Gear Lube

[steveimpala]

I have a 1969 C20 with the 4 speed ( 435 closed-ratio ) manual transmission. I need to change the oil, any suggestions on brand / weight that I should be using ? FYI... the truck has 88K miles on it.

Thanks !

[Sheepdip]

Originally Posted by steveimpala

I have a 1969 C20 with the 4 speed ( 435 closed-ratio ) manual transmission. I need to change the oil, any suggestions on brand / weight that I should be using ? FYI... the truck has 88K miles on it.

Thanks !

I use Lucas Synthetic 90 wt in both the tranny and rear diff.

[steveimpala]

Thanks !

[mr.mud1]

good advice.

[jeffahart]

Here you go. From Novak, plus they warn against flat towing. Info if you're interested.

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

When filling your 435 with gear oil, we recommend that you select a conventional mineral oil or a para-synthetic in lieu of a full synthetic oil. Properly assembled manual gearboxes do not have the thermal strains seen by combustion engines or hypoid gears. Synthetic fluid in these gearboxes, while not harmful, is probably an economic waste.

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.



A Cautionary Issue on Towing
Improperly flat-towing (pulling a vehicle not under its own power) any vehicle with the NP435 transmission can cause the very prompt destruction of third gear bore and its mainshaft journal due to insufficient oiling.

If you must flat-tow, and have a transfer case, you may set it in full neutral and place the NP435 in any gear to prevent mainshaft spin. However, note that many transfer cases themselves do not allow for flat towing.

Preferably, you may wish to disconnect the rear drive shaft. Rear axle lockout hubs may be a worthwhile addition for this reason.

We have seen and heard of a few incidents of this over the years, the worst of which producing a complete friction welding of third gear to its mainshaft.

This is one of the only quirks of the 435, and easily avoidable.

j