The Stovebolt Site Forums The Parking Lot Big Bolts 2 speed rear troubles

I have an Eaton 17220 or 17221 rear axle.

I cannot figure this out...
It drives in low range fine. It shifts into high range smoothly.
But in high range it will seemingly slip out of gear and start an absolutely horrible racket back there that sounds like I just pushed the "commence self destruct sequence" button.

I removed the shift motor and blocked the shift arm over with a dummy motor (hard into the "high range" position) and it worked fine. Then I checked the motor and the electrics. Everything "seems" to be fine.


I always thought the 2-speed rear end was supposed to as reliable as the day is long...

Any ideas?

The shift motor linkage includes a spring which is tensioned when a shift is pre-selected, and allows the low/high shift to be made by simply releasing the power momentarily. If the springs are weak or broken the shift will not be made fully and the gears will grind as soon as power is applied. Open up the shift motor assembly and look for weak or broken springs.
Jerry

Jerry, does the vacuum shift on a 55.2 2-ton work the same? Mine was in low, I turned the engine off and was coasting slowly down the driveway yo the shop, I was using the park brake to keep it slow (was going to let the clutch out if I need more stop power as well) but the rear came out of gear and now I was free-wheeling towards my shop and my 58! (not a good day for the 55!)

The vacuum shift units use the diaphragm to preload the shift direction, and I don't think they have any springs, but it's been a long time since I've been into one of them. The electric motor runs for a short time and winds up the shift spring, which snaps the shifter into place once the gears are unloaded, either HI or LOW. Without engine vacuum holding the shift collar in place, that one can find a "false neutral" between the high and low positions, particularly while rolling along in neutral. If the engine had been running recently, the reserve tank would have probably had enough vacuum to keep the shifter in one position of the other.
Jerry

Are you sure you weren't in Hi rear? Gravity could have pull the rear shift linkage down while you were "free wheeling". That's why they say to never park a 2-speer rear in Hi range (something bumps the truck and the next thing you know it's at the bottom of the hill).

If you are positive you were on Low rear you must have hit a pot hole while free wheeling that jumper the unloaded rear out of gear.

That's my thoughts...

EDIT, I was typing while Jerry posted his thoughts...I think we are saying the same thing...

Mike B

The engine had been running, not sure where there is a reserve vacuum tank though.

It may have a vacuum leak, because, thinking about it, I am not sure the vacuum tube under the dash for the speedo adapter is plugged. I think it may be open. What you are saying is, the vacuum-shifted rear needs vacuum to keep it in gear? (or at least in high gear?) I am not 100% sure whether it was in low or hi. ONe of the vacuum lines was off the truck when I got it and I noticed the metal tube on the rear was full of mud! I cleaned it out with an awl and stuck the vacuum line back on it. I will be checking it out some more. Thanks.

I purchased the shift motor new... Maybe it is defective? My assumption was that all the components would be good. Possibly NOT a good assumption.

The shift from low to high is perfect. Almost silent (I am VERY happy with that).

When a slight amount of power is applied in high range it seems to work OK. But when a lot of power or else hard variation on the gas pedal, it will slip out of gear and only be remedied by shifting into low range.

I think this is the vacuum tank on my truck. It's bolted outside the passenger frame rail near the tranny.
Vacuum tank location

Vacuum tank close-up

I don't have a vacuum tank on my 58, I'll have to look under the 55. I had one on my diesel stepvan but that is gone now.

How can I test the spring in my electric shift motor?

Everything "looks" good, I think, but how can I tell if the main spring in the motor unit is actually producing the force it is supposed to?

Or are there other things that I should be looking for?

A new shift motor assembly is most likely in good shape. There is also the possibility that the internal gears are worn from too many missed shifts and they disengage on a hard pull. Unfortunately, it takes a full teardown to inspect those parts. There is a sliding gear that either engages a planetary gearset for low range, or shifts to direct drive for high. There's no way to see those parts with the rear end assembled.
Jerry

Is there any way to adjust anything on the shift mechanism?

Since I can hold it in high gear with a dummy motor (that holds the shift fork in the high direction) it seems like the new shift motor does not push the shift arm over far enough.

It sounds like you have confirmed it's not an issue with the rear by installing a dummy motor. There are no adjustments.

Next step is remove the electric motor and bench test it, they are easy to take apart.

Don't forget to refill the lower gear case with very light weight oil (10w) when you are done reinstalling it on the rear.

Mike B

Lower gear case? 10w oil? Hmmm. I am not sure what you mean... The electric motor has a greased, plastic gear with a slot that moves the lever. Is that what you are referring to?

Is this what shift motor you have? Look at the 6th posting down on this page.

http://www.mylittlesalesman.com/find/eaton-17220-i4c0f1268m390749

Mike B

I think that is pretty close... Unfortunately, I am overseas right now and am going by memory. I do know that the motor itself bolts on with 3 small bolts, and I think it sticks up... but possibly not.

I think it looks like this:
https://ixquick-proxy.com/do/spg/show_picture.pl?l=english&rais=1&oiu=http%3A%2F%2Fthumbs2.picclick.com%2Fd%2Fw1600%2Fpict%2F151858484713_%2FDana-Eaton-2-Two-Speed-Complete-Unit-11343.jpg&sp=903e90b0c095c89dc8a11fb8bb7dde9c

The bottom half of that motor is a gear case with a worm gear on the motor shaft and a traveling shifter block that runs up and down the worm gear. Take that lower case cover off and see what you have inside...

The one in the picture I linked you to requires about 1 ounce of 10w oil to lubricate the worm and bearing. I've never seem the one you linked, so I can't help with how that one works.

Mike B

I suspect that the problem lies in the shift mechanism within the axle. As HotRod said the dogs on the shift collar can get rounded off to the point that they will no longer stay engaged and the spring in the shift motor isn't strong enough to hold the collar in position. It could be locked in position with what you're calling a dummy motor; did that have a spring or did it rigidly lock the collar in position?

I once had a 57 GMC 450 with a 2-speed axle in the shop with symptoms the OP reported. Wouldn't stay in hi range. On tear-down, this turned out to be worn dogs on the shift collar and the gear it engaged. So rather than overhaul the axle, it was cheaper to buy one from a local breaker. But this turned out to be one from a 6-volt truck. I didn't know there were any 6-volt electric shift motors. I thought they were all vacuum in those days. I thought maybe is would just shift faster but no. I had to get a 12V motor. After which all was well. It seems unlikely that a new shift motor would be faulty but it does happen and it seems even more unlikely that you got a 6V motor by mistake.

Hmmm.

This is not good news. I was hoping it would be something EXTERNAL, as the pumpkin itself weighs more than some small car engines. Ugh.

What you are saying makes sense because until I apply or release power, it seems OK. Once I get a significant amount of torque variation to the diff, it gets not-pretty really fast.

Unless you're in the habit of hauling loads close to max gross weight, the simple fix would be to fabricate a plate to lock the axle in high range. Even in HI, you're going to have a pretty low gear and fairly low top speed.
Jerry

I actually have the 4.11 / 5.63 gearing.

Low HP with heavy loading means I really need both the low range (when towing) and the high range (when solo).

I wish there was an easy solution.

That is what I will most likely be doing with my 1954/55 GMC 350 COE.

I suppose I should clarify my post about the GMC 450. This truck had the double-reduction Timken axle not the planetary type. Having never worked on the planetary type I can't say for sure but I suppose that the worn dog-clutch issue would be similar.

Low range on the planetary unit slides the sun gear in and out of engagement with the planet gears, and has a different area to engage the carrier assembly for high range. The high range engagement has a fairly small area of contact and is somewhat susceptible to wear from poor shifting habits, IE, getting back on the throttle too soon before it engages fully.
Jerry

My Eaton 1350 uses a check valve in the vacuum line. There a few on ebay right now. The fact that you have problems at time of high RPM(low engine vacuum) points to a vacuum problem.

Ever heard of the R.I.F. program the public education system has? It stands for:

Reading
Is
Fundamental

How does a vacuum problem keep an electric-shift 2 speed from working properly?
Jerry

So it seems the only thing I can do now is pull the pumpkin (that thing weighs as much as a small car engine!)and inspect the sun gear and carrier... Ugh.

I was really hoping for an external fix!

LMAO

Jerry, are you saying that the sun gears are what wear? The planet gears, or both?

Also, what is the best manual to look at before attempting a repair?

Thanks!

If you have an electric shift motor,you don't have to worry about vacuum leaks,or extra equipment,like splitter valve,and speedo adapter.

There is an area of the sun gear that engages the carrier assembly directly for high range, disabling the planetary system. This small toothed area can wear tapered, causing it to overpower the shift motor and disengage as a heavy loads is applied. Sometimes the carrier also wears, and both parts must be replaced. That's when the checkbook tends to have a coronary!

My Motor magazine heavy truck manual from the mid-1970's has a very good section on rear ends, including 2-speed service and overhaul. I've found a pretty good selection of those manuals, and also original factory service manuals on Ebay, usually at pretty reasonable prices.
Jerry

Thanks, Jerry.

I did a bit of searching and found this:
Old Car Manual Project

So, it looks like I am basically in for replacing the Ring Gear (capitalized because they cost so much) and of course with it, the pinion. OUCH!

HOWEVER,

I did see this:


Is it possible that there is something in the shift fork (pivot or arm or something else) that can be adjusted or replaced?

It does seem like the problem is deeper as it 'acts up' when power is applied, but I am still hoping against hope to find something simple [read: low cost] to make this thing workable.