4spd np435 fluid

[1971ford]

What fluid do you guys recommend to put into my 4spd np435?

Do you guys believe that buying an expensive fluid would help milage enough to pay for itself plus more?
Is the only to put fluid in to the tranny to pull the top cover and put it in the top? How much do i put in? Should I drain everything and start fresh or can I top off?

[1971ford]

ok sounds good I'll replace all the fluid.
I'll go for the higher end stuff i suppose since it isn't too much more and might get me .0001 MPG's
I need to do the same with my rear diff.
The fill plug won't be hard to find since my tranny is all cleaned and has fresh paint. I forgot to look for it earlier.
My fluid is about half way up the gears right now.

[fordman]

when toppping off a fluid in a trans or a rear end. you use the filler hole and fill it until it starts to try and run out the fill hole. that is when you know its full. when checking it. you remove the plug and stick your finger in there plug hole. if you can touch the fluid by barely putting your finger in. then it is full.

[Caseys71]

Checked and your tranny takes 3.5 qts. like fordman said it is best to fill it by the plug so you don't under/over fill but since you know it takes 3.5 qts. you could fill it from the top and only add 3.5 qts. and it would be just as easy as filling it at the plug . As for your fluid being half way up the gears that sounds about right, I believe that was about where mine was at once I filled it, I guess what I was trying to say/should have said was that you don't want to fill it past the top of the gears or all the way up to the rim of the case just like you don't want to over-fill your oil in your engine.

[1971ford]

I got a gallon of 80w90, not the super special stuff but It'll do just fine.
This weekend I'll swap the oil out with the new stuff.

Thanks for the help

[1971ford]

what about my rear diff, I looked in the fill hole when adding more oil after re-doign the brakes and it looks like mud in there.
80w90 work well for rear diff??

[fordman]

yes that is what is used for the rear end also.