Hello and welcome to JustAnswer!
Have you checked for vacuum at the transfer case with the engine running?
With it in four wheel drive have you checked for vacuum at the vacuum disconnect with the engine running?
You should see closer to 20" of vacuum both at the intake and at the transfer case. Let me know what you find for each and we'll go from there.
Leave the transmission in park for safety, instead of neutral. Start the engine and put it in four wheel drive, us a vacuum gauge right at the disconnect actuator and check the vacuum. You should have close to 20".
If it's lower than that, remove a small diameter vacuum line from the intake manifold and check the vacuum there and let me know what you see for both readings.
thelines i see on the brake booster are hard lines is there a vacum line on the intake that is rubber?
The hard lines you see are the brake lines coming from the master cylinder. The booster is the large round unit behind the master cylinder and has a large vacuum line going to it. You could either remove that large line and check the vacuum there, or you could disconnect one of the smaller lines at the intake, which would be more convenient.
Yes, the disconnect actuator is the vacuum operated unit on the right axle tube that slides the collar to lock the shafts together.
I never got a reading above 12 " at idle, increased the rpm no change,applied the brake and reading went up almost to 15,take pressure off brake and reading falls
Where did you see 12" at, the intake or the actuator?
The next step was to check the vacuum right at the intake manifold. Have you done this?
I figured it out, there is 161/2" at the manifold
Remove the breather line that goes from the left valve cover to the air filter box. Remove the PCV valve from the right valve cover and plug the hole. Start the engine and see if you feel vacuum on the breather hose from the left valve cover.
The PCV valve is on the right valve cover and it's hose goes to the intake. Remove the PCV valve and plug it with something that will seal - a rag won't seal to do this test. Once that is plugged go to the left valve cover. Near the brake booster you will find the vent hose that goes from there to the airbox. Remove this hose from the airbox end. Start the engine and put your finger over the hose for a couple minutes and see if you feel any vacuum. You could also adapt your vacuum gauge to this large hose.
Is it 1 PSI, or is there vacuum?
I have an hour drive home from work, which is why I couldn't respond to you sooner.
Your vacuum at the intake is a little low, and 12" is pretty low at the disconnect actuator, but 12" could be enough to get the actuator to move.
Did you replace the actuator with a new one or used one?
Did you inspect the splines on both shafts and the collar when it was taken apart?
Are you positive that the lines are on the vacuum switch at the transfer case correctly? If two of the lines got swapped around then you would be sending vacuum to the wrong side of the actuator.
I was very careful when I did that. Nothing changed when I switched out that rubber gromet to vacum lines
If you could get a pump on it then we would know for sure if we had an actuator/shaft/collar problem, or if we are fighting a vacuum supply problem. Your vacuum is low, but I'm torn as to whether or not 12" is enough to run the actuator. If we find that it will engage ok with the pump then we're going to draw vacuum on the rest of the vacuum supply to see if we have a pinhole in a line between the actuator, transfer case, and to the engine.
I'm assuming that we have a vacuum problem too if the actuator, fork, intermediate shaft and the vacuum switch have been replaced. Just to verify we're not fighting bad parts or an outer shaft spline problem I'd like to run it with a vacuum pump to make sure it will engage.
Yes, 16" from the engine is a bit low.
Yes, you could definitely try that if you had enough vacuum hose available.
I'll be at work in the morning, and then I'll be online for the rest of the weekend. If you reply while I'm offline I'll get back to you as quick as I can!
Sounds great. Talk to you tomorrow!
You replaced the intermediate shaft because of spline problems, what about the outer axle shaft? I've seen the ends of the splines wear there and the collar has nothing to grab when it tries to engage.
And you were able to hold the disconnect actuator in your hand, apply vacuum to it and watched it move full travel? I've seen some that would move but they wouldn't fully move to lock the shafts together.
I never asked you to elaborate on why you thought the shafts weren't locking together. Obviously you have a four wheel drive problem of some sort. Did you get all four wheels of the ground and put it in four wheel drive to verify that the axles aren't locking together?
All four wheels do spin in four wheel drive? If the wheels will all spin in four wheel drive then the axles are locking together. If they weren't locking together and you had it in four wheel drive, in gear, all wheels off the ground, only the rear wheels would be spinning.
If the collar didn't engage when you were in four wheel drive the only thing that will spin is the front driveshaft. The front driveshaft will drive the front differential carrier, which will then spin the component with the least resistance - the intermediate shaft that you can't see.
There isn't any limited slip in the front differential. Limited slip was optional in the rear, but all front differentials are open type.
Both front wheels aren't going to be locked together and driving at the same speed because it's an open differential and not limited slip. The only time they would spin at exactly the same speed is if it was limited slip.
If you had all four wheels off the ground, in gear and in four wheel drive, the front and rear driveshafts should be driving. If the collar is locked in then you will have at least one front wheel driving, the other front wheel may be spinning a little or stopped. If you have either front wheel driving when it's in four wheel drive, then the truck is operating normally.
Then at those times the axle shafts aren't locked together. At those times is when testing would need to be done. Only when they aren't locking together would be checking for vacuum, etc, be valid.
But you applied 16" of vacuum right to the actuator, drove the truck with all wheels off the ground and nothing in the front would drive but the driveshaft? If that's the case then the problem has to be the actuator, shaft splines, or internal in the differential carrier. Everything but the differential internals you say are new, but if you had damaged gears in the carrier the problem shouldn't be intermittent, and if it was then you would have some pretty extreme noise up there.