't regear with bigger tires and the loss of power is across the board.
At some point you'll come to the conclusion gears and tire size played a major role in it's down time .. The good news is they're fairly cheap to repair .. Think 4:56es and a 5-speed of your choice since you already have a divorced transfer case 
You should get some money for the highboy NP435 since it is somewhat of a specialty transmission .. Seriously though if your going to keep running 37" tires I would consider the 4:56es at a minimum and rebuild the NP435 with some good parts .. If you need help picking out the right parts I'd be glad to help ..
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Junior User
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Thx guys. I love the NP435 so I will be keeping that. The 37s came on it, a bit to big bit they are brand new so I'm gonna run them until they go and then hit 35s. I may just have to deal with it for now. I am goon to double check the clutch though. Just for the heck of it what would 4.56 gears run a guy if labor was done by me?
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Mountain Pass
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Thx guys. I love the NP435 so I will be keeping that. The 37s came on it, a bit to big bit they are brand new so I'm gonna run them until they go and then hit 35s. I may just have to deal with it for now. I am goon to double check the clutch though. Just for the heck of it what would 4.56 gears run a guy if labor was done by me?
Sorry had to gloat a little, good gear ratio, I highly recommend
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
Ck the clutch adjustment, and with a NP435, 2nd is 1st so to speak. So yea you need to be all the way in on the clutch and coming off the RPM's to go from 3rd to 2nd.
But sometimes a double clutch and a throttle blip will work too.
Stock or tired motor and stock gears and small tires you can get by. Stock motor, bigger tires and stock gears you are working that clutch and that tired motor over for no reason.
A rear gear can make for the feeling like you got a whole new truck.
But sometimes a double clutch and a throttle blip will work too.
Stock or tired motor and stock gears and small tires you can get by. Stock motor, bigger tires and stock gears you are working that clutch and that tired motor over for no reason.
A rear gear can make for the feeling like you got a whole new truck.
Lead Driver
Joined: Nov 2006
Posts: 5,217
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From: Pa.
Just for the heck of it what would 4.56 gears run a guy if labor was done by me?
Rear axle - YG D60-456
Front axle - YG D44-346
You'll have another $150 per axle in rebuild kits if you choose to rebuild while your in there ..
More info
https://www.yukongear.com/DiffDetail...%2b30%2bSpline
https://www.yukongear.com/DiffDetail...ard%2bRotation
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Junior User
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Thanks for all the info guys.. Reading that chart on mileage and power it may be smart to go with even a 4.88 for the 37's......
Curious to anyone out there that has the Np435/390 with 4.56 gears with 35 or larger tires.. How does you rig run? What the RPM on the highway and what the power like off the line. Or any experts have an opinion on this..
Curious to anyone out there that has the Np435/390 with 4.56 gears with 35 or larger tires.. How does you rig run? What the RPM on the highway and what the power like off the line. Or any experts have an opinion on this..
Lead Driver
Joined: Nov 2006
Posts: 5,217
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From: Pa.
It 's going to depend on how many horse power the 390 is still producing and what kinda of driving you're doing most of the time .. Is it a daily driver ? Do you tow with it ? Off road ? etc. The more info you can give us the better ..
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Junior User
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Early October I'm gonna put a crate longblock in it.. Going to ad a mild cam and headers to it.. Its a daily driver, highway on occasion. I'm in a small town so my commute is maybe 2 miles each day so I don't mind crappy gas mileage, just want to make it reliable with some power!! No towing and rarely off road anymore..
Lead Driver
Joined: Nov 2006
Posts: 5,217
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From: Pa.
Based on your driving habits I think I'd go with the 4:56es and then if you feel it needs a little more drop down to 35" tires next time you need tires .. Have you done any mods to the steering or is it still power assist ?
