2 speed rear end in my 1947 2 ton truck

[Dunkin]

Howdy,

 

I am looking for any feedback regarding my 2 speed rear end that is not working properly.  I posted about this a few years ago, but had other more pressing issues at the time to repair.  I am now getting around to fixing this problem.  The issue is that when I am in high gear it will jump out of gear as the engine's rpm's increase...I think I am basically losing vacuum which is disengaging the rear end.  If I back off the gas pedal for one second it will kick back into gear.  Any thoughts on how to best diagnose this problem?

 

Warm regards.

[kencombs]

I'm not familiar with the Mopar use of vacuum 2 speeds, but the ones Dad had way back when had a check valve and vacuum reservoir to provide the power for the shift.  The check valve opened only when engine vac was higher than the storage container. 

[Dunkin]

4 hours ago, kencombs said:

I'm not familiar with the Mopar use of vacuum 2 speeds, but the ones Dad had way back when had a check valve and vacuum reservoir to provide the power for the shift.  The check valve opened only when engine vac was higher than the storage container. 

I don't believe that is how my truck is set up.  I know there is vacuum mechanism on the firewall that goes back to the rear end, but I have yet to find out if this may be the culprit and whether is can somehow be repaired/rebuilt.  

[Brent B3B]

On 1/23/2022 at 7:44 PM, Dunkin said:

I don't believe that is how my truck is set up.  I know there is vacuum mechanism on the firewall that goes back to the rear end, but I have yet to find out if this may be the culprit and whether is can somehow be repaired/rebuilt.  

i have gone through two of mine

 

not much to them…..
 

sorry I don’t have a service manual for the 47 but, the B series also has an inline check valve along the frame on the passengers side that I’ve also taken apart and cleaned up

Edited February 4, 2022 by Brent B3B
Remove photo, clean up thread

[Dunkin]

Here's what my vacuum valve looks like.  Interesting enough, I have had a rough running engine for years and just didn't do much about it.  Well, I finally decided this past weekend to get to the bottom of it and to make a long story short, it was a faulty coil wire that zapped many HP's from my engine the past 4 years.  This truck now moves and I gave the high gear a try today and I couldn't get it to disengage.  I would assume that with an engine running properly with good vacuum, the rear end is good to go.  I would still like to break down the valve and clean it though. I was also thinking about rebuilding the canister that sits on the rear end.  I remember a few years ago a diaphram for this unit for sale and I hopefully will be able to once again find it.

 

I'll have to look for a check valve.

Edited January 25, 2022 by Dunkin

[Dodgeb4ya]

I have used my low pressure air hose to to be sure the rear axle shifter diaphragm assembly works...and that the rubber diaphram does not leak.

This on the Timkin axles...block thr vacuum inlet port and apply air thru the backside removable plug.

The axle shift arm and bellows should apply and release quickly and positively.

Probably will work the same on the Eaton 1350 2 speed axles.

[Dunkin]

"....the backside removable plug."?  Are you saying there is a plug on the rear axle shifter diaphragm?  Sorry, maybe I am not understanding.

Edited January 25, 2022 by Dunkin

[Dodgeb4ya]

 I said on the Timkin axle there is a plug on the back side of the shifter housing.

But not sure on the Eaton like you have...but I will go out and look at one tomorrow...

 

[Dodgeb4ya]

I went out and looked at my 52 2-1/2 tonner with a Eaton 1350 like you have.

The diaphragm assembly is a sealed unit...no backside plug sorry to say.

But you can blow very low air pressue say no more than 5-10 lbs into the hose fitting and make sure no air is leaking out the bellows back side.

Then at least the diaphragm is good and operating as long as it's flexible enough.

It probably is as it shifts at times.

If someone operates the shift button you can watch the shifter diaphragm move the rear axle shifter lever as the button is pulled up (low range) and pushed down ( high range).

No vacuum tank is used from the factory. There can be no vacuum line/ hose leaks.

 

Edited January 25, 2022 by Dodgeb4ya

[Dunkin]

13 hours ago, Dodgeb4ya said:

I went out and looked at my 52 2-1/2 tonner with a Eaton 1350 like you have.

The diaphragm assembly is a sealed unit...no backside plug sorry to say.

But you can blow very low air pressue say no more than 5-10 lbs into the hose fitting and make sure no air is leaking out the bellows back side.

Then at least the diaphragm is good and operating as long as it's flexible enough.

It probably is as it shifts at times.

If someone operates the shift button you can watch the shifter diaphragm move the rear axle shifter lever as the button is pulled up (low range) and pushed down ( high range).

No vacuum tank is used from the factory. There can be no vacuum line/ hose leaks.

 

Thanks Dodgeb4ya, great info.  I will check it out.  Could there not be a crack in the line somewhere?  Would it make sense to go through the valve on the firewall? 

[Dodgeb4ya]

Yes you could apply low 5-10lbs air pressure to the vacuum line starting at the shift control valve on the firewall.

Use a spray bottle will real soapy water and spray complete line with it looking for leakage bubbles.

If the factory line has never been cut or modified with poorly done hoses it really should never leak.

At the control valventhete is a small 3/16" steel vacuum line leading thru the firewall and onto the speedometer adapter gearbox.

I have seen that line on the "B" series trucks get worn through by the firewall metal cutting the line because of vibration.

Check that line out too.

Should be setup on your "W" truck very similar to the 1948-53 "B" trucks I think.

The Dodge truck 2 speed axles are really pretty trouble free and are excellent fast and accurate easy shifting  when all is factory installed and no funky repairs to manifold and or any other vacuum lines.

The speedo needle should bounce just a bit to match rear axle up/down shifts...that small 3/16" vacuum line supplies vacuum to a small diaphram on the speedo adapter causing the little gear box to do a high/low shift just when the rear axle does.

[68dodgeramman]

I'm a little late to the party here, but I did a search and found this thread. I'm hoping someone here could offer a little info for me. My son bought a 1947 Dodge WFA32 with the 2 speed rear end. He's the second owner, lol. Anyway the vacuum shift chamber has some rust holes in it. He's trying to take it apart so he can repair the holes but doesn't want to destroy it in the process. What's the best way to disassemble it? Also, which is my idea, where could he get a replacement/universal one that might work? Thanks in advance! 

Edited November 12, 2022 by 68dodgeramman

[MBF]

Make sure that your vacuum valve  is getting full travel throw at the firewall mounted valve.  I had this problem w mine and it was just that the cable had slipped in the clamp.  Also check the cable housing to make sure it isn’t sliding in the clamp in the shift lever.   Simple stuff first.