Kurt;

Used yoke for cheap cheap, pack with JB weld during assembly? Might be worth a try to avoid R&R the transmission.

Get a quote for transmission repair for comparison.

Agreed, that spline is toast. No JB weld would give you any reliability. You'll soon be in the same situation getting a tow.

Time for rebuilding and getting a new shaft. Or just swapping out the trans.


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Yes, my initial feeling on the shaft splines was that they are toast. Maxbumpo’s comment got me thinking, though: what if I were to install a hardened dowel pin through the shaft and yoke, transverse? The pin would stick out through either side of the shaft, and those two points of contact would drive the yoke through corresponding holes in the yoke body where it encloses the transmission shaft. The difficulty being that the spline contact area is mostly within the protrusion of the housing, and the dowel pin would need to be located outside the housing.

Here are some back of the envelope calculations on this. Read somewhere on the internet that the OM616 puts out 67 hp and 97 ft-lbs of torque at 2400 rpm. A typical gear ratio on a four speed transmission’s first gear is around 3.2:1, so maximum torque at the output shaft of transmission is 310 ft-lbs. 1 foot is 305mm; my eyeballed estimate of the shaft diameter is 20mm. The radius is thus 10mm, and thus the multiplier on the force is (305/10), or 30.5x. 310 lbs times 30.5x is 9467 pounds. This assumes all force is exerted on one side, which would likely be the case until the soft steel of the yoke deforms enough for both sides to carry the load.

McMaster-Carr carries alloy steel dowel pins in various sizes. They rate them for breaking strength in the scenario where a dowel pin goes through a shaft to drive an enclosing part with two points of contact 180 degrees apart, similar to what I’m sketching out here. A 0.250” dowel pin breaks into three pieces with 10,000 lbs force; 5/16” rating is 16,000 pounds; 3/8” rating is 23,000 pounds. The question would then become at what diameter do you equalize the likelihood that the shaft would break or deform relative to the pin?

I would probably shoot for a scenario where the shaft has 50% more cross-sectional area relative to the pin. The cross section of the unmodified shaft is pi() * r^2; using 10mm (0.394”) for radius, I get 0.487 sq inches for shaft cross section. Pin cross section is just length times diameter; for the 5/16” shaft we get 0.246 square inches. I can already see that when we subtract off the pin area from the shaft area we are going to get areas that are approximately equal. So, the 3/8” pin is definitely out. 5/16” pin puts the shaft at risk for breakage, probably. 1/4” pin is definitely at risk for pin breakage. I might refine these numbers a bit with real measurements, but right now the 5/16” pin looks like the best bet.

This is probably a short-term fix at best. But it is cheap and seems do-able. In one sense, what have I got to lose - the transmission is toast at this point regardless. Long-term I would worry about deformation of the mild steel yoke. JB Weld would probably have a place in this type of repair, as a filler/stabilizer between the yoke and shaft. If nothing else it would probably allow me to drive the car to the shop that is going to R & R the transmission.

And that concludes today’s thought exercise in hillbilly engineering!

Clearly you have anticipated a pin-location/assembly-sequence conflict.
To place the pin aft of the tail housing, it would pass through the threaded portion of the shaft. And then, where would the nut go?

A solution, though not the only one, is to place the pin, with a press fit, in the splined area of the shaft. To assemble the yoke, the yoke would be slotted axially to allow it to be slid over the pin and splines.