Ideas for tracking vacuum leak?

[Pocket]

Got a vacuum leak, and it's not the lines at the ESOF hubs. I already pulled those lines off and capped it at the mount on the top of the wheel well. Even with both of them capped, if I select 4x4 on the dash switch, the A/C switches to defrost every time.

Now on the other hand, the vent controls work just fine. I can switch from defrost to dash vents to floor and there's no issue. Again, only when I select 4x4 does everything go to defrost.

So I've eliminated the possibility of the hubs and the lines at the hubs. What next? I'm gonna have to trace the vacuum lines that lead to each wheel from the vacuum pump. Any easy way to test and figure out where my leak is?

[That_Guy]

I think the only way is just the old fashion way of following all the lines, Id start near the tranfercase since its only happing in 4x4, but Im sure someone smarter will chime in

[Pocket]

I was thinking of a bicycle pump and a sprayer with soap and water........ Dunno if that's a good idea or not.

I did find the lines. They tee off near the passenger's side wheel well and the one for the driver's side wheel runs along under the engine.

[megawatt00]

I don't know how much vacume the pump will pull, if you take a can of spray smoke and you spray near the lines maybe you would see the smoke getting pulled into the break in the line. Kinda like you do with food coloring to find a leak in a pool.

[F350-6]

This may be a waste of time, but at least it's not much time. It seems like I remember reading of a similar issue where the after the ac switched to defrost, the guy would pop the hood and hit the vacuum pump with a wrench. That would temporarily fix his problem and it was a sign of a bad vacuum pump.

[zx250]

Unplug and cap at the 4x4 soleniod. If it still defaults, you have a bad soleniod. If not, continue to next fitting, the T fitting is bad to crack. The connection over the axle is probably where it is at. And your idea about soapy water will work, just rememer the lines and fittings are vacuum and not pressure, they will blow apart fairly easy.

[Pocket]

Originally Posted by zx250

Unplug and cap at the 4x4 soleniod. If it still defaults, you have a bad soleniod. If not, continue to next fitting, the T fitting is bad to crack. The connection over the axle is probably where it is at. And your idea about soapy water will work, just rememer the lines and fittings are vacuum and not pressure, they will blow apart fairly easy.

I think I'll try that.

One thing I did notice is there's no vacuum whatsoever at the end of those lines at each wheel.

[zx250]

I finally got tired of tracing those leaks, plugged all my lines, and installed my Warn Premiums. Haven't regreated that move yet.

[Pocket]

Originally Posted by zx250

I finally got tired of tracing those leaks, plugged all my lines, and installed my Warn Premiums. Haven't regreated that move yet.

I thought about that, but dang it's nice when the snow hits and I can just flip a switch and have 4wd without ever having to step out of my truck. My stock hubs still work perfect too.

[donewithsparkplugs]

this a good way to find the really hard to find leaks. they sell a tool to do it for about 2500.00. it blows smoke. It works great.
step 1 go to local smoke shop buy stogy
step 2 goto auto store buy 1 foot vac hose and connector
step3 get a friend to look for smoke
step 4 hook up 1 end of hose at 4x4 sol to the side with out vac blow smoke in the other end of hose.

total cost less than $5

[Pocket]

Originally Posted by donewithsparkplugs

this a good way to find the really hard to find leaks. they sell a tool to do it for about 2500.00. it blows smoke. It works great.
step 1 go to local smoke shop buy stogy
step 2 goto auto store buy 1 foot vac hose and connector
step3 get a friend to look for smoke
step 4 hook up 1 end of hose at 4x4 sol to the side with out vac blow smoke in the other end of hose.

total cost less than $5

But I have asthma, so I'll let the friend blow smoke while I look

[mueckster]

Originally Posted by Pocket

But I have asthma, so I'll let the friend blow smoke while I look

You know second hand smoke is bad for you too.

[donewithsparkplugs]

if done right it wont just be your 7.3 bowning smoke.