The Stovebolt Site Forums The Parking Lot Early 'Bolts (1916-1936 1st Half) 1927/8 3-speed vs 4-speed & ujoint discussion

Edit 8/20: This is from a discussion that was in the Project Journals: 1927 Chevrolet Capitol 1-ton -- Full frame-off resto. If you want to see any of it. (The *you* in these posts is John. )



As I'm going through Lurch's clutch area, I noticed something that would be useful for you (John M.) to check out on your 1927 truck build.

In 2017 when I rebuilt Lurch's engine, I also switched over from the 1927 worn out 3-speed transmission to a refurbished 1928 4-speed.

The 4-speed had the front yoke of the u-joint already on it and I just bolted it to the 1927 rear yoke that was already on Lurch's drive shaft. Now that I've taken this u-joint out of my truck, I've learned that the '28 trunnions (the donut u-joint bearings) are larger in diameter than the '27 trunnions. That made the rear yoke loose as a goose and caused a lot of scraping and scoring inside the u-joint ball housing.

Sooooooooo, since you've got parts from multiple trucks, some '27, some '28, and who knows what, I strongly suggest the u-joint that you put together has has a matched set of the larger trunnions and that they fit well.

I don't know what the clearance specs are for the tunnions on the yoke shafts, but if you have a bunch of parts, use the ones that show the least wear.

Update: I realized that I have a NOS u-joint assembly for a '25-'29 Chevy car in my stash of parts, so I disassembled it and measured the gap between a trunnion bearing ID and the shaft that it runs on OD. The difference in diameters is .004 inch. ;-)

Also make sure that when you assemble the u-joint, face the side of the trunnions with the bevel towards the center of the u-joint.

Ever onward, Dean

Dean- - - -what material are the trunnions made from? Steel, bronze, or some other material? It's fairly simple to fabricate something like that with a lathe and a chucking reamer for an exact fit. I'm machining some alloys the foundry where my son works send me that are harder than woodpecker lips, and holding a diameter tolerance of <.0005" on the outside diameter. They wear out carbide cutting tools in a hurry!
Jerry

Geez Dean ... Just when I start thinking I'm getting my head wrapped around this thing ...

So the 4-speed is preferred over the 3 speed? The 3 speed is the one with the reverse lock out? I have two of one and one of the other

BTW Jerry .... did I tell you that the collar you made me for the mortising tool that Mark sent me works perfectly? Thanks again.

The 4 speed has the reverse lockout lever. And yes, it is preferred because of the granny first gear and heavier u-joint yoke and trunnions. Great for parades, pulling up stumps, and towing other vehicles that need a helping hand. ;-)

The 3 speed, which was standard for 1927, has the smaller u-joint yokes and trunnions; the same parts that were used for cars.

The trunnions are made from steel. I have no idea about hardness.

The inside diameter is a straight through bore, but the outside surface is domed. Also, one side of the ID has a bevel cut into the edge so as not to interfere with the curved inside edge of the yoke trunnion shaft.

While you're inspecting this area, what is the condition of the front drive shaft bushing in the torque tube? Mine was worn enough to allow the drive shaft to be wiggled sideways about 1/16 of an inch. Luckily, I found a NOS bushing (part number 345734) on ebay for $20. Score!!

There's a cork seal and a steel flat washer behind that drive shaft bushing. This seal is meant to keep the oil in the u-joint area from leaking too fast back into the differential. When I took the seal out, it crumbled into pieces. Not surprising for a cork washer that is 96 years old.

I went to a local bearing house and they determined that a new 11730 CR neoprene seal could replace both the cork seal AND the steel flat washer. This new seal is .040" thicker that the old cork and steel set up, but I think it will work okay. I have not installed the new bushing and seal yet, but I will report what happens when I get to this part of my rebuild of this area in Lurch.

The devil is always in the details!

;-) Dean

It wouldn't be terribly difficult to duplicate those trunnions, and even harden them if a material like drill rod was used for the base stock. Drill rod is made "tough" not "hard" so it can be machined to the desired shape, and then hardened by heating, then quenching the part in either oil or water, and there's even an "air hardening" type that's just heated to a specific temperature for a time, and allowed to cool down without quenching. Let me know if you need something like that fabricated.
Jerry

Thanks, Jerry. I'll be in touch if I cannot find viable used parts Lurch's u-joint.

Cheers, Dean