9 inch third member swap question?

[greentruck]

My truck has 3.50 gears. I am swapping my front axle out for an 77 axle with 4.10 gears and disc brakes. The donor rear 9 inch obviously also has 4.10 gears. I do not want to swap out the whole rear axle because mine has been blasted and painted all pretty, so I need to put the 4.10 third member in my axle housing. Can I take the third member out of the donor and bolt it to my axle? Other than spline count, what else do I need to check? What about shims or backlash, anything like that?

These are the steps I found on another post, are they missing anything:
take the wheels off, pull the drums and there is a hole between your studs. spin the axle around until you get to a bolt, stick a socket through the hole and unbolt, 4 bolts. slide the axle out of the housing about a foot and let it hang there. drop the drive shaft, unbolt the third member and pull it out. have to have a pan to catch your gear oil. Put on a new gasket. take the new third member and stick it on and reverse the take off and there you have it.

Thanks for your help,
paul

[71PA_Highboy]

Your 77 donor may have 31 spline axles, while your 69 most likely has 28 spline... validate spline count before you do anything else....

I am unsure about the bearing OD and axle length between them, but if they are the same you can put the 77 guts into the 69 housing...

Not a lot of info here that you probably don't already know, just thought I would throw it out there.

[basketcase0302]

Have the pan ready when you pull each axle shaft as you usually get some gear oil out of there.
If memory serves me correctly there were two different axle shaft bearing sizes on the 9". Maybe coincides with the spline count? I'm not sure about that...

[Hawkrod]

Not really important but I think you will find that the rear is not a 4.10, Ford 9 inch rears are 4.11 which does not "match" the Dana front. It is odd but tht is how they did it but you could find a 28 spline axle center from a 2WD with that ratio and use it. Also note that 68-72 can have 31 spline axles so you may be able to use what you have but you will need to verify what is already in there. Post teh axle tag info and we can tell you if it is 28 or 31 spline. Hawkrod

[greentruck]

Your 77 donor may have 31 spline axles, while your 69 most likely has 28 spline... validate spline count before you do anything else....

I am unsure about the bearing OD and axle length between them, but if they are the same you can put the 77 guts into the 69 housing...

Not a lot of info here that you probably don't already know, just thought I would throw it out there.

71PA_Highboy you are correct, the 69 is a 28 spline and the 77 is a 31 spline. I will just have to swap the enitre axle. Not a big deal, but the donor needs brake work and will have to be cleaned and painted. Thanks for your help.

For what it is worth, axle removal on a 9 inch is super easy. This tech article has pictures and a good write up: http://www.pavementsucks.com/tech-article-20.html

[basketcase0302]

I will just have to swap the entire axle.

Isn't the spring pad spacing different-between the dent axle and our bumps?

[forrestbump]

Isn't the spring pad spacing different-between the dent axle and our bumps?

Yup. Bumps are 34" width at the rear of the chassis and Dents (other then F250 4WD) are 38".

If I'm not mistaken, Dents went to a wider rear axle housing too. If so, the 31 spline Dent axles just may be too long for a Bump 9" housing. I'd recommend measuring axle lengths...comparing the 28 spline axles to the 31 spline axles.

[greentruck]

Wow, I am an idiot. The widths are different. The whole time I was planning this project I only was focused on the Dana 44 front swap and I assumed that the 9 inch rear was the same up to 79. You know what they say about assumptions...These are not scientific measurement, but it was clear that the two are different:
Bump - spring preachs are 44ish inches apart and about 56 inchs drum to drum
Dent - preachs are 48ish and 60 inches drum to drum

I figure my options are:
1. Weld new spring pads on the 77 axle at the correct width and get wheels with different backspacing to compensate for the wider axle.
2. Put 4.10 gears in the 69 axle
3. Try to find 31 spline 69 axle shafts, then swap the 77 third member and 31 spline axles into the 69 housing (need to check the bearing size too with the axles)

Whatever I do I need 4.10 gears in teh rear because I am to far into building my new front axle to turn back now. What would yall do?

[forrestbump]

I'd go with option number 1:

Weld new spring pads on the 77 axle at the correct width and get wheels with different backspacing to compensate for the wider axle.

Another option is to use the 31 spline center section and have your Dent axles shortened to fit your Bump housing. This option is probably going to cost more and this is assuming both axle housing you have are big bearing...most Bump 9" housings are small bearing and I believe most Dent's have big bearing...the more I think about it, stick with option number 1.

You'll get the best 9" rear axle this way...

My

[Doug Comer]

I have heard many rumors about this, is it possible to switch the side gears from a 28 to 31 and vice versa?

[forrestbump]

Yes you can but if you're putting Dent parts in a Bump housing, you'll still have to deal with the too long axles and bearing size differences between the two different era trucks.

[michael69]

If you go with option one, no need to get different wheels. The extra 4 inches will just make your rear wheels even with the front wheels so they track the same. If you look down the side of the truck you will see the front wheels stick out farther than the rear from the factory. So when you put the dent rear in they will match up.

[basketcase0302]

1. Weld new spring pads on the 77 axle at the correct width and get wheels with different backspacing to compensate for the wider axle.

Another vote for option#1 as spring pads are cheap, (like $10-$15 each). Just make sure you get the final axle drive angle back to where it should be. There's a thread here somewhere about how to set-up the angle correctly.

[greentruck]

If you go with option one, no need to get different wheels. The extra 4 inches will just make your rear wheels even with the front wheels so they track the same. If you look down the side of the truck you will see the front wheels stick out farther than the rear from the factory. So when you put the dent rear in they will match up.

I love this website, there is so much knowledge on here. michael69, is correct I measured my stock 69 axles and the rear is 4 inches more narrow than the front. I never noticed this. Option 1 it is and I am stoked that I dont have to buy new wheels because i dont have it in the budget. thanks for the advise guys.

[basketcase0302]

Also advise on using a wire feed welder when you do option #1 so as to not heat the axle tube and warp it. Pinion angle is pretty important also, (when you weld the new spring perches in place). There's a tutorial here somewhere on how to properly set up pinion angle.