The truck has a shudder when on the road but sounds fine at idle. I suspect a vacuum problem. So far, I've replaced all of the top end hoses and checked the vacuum up top with a MightyVac. The vac system holds a vacuum all across those hoses, the CC actuator and the storage ball on the passenger's side fender. There is a hose that run from a tee at the firewall down towards the transmission and it holds vacuum as well. CC does not work and when in 2WD, the truck whines loudly and clunks and the whine goes away, rinse and repeat. I believe it's the hubs and/or rear locking in when they shouldn't be. I have not accosted the actuator that lays below the battery yet. Any suggestions?

 

OK, I think I'm making progress here. I removed the vac hose from the 4WD actuator and put a halt to that problem for now. It seems like I need to fix or replace the transfer case vacuum switch. I am still not getting cruise control. Vac system supplies 20 lbs of vacuum and the CC unit holds vacuum. I'm going to guess that the controller that sits there is not opening to apply vacuum when the button is pushed. Any tips on how to test both the power to the controller and to test the controller for function?

 

Working on my cruise control. I am looking at the servo under the hood with two vac hoses connected to it. I broke the large nipple off of the existing servo so I had to get another one. Got a rebuilt one off of Rock Auto and I think it's defective. On my old unit, the small nipple would yield a vacuum when vacuumed down and the new (rebuilt) one will not. Is the old one defective or is the new one? My thoughts are that the new one is because if it didn't hold vacuum there, my whole vac system would be non-functional.

 

Can you post a picture?

Not too sure which part causes trouble. IMHO the general direction of investigation into the problem is the right one.

Not sure about the 1991 transfer case. The Blazer would always bee rear wheel drive with front axle being switched on the transfer case electrically (or is the 91 pneumatic/vacuum?) and only the front hubs locking is with vacuum.

There are no issues with instrumentation, especially speed indicator?

 

I returned the defective solenoid valve and received another one. It too has a broken clip on it for holding the connector on but it will suffice and it functions as it should. It does hold vacuum on the small nipple and when activating the vent valve, the large one does too and works the actuator. Thanks

Now I'm going nuts trying to figure out this 4WD. I had my mechanic install a new valve on the transfer case and replace the vacuum lines but it won't function for me for some reason.
We were all over this thing yesterday and can't figure this one out. I came home to think on it and will work on it some today. Everything seemed to work but the valve would not active the 4WD actuator.

I replaced the vacuum check valve and I think I blew that one out by drawing too much vacuum on it. It worked fine then suddenly it didn't and the only thing I can think of is that I overloaded it when I went beyond 20 lbs of vacuum. I have two of them on order now but they shouldn't stop anything from working.

 

Aright, I'm stumped here. All vac hoses replaced and installed and ruined one vac check-valve and might have ruined the initial one. Lesson learned; to not draw over 20 lbs vacuum on the system or you will ruin that check-valve.

On the cruise control:

I have trouble shot the solenoid, the vac system and the switch on the brake pedal. It looks to me like my options now are the controller or the speed sensor but I'm not able to find how to check those components. The switch on the column seems to work. The speedometer works. Any ideas?

On the 4WD:

I had my mechanic replace the switch because I don't have a lift. 4WD still not working and I had a vac leak down to the switch. He was awesome about it and he and I tried to tackle this problem on his lift for about 2 hours and still no luck and we gave up for now. Everything seems to work but when installed, we get a vac leak and no function of the switch. The next thing I'm going to do is pull the switch and hook it up under the hood and test it there.