The Stovebolt Site Forums The Parking Lot Big Bolts 1948 Chevy COE 2 speed axle shaft stuck

I'm working on my '48 COE 2 speed axle, I removed the diaphragm to get at the shaft that I believe should move in or out to shift. It won't move inward and prying it outward it seems to be spring loaded and pulls right back inward. It's in a gear, either high or low, I'm not sure. How can I get this freed up to shift? I replaced the vacuum lines and this is the final step I think. I still have the cab removed until I get everything beneath it working, then it will be out back on. Thanks

Hy FMM, the normal position of the rear axle two speed gears is being in low gear (low speed) without vacuum or manually shifted linkage the rear axle goes back into low gear. There used to be a plaque on the dash which said park in low, because once the engine is shut off the gears will try to go back into low range. Are you sure there is a shifting problem, or are you just inspecting things?

Thanks for your reply. Well I think it's not shifting because I jacked up one wheel and when shifting the vacuum either way the drive shaft turns the same speed always. I have good vacuum and the diaphragm looks fine. What actually moves inside that the diaphragm shaft hooks too. When I removed the three nuts that holds the housing into the differential and prayed it out a little it springs right back, is that normal?

The driveshaft does not change speed. There is a planetary gear unit in the differential that changes the speed of both axle shafts when going from high to low range. "High" is the actual ring and pinion gear ratio, while "Low" reduces the axle shaft speed with planetary gears. As above, the unit is spring loaded into the Low range. Jacking up only one axle will double wheel speed with the differential gears, just like it does with a single speed rear end.
Jerry

Ok Jerry, so what you're saying is it's normal for the shaft going to the diagram to spring right back in when pulling on it, right? So when vacuum is applied to the outside of the diaphragm it will pull the shaft out some and engage the high range. That makes sense to me now.
When I jacked up one wheel and spun it by hand I was of course turning the driveshaft too, then tried to switch the vacuum back and forth expecting to see a change either faster or slower to the driveshaft rotation but I saw no change, that's why I thought the shaft or something must be stuck in low. It must need continuous vacuum then to hold it into high range, correct?

FMM, do you have an Eaton or Timken rear axle? They are different in how they operate. My meager knowledge is based on the trucks I own and drive;

1) 1947 Diamond T model 509 with Eaton 2 spd rear end. Vacuum pulls differential into high range. Spring pressure brings it into low range. The truck dash plate and owner's manual instructs you to NOT park in high range because as the vacuum bleeds down the rear end may try to shift to low and there is a spot where it is in neither high or low. This fact, coupled with the parking brake on the driveshaft means the truck can roll if unattended.

2) 1950 Chevrolet COE with Timken rear axle. Vacuum pulls it either into high range or low range, depending on where shifter valve is set. It does not change as vacuum bleeds off. There is no mention of parking in a specific axle range in the owner's manual or other liturature. Parking brake connects to rear brake shoes by cables (much safer than the above system).

The Chevy has two vacuum hoses to the diaphragm, the Diamond T has one. Which do you have?

Kent

Thanks, I have 2 hoses and a parking brake with cables to rear brakes.

My 1957 2 ton has the GM Corporate axle, vacuum shifts it both ways, no spring loaded position, two vacuum lines.

If there are two vacuum lines, one on each side of the vacuum chamber, there will be a vacuum assisted shift both ways. You're probably getting a little bit of flex of the rubber diaphragm trying to pull the shifter in one direction, not fighting a spring.
Jerry