Lately the pinion seal on my 1986 F150 300-6 4x4 has been leaking to unacceptable levels. Since I'm currently using this as my daily driver, I was thinking I could get a third member from the junkyard, if I'm lucky with the same ratio, rebuild/replace the seal, and put it in the axle I have under the truck. This way the truck wouls be out of service for as little time as possible.

My question is, which 9" axles had 28 splines and which had 31? My axle code is H6, according to the door. I found a bronco with a v8 in the junkyard with the same code, but want to be sure before I pull it. Somewhere I heard v8's got 31 splines and I-6's got 28 splines. I don't want to be ready to put the third member in only to find I have the wrong splined axles.

Any help would be appreciatted!

 

Both trucks will have the 31 spline shafts, no worries

 

To my knowledge any 9" 1980-1986 should be 31 spline. 1979 and older could be either 28 or 31.

I pulled a 3.25 ratio third member from a 1982 F150 and it is a 31 spline.

This is a complete guess, but if there is any 1980-1986 out there with 28 spline it is likely one with the smaller 4.5" car bolt pattern but I still doubt it. You don't have to pull the third member to check the splines. Just pull one wheel and pull an axle shaft and start counting.

 

Thanks for the info! It is most appreciated.

 

If its just a leaking pinion seal - it would be much faster and cheaper to just replace the seal. Less than $10 and a hour of work.

I assume you suspect that the entire differential is worn out (which is rare).

 

If the chilton manual is any indication, this will be more than an hours worth of work. I also have a saying-"If your doing it for the first time, might as well assume you'll be doing it twice." I'd rather do this on a benchtop than under the truck.

A few weeks ago I attempted to replace the 4 piece oil pan gasket. ignoring ctubutis' advice that the best way is to pull the motor. Needles to say, after two days worth of work, I'll be pulling the motor to do it right this winter.

 

The hardest part of changing the pinion seal on the truck is getting the nut loose. But, once you take the driveshaft loose and go to loosen the nut, you may find it loose already, and that may be your problem, the yoke is flopping around causing the seal to leak.

If the nut is tight, the best way is to take a impact wrench and take it off. Take a punch and mark the nut's position first, then take it off(drain the oil a little bit first). Then dig the seal out, install the new seal and then tighten the nut back and put it back in the same position that is was in when you started.

If you do not have a impact and the nut is tight, it is very difficult to get it loose. 1st, you need to jack the truck up some to get room to work, so use some jack stands. When you do that, there is no way to hold the rearend to keep it from turning, so what I do is find a scrap piece of heavy angle iron, drill two holes in it to match the holes where the driveshaft mounted to the yoke, stick some bolts int he holes, and let the angle iron hit the ground or the truck while you take a big breaker bar with a pipe and try to break the nut loose.

You can try taking it loose with the wheels on the ground, but it's hard to hold the truck still while you do this.

 

These kinds of seals scare me, mine also leaks but not to unacceptable levels (at least not yet).

On a similar note, the input shaft to my transfer case leaks, I end up with transmission fluid in the transmission <-> transfer case adapter.

I replaced the seal once thinking that was the fix, but was in there a year later and found it was still leaking.

Took the case + another new seal to some guy who replaced it as a professional courtesy BUT he showed me this isn't the problem and this new seal will also leak...

He showed me that the input shaft was able to wobble back and forth, indicating the bearings are shot.

Those seals are more of dust seals than anything, the actual oil-sealing functionality is supposed to be happening inside.

I would expect the same is the case with the rear axles.

I know virtually nothing about rear axles & transmissions & such, only that they involve terms like "backlash" and "crush bearings" and "feeler gauges" and "dial indicators."

In my opinion, unless you know what you're doing here and have the training and specialty tools, the best thing to do is bring all the components and new parts to somebody who knows what they're doing and have them do it. I would think getting a rebuild kit for the axle is the best thing to do, do everything while you're in there.

Of course, now that I've said this, now there'll invariably be some chest-beating, snot-nosed child showing up saying there is nothing easier than replacing bearings & seals in an axle, just like has been said about replacing ball joints......

As a snot-nosed teenager in the late 1970s, I replaced the oil pan gasket in a 351W in my 1970 Mustang with the engine still in the car, I think it took me a little less than a week.

Afterwards, I told myself: "Never again."