C6 or Np435?
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C6 or Np435?
My 96 F350 4x4 with the 460/C6/BW4406 combo gets terrible mpg. I have 33" tires on it and still at 55mph I am at 2200rpm. I also want more low end grunt for pulling my trailer. I have an NP435 tranny with the 351m/400/460 bolt pattern and would like to put it in my truck. I also have the transmission to t-case adapter as well as an NP205 to use. The only thing I really need is a new flywheel and I'm set. I was just wondering what you guys would do if you were me? Would you do the tranny swap or keep the C6 and do something to boost power like a chip? I already have long-tube headers and a cat-back dual exhaust on it. I still need more power and I think the C6 is robbing too much off the line. I can't go smaller on the tires because I need the clearance and my highway rpms are too high already. I need help.....
Fleet Mechanic
Joined: Mar 2005
Posts: 1,603
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From: St Louis
A NP435 is a great tranny, but like the C-6 it only has a 1:1 final gear ratio out to the axle. You wont be gaining anything on the highway, also if the NP435 came from a 351M/400 you will need to increase the distance between the tranny and the motor due to the input shaft. 460's flywheels are further into the bell housing than the 351M/400 even though they both share the same bell housing. If you want to go manual and get a tranny that is a bolt in for the 460 as well as has a high gear to reduce the highway RPMS a ZF5 would be the way to go.
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Not to be rude but I have the np435 and not a zf5 so that is not one of my options. I also know that the c6 and 435 have the same final ratio but I want more low end grunt. Would you guys take the c6 or np435?
Fleet Owner
Joined: May 2009
Posts: 21,437
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From: Gilbert, PA
Its all prefference. Do YOU like to shift? If not use the C6. If you like shifting use the 435.
As for the zf i know more than 20 ZF5 transmissions w more than 200k+ miles without one problem. Most behind diesel and big blocks. The BBF gasser pattern ones go for cheap
As for the zf i know more than 20 ZF5 transmissions w more than 200k+ miles without one problem. Most behind diesel and big blocks. The BBF gasser pattern ones go for cheap
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Fleet Mechanic
Joined: Mar 2005
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From: St Louis
Personally, I would take a NP-435 over a C-6 anyday. I am biased because I learned to drive the NP-435 first, and it just has more gears than a C-6. I also just like shifting gears and working the clutch.
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Joined: Feb 2003
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From: Muskegon, MI (home)
If you are looking for brute stump pulling low end torque, the NP435 is king it has a super low 6.69 to 1 ratio first gear. That is much lower than the C6 (not sure what ratio) and still lower yet than a ZF (5.72 to 1). For straight up bulletproof reliability you just can't beat the old granny 4 speeds. I broke the pos M5OD in my 96 F150 (formerly 4x2 now 4x4) and swapped in a ZF 5 speed I absolutely love it. It still has the same ratio OD as the M5OD, but has that nice deep first gear for towing and 4 wheeling. So you have the perfect combination of good low end grunt for work, and a nice tall overdrive for cruising on the interstate. To answer your question, I would say go with the NP435.
Senior User
Joined: Apr 2003
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From: Southeastern PA
I swapped a T18 in place of my 91's C6 and couldn't be happier. It's very nice being able to use gearing to slow you while towing, and driving it how you want to. I usually skip 3rd unloaded and the 460 does not care at all. Even with 3.55's it does leave overdrive to be wanted. I am looking for a ZF5, but will miss the T18 when it goes.
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I have (4) C6's, (3) NP435's, (1) T-18, and (1) SM465. What do you guys like the best and would you use? I know the SM is GM but I thought I would throw that in there in case one of yall wants it...haha.
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