Vacuum shifter/FWD issue (1 Viewer)

[illinikev]

wanted to consult the experts on something that has me stumped.

executive summary - I accidentally shifted my '68 into FWD, and then couldn't get it back to 2WD. tested vacuum lines and they are working. replaced them anyway with new just in case. it certainly appears as the vacuum shifter on the transfer case is inop. I'll deal with that later.

so I took off the side cover of the vacuum shifter to see if I could tell what's going on. sure enough, lever isn't going back and forth with pull/push of the FWD cable. So ok, I thought I'd just manually click it to 2WD while I learn how to rebuild/replace the vacuum shifter.

what I really need help with is this - it seems like I can't fully disengage FWD. the closest I get is that the front driveshaft clicks in the transfer case when I turn it by hand in 2WD. it doesn't appear as though there's any adjustments that can be made to the shift mechanism to get some more travel on it.

Anyone seen this before? I'm way out of my league when I start disassembling transfer cases...

thanks in advance.

 

[Paul_A]

Did you run it backwards to take the load off the drive line?

 

[charliemeyer007]

+1 for backing up a few feet, (to unwind any stress built up from slightly different size tires or recent turns) try to disengage; (perhaps pulling forward again, try to disengage - might take several tries. It helps is the rig is warmed up - cold stiff grease in the mechanisms is like just like glue. If you have hubs turn them until you get it out of 4H or you give up and need to drive any distance.

 

[Green Bean]

This may sound silly, but have you tested to make sure that you have good vacuum going all the way down to the 4WD shift mechanism? You can take the vacuum hoses off where they connect to the shifter and test. I found a bit of debris at the block on the driver's side of the firewall that I was able to blow out with compressed air.

 

[middlecalf]

A quick way to determine if the internal diaphragm that moves the shift lever with vacuum is compromised is to put a long clean (fuel) hose on one of the vacuum feeds to the TC and suck on it. If nothing happens, put it on the other feed and suck. If nothing again happens then the diaphragm is probably compromised. If it isn’t compromised the shift lever should move (in or out) using this method.

 

[illinikev]

+1 for backing up a few feet, (to unwind any stress built up from slightly different size tires or recent turns) try to disengage; (perhaps pulling forward again, try to disengage - might take several tries. It helps is the rig is warmed up - cold stiff grease in the mechanisms is like just like glue. If you have hubs turn them until you get it out of 4H or you give up and need to drive any distance.

yes I've been back and forth in it several times. also tried pushing the H/N/L lever forward as suggested in some threads.

 

[illinikev]

A quick way to determine if the internal diaphragm that moves the shift lever with vacuum is compromised is to put a long clean (fuel) hose on one of the vacuum feeds to the TC and suck on it. If nothing happens, put it on the other feed and suck. If nothing again happens then the diaphragm is probably compromised. If it isn’t compromised the shift lever should move (in or out) using this method.

such a great idea. I did use my air compressor on both sides with no luck. I'll try this in the morning.

 

[illinikev]

This may sound silly, but have you tested to make sure that you have good vacuum going all the way down to the 4WD shift mechanism? You can take the vacuum hoses off where they connect to the shifter and test. I found a bit of debris at the block on the driver's side of the firewall that I was able to blow out with compressed air.

yes I did check this. I get alternating vacuum on both hoses when pushing/pulling the FWD button. so I'm assuming the front system is working correctly.

 

[illinikev]

ok crawled under it some more this evening and this is what I "think" is happening, but y'all know better than I.

first of all, I can't get any movement from the vacuum shift at all. I'll try a few more things tomorrow to verify this.

when I take the side cover off and actuate the shifting lever manually, it seems like I can't press it in far enough to fully disengage the FWD. I can pull it out far enough to fully engage the FWD, but trying to click it back in doesn't fully release the front driveshaft. so my working assumption is that something within the diaphragm isn't allowing the rod to travel far enough in.

I really don't want to take the whole system off, but it's trending that way.

thoughts?

 

[middlecalf]

Can you put the rig on jack stands so you can spin a front wheel (or the drive shaft) with hubs locked and tranny in gear to see if that frees it up? Also, try unscrewing the indicator light switch housing and see if it will disengage then, but be aware that there’s a ball bearing under the switch that you don’t want to lose.

 

[illinikev]

Can you put the rig on jack stands so you can spin a front wheel (or the drive shaft) with hubs locked and tranny in gear to see if that frees it up? Also, try unscrewing the indicator light switch housing and see if it will disengage then, but be aware that there’s a ball bearing under the switch that you don’t want to lose.

yessir will do this in the morning. thank you so much for your help.

 

[illinikev]

As a followup, today I removed the vacuum shift assembly to see what was going on. Immediately figured out something was amiss because I could hear parts rattling inside. upon disassembly, found that the actuator rod had become unscrewed from the diaphragm. Cleaned, rebuilt, reassembled, and voila everything now works.

lesson learned - assemble the diaphragm chamber with the J-bolts *last*, since you need to rotate the actuator rod 45 degrees in order to attach the pivot arm.

thanks again for everyone's help here.