2nd Gen Non-Engine/Transmission Vacuum problem with 4 wheel drive.

[RNelson]

Hey guys,

I'm troubleshooting a couple of problems that may be related.

1. My 4 wheel drive won't engage. I can shift into 4H or 4L, but I don't get the indicator light, but I do get the front drive shaft turning. I have no vacuum to the vacuum shift motor on the front axle.
2. My cruise control doesn't work (can turn on, but it won't accept any settings or resume).
3. No A/C

I have an '01 with the 6 speed manual. The service manual says speed control system is fully electronically controlled by the Engine Control Module (ECM). A cable and vacuum controlled servo are not used if the vehicle is equipped with a manual transmission and a diesel engine. This is a servo-less system. In the attached photos it looks like I have a servo. This is mounted under the driver side battery tray. There is a vacuum line that has been disconnected from something and I can't find out where it's supposed to go. I can feel a vacuum suck if I hold my finger over this line. Any idea what this is supposed to go to?

 

[mwilson]

Hey guys,

I'm troubleshooting a couple of problems that may be related.

1. My 4 wheel drive won't engage. I can shift into 4H or 4L, but I don't get the indicator light, but I do get the front drive shaft turning. I have no vacuum to the vacuum shift motor on the front axle.
2. My cruise control doesn't work (can turn on, but it won't accept any settings or resume).
3. No A/C

I have an '01 with the 6 speed manual. The service manual says speed control system is fully electronically controlled by the Engine Control Module (ECM). A cable and vacuum controlled servo are not used if the vehicle is equipped with a manual transmission and a diesel engine. This is a servo-less system. In the attached photos it looks like I have a servo. This is mounted under the driver side battery tray. There is a vacuum line that has been disconnected from something and I can't find out where it's supposed to go. I can feel a vacuum suck if I hold my finger over this line. Any idea what this is supposed to go to?

It looks like the battery acid / fumes have rotted the line off. My '97 and Seth's '97 both did the same thing. That line that you have pictured is the feed line for the cruise unit. That leak is affecting the 4wd and the heater.

I've got a spare cruise servo out in the shop. I will take a picture of it in a bit so you see where the vacuum line attaches.

Mike.

 

[RNelson]

Thanks Mike. I'm still confused though, because according to the service manual I shouldn't even have a cruise servo since I have a diesel with the 6 speed manual transmission.

 

[mwilson]

Service manual is wrong, an '01 Ram with a VP44 will not be drive by wire AFAIK.

That is a cruise servo in your pictures for sure. I'm headed out in a minute, will get a picture of the line connection.

 

[mwilson]

The vacuum line is on the opposite side from the wiring connector.

 

[RNelson]

Mike,

thanks for the great pictures. That helps a lot. Now to see if I can manage to reconnect the line without having to pull out the battery and battery tray.

Reed

 

[SnoKing]

Somewhere in late 2001 early 2002 models they switched to cruise by wire. My May 2001 build has the vacuum cruise. The vacuum line from the pump should go up to the top of the firewall to a four way splitter. Coming off the lower drivers side of the splitter the cruise line comes down and enters the braided cover with the cable going back up to the APPS and connects to the servo.

If the line is just cut, slip a piece of rubber vacuum hose over the ends to reconect. Chris

 

[RNelson]

Got the vacuum line reconnected to the servo, but still no 4 wheel drive or cruise. Must have another vacuum leak somewhere else. #@$%!

 

[SnoKing]

Got the vacuum line reconnected to the servo, but still no 4 wheel drive or cruise. Must have another vacuum leak somewhere else. #@$%!

Take the line off up on the firewall and put your vacuum gauge there or block it and try 4x4 mode. Servo may be rusted out. Chris

 

[RNelson]

good suggestion, thanks Chris.

 

[BDaugherty]

My 00 truck had vac cruise, but my 01 did not...I can't remember the build dates.
Start at the vacuum pump and follow the plastic line up to the firewall. I see most of the breaks in that section. If it's good there, check it for vacuum and then trace it further.

 

[Road Dog]

My late build '02 has a servo for cruise control. It was also built in Mexico.

 

[SnoKing]

My late build '02 has a servo for cruise control. It was also built in Mexico.

Mine is a Taco Truck also. Chris

 

[RNelson]

Bought me a vacuum check tool from NAPA. I have good vacuum out of the pump and good vacuum to the outer port of the vacuum shift motor on the axle. I also have good vacuum to the cruise servo. Still can't get 4 wheel drive to engage or the cruise to accept a setting. I took the vacuum shift motor off to make sure it moves freely and it does. Reinstalled shift motor, added my gear lube and tried it again. No luck. Troubleshooting guide says if vacuum is okay, apply vacuum pump to the outboard shift motor port and rotate wheel to see if front axle engages. It does not. However, if I apply vacuum pump to inner port and rotate the wheel, the axle engages. I can't seem to find out what triggers vacuum to the inner port.

 

[RNelson]

OK, think I've found the problem now. The black line coming from the transfer case switch going to the vacuum shift motor is the leaking culprit. It had rubbed against the front drive shaft and wore a hole in it. Off to NAPA to get a vacuum line repair kit.

 

[RNelson]

Sigh, fixed that leak, but 4WD still won't engage. Back to the drawing board checking for leaks.

 

[SnoKing]

Put the vacuum gauge on the front axle on the line that should engage it. Then try 4x4 position on the shifter and see if it gets vacuum to the from axle. Diaphragm in the CAD motor is noted to fail. Chris

 

[RNelson]

That was going to be my next step. Diaphragm is good as I can manually apply vacuum with the tester and get it to engage.

 

[RNelson]

So I fixed the vacuum line from the transfer case switch to the vacuum shift motor on the front axle, still no vacuum on the inside port when I switch to 4WD. Vacuum does go to zero when in 4WD on the outside port and produces vacuum when I switch back to 2WD. So, I figured the transfer case switch must be bad. Ordered and installed a new switch, but still can't get vacuum to the inside port when in 4WD. I verified there is no longer a leak from the inner port to the vacuum switch. I'm at a loss now. #@$%!

 

[SnoKing]

What about the diaphragm in the CAD motor? Chris