CHASSIS, Assembling a '40 Ford rear axle

[the-rodster]

First, I'm no expert, and this is my first time setting up a banjo rear.
Second, most of these instructions are based on an existing article at Flatheaders Online (http://www.btc-bci.com/~billben/rearend.htm).

I decided to swap axle housings on my '40 rear to get the spring perches in front of the axle, and while I was at it, check out what the bearings and gears looked like. I did end up replacing a carrier bearing and race, but everything else looked OK, so now it's time to reassemble the rear. This post just deals with trying to setup the diff correctly.

There are three things to keep in mind during assembly.
1. Carrier bearing preload.
2. Pinion bearing preload.
3. Ring Gear/Pinion backlash.

Carrier bearing preload is established by the total thickness of gaskets on each side of the banjo center. You want the total gasket thickness to provide a snug fit of the bearings in their races.
The best way to get a starting reference for the total gasket thickness is by stacking the axle housings vertically, without gaskets, and measure the gap that will need filling. To do this, bolt the right axle housing securely to the banjo center. Stand the housing vertically, with the banjo facing upward. Now slide the axle assembly into the right axle housing and center, then slide the left axle housing over the axle assembly. Make sure the top axle housing is seated by rotating it back and forth. You should see a small gap between the top axle housing and the banjo center. Use a feeler gage to measure this gap.

http://www.scrtc.com/~wells1/rear1.JPG

In my case, the gap was .032". This measurement should be very close to the thickness of gaskets to achieve our desired preload. The next thing that I did was release any preload on the pinion bearings. It is extremely hard to "feel" the preload on the carrier bearings, if there is any significant preload on the pinion bearings.
Wedge something in the pinion housing to keep the pinion from rotating, bend the locking tabs back, then loosen both nuts on the pinion stem. The pinion should now rotate freely without any drag.

http://www.scrtc.com/~wells1/rear2.JPG

Next, secure the banjo center in a vise, or something similiar, to allow easy assembly of the axle housings - because you are going to do this several times.

http://www.scrtc.com/~wells1/rear3.JPG

We need to work with a thicker gasket pack and gradually work our way thinner until we can "feel" the drag of the carrier bearings. Since I know that the total thickness of the gasket pack is somewhere in the neighborhood of .032", I decided to start with .037" and work my way down.
This is what we have to work with, a standard rear axle gasket pack with color coded paper gaskets in thicknesses of .003", .005", .007", and .009".

http://www.scrtc.com/~wells1/rear4.JPG

Again, I'm going to start with a total gasket thickness of .037". When removing gaskets, you want to do this on the right axle housing, so I will start with .021" on the right, and .016" on the left.
So, install the gaskets on the right housing and bolt it up.

http://www.scrtc.com/~wells1/rear5.JPG

[the-rodster]

Slide the axle assembly into the housing.

http://www.scrtc.com/~wells1/rear6.JPG

And install the gaskets on the left housing and bolt it up.
At this point, both axle shafts must be rotated in the same direction at the same speed. This rotates the entire carrier assembly on the carrier bearings. It helps if there are two people, but you can do it by yourself if you clamp some vise-grips on the ends of the axle, and you have fairly long arms. Without any preload on the pinion bearings, and assuming there is no preload on the carrier bearing yet, there should be no drag when you turn the axles. It should feel completely "free".
With a starting point of .037", the axles did indeed feel free, with no drag. Now we must separate the right axle housing from the differential housing and remove some thickness from the gaskets. I started with .021", so now I will try .019" on the right side, giving a total thickness of .035" (.016" is still in the left housing). The right axle housing was reinstalled, and both axles were turned to feel drag. It still feels free, with no noticeable drag.
Again, separate the right axle housing from the differential housing and remove some thickness from the gaskets. Next I tried .016" on the right side, giving a total thickness of .032" (.016" is still in the left housing). The right axle housing was reinstalled, and both axles were turned to feel drag. At this point, I could definetely feel the drag of the carrier bearings, it is light, but you can tell that they are now firmly seated into the races.
Hey, that wasn't too bad, and now we know our total gasket thickness - 0.32"
Now we can reset our pinion bearing preload. Remove both axle housings, and clamp the banjo center in a vise - pinion stem up.

http://www.scrtc.com/~wells1/rear7.JPG

I remember reading somewhere that pinion bearing preload should be 12 to 17 inch/lbs - (torque required to turn the pinion) This is only 1 ft/lb, which isn't that much. This will yield a very slight drag to start the pinion turning, yet turn smoothly with no bind once it is moving. One way to accomplish this is to firmly tighten the adjusting nut and then back it off 1/6 of turn and secure the jam nut and locking washer. Again, the pinion should turn with no bind, but there should also be no slop in the bearings.

Now we can address ring gear and pinion backlash.

Reassemble the axle, using the gasket thickness determined earlier, divided equally, side to side. In my case I reassembled the axle with .016" of gaskets on each side. Next, mount a dial indicator so that the movement of the splines of the pinion shaft can be measured. Rotate the pinion shaft back and forth, not enough to move the gear, but just enough to measure the "play". Take note of where the dial is at each point.


http://www.scrtc.com/~wells1/rear8.JPG

Backlash should be .003" to .008". If it is less than .003", place a thicker gasket between the left axle housing and the differential housing, and if more than .008", use a thinner gasket.

Note: In order to preserve the differential carrier bearing adjustment, whatever gasket thickness is added at the left housing joint, the same amount must be removed from the right housing joint, likewise, if gasket thickness is reduced at the left housing joint, it must be increased at the right housing joint by the same amount.

My initial reading, with .016" on each side, was .010", so the left housing needs to move closer to the banjo. Next, I disassembled the axle, and reassembled it with .020 at the right axle housing joint, and .012 on the left. The backlash reading was now .008". This is at the high end of the specs, so I chose to remove a tad more from the left axle housing joint. With .023" at the right axle joint, and .009" on the left, the backlash was now at .006"- right where we want it.

Well, that's about it, and I only had the take the axle apart about 10-15 times :)

[Harrison]

Please "Tech-O-Matic" this one immediately.

JH

[Chopped50Ford]

nice post...I too ask for this one to be sent to the "Tech-o-matic"

Im exhausted reading it...almost like I had my hands in the job...great post.

[Paul]

Please "Tech-O-Matic" this one immediately.

JH

there is no "Tech-O-Matic" ;)

this is Tech Week so it will stay up at least that long

so far this thread has my vote

matter of fact, I am printing it and will save as hard copy as well

I need to do this to my modified rear,
I just threw it together with '40 brakes, '36 housings and axles, '48 truck center and ring and pinion thinking I would have a pro set it up,

with this info I am going to try it myself

Thanks rodster!!

[FiddyFour]

AWESOME tech. like the man said,,, im printing this one out an stuffin it in my "things i need to know that i didnt know i needed to" folder


:D :D :D

[Baron Von Mike]

Very nice. Wish I would of had this last year when I rebuilt my 41 rear end. I put all of it back together by feel. Oh well, been fine so far.

I was hoping for more on the pinion. That thing is a bitch to put back together with both its bearings, at least in my experience. Then you have to put the whole assembly back in the housing AND try and set preload. Ugh. It was quite fun.... NOT.

Anyway, if ya don't mind I'll add a helpful trick to pop out the pinion if you ever need to do so. I thought about this for a while and ended up just buying a really cheap bottle jack from Kragen. The smallest one they had fit just perfectly so that I could do the following.

Mike

[joeycarpunk]

Cool tech, I just went through all this putting 3:54's in.

[Kevin Lee]

Useful, well written, nice photos. Rad post.

[rodrelic]

Useful, well written, nice photos. Rad post.
Yes, and although I used the same proceedure I also did it by feel and when it go's to hell THEN I will use a scale and the dial indicator to do it right as shown here.
I would also mention that I was warned too late that the threads in the housing bolts are unique. Although the common fine thread count, the thread profile is different. I had to swap out a few that were corroded too badly to use a wrench on. Went in hard, and cosequently had to clean out shavings during disassembly/reassembly, make sure I had them in the same holes every time. The grade 8 bolts eventually rethreaded and torqued up well, but who would of thought?

[DICK SPADARO]

Excellent job and very good pictures. Accurate and straight forward information. Recommend printing for reference.

[zgears]

good info. bttt

[alittle1]

Seems like an excellent TECH article and the photos help.

[HighSpeed LowDrag]

Nice Tech article.


Getting all the fotos and putting it all together in a post would have taken me longer than the rear axle assembly took you.

Good job on both accounts!

[the-rodster]

Thanks for the nice comments, I know that I couldn't build my car without the information of the HAMB and it's members, just trying to help out.