I created a huge problem for myself and thought it would be interesting to others on the HAMB. My 30 Sport Coupe has an 8BA flathead, 41 pickup transmission and a rebuilt 30 rear end, have about 900 miles on the car. I seem to have ran the rear end low on grease (600 weight) and was running down a secondary road around 55 mph when the pinion bearing seized up. When the bearing failed it locked up the rear end, slid a little and then sheared the key on the left axle. Had it towed home and when I took the hubcaps to see what I would find there was a sheared cotter key in the left hubcap. Decided to pull the rear end, couldn't turn the drive shaft so disassembled the rear end and found the failed bearing. Looked the trans and rear end over and didn't see any other damage so replaced all the bearings and races. Put the rear end back together, back in the car, filled with grease and started the car and run it through all the gears. Everything worked fine so went to install the rear hubs and the left hub wouldn't go back on, took a while to figure out why. The left axle actually twisted when the rear end locked up and sheared the axle key. The third picture is the right axle and the fourth picture is the left axle that is twisted just enough the hub won't go on. Had to pull the rear end again and replaced both axles since the right axle keyway was sloppy, have several axles but bit the bullet and bought two new axles.
The 600W that is specified for these axles is 600W steam cylinder oil. It is an ISO Industrial Oil. It is not measured using the same methodology as modern gear oils, like 80W-90 or 85W-140, etc. Those are SAE Gear Oils. While a stock Model A was indeed capable of 65mph, finding a place in 1928-1931 that you could maintain sustained 55mph operation would have been a neat trick. I would stop trying to use the 600W steam cylinder oil, and start using modern hypoid gear oil. 600W was the best thing that they had almost 100-years-ago. Today we have better.
According to my book*, by 1934 Ford had changed the specification for the lubrication in the rear axle to SAE-110 Winter, and SAE-160 Summer, with no substantial design change to the layout or function of the axle (except for bigger stronger stuff). If Ford determined that there was a reason to change this specification, there was probably evidence that gave reason to do so. *Ford V-8 Cars and Trucks, Victor W. Pagé, The Norman W. Henley Publishing Co, New York, NY, 1937 Also, the service interval for that change was drain, with a Kerosene flush, and refill twice-a-year, or 5,000 miles, whichever came first. For those of you who would love to have this treasure trove of Ford information, various editions can be had here: https://www.abebooks.com/book-search/title/ford-v-8-cars-trucks/author/page-victor/
I have suspicion that the 600 weight oil the vendors sell is actually not that heavy. It pours too easily, it seems. You can make a good oil for the Model A using 140 weight with some STP mixed in. The STP clings to the gears really well, has zinc, good high pressure characteristics. Be sure, if you do this, that the oil and the STP are hot when you mix them. I have the exact same set up in my A-V8 and have never had a problem but the A rear end won't hold up well under a lead foot and high H.P.
Modern ISO 600W is about the equivalent of SAE-140 in viscosity, but lacks the lubrication properties that SAE hypoid gear oils have. Yes, I know that those rear axles do not have hypoid gear sets, just spiral bevel. That just makes conventional gear oil effectively overkill. No STP is necessary. STP additive is an engine oil additive, which can thicken engine oil. Adding it to already thick gear oil thins that gear oil, if it will even stay mixed. SAE-140 will work fine, as will 85W-140.
I've been using 90-140 gear oil like gimpy says for fifteen years now in my sedan. It drips a bit, so I check the level every spring when I grease everything.
The grease they sell as 600 weight is actually around 250 weight. The other option is to run 140 weight with STP added according to the Model A sites.
Well I've got the coupe back together and on the road. I think I found out where the rearend grease went There is a seal at the front of the torque tube that's supposed to keep the grease in the u-joint from running into the torque tube, I've always had a leak there that I couldn't seal. I've been watching the grease level in the rearend and it's slowly going down and my leak has returned. Car has a fair rake and thought that maybe the rearend grease was running down the torque tube and leaking at the u-joint housing. I did a little measuring and the bottom of the fill plug is 11 1/4", the bottom of the torque tube is 10 1/2" at the rearend and the front of the torque tube is 10". Looks like it's seeping past the seal and leaking out of the u-joint housing, I'm going to pull a bolt out of the speedometer gear housing and pump Cornhead grease into the u-joint housing until it comes out and see if that slows the leak down. Don't really want to pull the rearend again and pull the torque tube and replace the seal, put a new seal in it about 800 miles ago. On my stock Model A the torque runs down hill from the u-joint housing to the rearend, the rake on the coupe causes it to run down from the rearend to the u-joint housing.
Are you sure the seal is installed correctly? The lip on the seal should face the back of the torque tube. This may sound silly but you could make a gasket for the rear of the tube with a dam at the bottom or with a hole in the middle that fits close to the drive shaft to help deflect the oil splash. It would need a little drain back hole at the bottom. Don't over fill the rear end. With modern oil the level should be 3/4" below the fill hole. Perhaps one could adapt an oil slinger from a crank shaft or transmission. Make sure the torque tube ball is packed with grease. Did you replace the front drive shaft bearing and sleeve?
The transmission oil level is at the bottom of the fill plug, I pulled the top on the transmission and made sure there was no damage to it when the rearend locked up. Been there done that, all of the above are correct, I checked the angle on the torque tube with a level with the car sitting on the ground and had about 1/2" drop towards the u-joint housing over a 2' level. Replaced the front bearing, sleeve and torque tube seal when I rebuilt the rearend and pulled the back bolt on the speedo gear housing and pumped grease into the u-joint housing until I got grease out the bolt hole. I'm running John Deere Cornhead grease in the u-joint housing, is lighter than chassis grease which is spun away from the u-joint leaving a void. I've done 4 Model A's this way including my 28 avatar which was also flathead powered without a problem, that's what has me scratching my head.
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