Pressurized drivetrain?

I recall reading in an issue of JP an article about an early 40's vintage jeep, i think it was military. It mentioned something about a system that uses positive crankcase pressure to slightly pressurize the transmission, transfercase and differentials to keep water out when fording. It looked like it was a special manually controlled pcv valve type deal. Anybody know what i'm talking about? And has anyone tried to make their own system? Seems like a good idea to keep water out. I'd like to try and rig something similar on my 66.

thanks

Austin

 

it seems to me my m38a1 had a setup kinda like what you describe. it had steel lines coming from the vents on the transmission, or maybe the transfercase or both going to the air filter and there was a valve on the pvc system. but it was not all there, so as far as what the valve did i am not sure.

 

there was nothing special about the venting on my diffs though, it was same as a civvy

 

I guess they'd need the vents on there to keep the pressure from pushing seals out.

 

http://www.jpmagazine.com/featuredvehicles/154_0711_1958_us_military_jeep_air_farce_m38/index.html

M-38 and on. My '68 M-715 had a similar setup when I first bought it.

Puts a positive pressure in the gearboxes/axles/engine to keep water from getting sucked into the systems. When a hot axle or engine encounters cold water it can sometimes suck in water even if the seals are in decent shape. With the positive-pressure system you can pull the fording lever before hitting a water crossing. If you park it with the diffs/gearboxes under water and the engine running you can actually see little bubbles coming out.

 

Yeah thats the article i was thinking of. That is a sweet looking rig with the 34's on it. Thanks for the info.

 

hmmm, intresting idea.
Now that I think about it, whilist I was in the army in the 70's there were these mobile bridge units called M.A.B.s. They rolled into the water, the decking would turn and thye hook together to build bridges or rafts.
A G.I. would hit a lever and bubbles would come from the wheel wells.
I would think if you do a LOT of stream crossing,, if you took a small 12 volt compresser, some sort of regulator, (you'd have to keep the PSI down to 1-2 PSI, you could make one that'd work dandy.
Hmmmm intresting idea.....
Joe
One idea get's the rusty gears in my noggin to turning!

 

Its a cool system but think it all through before jumping in. The M38 had a control on the dash "pull for fording" you also were supposed to install a 1/2" pipe plug in the bellhousing before fording. The lever pull blocked off the PCV system and also closed a vent on the block. The block then was developing internal pressure.
That pressure was plummed with steel tube from a vent on the fuel pump to the bellhousing, transmission and transfer case. The production jeep did not have axle pressurization, the 7 prototypes may have tinkered with it. The system works if all gaskets and seals are in place. The M38 is meticulously sealed with o-ring seals on the disto and a sealed carb. All venting routes back to the air cleaner including the master cylinder and there is a snorkel kit for the AC and exhaust.
Since the coil is in the distributer, one of the vents forces cooling air through the inside of the dist to keep the coil from overheating.

That system stayed in place for the first run of the M38A1 but was soon dropped.
It takes some work to get it right, when it is not set up properly you create all kinds of pressures in places where it shouldnt be and can blow seals or cause your engine to run poorly.

If you go the external pressure route be sure you have pressure relief valves so that your seals dont take the beating.

It was definately a cool idea.

Tom

 

someone on my local board mentioned something about using a fish tank air pump into the trans dipstick tube (32rh with the horrible vent hole behind the torque convert)..i inquired as the tj has a 32rh,,but never heard back..

 

Jeesh, my HEEP leaks enough oil unpressurized, I think I'd be out of fluid in a hurry if I actually forced it out.

 

That's what I don't understand about all these guys putting snorkel's on their Wranglers and calling it waterproof. The intake on the engine is only one part of making a jeep waterproof, especially on new vehicles with electronics. Before the M-38, during WW2, there was a water fording kit the GI's could put on the GPW's and MB's. It was kind of messy though. Ontop of putting a snorkel on the intake and exhaust, they would use this white plaster goop on the sparkplugs, electrical and so on. The jeeps most seen doing this was on the French landings. If you guys ever see any old WW2 jeep photos, the way you can tell if it was "waterproofed" was they would put a small american flag sticker in the bottom left hand corner of the windshield about 7"x5" On the back it had a checklist of all the stuff done.

 

The WWII windshield flag was awesome.
the back had "just before you wade" and a checklist on what to put AWC (asbestos waterproofing compound) smear all over.
then it also has "when you get there".
clear he beach and head to the de-waterproofing area!
open the battery vents!
open the distributor vent!
Check the oil level for water
use flushing compound on generator and starter
get the air cleaner back on
- your vehicle needs maintenance - get it done!!

what they dont say is that people are shooting at you from all directions .

 

Wow...impressed....didn't know anyone else knew about those. My dad has a reprint of one that's in his GPW

 

Ive seen an article somewhere about doing this with on-board air.....junkyard genius i believe....