Np 435
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Junior User
Joined: Aug 2003
Posts: 81
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From: Newtown, CT
Np 435
Hey, i just switched from a BW T-18 to a NP 435 tranny in my 1970 f250. Before with the T-18 i was cabable of going at least 70 + mph but now the truck will not go over 50. I know the NP 435 is geared low but i didnt think this low. Does anyone else with this tranny experience the same result? Thanks alot
Senior User
Joined: Sep 2000
Posts: 435
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From: Central Oregon
Most all manual transmissions without overdrive have a 1:1 output ratio, so it's pretty doubtful that you are actually going any different speed now. More likely is that you need to change out the speedo drive gear in the 435 to make your speedo read correctly. You could always check that by timing how long it takes you to go a mile at some set speed. I.e., at 60 mph it should take exactly 60 seconds to go a mile, 55 mph it would be about 65 seconds, at 65 mph it's 55 seconds, etc. Steve
Senior User
Joined: Sep 2000
Posts: 435
Likes: 1
From: Central Oregon
Should have added "in 4th gear"
Yes, that's certainly another way to check your actual speed. It's probably pretty obvious, but in my previous post I omitted the fact that your tranny is operating at a 1:1 ratio in 4th gear only. That of course doesn't affect the speedo readout in any event, but wanted to be clear. Steve
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Junior User
Joined: Aug 2003
Posts: 81
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From: Newtown, CT
I found out the gear ratios for the T-18 and the NP 435 and they were pretty similar from gears 1-3 but in 4th they were both 1.1 like you said. The NP was out of a f350 so when i swapped it i also had to change the output shaft to compensate for the smaller yoke joint if this makes any difference. I also have the speedo cable from the f350, should i try that?
Senior User
Joined: Sep 2000
Posts: 435
Likes: 1
From: Central Oregon
You will have to figure out which speedometer cable drive gear you need for your particular rear-end ratio and the size tires you are running, and then replace the existing gear in your 435 with the correct one. Neither the output shaft nor the speedo cable have anything to do with the speedo cable drive gear selection. The gear is in the side of the tranny where the speedo cable connects to it, behind a removable "keeper". You are looking for the plastic drive gear which has the correct number of teeth to make your speedo read correctly. Any tranny shop should be able to help you select and get the right gear, and probably a good parts outfit could do the same if they were willing to put a little effort into it! Good Luck!
