Hi all

Got a few questions...noticed a puddle of gear oil under my '99 Dodge 3/4 ton 4x4 (V10). After poking around under the vehicle and looking in a Haynes manual, it appears that the gear fluid came from the vent hose from the vacuum shift motor. #1, why would fluid shoot out of the vent line? is the motor faulty? #2 what exactly is this vacuum motor's function? #3 Do I need to replace it, or just top off the fluid? if so, how do I top it off? Thanks for any tips or advice...

Armor

 

Not sure if I helped any, just sharing info.

OPERATION
The shift motor receives a vacuum signal from the switch mounted on the transfer case when the vehicle operator wants to switch from two wheel drive mode to four wheel drive mode, or vice versa. When this signal is received, the shift motor begins to move the shift fork and collar within the axle housing. In the four wheel drive mode, the shift collar connects the axle intermediate shaft to the axle shaft to supply engine power to both front wheels. In two wheel drive mode, the shift collar is disengaged from the intermediate shaft and the intermediate shaft is allowed to free-spin. When the two shafts are disengaged, the load on the engine is reduced, thereby providing better fuel economy and road handling.





LUBRICANT CHANGE
[*]Raise and support the vehicle.[*]Remove the lubricant fill hole plug from the differential housing cover.[*]Remove the differential housing cover and drain the lubricant from the housing.[*]Clean the housing cavity with a flushing oil, light engine oil or lint free cloth. Do not use water, steam, kerosene or gasoline for cleaning.[*]Remove the sealant from the housing and cover surfaces. Use solvent to clean the mating surfaces.[*]Apply a bead of Mopar® Silicone Rubber Sealant, or equivalent, to the housing cover
Typical Housing Cover With Sealant

[/ol]
Install the housing cover within 5 minutes after applying the sealant.
[*]Install the cover and any identification tag. Tighten the cover bolts in a criss - cross pattern to 41 N·m (30 ft. lbs.) torque.[*]Refill the differential with Mopar® Hypoid Gear Lubricant, or equivalent, to bottom of the fill plug hole. Refer to the Lubricant Specifications in this group for the quantity necessary.[*]Install the fill hole plug and lower the vehicle. [/ol]

 

i would guess that the vent hose is split, allowing oil from your differential to leak out. if so, just replace it. the vent hose is routed up to the top of the fender liner, and should be attached up there. it should also have a check valve thingy at the end that lets air in/out but keeps dirt and bugs out.

the vacuum motor is mounted outside the differential, and has a shaft and seals (i think) that stick through the cover. it might be leaking around those o-rings.

you don't need to worry about the vacuum motor itself unless its not shifting in/out 4 wd. its really nothing more than a vacuum diaphram with a fork attached to it.

check your front fluid by removing the plug on the front side of the pumpkin, about 1/2 way up. fill it with 75w90, or 80w90, or 85w90 (doesn't matter), until it starts to run out the plug hole. full is actually just below the hole, but a little below or at the hole doesn't matter.

its a good idea to change the front and rear diff oil every year or two.
http://www.pavementsucks.com/tech/diff.php

 

thank you for the replys....

I checked the fluid back in June when I got the truck and topped it off. The gear fluidcame out of the very top of the vent line and dripped down from there. I guess I'm wondering what would cause fluid to get forced all the way up that vent line. Also, I was under the impression that the vacuum motor had its own supply of gear oil (the manual says to add 5 oz. of it into the motor when replacing it)...does it share gear oil with the front differential?

Armor

 

i guess it depends on what we're talking about vith 'vacuum motor'

there is no oil inside the vacuum diagphram, which is the round shiny piece sitting outside the differential. it has a shaft that enters a square block cast into the axle tube.

inside the square block, you are now inside the axle tube, and yes it does share oil with the axles, r&p, bearings, etc. inside this block is the ends of the inner and outer axles, the coupler, shifting fork. there is a fitting screwed in there, which the vent hose attaches to, and its routed up inside the fender.

oil should not be squirting out of this hose. i'd remove the hose and check it out. the fitting should be open into the differential and you should be able to squirt air or oil through it. a few drops of oil might drip out, probably not a lot, as its pretty high up, and above the normal full level of the oil. the hose should be open and you should be able to blow air through it, and maybe suck air through it (not sure), i don't think its a true one-way check valve. i think its lets air pass both ways.

 

Thanks for the help. I checked the front diff. gear oil, it was about a pint low, so I topped it off. 4WD still engages and disengages fine....anybody have any ideas on what would cause it to puke gear oil out through the vent line?