9 inch axle question
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Senior User
Joined: Jun 2009
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From: Mt. Clemens Michigan
9 inch axle question
i have a 79 f100 2wd and the gears in it wear worn something terrible. making alot of noise and had a ton of backlash in it. i got a third member out of a 86 in the junk yard that had gears that wear in great shape. i got the new third member in the truck but found out the hard way that between 79 and 86 they changed from 28 splines to 31. when i got it all together the axles slid in but just spun in the spider gears when turning it by hand. i was thinking of just going back to get the axles from the 86 that i got the third member from. i just want to make sure that they didn't change the lengths of them also when they went to 31 spline. will the axle from the 86 work in the 79? or will i have to use the old carrier with the new gears? i would rather not start taking apart the new third member as it is in great shape. any help much appreciated
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Senior User
Joined: Jun 2009
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From: Mt. Clemens Michigan
yes i took the axles out and just left them in the bed of the truck as i didn't know i may need them. how big of a difference is there in the bearing size? is it noticable by eye or should i go to a parts store and look at a bearing for both of the trucks next to eachother?
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
Ford offered 31 spline axle shafts beginning in 1973, not 1979.
The problem is...that from 1973 thru 1979, the 9" could have either 28 or 31 spline axleshafts, it all depends on the application.
If your F100 has a 2900 lb. rear axle, the axle bearings are different from the 3300 lb. rear axle used thru 1986.
1980/86, all the F100/150 & Bronco 9" axleshafts are 31 splines.
IMO, you have two options. Swap the Ring & Pinion from that later rear end into your present third member, you will have to reset the lash.
Or, return that later third member, get one from a 1973/79 with 28 splined axle shafts.
The problem is...that from 1973 thru 1979, the 9" could have either 28 or 31 spline axleshafts, it all depends on the application.
If your F100 has a 2900 lb. rear axle, the axle bearings are different from the 3300 lb. rear axle used thru 1986.
1980/86, all the F100/150 & Bronco 9" axleshafts are 31 splines.
IMO, you have two options. Swap the Ring & Pinion from that later rear end into your present third member, you will have to reset the lash.
Or, return that later third member, get one from a 1973/79 with 28 splined axle shafts.
Save the old ones
Joined: Dec 2002
Posts: 666
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From: Boyne Mich
ND,
is it fair to say all 28 spline axles have smaller bearings than the 31 spline axles?
MAS,
I would use a set of vernier calipers to measure the OD of the bearing seal. I have a set pulled on a F150 4wd. they are 31 spline and the bearing seal OD measures 3.140" and the flange plate bolt holes are 2-3/8" x 3-1/2" ctc
If you stay with the 28 spline axles, 2 things to check out
1. It may be easier to put your differential housing (big part that the ring gear bolts to) in the newer 3rd member housing. that way you would not have to deal with the pinion bearings or setting the pinion hieght. which is critical to any rearend.
2. I wonder if it could even be simpler, like just swap out the the spider gears with in the differential housing. that is the part that has the 28 spline.
I am not telling you that these things would work, but that's what I would try to check out. Just Ideas, that's all
In the end, If you could end up with the 31 spline axle, it would be better. IMO.
is it fair to say all 28 spline axles have smaller bearings than the 31 spline axles?
MAS,
I would use a set of vernier calipers to measure the OD of the bearing seal. I have a set pulled on a F150 4wd. they are 31 spline and the bearing seal OD measures 3.140" and the flange plate bolt holes are 2-3/8" x 3-1/2" ctc
If you stay with the 28 spline axles, 2 things to check out
1. It may be easier to put your differential housing (big part that the ring gear bolts to) in the newer 3rd member housing. that way you would not have to deal with the pinion bearings or setting the pinion hieght. which is critical to any rearend.
2. I wonder if it could even be simpler, like just swap out the the spider gears with in the differential housing. that is the part that has the 28 spline.
I am not telling you that these things would work, but that's what I would try to check out. Just Ideas, that's all
In the end, If you could end up with the 31 spline axle, it would be better. IMO.
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Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
D8AZ1225C > > replaced C9AZ1225A, C1SZ1225A and B7A1225A.
Most 1970/72 F100's have this same large ball bearing...but some 1970/72's have a ring gear that is 9 3/8" and 31 spline axle shafts.
This rear end, even though classified as a 9" shares next to no parts with comparable 9's including the axle bearings.
Excepting this 9 3/8" rear end, all 1957/72's have 28 splined axle shafts.
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Some 1974/86's have the tapered roller bearing/seal combination: D4AZ1225A.
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Thread Starter
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Senior User
Joined: Jun 2009
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From: Mt. Clemens Michigan
well i just got home from work and i will go measure the bearing on the 28 spline axles to see if it is even worth going to the junk yard. my luck i cant just swap axles and call it done. does anyone know if i can just swap the spider gears inside the differential? that would be alot easier than swaping the whole thing but i will if i have to.
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Senior User
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From: Mt. Clemens Michigan
ok i got it all together and let it run on the jack stands to make sure it was all good and its making a pulsating noise like something is rubing. when i took it all apart i made sure to make the teeth on the ring and pinion because someone told me that even gears (these are 3.00) the teeth on the ring dont touch all the teeth on the pinion and will wear bad if they are put in off a tooth. so i dont think it is that. i dont have a dial indicator to check backlash so i painted the gears before and after and made sure to get the same pattern. i know i have it set up wrong somewhere but would like some ideas as to what i did wrong. it dosen't seem like the backlash is to tight, wouldn't it make noise all the time not a pulsating noise? any help is good as this is my girlfriends truck and i leave for school sunday so i kinda git to get it fixed
Tuned
Joined: Oct 2009
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Wow, you really made a boo boo! Your best bet now is to take it to somebody who sets up gears. It's alot harder to get used gears set back up than it is to start new. If you don't get it done right, it'll whine forever....& so will your woman!!!
Post Fiend
Joined: Jun 2002
Posts: 13,873
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From: Atlanta GA
> i was thinking of just going back to get the axles from the 86
I just wanted to point out the later 31 spline axles had the seals on the axle instead of the axle housing.
As for the noise, is the axle dropping? Unless the jack stands are at the very outer edges of the axle, it might be drooping and causing the rubbing noise. It is one reason they say not to run an axle off the ground. If you want to test it for rubbing etc. then remove the wheels and drums and spin by hand.
I just wanted to point out the later 31 spline axles had the seals on the axle instead of the axle housing.
As for the noise, is the axle dropping? Unless the jack stands are at the very outer edges of the axle, it might be drooping and causing the rubbing noise. It is one reason they say not to run an axle off the ground. If you want to test it for rubbing etc. then remove the wheels and drums and spin by hand.