2nd Gen Non-Engine/Transmission Vacuum pressure. How much?

[MKopf]

How much pressure should I have at the front axle cad to slide the collar inside? And should both lines have the same amount when I engage 4wd from 2wd. Thanks Mark

 

[budnate]

a hand held vacuum gauge is your friend, it will show where your weak signal is, by finger you cant tell very accurately.



one other thing I will add as I did not read it anywhere in my search to sort this out and would have helped me the first time I went under the truck.



, the red line is what holds you out of 4x4 and the black line pulls the cad over to lockup the front axel.



jack up the pass front tire and shift the transfer case back and forth with the motor idleing and spin the tire, when in 4x4 it will lock up with hardly a spin of the tire if your not locking up your tire you are not getting vacuum to the cad or the cad is toast poke around with your gauge and see if you have 20" on the black line everytime you shift into 4x4 its your cad if you do, if your not seeing vacuum your open somewhere or the transfercase switch is hung up.

and not passing vacuum through it.



also zip tie all your rubber connections mine are getting sloppy from old age and I am pretty sure were weeping vacuum, I also had a burned half "open" black line abour 8" up from the cad in the split loom out of sight made for a week signal... drove me crazy looking for the week vac signal.



I just tossed my old parts in the shop trash this weekend I think they were good I bought a new switch and cad when I did my truck thinking that was my problem... . if your cad is broken I can dig them out and you can have them for free... 4x4 is pretty imp right now in our area. pm me if you need help.







peace, B.

 

[MKopf]

OK I checked the lines with a vacuum gauge and I have 27in Hg on the 2wd line and 20in Hg on the 4wd line I had the Cad off and when shifted into 4wd the fork moves a 1/4 in or so and I have to push it the rest of the way and when it's shifted back to 2wd it goes right back on its own. Is 20in enough to slide the fork? or is there a leak somewhere. budnate thanks for the offer maybe I should try your old 1 and see if it works both ways. Mark

 

[budnate]

that is about what my readings were... I assumed cause my parts looked pretty dirty they were old, so I replaced them then found my leak when it didnt fix my problem,



reverse the lines and see if 27" snaps it in quick...



with the new parts it acted the same as the old..... I would replace the cad with a new one, who wants to crawl under there twice?, if no-one has one local... your welcome to my old one.



B.

 

[MKopf]

I will try that tomorrow turning the vac. lines over so the 27in is on the 4wd side will let you know tomorrow. Mark

 

[WilsonF]

I would think if you had 27in on one you should have 27 in on the other, same vacuum pump. Check for leaks in the low one.

Floyd

 

[DieselDoghouse]

What WilsonF said. Since the "switch" on the Tcase is merely a routing valve, you should (alternately) have 27/27 or whatever. REMEMBER: its not just the vacuum that moves the yoke - You hafta have FREE FLOWING relief air (at atmospheric pressure) in the other line (done by the routing valve) to allow free movement. Otherwise you're drawing a vacuum against a vacuum. And here, I'd suggest you do a search on prior posts (not just mine) about repiping with hard line (air brake line) and moving your relief 'stack' (which currently has a vent cap down by the transmission to catch all the road moisture!!) on up to the top of your firewall where it can breathe better!!