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Old Chevy S 10 How does the 4x4 engage?

L

LeakyBoot

Member
Got a mid 80's with auto trans I'm going to use as a dedicated firewood hauler. Rescued from the crusher as that was the original plan, until I put a battery in it and discovered just how well it ran after sitting for years. Now the questions. It looks like the transfer uses a lever in floor with a rod to shift from 2 to 4 and high to low, but also uses a vacuum/cable actuator located on fenderwell to engage the 4x4 system?? I thought this was all working until my first firewood run today and we figured it out it was not while sitting in a big mudhole spinning the rear tires only. Where is the control valve for the vacuum actuator? Where does the vacuum line hook to the carb/manifold at? These questions are for someone who knows these old trucks inside and out. THANKS! LB
 
I'll ask my dad, as I am not %100 positive, but on a large majority of those trucks, they had a little gas shock type deal, with a heather element that locked up the front Diff. My 1995 K1500's would fail ONLY when it was about 20 degrees (right when you really need it). Aftermarket has a electric motor conversion kit that is instant lock up, as where the glowplug/element style could take 5 or 10 seconds to kick in, sometimes more like a minute on my truck.
 
There's a vac. switch on the left rear side of the transfer case, think there's 3 hoses on it, replaced many of them, most times the plunger was stuck in. Vac. hoses down over the top of transmission could also be rotten or rubbed through.
 
The vacuum actuator on the fender, pulls a cable that goes to the front axle to engage, sounds like you already know that. There is a vacuum switch on the t-case that when shifted to a 4H/4L sends vacuum to that actuator on the fender. A few problem areas for those were vacuum lines rotting, cracking or rodent chewed. T-case vacuum switch picking up fluid and ATF eating the vacuum diaphragm in the actuator, if ATF is found in switch or actuator the t-case was either overfilled, or rear trans seal is leaking and overfilling t-case.

If you can't find a problem or don't want to put a lot of time or money in it then try a cheap fix. If this truck stays off road, or most of the time and you can disconnect actuator and pull cable to engage frt axle. Use whatever you want to keep cable pulled for 4wd.
 
It was already mentioned, but there are 3 vac lines going down to the switch on the t-case. 1. vacuum supply line to the switch, from engine. 2. line to the actuator on fender. 3. vac vent line just tee's into the vent line for the t-case.
 
Thanks, good information. Yes, I replaced several small vac lines on engine already. I expect to see more rotted lines going to transfer case too.
 

Those vacuum switches are bad to stick even new switches stick. On a Jeep it will burn the transfer case up if ran in 4X4 all the time it made a believer out of me if the 4X4 light stays on find out WHY...

As stated its straight forward and simple...
 
My 86 has been like that for 10yrs, only use 4wd a few times, do it manually. You must have trans in fwd, I do that and have
parking brake on, then under the hood pull the vac actuator shaft (on front right side fender well) out and lock it with visegrips.
 
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