I have just purchased an 1986 F150 4wd with the 300 6 cyl. I bought a haynes manual and was getting everything together to do a comlete tune up / service. I have had no issues until i got to the rear end fluid. Apparently there were several different rear ends (Dana, Ford, conventinal, and limited slip). How do i find out what i have? The transmission is a 4 speed manual does anyone know what kind it could be? I have read about a t-18 and t-19, and although i am somewhat mechanically inclined i have never worked on a 4wd system. Thanks for any help in advance.

 

If the truck is box-stock, then the VIN will contain the basic information you require.

 

Not the VIN - the door jamb sticker. What are the trans and axle codes on the sticker?

 

Thanks the trans code is "A," and the axle code is 183. Can you teel me what this means or where to find out?

 

Trans "A is a NP-435.

Model: NP-435
Type: Four speed non overdrive
Years: 80-87
Engines: 300, 302
Display:
1.2
3.4.R
Construction features: Cast Iron w/aluminum top plate, shifter in top, PTO Pass side
Ratios:
1st 6.69:1
2nd 3.34:1
3rd 1.79:1
4th 1.00:1
Reverse 3.25:1
Trans code: A

It takes 75W90 or 80W90 gear lube, somewhere between 3 and 4 quarts.

That's not a valid axle code - it will only be 2 characters - either 2 numbers or a letter and a number. Can you look again? Also - see if the tag is still attached to one of the bolts on the rear (if so, please copy down everything it says on it), and if possible, can you take a pic of the diff housing from the rear side?

 

183 is a valid axle code. It means an open 3.08 rear and limited slip 3.07 front. Read this caption:



If it's an NP435, read the captions in this album:

 

Thanks. I had driven a 1980 300 6 with a t18 i believe. 1st gear in it seemed alot lower than my 1986 np435, but the charts show the np435 having a lower "granny" gear. I still dont know if my rear end is a ford or dana. Is there any way to tell? Also is what i have a good combination for pulling?

 

3.08's are not ideal for pulling, but you do have a torquey low revving engine and a tranny with a granny. It's a durable tranny.

Without pictures, I can't even speculate on what rear you have, sorry. I do know that Ford 8.8" rears have a removable rear cover and Ford 9" rears do not have a rear cover at all. I wouldn't know a Dana if it bit me. I think it would be completely safe to use the same weight gear lube in it that you use for the tranny, and 3 quarts will probably be enough.

Note that the transfer case takes ATF.

 

There are MANY other variables that could have made the other truck feel different.

'80-up F150s (and possibly some older ones) only got Ford rear axles from the factory. Read both of these:

.

You can tow safely & effectively with any ratio, depending on how the rest of the truck is configured. I've towed over 10Kip with my 3.08s because I also have an NP435. 3.08 gears are physically stronger than 3.55s and all numerically higher ratios.

 

[QUOTE=Steve83;4351413]There are MANY other variables that could have made the other truck feel different.

Ok the rear end tag says 580GA and underneath it it says 308.

 

Whether it's a Ford 8.8 or 9 inch, they both take 5.5 pints of 75W90 or 80W90.

 

Exactly. People focus too much on the final drive ratio and not enough on the overall gear ratio.

1st gear in your rig: 3.08 x 6.69 = 20.61
1st gear with an M5OD and 3.55 = 3.90 x 3.55 = 13.84

similarly

Top gear in your rig: 3.08 x 1 = 3.08
Top gear with an M5OD and 3.55 = 0.8 x 3.55 = 2.84

You're pulling way more gear where you need it to get things moving and only slightly more at highway speeds. Gear reduction is torque multiplication which increases towing capacity. Add to that the fact that the M5OD is inherently weaker with smaller teeth and a closer center distance and there really is no comparison between the two.

 

That's true, but I'm talking about the physical strength of a 3.08 pinion gear vs. a 3.55 for the same axle. The larger (numerically lower) pinion gear is stronger, and so can tow more weight. Given the same trans/tire, it will be slower to accelerate, but it's less-likely to break.