4-Wheel Drive actuator vacuum lines - Help

[dresslered]

Which of the two vacuum lines (red or black) leading up to the Front Axle Shift motor should measure a vacuum while in two wheel drive mode? (Please specify by inner/outer port as well as color)

My '01 Service Manual says that the inboard port should have the vacuum. My '01 truck indicates that the outboard port (red) has about 24 inches. of vacuum. Is this one of those things where it doesn't matter, or was it installed backwards at the factory? The 4WD feature has always worked fine. It just happens to make a difference when installing the new style BD 2WD LO kit. Thanks,

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David Dressler
2001 Driftwood 3500 Quad Cab 4x4, 155 inch WB, HO Cummins (ETH), 6-Speed (DEE), SLT+, 3. 54 LSD, Camper Special, Trailer Tow, Heated Leather, Sliding Window, Jacob's E-Brake, Rhino Liner, VDO Vision (pyro, boost, engine + diff. temp. ), Weather Guard Diamond Plate Saddle Box, Tork Lift camper tie-downs, Mag-Hytec, Mopar Tow Hooks, AND functional Halo light!
Bigfoot 3000 10. 11 Slide-in Camper. "Do it in a Dually"


[This message has been edited by dresslered (edited 01-15-2001). ]

 

[Gohon]

Originally posted by dresslered:
Which of the two vacuum lines (red or black) leading up to the Front Axle Shift motor should measure a vacuum while in two wheel drive mode? (Please specify by inner/outer port as well as color)

My '01 Service Manual says that the inboard port should have the vacuum. My '01 truck indicates that the outboard port (red) has about 24lbs. of vacuum. Is this one of those things where it doesn't matter, or was it installed backwards at the factory? The 4WD feature has always worked fine. It just happens to make a difference when installing the new style BD 2WD LO kit. Thanks,

David I don't have a service manual nor am I a 4X4 tech but 24lbs is not a measurement of vacuum but a measurement of pressure. Vacuum is measured in inches. If this is not a typo you might want to double check the service manual.

Jerry



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1999, 2500 QC 4X4, Driftwood,Auto, Stock, Cab High Shell, Tow Package, Camper Package.

 

[Jff24Gordn]

Fluid dynamic lesson...
A pure vaccume has 0 air pressure. The atmosphere has 14. 7 psi of pressure. All pressure gauges that you are gonna run across on a truck use the atmosphere pressure as 0 to make life easy. Except barrometric pressure s measured from a vaccume and measured in inches of mercury. So a pure vaccume has 14. 7 psi of vaccume. There is no way in he| | to get more then 14. 7 lbs of vaccume unless you are in a pressurized enviroment.

Still awake?

dresslered states that he has 24 lbs of vaccume. This aint possiable. More than likely, you put the wrong unit and its 24 inches. I think it would be in inches of mercury. The most vaccume that you can get is the same at the barrometric pressure. Around 30 inches.

I think the manual or the hoses are backwards. What is the pressure reading on the other hose?

If you want more of a physics deffinition, ask.

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1996 2500, 4x4, 5 speed
-- email address removed -- Great Lakes TDR
PURDUE STUDENT 
GO BOILERS

 

[dresslered]

Now don't I feel like the horses A$$. Can I change my post to read "inches. " I was also adjusting the tire pressures at the time and had "psi" stuck on the brain (the difference between sucking and blowing).

Actually, one line is suppose to have vacuum (measured in INCHES) in the 2WD mode and the other is suppose to have vacuum (measured in INCHES) in 4WD mode. I was just wondering about the discrepancy between the manual and the way my truck is "hooked" up? Sorry for the confusion.


[This message has been edited by dresslered (edited 01-15-2001). ]

 

[Jff24Gordn]

Sorry, that might have been a bit harsh, some stout helped me on the wording of that post.

Do you think the guy who wrote the service manual was ever under your truck?? I bet the book is wrong, or someone at the plant thought someone will go nuts trying to figure out what goes where if I switch the hoses around.

 

[Gohon]

Originally posted by Jff24Gordn:
Fluid dynamic lesson...
A pure vaccume has 0 air pressure. The atmosphere has 14. 7 psi of pressure. All pressure gauges that you are gonna run across on a truck use the atmosphere pressure as 0 to make life easy. Except barrometric pressure s measured from a vaccume and measured in inches of mercury. So a pure vaccume has 14. 7 psi of vaccume. There is no way in he| | to get more then 14. 7 lbs of vaccume unless you are in a pressurized enviroment.

Still awake?

dresslered states that he has 24 lbs of vaccume. This aint possiable. More than likely, you put the wrong unit and its 24 inches. I think it would be in inches of mercury. The most vaccume that you can get is the same at the barrometric pressure. Around 30 inches.

I think the manual or the hoses are backwards. What is the pressure reading on the other hose?

If you want more of a physics deffinition, ask.

Hmmmm..... you were right all the way up until you said "a pure vacuum has 14. 7 psi of vacuum". PSI (pounds per-square inch). Vacuum (the absence of pressure). A compound vacuum pressure gauge has the 14. 7 built into the "0" reading. You show 150 # on the gauge you have a 164. 7 # true reading. On the vacuum side the gauge will not read the first inch of vacuum until the 14. 7 psi has been removed from the line or container, thus moving you into a vacuum state. A true vacuum is 0-29. 9999 inches of mercury. A perfect vacuum is 30 inches of mercury but is impossible to obtain so I'm told. Wow... David I'll bet you wish you hadn't been putting air in your tires last night.

Jerry

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1999, 2500 QC 4X4, Driftwood,Auto, Stock, Cab High Shell, Tow Package, Camper Package.

 

[Phil Stuart]

Gohon,
You are correct. There is no such thing as a perfect vacuum here on earth. Only out in space. A lightbulb has a vacuum(not sure how much)but if it did have a perfect vacuum the glass surrounding the element would implode. As for pressure,PSIA=Pounds per square inch absolute. PSIG=Pounds per square inch gauge. PSIA is Pressure minus atmosperic pressure of 14. 7. PSIG is Pressure plus the atmospheric of 14. 7. When you look at a gauge that reads say 30psi,this is including atmospheric pressure(30+14. 7)even though the gauge reads only 30PSI. I learned this in air conditioning service. Hope it helps.

Phil

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`01 2500,4x4,QC,LB,ETC,DDX,DHG
3. 55 LSD,Tow Pkg. ,Snow plow pkg. ,Forest Green PC,Mopar alum. side steps,Mopar mud flaps with Cummins logo,Mist grey seat covers,Tekonsha brake controller,Hadley air horns,Pacbrake.
Built in St. Louis
THE BIG GREEN MACHINE

Phil Stuart

 

[dresslered]

Now that I think that we've got the pressure thing worked out, let me re-phrase the question:

I am trying to understand how the "new style" BD 2LO SW kit is suppose to work by venting one of these lines continuously. I have been unable to get any technical support from BD over this matter (it seems that MANY of the people that know are out of the office). Thanks for any help on the matter. I've got my thermodynamics book in front of me so that I can brush up on my units.

[This message has been edited by dresslered (edited 01-16-2001). ]

 

[dresslered]

Thank you TDCanuk!

I am not trying to critizise BD in any way--just a little impatient since I ordered the original kit in August of last year which was found to be defective. My concern with the new set-up is that my red line is a constant vacuum source when in the 2WD mode. This source is then constantly vented at the spool valve. It doesn't sound right to me to have the vacuum line constantly opened unless I am missing something.

I realize that there are quite a few truck shows going on and that is why I have been sitting on the sidelines patiently. Thanks for your help.

[This message has been edited by dresslered (edited 01-16-2001). ]

 

[Dak - BD Power]

OK, I went out on my own and tracked down the minds that be on this little beauty #ad


At the front diff is the actuator diaphram of the front diff locker and there are 2 hoses, one black and one red. The red one is to the passenger side or outside and the black is inside or to the driver's side.

STOCK OPERATION
When the lever in the cab is in 2-wheel position the vacuum switch on the transfer case allows engine (vacuum pump) vacuum to be switched to the Red line which in turn applies vacuum to the outboard side of the actuator, keeping the front diff disengaged.

Still with me I hope #ad
When the lever in the cab is put in the 4-wheel position, the vacuum switch on the transfer case vents the Red line vacuum to atmosphere and applies vacuum to the Black line, thereby applying vacuum to the inboard side of the front diff diaphram and engaging the front diff locker, ergo 4-wheel drive. #ad
(Am I getting good at this or what #ad
)

BD 2-LOW KIT
BD installs a T-fitting into the Red line and by throwing the switch to engage the 2-Low control valve it controls the vacuum in the Red line to ensure the valve stays disengaged.

In the old design the 2-Low control valve only cut off the vacuum to the Red side leaving the diff diaphram to 'freewheel', lets say, which sometimes allowed for 4-wheel application when going over rough terrain because nothing was keeping the diff diaphram from moving either way.

Whew, I think I'm finished #ad


Vic... BD Product Support

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Real BOMBers never get speeding tickets. . just a lot of warnings!

 

[dresslered]

Gosh Vic, you're great! You have now confirmed the error in the service manual (either that or both of our trucks are hooked up backwards). Perhaps, if you could supply me with one more bit of information, I would be on my way.

Could you please indicate which ports of the spool valve get which vacuum line (instructions actually refer to hooking two separate hoses both to the right front fitting). The picture shows otherwise. I interpret that the firewall vacuum splice goes between ports 1 and 2. The long hose from the drive actuator goes to port 4. The vent goes to port 3.

The problem that I see with this, is in the "unswitched" position, the red actuator line (port 4) is connected directly to the breather (port 3). This results in a constant vacuum leak. Is this really correct? Thanks again for your wonderful support. You never even mentioned the use of improper units of measure. #ad


UPDATE:
I was at a local TDR meeting (RamRunner's) last night and a couple other new 2WD LO switch kits had showed up. So far the concensus is that these kits can not be hooked up according to the instructions. It almost seems to make more sense if the filter is replaced with a plug. Please correct me if I'm wrong.

-David

[This message has been edited by dresslered (edited 01-17-2001). ]

 

[Dak - BD Power]

dresslered, obviously there is a small communication problem at BD. . about half the staff are all over the continent attending RV shows, etc...

The 'new style' which BD calls a RetroFit kit incorporates some extra hose and tees and is designed to apply vacuum to either side of the control valve at the diff to ensure either positive engagement or disengagement of the valve. This is done by teeing off of the Red actuator line at the front diff.

The first generation, lets call it, only vented the valve to ensure it did not engage but it was found that when going over rough terrain the valve would jump into application after a good bump, this was not good. So now they control the valve on or off.

Hope this helps, and yes there are more than 2 or 3 people at BD that knows how things work #ad


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Real BOMBers never get speeding tickets. . just a lot of warnings!

[This message has been edited by TDCanuk (edited 01-16-2001). ]