C1 Axle Housing Vent

[John H.]

The rear axle housing vent hole has been welded/brazed shut on my 61 posi rear end. Both rear axle bearings are leaking. I believe as I replace the bearings I should also drill out and re tap the vent hole in the housing? I assume the vent is required to prevent pressure buildup in the housing due to temperature, forcing oil past the axle bearings? Can someone confirm my assumptions? Thanks for your time.
John

[Tom P.]

Re: C1 Axle Housing Vent

The rear axle housing vent hole has been welded/brazed shut on my 61 posi rear end. Both rear axle bearings are leaking. I believe as I replace the bearings I should also drill out and re tap the vent hole in the housing? I assume the vent is required to prevent pressure buildup in the housing due to temperature, forcing oil past the axle bearings? Can someone confirm my assumptions? Thanks for your time.
John

You have hit the tiny nail squarely on the head with a sledge hammer! When heated up and pressures build up inside the housing, the pressures have to have a means by which to vent off. Otherwise, if there is no vent, the seal is usually the weakest point for venting. Conversly, when the housing cools down, a negative pressure is going to occur inside the housing and there will be a tendancy for outside air to be sucked past the seal. After this process of venting back and forth through the bearing seals occurs (as well as the pinion seal), it is likely that your rearend will leak a lot.
The vent hole in the housing was not threaded, UNLESS it was a posi rear. The vent for a non-posi rear was steel and the end of the vent tube that went into the housing was serated, NOT threaded. I have to presume that the non posi vent tube was probably driven into the hole in the housing with a moderate whack of a hammer.
the Posi housings had a 90deg elbow that was threaded into the hole and then a length of 3/16 tubing was connected to the elbow and the other end of the tubing was retained by the clip at the center of the housing.

[John H.]

Re: C1 Axle Housing Vent

Tom,
This was my first ever posting with NCRS, thanks for confirming that vent issue for me, I really appreciate your quick reply and all the helpful information. After reading many of the C1 postings, I've come to appreciate your informative responses.
John

[Tom P.]

Re: C1 Axle Housing Vent

Thank you. You're welcome.

[James O.]

Re: C1 Axle Housing Vent

tom-that explains why my old vent won't unsrew. assuming i want to add the elbow and vent tube to a non-posi axle housing do i have to drill out the old breather vent and tap with the correct pipe tap thread? will the hole be the correct size to tap? thx, jim o

[Tom P.]

Re: C1 Axle Housing Vent

Jim,
If the original steel vent has not loosened up over the years, then it is TIGHT. I DO NOT recommend drilling because metal particles will for sure fall into the axle tube and eventually migrate to bearings and gears.
Here is how I have removed a couple.
Remove the left axle.
Using a long crowbar and something to slide under the end of the bar, I place the pointed end of the crowbar under the vent and push it out.
Next, shove some rags into the tube under the hole to catch metal particles.
Now you can thread the hole with a 1/8in pipe thread tap for the elbow.

[John W.]

Re: C1 Axle Housing Vent

James, you need to update your email address in the NCRS system. The email informing you of a response to this thread was bounced by verizon.

Go to the menu at the top of the page. Under SERVICES find "Change Your Address, Phone, Email".

[James O.]

Re: C1 Axle Housing Vent

thanks for good advice. will do. jim

[Ian G.]

Re: C1 Axle Housing Vent

Tom, any idea why the posi had the more elaborate setup? Just a little more icing for the cake?

[Tom P.]

Re: C1 Axle Housing Vent

OK, you asked, here is my speculation.
First, I've NEVER seen any official GM information explaining why the Corvettes did, and the pass cars (with positraction) did not have the additional vent plumbing.
For all practical purposes, the 56-62 Vette axle housings and the 55-64 pass car axle housings are nearly identical (as you know, they all share the same removable center section). The MAIN differences between Vette and pass car housings is the welded on attachments for springs and/or trailing arms. If you have ever seen the inside of a 62-earlier Vette POSI axle housing, then you've probably noticed some extra baffling which is NOT inside a NON-posi Vette housing nor a pass car housing. This baffling (hang on, I'm going somewhere with this) which is ONLY in Vette posi housings was an attempt to control oil slosh during severe (ie, competition) cornering and also keep the differential and gears lubricated.
I can only suppose that under very severe, high speed cornering, there may be enough lateral centrifugal force to cause enough rearend oil to go all the way to the end of the housing to the extent that oil possibly could come out of the regular vent tube. Thus, Vette posi housings got this additional tubing to prevent oil slosh from coming out the vent. Was it really necessary? I don't know, it never occurred to me to look under the rearend of these early cars to see if oil had sloshed over far enough to come out the vent tube. But that's my theory based on observing how hard these early cars were pushed on road coarses back in the day.
Soooooooo, why didn't pass cars with posi also have the extra baffling and the longer vent tube? Again, most probably because pass cars were never raced in the same kind of competition events as Corvettes, thus, no need for the extra baffling and vent in pass cars with posi.