Hey everyone I have a NP435 that won't downshift into second when cold ( California cold so 40 deg), after about 15 minutes or so of running it shifts like a dream. Any Ideas? It currently has 80w-90 gear oil and was re-manned at some point in its life due to the re-man sticker on the side. Its out of a junked 72 but has my old shift tower due to tower heights differing.

Side note/ questions- I've heard people say my issues are from bad synchro's but how can you tell when the tranny is apart? What should they exactly look like or feel like to be deemed as still operable? I had my old np435 torn apart for a month or so due to second gear grinding issues after it jumped out of third and having to replace the shift shoes and oil. I've looked at everything and they all look ok but this was my first time rebuilding and taking apart a transmission and I had no clue as to what may be considered a good or junk synchro or even if other components were still good to be used again. I through it back together yesterday so it still wasn't in a million pieces before I head back to school in a couple weeks.

Thanks for any help- Henry's 66

 

You might have a problem with synchronizer clearance not being adjusted quite right and when the transmission metals heat up that clearance changes to be within spec. Synchronizer clearance should be set to 0.050-0.070 inch. The procedure is in the 1966 Shop Manual Volume 1 Page 6-68 New Process Model 435. Step 1 talks about checking the distance between the synchronizer and input shaft gear. If that distance is more than 0.043-0.053 inch install the necessary thickness of shims between the third-speed gear and the synchro brake drum. Then in Step 11 they talk about using specialty tool T64T-7000-A to help with the adjustment of the input shaft clearance - installing a shim pack as needed to get proper clearance and once that is adjusted then recheck the synchronizer clearance.

https://www.ebay.com/itm/224902530809

 

Thanks I'll look in the shop manual and test the clearances. This has been one of the most helpful comments I've gotten in a while with helping me understand why its doing what its doing.
-Thanks again Henry's66

 

I also find with most older manual top shifted transmissions (T18 / T19 / NP435) when cold they shift hard till you drive a bit to warm them up.
I had a Toyota L/C that was that way and living in New England it got really cold at winter time. I would kick the transfer case in N, trany in gear and let it warm up as the motor got some heat to heat the cab.

My 81 F100 has a NP435 and when cold is hard to shift up & down till it gets some heat in it.
I have over drive between motor & trans so I kick it in OD, trans in N and let it warm up, carb with a choke, while I get my self together.

The other thing to try is running Red Line M90 gear oil in the transmission.
It is a little thinner but made for manual trans and did help mine to shift easier bout cold & hot.
It is not cheap but unlike todays gear oil (w90) that is GL5 spec and not good for yellow metal in manual transmission the Red Line is good to use.
They say you need GL4 or older w90 gear oil not to hurt the yellow metal in the trans.

BTW I got to be going pretty slow to down shift into 2nd gear.
3rd gear up or down I have to double clutch, bad syncro I am sure.
Dave ----

 

Thanks for that, I'll look into different oil and ill just let it warm up some more before I head down the road.
Thanks - Henry's66

 

I have the T-18. After seeing something here on FTE then doing some research, I found that 50 weight oil was specified or appropriate for these transmissions. I switched from 85w-90 to the 50 and found it shifter easier. Mine was not bad like you describe, but it was a little tough. I use the conventional Valvoline.

In addition to what TA455HO notes, you might check your clutch adjustment - it could be that you just need to get more throw on the clutch. About 9 months ago I started having trouble shifting and thought I might be in need of real work, then I found my z-bar was cracking and flexing, and I wasn't getting enough clutch travel because of it. Welded up the issue and the tranny worked just fine.