Pressure question.

[fng]

Here's a question I've pondered several times.
When you activate the fording handle in the cab, it closes off or opens up a valve under the aircleaner to provide possitive pressure to the drivetrain components...right?
So my question is, how much pressure is introduced? Is it enough to induce a leak in a weak seal? Would pvc flex line be strong enough to handle the pressure? As my truck was configured by the P.O., it had a pvc line running full length attached to the frame only (wasn't connected to anything, just flapping in the breeze). I wonder if this was the pressure line?
Thanks all.

[randyscycle]

I'd venture a guess that there wouldn't be too much pressure as the shifter boot would most likely relieve anything before it was enough to overcome the seal springs. That is of course, with new or very good condition seals.

I also doubt that the intent was to have the fording control closed for too long, but only the necessary time to get across the water obstacle and back onto terra firma.

[dave]

I cant see how it would build up any pressure but instead vacuum from the carb sucking in air so Im not sure how it could unless heat from the diffs, transfer case and tranny caused pressure to build somehow?

[kwai]

The fording valve does pressurize the axles, tranny and transfer case. The shifter boot should actually inflate since it is clamped around the tranny and the shifter rod. I would use fuel line which should hold the pressure. I wouldn't use the pvc pipe.

[k8icu]

What about the plastic tubing they use for the air lines on big rigs these days. Were talking 90-110 psi and those tubes handle it fine. I can't believe the pressure of the fording kit would get to that much pressure. It's only there to try to keep water out.

[randyscycle]

I cant see how it would build up any pressure but instead vacuum from the carb sucking in air so Im not sure how it could unless heat from the diffs, transfer case and tranny caused pressure to build somehow?

The fording system shuts off the PVC system to force the crankcase pressure up enough to pressurize the axles, t-case, diffs and master cylinder.

[2ndA]

I'll bet one of these will answer your question somewhere...

http://www.cj3a.info/sibling/cjv35u/evolution.html

http://www.steelsoldiers.com/deuce-m...it-update.html

http://www.archive.org/stream/Techni...rding_djvu.txt

[Warthog]

.... it had a pvc line running full length attached to the frame only (wasn't connected to anything, just flapping in the breeze). I wonder if this was the pressure line?
Thanks all.

If it is black and about 5/16", it may be your fuel tank vent. It connects to the fuel filler neck.

[Doug]

All you want it slightly more pressure than the water that's trying to come in has.

.43 pounds per foot of head, that's all your trying to overcome. IMO, 1-2 PSI would be plenty. How much the crank case creates is going to be determined by several factors. Total size of the leaks and condition of the rings being the biggest. A good engine with the crankcase vent plugged, or valved off, can create a bunch of pressure. Guy That used to work for us got the wise idea of replacing a faulty PCV valve with a plug for a temporary fix, once it built enough pressure it blew it out with enough force to dent the hood.

[Maingear]

I aree with Doug. If someone could put a T in the line and a small PSI gauge and check the pressure. If it does not maintain 2psi there is a potential for a leak in 5' of water.

It would be interesting to see if the pressure changes when rolling down the road.

My truck simply vents at air cleaner. The bulk of my transfercase oil leak came from the large hole in the T-case's top rubber line that went to the vent. I guess the gear oil slung over the vent hole as the oil expanded...?

I assume synthetic gear oil would absorb water like synthetic engine oil or brake fluid does.

Justin