I've got the 73 Explorer pretty well ready to go; new tires/wheels, Flowmaster Super 44's, plugs/wires/cap &'internals. Looking to change the transmission and rear diff lube and not sure what viscosity is correct. My owners manual doesn't go into detail, while the Haynes book says the trans is 140w and diff is 90w. Is this correct? I find it hard to believe the tranny would require 140w, that stuff is like mud....my trans is a 3 sp on column and rear diff is an open 3.90.

 

90W in the rear diff sounds correct and yea I think the same in the trans. Hang on some one else will wake up and help us out.

Ever thought of synthetic in the diff?

 

Great idea on the synthetic....

 

I heard that anything that will make for less drag applied to any dragging surface will help with to increase speed, but maybe thats horse pucky?

Sounds like that's a old drag racer urbane legend thing?

 

Not really anything urban legend about it......it's just simple physics. Any time you can reduce the forces acting upon a body in motion, that body will continue to be in motion longer. More to the point, if you have so much engine power acting upon a body in motion in one direction, and you have other forces acting against it (wind resistance, friction, etc.), you can make better use of the engine power if you can reduce or eliminate parasitic drag.....which translates into more speed.


A simplified example.......you have a 100hp engine pushing a body down the strip.....if wind resistance takes 10hp, parasitic loss from engine to tire of 10hp, tire contact patch loss of 10hp, weight loss of 10hp, and 10hp loss due to a hot day.......you'll only be able to push with 50hp.

If, however, you could cut some of the weight to make that loss only 5hp, increase aerodynamics to reduce loss to 5hp, increase engine to tire efficiency to reduce loss to 5hp, use an intercooler to have a cold air charge to reduce that loss to 5hp, and run with appropriate tires for the type of run you're making (drag, road course, etc) to reduce loss to 5hp.....well, then you're making use of 75hp, instead of 50......one would think you could get more speed out of that body.

I know it's an oversimplification, but it's essentially what the chase for speed is......once the engine is built, its peak power is a constant (without the addition of power adders...those are assumed in the build).....so the trick is to reduce as much power loss as possible. Engines don't get more powerful as they age (contrary to how many stickers one might put on their car), so it's all about preventing power loss.

So, if you can reduce friction in your transmission, you're effectively reducing parasitic drag, and reducing loss of power to the tires. It may not be a lot, but every little bit helps.

 

Ok there MIT grad thanks for the science of all that, I think I just had a aneurysm, lol. So I am right to suggest synthetic oil in the rear diff.

302, 35" tires, 5.58 gears and locker and a spool, if goes no where fast, but it will go straight up what ever is in front of it, as long a I can get a tire to grab, and they are at 8 psi and beadlocked.

I would give any racing shops in the area or drag racer dudes and pick there idea dept for free advice, free does not make it right, but its a good price for an idea?

 

Well, all of the physics stuff aside, whether to run synthetic or conventional is typically a hot topic of debate. You can go on the oils and lubricants forum on this site and get a LOT more input on the subject. Synthetic has some benefits as it may not break down as quickly if put under serious service for extended periods of time....but....if you keep up with your fluid changes, engage in normal maintenance, and don't put your rig through hell every day, then conventional can do the job just as well. If that's the case, then it could just boil down to dollars, as synthetic is typically more expensive. If you change the fluid at the same interval so that both could be serviceable at about the same level, then it'd be more expensive to run synthetic for relatively little appreciable gain.

More than any of that, it's a matter of personal choice. If you think synthetic does the job better, then use that. If you think conventional does better, use it. Until someone comes out with a definitive study saying that synthetic is waaaaaaaaaaaay more effective than conventional for a vehicle under typical abuse, then I think it's a toss up, and is dependent upon taste and cost. If you're running the Baja 1000 professionally, have the sponsoring, and have the track time to notice that synthetic has actually shaved time off your runs, or reduced the incidence of part failure, then it's a more direct decision.

Myself?......I'll more than likely be running synthetic as I've kinda gone overboard on every other aspect of my truck, so why not lubricants too? My truck will probably never see any harsh use, and it'll spend it's life as a big ol shiny baby, but that's fine with me. My decision wasn't based on the physics, or dollars......it was based on lunacy and personal choice.