Hi everybody,
I have a question that I know will be hard to quantify, but I just picked up a '76 f250 4x4 with the NP435 4 speed and the trans seems pretty stubborn. I know it's a heavy duty trans, but it seems a little stubborn. For example, it will almost never engage 2nd from a stop without tapping 1st first (1st being a granny gear). And 3rd is very tricky to find and takes skill to engage. Also, down shifting while cruising from 4th to 3rd doesn't happen and usually results in grinding into any gear to recover. Except for the downshift grinding, it doesn't grind or half engage in other situations, it's just stubborn to enter gears. Clutch disengagement seems ok and not dragging. Is that just the nature of this beast or should I look for a rebuild kit/replacement?
Thanks!

 

IMO, the NP435 doesn't like to downshift, period. And don't ever try to downshift into 1st gear cuz it just wont.

Try double-clutching and see if acts differently - without grinding or feeling notchy. I'd prolly change out the gear lube just to establish a good baseline... ya did check its lube level, right?

I think ya need to drive if for a while to get used to your tranny's idiosyncratic behavior. It's like a new girlfriend.... she'll tell ya what she likes after a while.

 

141bpm, HIO Silver gives good advice,oil viscosity really affects the shifting on these transmissions.When I first got my truck I changed the oil in the shift cases to 90 weight thinking it would make them easier to shift,it wasn't too bad until it started getting cold up here then it got real hard to get in and out of gear. I drained the 90 and put in the recommended 65-80 weight and now it shifts much better but still a little stiff in the cold mornings until the oil warms up.Fourth to third has always been a slow move for my tranny as well as second to third.In my experience with the 435, when the tranny starts to pop out of third under acceleration then it's time for a rebuild.The gears in this tranny are huge so the thicker the oil the slower they move when shifting.You have to give this tranny a little more time when you shift, like HIO says, drive her easy for awhile.

"bowties in the rearview mirror"

 

From what I've seen, Ford spec'd 50wt motor oil for these transmissions, I've heard it makes shifting much nicer! I run 90wt in mine, and it's a grumpy downshifting into 2nd, but 3rd and 4th are no problem. The shifts are also very firm and precise, it's not bad to drive at all.

In these trannys there are some little nylon inserts on the end of the shift forks, I'd bet they've disintegrated over the years. Once they go the shifting will get very sloppy. They aren't hard to replace, and you can do it with the tranny still in the truck. Bronco graveyard sells the inserts in a kit with everything to re-build the entire top cover/shifter housing for about $30, and it may not solve all your issues, but it sure will help!

Sam

 

Thanks guys!

Hio Silver, when I bought it a month or two ago I put my finger in all her holes...I mean...all the diff/trans fluids were good to go. I do this with all new girlfriends too
It's definitely got its quirks, but I'm getting the hang of it. Otherwise it seems pretty solid, never pops out, doesn't grind except that 4-3 downshift.

R-O F250, thanks for the heads up on the fork shims and being able to do them without pulling that cast iron beast. I've done those on T5's and noticed a difference.

Theres a guy on Craigslist here in Vegas that has a shop rebuilt NP435 for $200. Just wanted some advice before spend the $ on it for no reason. Could use that for other fixin'.

 

My shift lever doesn't return to center when released; it goes into gear fine but over on the 3rd / 4th gear side of the shift pattern it flops.

Does this type of kit address this issue? Is it very complicated? Thanks!

 

Well my 78 bronco has 105xxx miles and shifts perfect 4th to 3rd its gravy, 3 rd to 2nd can be done just just at low speeds. But I run 80-90 does shift slow in winter, might try the 50wt

 

50W motor oil and 90W gear oil are the very same viscosity.

 

I have a T-18 but it's basically the same tranny. You cannot go from 2nd to 1st unless you are at a dead stop pretty much, and going from 4th to 3rd grinds most times unless I try to lightly put it in 2nd (but not all the way) and then go back to third and it shifts in fine. Now speed shifting/high performance welcome here.

 

None of them return to center in neutral. Only the reverse gate is spring loaded to center. Definitely put lighter oil in for better shifting. I run one quart of Lucas and three quarts 50 weight engine oil in mine. A master rebuild kit from bronco graveyard is less than $200 iirc. This is about one of the simplest transmissions you'll ever build too if you want to try it yourself. Lots of writeups online, including a copy of a factory manual if you search for np435 rebuild instructions.

First I would try flushing it out with fresh oil.

 

141bpm: Glad I could help! And I hear ya on pulling that beast- I did it without a tranny jack once, and I've never been that sore before or since!

So the shifter flops/rolls/twists in ways it shouldn't? That's a classic symptom of wore out inserts, replacing them isn't bad. They're included in the kit I mentioned earlier.

First: Pull out your shift boot, the floor mat, anything else in the way (pulling the seat will help but isn't necessary) and transmission hump. You should be able to access the top of the transmission.

Then make sure the transmission is in neutral

It's your call whether to pull the shifter or not, but to pull it out there's a little metal cap where the shifter enters the top cover. All you have to do is push down on it and twist counterclockwise, and it will pop right out.

Then unbolt all the bolts on the top cover of the transmission.

The top section (aluminum) will seperate from the case (cast iron)

Take it over to the work bench and pull off the old inserts and pop the new ones on.
Here's a diagram of what the top cover looks like:
http://broncograveyard.com/images/ad...35shfthsng.jpg
The diagram calls the inserts "fork shoes", but they are the same thing.

Then, put it all back together. The only difficult part is getting the forks to line up with the gears inside the transmission. It might take a few trys, but it's not that bad.

Sam