Later year diff 3rd member in earlier car?

GoodEnuf

New Member
Joined
Aug 24, 2020
Messages
36
Reaction score
14
Location
michigan
Can a complete 3rd member from a later year car be swapped into a 64 with no issue?

Would any adjustments need to be made?

Both centers are complete assemblies, open gears, stock is 2.76, other is 3.55. both cases are 741.
 
Last edited:
Can a complete 3rd member from a later year car be swapped into a 64 with no issue?

Would any adjustments need to be made?

Both centers are complete assemblies, open gears, stock is 2.76, other is 3.55

They will bolt in, you would need to check the spline count on the axles to verify that they are the same. '64 still had tapered key lock axles and some of those had a different spline count. The later axles do not fit the '64 housing. You would also need to check the yoke size.

Dave
 
Does your 64 have an open differential? If it is open then it won’t work. Axles are the wrong length. Centering block in the differential is different width.

If your 64 has a sure grip now then you can put any 65 and newer 3rd member in there. The splines are fine. Follow the link. I have photos in there.

Sure Grip ?
 
Last edited:
I swapped a 742 unit with a 3.23 sure grip into my 60 Dart years ago. I remember having to add some shims on the axles to make it work. I don't recall exactly what the issue was but I think the center section was too wide and the axles needed to be spaced out a few thousands. Not sure you will have the same problem though.
 
Does your 64 have an open differential? If it is open then it won’t work. Axles are the wrong length. Centering block in the differential is different width.

If your 64 has a sure grip now then you can put any 65 and newer 3rd member in there. The splines are fine. Follow the link. I have photos in there.

Sure Grip ?

I believe what is in it now is open gears, the tag on the diff is long gone....but with both wheels in the air, they spin in opposite directions. Any way to tell other than trying a burnout or the tag?
 
I believe what is in it now is open gears, the tag on the diff is long gone....but with both wheels in the air, they spin in opposite directions. Any way to tell other than trying a burnout or the tag?

If it was a sure grip, they would both spin in the same direction. You have an open rear end.

Dave
 
If it was a sure grip, they would both spin in the same direction. You have an open rear end.

Dave
Thanks, that's what I figured and experienced in the past with modern stuff.

That brings another question now....can I just cut the axles down 1/8" each to make up the 1/4" length difference?
 
I swapped a 742 unit with a 3.23 sure grip into my 60 Dart years ago. I remember having to add some shims on the axles to make it work. I don't recall exactly what the issue was but I think the center section was too wide and the axles needed to be spaced out a few thousands. Not sure you will have the same problem though.
Where were these shims added?
 
Where were these shims added?

Tapered axles used a shim pack behind the axle mounting flange to adjust the end play for the bearings. A very big shim, something on the order of 1/8" would be needed to compensate for the longer axle. Not so sure that would be such a good idea although it might well work.

Dave
 
Tapered axles used a shim pack behind the axle mounting flange to adjust the end play for the bearings. A very big shim, something on the order of 1/8" would be needed to compensate for the longer axle. Not so sure that would be such a good idea although it might well work.

Dave
Would it be crazier to do the shim or cut the axles?
 
Would it be crazier to do the shim or cut the axles?

There are racing shops that can cut the axles, question would be if there would be enough spline to have the axle fully seated in the 3rd member. Interesting idea, I don't know anybody who has tried it though.

Dave
 
2.76 TO 3.55 ?
Forgive me, but it sounds like you're signing up for the Red Light Bandit League! LOL (Don't get me wrong I have a 489 with 3.73 / Truetrac & a Gear Vendors)
Fitting a Later Complete Assembly might be a better Idea. You should be able to find Something that will Bolt straight under & it's a hell of a lot easier to do Brake Work.
I had a 59 Custom Royal that I threw a B Body L.S. Assembly Under. If you're a Purist & wish to retain the Key way Axles please ignore my Comments.
Tony.M
 
2.76 TO 3.55 ?
Forgive me, but it sounds like you're signing up for the Red Light Bandit League! LOL (Don't get me wrong I have a 489 with 3.73 / Truetrac & a Gear Vendors)
Fitting a Later Complete Assembly might be a better Idea. You should be able to find Something that will Bolt straight under & it's a hell of a lot easier to do Brake Work.
I had a 59 Custom Royal that I threw a B Body L.S. Assembly Under. If you're a Purist & wish to retain the Key way Axles please ignore my Comments.
Tony.M

The 3.55 complete pumpkin was free to me so I'd like to make that work....I could just take the ring and pinion from it and swap that in to mine I guess but that's gear setup work which I've never done. But, at least there isn't a crush washer to deal with. I'd like slightly lower gears but the stock 2.76 highway gears aren't going to cut it for me, she ain't going on the highway at 70+, 60 is about the fastest I'll cruise her.
 
Last edited:
Yes you can cut them, but with precision, not “close enough”

I’ve had them done on a lathe, but they need to be chucked up true.

take off exactly .125 and they fit perfect. No shim change. Yes there is plenty of spline length there.
 
Last edited:
Hi Guy,
Stating the Bleeding Obvious here, but from 2.76 to 3.55 is going to have Effects on Fuel consumption.
Here in the Mystical Land of OZ about the only Ratio we saw for about Ten Years was 3.23 in both 318 & 383 Equipped C Bodies.
And in All Honesty it Sufficed Extremely Well. (Reasonably Swift off the Line, for a Big Car. 383 C.I. also gave Reasonable Fuel Consumption when driven carefully)
Had a couple of Friends fit 2.76 to 318 Cars & found them to be downright Sluggish, Had to haul them back to Second on Slight Inclines. LOL I have often found that Free Items while always welcome can sometimes have unexpected complications, as stated "Cost" of change over.
No one in your area able to assist? You do need to set a Diff up Properly the First Time. Pain in the Rear even when you're Young having to pull & replace a Centre Multiple times. Too Far away to help unfortunately.
Regards Tony.M
 
Where were these shims added?
I think the 1/8" was about right for the shims I added. (Axle mounting flange) My car had one shim on each side when I took it apart. I took one of the shims to a machine shop and had them copy it. I think I had 5 made and still have one left so must have added 2 on each side. This was 20+ years ago. I don't drive the car that much since I have a few others but I probably put 10-12K miles on it with no leaks, noise or other issues. Since it is a stock 318 Poly 4BBL car with 255 hp., it don't get too much abuse these days. If I were you, I'd shim it and not look back.
 
I think the 1/8" was about right for the shims I added. (Axle mounting flange) My car had one shim on each side when I took it apart. I took one of the shims to a machine shop and had them copy it. I think I had 5 made and still have one left so must have added 2 on each side. This was 20+ years ago. I don't drive the car that much since I have a few others but I probably put 10-12K miles on it with no leaks, noise or other issues. Since it is a stock 318 Poly 4BBL car with 255 hp., it don't get too much abuse these days. If I were you, I'd shim it and not look back.

That's what I think I'm going to do, that way I can just go back to the 2.76 if I don't like the 3.55. I suspect I'll like the 'stoplight bandit' performance quality of the 3.55's.
 
Does your 64 have an open differential? If it is open then it won’t work. Axles are the wrong length. Centering block in the differential is different width.

If your 64 has a sure grip now then you can put any 65 and newer 3rd member in there. The splines are fine. Follow the link. I have photos in there.

Sure Grip ?

Looking at the service manual for the '64, it does state that the axle shafts are the same length between the sure-grip and non sure-grip differentials. I guess the only real way to find out for me is to stop reading and get it cracked open.

axle shaft service man.png
 
That is pretty odd. When you take the 2.76 out compare the center block to the photos in the other thread I put up and see what you have. Take a photo for us and get the date off the ring gear.
 
Back
Top