Disassembling the rear axle

The engine and rear axle of the Model T are the most mechanically complex assemblies that need to be taken apart for the restoration.  Like removing the engine, it is good to have some help getting the axle removed from the car.  Fortunately helper Alec was once again avialable.

The basic design of an automotive rear drive axle/rear axle engineer brother.  I'll take his word for it.  I kind of fog over when trying to understand how the Model T planetary transmission and differential in the rear axle work.  Anyway, here is a cutaway picture of what the Model T rear axle looks like for those interested.

Model T Rear Axle/Driveshaft assembly

This cutaway does not clearly show the two diagonal radius rods that attach from the front of the driveshaft to each end of the rear axle.  This can be seen in the picture below.  Engineers love triangles because they make a very stable structure.  These radius rods allow the driveshaft to stay properly oriented to the rear axle when the frame of the car is twisting as it goes over rough terrain.  The Model T was really the first successful SUV, because there were very few paved roads when it was introduced.  

Disassembling the rear axle/driveshaft

Following the handy Model T Service Manual made disassembly pretty uneventful.  My only problem was not covered in the manual; which was how to get the stuck driveshaft out of the rear axle "pumpkin".  It was supposed to come right out, but this one would not.  I finally hung it up like a deer hunter would do after a successful day out in the woods, and the driveshaft finally came free.  The problem was caused by a previous mechanic using sealer along the attach flange to keep it from leaking.

The Model T rear axle was pretty reliable, but had one design issue that every T owner should know about.  There are thrust washers installed on each axle shaft near the differential assembly.  These washers were originally made of a babbitt, a soft alloy used as the bearing surface for the engine crankshaft and piston connecting rods.  While it was (and is) a good solution for the engine, it was not a good thrust washer material.  Bad things can happen when a T driver least expects it if the babbitt washers disintegrate while driving.  Unfortunately, the only way to determine if these thrust washers have been replaced with more durable ones made of bronze is by removing and disassembling the rear axle.   Sort of like having to kill your pet to find out if it has rabies... 

I was planning on rebuilding this rear axle no matter what, so the difference would only be if I had to buy bronze thrust washers.  The good news was that the offending babbitt washers had been replaced sometime in its past.  One of the bronze washers can be seen on the axle shaft on the right side of the picture below.  

I should point out that the actual turning portion of the driveshaft and axles are enclosed in  cylindrical housings.  You can see how skinny the axle shafts are in the picture, compared to the robust axle housings.  The driveshaft is similarly skinny.  I went over to one of the local Model T guys to use some specialty tools that he had that make it easier to disassemble the driveshaft.  One of the parts that was supposed to be pressed on the the shaft just fell off.  Well that was not good.  The driveshaft bushing was pressed into the driveshaft housing and his special tool was very helpful in getting that out.  After that, the parts were all cleaned and the housings stripped of there paint.  The axle will be painted and reassembled later.  The only part that needed replacing was the driveshaft due to some cracking around the keyway at where the drive gear attaches.  The original driveshafts were forged(!) and only machined where they needed to by round.  The modern replacements are machined from a round steel rod and result in smoother ride.  If you have ever ridden in a Model T, you know that anything to make is smoother is a good thing.

Rear axle disassembled