NP435 4sp Trans (fill plug question)

[KevinK7]

My '68 C20 has the Close Ratio NP435 4SP Trans. I'm planning to change the fluid and wanted to confirm I have the plugs ID'd correctly. The Drain seems pretty obvious, but the Fill seems low on the casing, I thought it would be more towards the top.

Thanks in advance,

Kevin

This photo is of the PASS side of trans



For those interested, here are the codes on it:

[kwmech]

That is correct..fill it 'til it runs out

[WorkinLonghorn]

Don't forget to clean that fill area well before removing the plug and also be sure NOT to use "Hypoid" oil.

"Hypoid gear oil is sulphurized higher than transmission oil and can be mildly corrosive to the non-ferrous alloys used for synchros, bushings and thrust washers in these transmissions.

An 80W-90, API-GL5 or MT-1 rated fluid is very good. Some claim faster shifts from using a 50W engine oil in their transmission and we do not consider this to be contraindicated unless you operate your vehicle in a very warm environment".

https://www.novak-adapt.com/knowledg.../manual/np435/

-BA

[KevinK7]

Thanks for the replies, and I'll definitely clean well near fill before I even loosen the plug.

Do NOT use hypoid oil?

Based on a number of searches, I purchased a gallon of Valvoline Full Synthetic 75W-90 Gear Oil that is GL-4/GL-5 compatible. https://shop.advanceautoparts.com/p/...505/12048192-P
I just checked and it states, "SynPower Gear Oil is specially recommended for limited-slip hypoid differentials".

Upon further review (and thanks for the input on the low sulpher content) From what I'm reading there are brass synchros in the NP435, so I'm not going to take any risks. A bit pricey, but it's worth saving a tranny.
https://www.amazon.com/gp/product/B0...5E2OBSIO&psc=1


Thanks again,

Kevin