Urgent 9" rearend knowledge needed

[motzingg]

I'm looking at some 9" parts tonight after work, guy doesn't know exactly what he has just said he has a 31 spline 3rd member and axles.

I've got 28 spline in my truck right now... doing some research it looks like i can get the right bearings to adapt the 28 housing to fit a 31 spline axle.


quick question is, is there any way to tell how long my axle shafts are without pulling them out? Were all the truck rear-ends ( i assume truck because of the 31 spline) pretty close to the same length?

Chances are its from a 1980 full size bronco... anybody know off the top of their head what the length on a 68 F100 would be?


Also, the bearings and axle rebuild, is that something i can do in my driveway or is it a major job? It looks like the bearings just come out with the axles, is there any big pressing operations that would need to be done?

This would have to be a 'start friday night and drive to work on monday' kinda thing.

Thanks in advance!!!

[youngone]

The 73 to 79s had the 31 splines and were wider than the 67 72s by 4 inches. I don't know anything about the broncos. To put the whole rear end in your truck I think you would have to move the pad for the springs to sit on plus the shock mounting points on the axel. So they would have to be cut of and rewelded.

I hope this helps.

[youngone]

I forgot the bearings would have to be pressed on and off. Some guys cut them off with a grinder or a torch. The bearing actually goes on not to bad. The lock ring can be heated in a toaster oven so that it expands slightly the slipped on. A friend of mine has a pipe the same size as the lock ring about 3 feet long and slides it up and down the axel like a battering ram to slide the lock ring on.

[motzingg]

damn, thats what i was afraid of... bummer. It sounds like this guy just has the axles themselves and not the whole rear end assy.

gotta make a hard decision, upgrade everything and pay money to get the axles re-splined, or stick with the 28 and find another 3rd member.

i was hoping to avoid this decision until this summer, but i'm pretty sure my pinion bearing(s) is a gonner... and this trade kinda works. having posi or not might be the deal maker

[motzingg]

also, found a few more good sources for axle info... there is no 'ultimate source' for 9 inch data, but 5 or 6 good websites with overlapping (mostly agreement) data.

From brake flange to flange: (ultrastang.com)

8. *1957-1972 Ford pickup 9-inch housing width: 56"
9. 1973-1979 Ford pickup 9-inch housing width: 59¾"

from another website: assume the wheel flange spacing...

61.25 1957-1972 Ford F-100 Pickup
65.25 1973-1986 Ford F-150 Pickup

which probably explains why my one mismatched wheel has 2" less backspacing than the other wheels... interesting.

[sargentrs]

You're better off taking your axles to a shop and having them pressed off/on. You need a pretty tall press.

[motzingg]

eh yeah, i took a second over my lunch break to dig around on the internet and check all this out. looks like i'm gonna be 2" too long on those axles if they are, in fact, from the bronc. I'm pretty sure they are... even if they aren't chances are pretty good that anything 31-spline is going to be that same size, since 1/2-ton F, E, broncs all would have been the most common application for that.


I dont suppose there is any way in heck that my original light duty (68 short f-100 without helpers and 240/3 speed) were 31 spline, just because they have the countersunk/divots instead of the 'oval slot'... is there?

looks like it might not be that expensive to get them done, but this is quickly turning into a bigger project than i was hoping for. good news is that 31 spline axles will be a 'fix it forever' proposition behind my little 6 cylinder, even as i plan on towing crazy loads behind this. If this thing is a posi, it might be worth the hassle... if not, its going to be a tougher sell.

[ultraranger]

also, found a few more good sources for axle info... there is no 'ultimate source' for 9 inch data, but 5 or 6 good websites with overlapping (mostly agreement) data.

From brake flange to flange: (ultrastang.com)

8. *1957-1972 Ford pickup 9-inch housing width: 56"
9. 1973-1979 Ford pickup 9-inch housing width: 59¾"

from another website: assume the wheel flange spacing...

61.25 1957-1972 Ford F-100 Pickup
65.25 1973-1986 Ford F-150 Pickup

which probably explains why my one mismatched wheel has 2" less backspacing than the other wheels... interesting.

The Ultrastang website site is my website. The (bare) rear housing widths I list are from housing end flange to housing end flange (minus the axle and brake assemblies). If you add approximately 2.5" per side (5" combined) and add that total to the bare housing width, you'll have the overall wheel flange to wheel flange distance of the complete rear end assembly width.

[motzingg]

steve, thanks for that very well organized website. if you ever wanted to put together the 'ultimate' 9-inch table/guide, i think you and kevinstang and a couple other folks have most of a complete list between all of ya, just not in one place.

if i were to feel ambitious it would be nice to re-write what kevinstang, you and those other sites have for a bit better clairity and completeness. i'm sure its in a paper book somewhere, that i don't own, because i'm 27 and too reliant on the interweb.



anyhow, i did the deal. i traded him a running EFI 4.9 L motor for 200 bucks, the 3.0 diff, and 2 axle shafts that could be shortened.

the crazy thing is, the more i look at my rear-end, the more i think I might have a 31-spline.... The bearing housings are big externally, and the backing plates look like the 'big ones' without a flange on the bottom.

I've also got the '3 divot' axle flanges that they say are likely to be 31 spline.

I guess i'm going to have to pull an axle shaft to find out, it seems pretty unlikely that a light-duty f-100, no helper springs, and a 240/3 speed would get the beefed-up 31 spline axles.

it is a 3.7 rear end, which is one of the lower gear sets that they came with, so who knows....


next question is, to re-spline or just buy new axles? I'm going to have to buy converter bearings anyhow, if i have 28-spline housing, right? I hear you can get axle shafts for like 100/pr on ebay... probably from china... hmm tough decision.


all this, and my input shaft bearing is probably getting ready to let go as we speak. yikes!

[70shortwide]

You can put the 28 spline spider gears into the 31 spline carrier. that is your cheapest and easiest solution IMO.

side note: You cannot put 31 spline spiders into a 28 spline carrier though, you wont get your axles through the hole in the carrier.

[ultraranger]

What 70shortwide says is true. Another problem is shortening/resplining 31-spline axles to a 28-spline. I'm guessing you have dentside 31-spline axles (?). If you do, they will have a couple of steps or a reduction in the taper of the diameter from the flanged end towards the splined end. I've heard of people getting these axles cut/resplined but it's not recommended. Those axles are induction hardened meaning they are only hardened for a certain depth into the shaft material. If the axles are cut, turned down and resplined, then much of the induction hardening in the area of the new splines will be lost.

The only factory 31-spline axles I know of to come in a bumpside would have been in the trucks that had a 9-3/8" ring gear/3rd member. These axles would have the same diameter across the entire length of the axle shaft from wheel flange to the splined end. These are the only 31-splined truck axles that could be safely shortened and resplined --of coarse for a bumpside they wouldn't need to be shortened ....but if they were going to be used in an early Mustang with a large bearing 9-inch housing, for example, then they could be shortened and resplined for that....

Edit: after doing some more research, I see I was partially right about my statement in the last paragraph above. For the '68-'70 model F-100s, 31-spline axles were optional with a 9-inch rear. An F-100 bumpside Camper Special would have come standard with 31-spline axles in a 9-3/8" rear. The (optional) 31-spline axles of the bumpside F-100 9-inch rear and the (standard equipment) 31-spline axles of the F-100 bumpside Camper Special 9-3/8" rear are interchangeable.

Unfortunately, factory 31-spline axles from either of these bumpsides is pretty rare --but does exist.

[motzingg]

awesome, thanks a bunch guys, this is all great info.... the kinda stuff that you can read and read but sometimes you just gotta ask someone who knows!!

I've definitely got 'large bearing' housings, from what i can tell externally. They aren't necked down and they are huge. Plus they have the large bearing backing plate with the big (3/8) bolts. From some of the stuff i read, that would imply they are 31 spline axles, plus they have the 3 divots, but i'm not going to pull it all apart assuming that. In fact, i'm going to assume they aren't until i can get the chance to pull them out. Maybe this weekend depending on how some other projects go.

The 'donor' rearend is an '80 bronco. The shafts are definitely heat treated somehow, but based on the machining it looks like they were heat treated before being machined. They have a rough scale on the shaft, but the turned down and splined part is clean shiny 'as machined' steel. These are the axles with the tapered roller bearings lubricated by gear oil, not sealed ball bearings.

The part that is turned down extends more than 2" (it looks like that is what i would cut off) past the edge of the spline, so even if i wanted to i couldn't re-turn them... that is the good (ish) news... The bad news is that it looks like the splines are rolled, and the turned down diameter is slightly smaller than the major diameter of the spline, because the rolling upsets the metal to be larger than the turned diameter.... meaning that i couldn't cut new splines in the turned section with a conventional mill/4-axis CNC, without having a slightly smaller (%80 engagement) major diameter.


BAH!

Unfortunately now that i've seen these big beautiful monster axles, i'm enchanted with the idea of having a gnarly unbreakable rear-end that i can forget about for the entire life of the truck.

Is it even in the realm of possibility that I will ever break a 28-spline axle? I mean, ford wouldn't have made the switch if there wasn't some reason for it, right? What about with a 200-250 hp/ 400 ft-lb motor that exists somewhere in my dreams?

The spider gear thing is a good tip, chances are pretty good, at this point, thats what i'll be doing...

[ultraranger]

Terminology; the (larger) splined gears inside the differential, that engage the axles, are axle gears. In a Traction-Lok differential, there are 2 axle gears and one splined hub gear that the axles engage. In an open differential, there is no splined hub gear --only the 2 splined axle gears.

There's a smaller set of gears inside the differential that are in contact with the axle gears. Many people commonly call these smaller gears 'spider gears.'. Ford's terminology for them is, 'pinion gears.' --not the same thing as the input driving pinion gear that meshes with the ring gear. Ford differentials can be either open (single track) or Limited-Slip/Traction-Lok. Within either of these types, they can have a 2-pinion differential or the stronger 4-pinion differential.

While you can swap out the axle gears and the gear hub inside the differential to make it into a 28-spline, you really would need to change out ALL the gears; axle/hub and the smaller pinion gears. All of these have broken in together and now have a certain wear pattern established. Changing one out without changing the other could cause excessive rear end noise, accelerated wear of the axle/pinion gears or, both.

All differential bearings, clutches and steels should be replaced too.

By the time you replace axle gears, bearings, clutches and steels, rebuilding the differential may easily end up costing
more than just buying a completely brand new 28-spline Traction-Lok differential. I see brand new units on ebay for around $310.00 bucks. I would shop around and compare the total cost of rebuild parts then compare that to just buying a new Traction-lok differential. --or, you can take your chances with swapping the axle gears and nothing else and just hope it works or holds up.

[elgemcdlf]

Ok call me devil's advocate but what is the importance of having 31 spline? Just to say you do? Unless you are doing some serious sending of torque down the shaft 28 will serve just fine. Why do I say this? I am running an IRS with 28 spline and a 460 out front. I have had no problems to date.

[ultraranger]

Ok call me devil's advocate but what is the importance of having 31 spline? Just to say you do? Unless you are doing some serious sending of torque down the shaft 28 will serve just fine. Why do I say this? I am running an IRS with 28 spline and a 460 out front. I have had no problems to date.

I suppose for the same reason you chose to put a 460 in a truck that's no longer relegated to work chores. You did it because the importance to you was because you could and not because it was necessary, when a smaller engine would have been able to motivate the truck just fine. Everyone has different ideas as to what parts they want on their trucks and what they want their trucks to be.

Different approaches leads to different builds that suits each owner. If everyone thought exactly alike, all the trucks would be cookie cutter copies of each other and that wouldn't make this a very interesting hobby.