Summer chores are winding down, so I took another swing at the Model TT. As a review, the engine and transmission are rebuilt and installed. The auxiliary transmission is in. And a rebuilt rear axle is mounted. It was pretty clear the old rear axle was badly worn, and the axles had excessive in/out motion, which kept pushing my brake calipers out. And judging by the rest of the truck, I expected the whole axle was pretty much shot. Today, I got to take the old axle apart and do an autopsy.
Here is the old axle with the case split to let the gear oil out.
You can see how thick the 600W gear oil is
Once the gear oil is mostly out, the two axle housing are scooted apart enough to free up the worm drive. Here is the end of the worm coming out, with the thrust bearing leading the way
Here is the entire worm gear extracted from the case. The worms are steel, and rarely wear out. This one looks like it can be used by somebody else
One thing I wanted to check was the rear axle ratio in the old axle. There were two ratios available: the low-geared Farm Gear which was a 7.25:1, and a high-speed Express Gear which was a 5.17:1. Once you pull the worm out you can tell what you have. This worm had 4 teeth, which makes it the farm gear. The ring gear that it meshes with will have 29 teeth (29 divided by 4 = 7.25). If it was the desirable express gear, the worm would have had 6 teeth and the ring 31 teeth (31 divided by 6 = 5.17). Having the farm gear in this old axle was actually good news for me, as I know I have done over 30 mph with it. The new rear axle in the truck now is an Express Gear, so I should be able to do 40-45 mph now, which will help me keep up with traffic.
Anyway back to the old axle. Here are the axle housings coming off
Here are the axle housings
Here is what the rear axle looks like with the axle housings removed
Next step is to remove the inner axle bearings. This bearing is completely shot. Slops around everywhere, Its scrap. The other side is ok.
Then, its time to disassemble the inner case. First up unbolting the 29-tooth ring gear. Here it is covered in gear oil. This is the gear that meshes with the worm.
Here is the ring gear wiped off a bit
This ring gear is badly worn. The teeth should have a flat on the top, not a knife edge. And the teeth should not be scooped out in the center - they should be straight across. This gear is scrap. It is unbolted from the inner case and tossed in the copper scrap heap.
Here are the inner case halves separated, and the axles pulled out
Here are the axles:
Lots of wear on the axle ends
Found a surprise on the inside of the inner case. The spider gear was a pre-1923 design with only two spider gears
My truck is a 1926, and should have a 4-spider gear like this
So, somebody swapped in an earlier rear axle. Pretty common. My new axle has the 4-spider gear as was correct for 1926.
In summary, what can be saved are the outer axle bearings, the worm, one inner bearing, the outer axle housings and the inner case and 2-spider gear.
The axle housings are supposed to have grease seals to keep the differential gear oil from migrating down the axles and out into the rear emergency brakes. One side had a shot seal, as shown below. The other side had no seal at all.
Putting in a new rear axle was a good call. The old one was on its last legs, same as the engine was. I will be much happier with the new axle, with its 4-spider gears and Express ring gear, not to mention good bearings, better axles and oil seals all around.
What's left to do is to get the rear wheels on, re-plumb the juice brakes, put on the radiator, wire up the engine, install the distributor, hook up the carb linkage and put in all the fluids.