vacum leak when you put it in 4wd

[poor boy pulling]

on my 45 it has the old vacum operated t case, my truck has a 350 chevy and a sm420 in front of it. when you go to put it in 4wd you can tell it is leaning out the engine. any ideas? thanks

 

[SteveH]

The vacuum system consists of three components that can leak - the lines, the valve (underhood on firewall) and the diaphram itself, inside the xfer case mounted shifter. I'd remove the vacuum feed line to the 4WD system, and apply a few PSI of pressure with the engine off (so you can hear the leak) and see where you hear the noise). The later vacuum systems used steel lines (much like brake lines), but the earlier systems had a few rubber fittings. While you have light pressure (not much) applied, cycle the 4WD switch and listen.

If you can't regulate your air compressor that low, use an old bicycle innertube or some other very low pressure source. Do not apply high pressure of any sort to your system. I'm only suggesting you use pressure for this diagnosis as most people don't have a good source of vacuum. A Mighty-Vac can't apply enough volume to be used for detection in this case.

Steve

 

[65swb45]

Since you say that it only makes the noise when you put it in 4wd, it should be simpler than that. Disconnect the hose that feeds the forward side of the diaphram at the control box [on firewall] and cap the box. See if the problem persists. If so, then cap off the diaphram end as well. THis should narrow it down.

FWIW, rebuilds for both of these are still relatively cheap AND available from a number of cruiser vendors. You might want to consider doing these for the peace of mind before you hit the trails. I rebuilt the ones in my 40 back in 1986 and they are still working well today.

Best

Mark A.

 

[poor boy pulling]

ya i never really liked the vacum operated stuff that much anyway so i built a machanical shifter through the floor thanks for your input guys.

chris