Technical Ford 9" rear axle

I'm sure a lot of you have changed the center chunk (carrier) in a 9" Ford axle, I have never changed one but I am planning on removing the 4.11 chunk and replacing it with a 3.25 which my pal Randy Nash gave me several years before he passed away.

Is this as simple as removing the 4.11 and replacing it with the 3.25? HRP

 

As long as the spline count is the same, and the pinion yoke is the same, yeah. And then change the speedometer drive gear.

If the pinion yoke is wrong, you'll need to swap them, but you have to make sure the pinion bearing preload is correct when you're done. Fortunately you can remove the pinion support to do this work, just make sure to keep the shim the same, and perhaps replace the O ring and possibly the crush sleeve, if it uses on.

 

Hopefully the 3.25 has been stored well, and is not rusty or dirty. Squirrel covered it well, and replacing the crush sleeve is the preferred method if you change the pinion yoke. If you are not comfortable doing that, I have used another method in the past that has worked well. Set up a dial indicator on one of the ring gear teeth, and while holding the pinion still, rock the ring gear back and forth from contact to contact on the pinion tooth to get a backlash reading. Swap the yoke, and tighten the yoke nut to about 50 ft lbs. Check the backlash again the same way, and tighten the pinion nut in 10 lb increments until the backlash is the same as original. The pinion should also have a very slight drag on it when you turn it after being done, indicating there is some preload on the bearings. If you do pull the pinion assembly, I think 3.25 is a ratio that does not require gear timing.

 

If you don't feel comfortable or want to bother messing changing a pinion yoke you could always buy a combo u-joint. They make a quite a few different styles to suit most any oddball or non-oddball setup.

 

the combo Ujoint will work for different size Ujoints, but not for different length yokes....and there are different length yokes.

 

Once there is zero play in the pinion bearings, which can be obtained with no pinion bearing preload, tightening the pinion nut has no effect on backlash. The tightness of the nut only affects pinion bearing preload and that is what is important.

 

One thing to check on is fill and drain plugs:

I once encountered, and it might have been an 8-inch, that had to be filled through the axle vent, due to mismatched parts.

 

That filler plug problem exists with 9" rears, also....good catch

 

Yes. I think there are two lengths, long and short. I remember I had to change to the short yoke when I swapped over to the larger Daytona support.

 

Buy a set on new copper washers , usually the ones you take off get damaged! Not always, but if your luck is like mine……they will!






Bones

 

The axle spline count can be a big deal. More than one guy has run out and snagged a 4.11 Locker out of a F150 and found out it wasn't going to be a direct bolt in in his 28 spline rear end.
I remember the fill plug thing too. a buddy of mine ended up drilling the housing and welding a bung in it for a fill plug. I just remember him cussing about having to take the rear end all back apart after he got it together and couldn't put gear oil in it.

 

Yeah, trying to force gear oil into the vent hole while my boss was screaming at me to hurry up seared that into my memory forever.

 

I found it was easier to jack up one rear wheel, pull the axle and squirt the gear lube in there....

 

Crazy Steve has it right

 

That worked OK for an initial fill, but if you had a leaker it could be a real pisser trying to figure out how much to add... Good test of your axle seals.... LOL

 

might make you want to remove the center and drill and tap a hole for a fill plug, eh?

 

Thats the racial I went to!----You'll like it too!

 

That ended up being the final solution....

 

May as well drill and tap the housing for a drain plug while your at it.

 

If I can piggy back on HRPs post without offending him? I have a 1975 Bronco 9 inch in my A which is supposed to be a 3:50 posi (trac lock?). Both wheels do turn in the same direction at the same time when up on jacks. It clunks backing up, around turns, and generally is a noisy pain in the ass. Is the simplest solution to pull the whole center carrier and swap a new one in (which isn't posi or trac lock) or is there something I could swap out to make it more street friendly. My flattie may have 150 HP so I really don't see a need for this rear end on a strictly street car.

 

@GordonC
Try changing the lube; it's worked out for me in the past.

 

I have a 3:23 ratio diff in my Model A, it seems like a good blend of highway/performance gearing. With 29" tall tires and non-OD trans the engine seems happy to cruise at 70 - 80+ mph.

 

Blues4U I am ok with the 3:50 gear just not having a rear end that seems locked. My trans is a top loader 4 speed from a 66 mustang which had a 3:25 rear in it. I have rear tires that are close to 31 inches tall. Thanks though.

Algoma56 thanks. Will try it.

 

Like mentioned change the oil and put the Ford additive in with it. Or if too difficult to change just add the additive. Then take your car and turn it 10 tight as possible turns to the right, then the left. Your Bronco “ posi-trac” ( trac-loc) will be smooth as silk! Unless some swapped in a Detroit locker ! Lol

My 1968 Bronco sounded like gears were crawling over each other, until I did the additive and turns!






Bones

 

Thanks Boneyard51! I'll give it a try. Easier than pulling the carrier!

 

Good idea!

 

No problem at all brother, this might help someone else with a problem. HRP

 

If you accidentally drop the center section into your drain pan full of 90w, you will wish you hadn't.

-Abone.

 

It's a rite of passage!

 

That sounds like the voice of experience!