Front Diff - leak identification (opinions / advice requested)

[Reprise]

Ok - to levelset before we get into the weeds...

This is for a Sierra 1500HD, with 9.25 front diff. 3.73 gear, but I don't think that is relevant here...

First, some pics for reference... (all are from the left / driver's side; the RH side is leak-free, currently)

Orientation - 1-3 'under' diff, looking 'up'
4-8 are 90' off - flip 'rightward' for correct orientation (I tried to reorient; they show up ok on my PC, but not here... (known issue, it appears))



Pics 1-2 have the axle shaft in for reference only. I was amazed (read: pleased) at how easily I was able to remove the shaft - with circlip intact. Yay me.

Fluid has been drained, but you can see...this is a fairly substantial leak. While I didn't measure the amount that came out (I can still do so), I'd estimate at least a quart was drained (cap is 1.8 qt, so we'll assume it was no less than half full). No (known) noises when I've engaged 4Hi / 4Lo, to check their operation.

My assumption prior to pulling the axle shaft was that the outer seal needed replacing - and I have a Timken, ready to go.
However (starting at pic 4 forward)... it doesn't appear *to me* that the fluid is coming from the outer seal area, but from *behind* it (that darker gray section with the retaining clip / bolt is ident'd as the Front Bearing Differential Adjuster - which seems (?) to be the source of the leak.

Looking at the service manual, when we start talking about R&R of that Adjuster, GM starts talking about special tools, preload this / that, etc., etc.
Online, when I look for leak resolution on the 9.25", people talk / show mostly outer axle seals, and sometimes the 'bearing' - but in all cases, the work is done without touching the adjuster 'cover'.

I'm fine with getting more parts, as needed (if I need to replace the bearing, I'll get one of the improved versions, with 'end to end needles' in the bearing race - which doesn't look especially bad, to my untrained eye, btw.)

What I don't want to do is put on the outer seal and find out I'm still leaking, later.

Thoughts? Replies appreciated, as always. I'm not in an extreme rush. And I don't penalize on longish posts...LOL

 

[Reprise]

Bumping my own thread (not 'cos I'm in a rush, but so that if I need to get some more parts (up to / including a 'full rebuild kit'), I can get them ordered / delivered by the time I get back in town; leaving today for 'points east'). Thx.

PS: If this leakage is indicative of something 'fatal' (thinking 'not'; based on my continued research, the 9.25" appears to be a fairly robust unit), I'm inclined to rip out the diff (if that's even possible, since it's apparently considered part of the 'Independent Front Suspension' - and I'm not looking to go 'solid axle').

Obviously, 4WD isn't an area of expertise for me
(but then, neither is HVAC, or body / chassis, or electrical, etc., etc., etc...)

 

[Sparky]

How does that adjuster come out? I'm guessing it screws in and that bolt holds it in place. Any idea how it seals - is there a gasket behind it?

 

[Reprise]

(on edit: "Yes", to Sparky's question about what's behind the adjuster - the exploded parts diagram / listing shows an O-ring immediately behind that adjuster. So I need to focus there, for starters)


That's what I was trying to find out...was hoping that someone here had 'been there' before. I didn't want to take it apart, and botch things up further (there's all kinds of stuff in this section of the service manual about backlash & preload - not just for the ring / pinion, but for the pinion bearings - and different specs for 'new' vs. 'used' bearings.

I had the feeling that if I moved that cover / adjuster, that I'd have to set preload again, and I really don't have a clue about doing that. Need to do some more research while I'm OOT; hopefully, I'll have an idea about what the hell I need to be doing, when I get back.

(This'll be my last post on GMTN for the next couple of days - thanks to all who did / will respond.)

I've read that the vent tube can be a cause of leaks sometimes (it gets blocked up, pressure builds up, and fluid starts leaking out of the seals). That's something to look into, as well.

I'll paste some info on 'leaks' from the documentation (if anyone would like a copy of either this section, or the whole damned manual (1999-2006 'OBS'), send me a PM, and we'll work out somewhere to either drop off a copy, or mail you a CD. The nice thing is that the '2006' documentation is keyword searchable (Ctrl-F), which is really useful - I tend to gravitate to that subfolder.)

From the manual: (and I'll comment with '###', just at the top )

FRONT AXLE LUBRICANT LEAK DIAGNOSIS
Front axle lubricant leaks can occur at the following locations:
 Axle shaft oil seals ### 'obvious', I thought, until I removed the axle shaft
 Differential carrier assembly mating surface ### not for this instance
 Drain plug ### no, but the casing appears 'porous', just as an aside
 Fill plug ### same; gaskets on both are ok (plastic)
 Inner axle tube assembly to differential carrier assembly mating surface ### ???
 Pinion yoke oil seal ### strongly suspecting
 Vent tube ### could be a factor

Determining the Cause

While most front axle leaks may be easy to find, determining the cause may not be. A thorough inspection of
the area around the leak may assist in determining the cause of the leak.

Oil Seals
Lubricant leaks from a oil seal may be caused by any of the following:

 An improperly installed seal
 A distorted seal
 A worn seal
 A worn shaft
 A brittle seal lip
 A hardened seal lip
To determine the actual cause of the leak, clean the area around the leak. Observe the area of the leak and
determine the if the seal or another component is causing the leak. A worn seal surface will cause a leak at the
sealing lip while a misaligned seal or a seal installed into a housing with an excessive bore will cause the seal to
leak at the outside surface of the seal. Hardened or cracked seal lips usually indicate the axle is operating
beyond the normal temperature limits for the axle. A seal whose sealing surface has been nicked or cut may
indicate that the shaft has a rough, burred, or gouged surface and will need to be inspected before the seal can
be replaced.
Sealing Surfaces
Front axles components are assembled using specific sealers. A leak at a surface sealed with sealant is usually
caused by a poor fit of the components but can also be caused by the use of the wrong sealant. When correcting
a sealant leak, inspect each component for distortion and for nicks or gouges that may prohibit the sealant from
sealing properly and when re-assembling the component, use the proper sealant.

Differential Carrier Assembly

Lubricant leaks at the differential carrier assembly can occur at the following locations:

 Drain Plug
 Fill Plug
 Vent tube
Drain and fill plug leaks are usually caused by a loose plug. A vent tube leak can be cause by a loose fitting vent
hose or by a vent tube assembly whose interior shield is stuck in the upside down position. Inspect the vent
plug's interior shield for unrestricted movement, repair or replace the plug as necessary. Drain or fill plug leaks
can be repaired by either tightening the plug or by using an approved sealer on the threads on the plug.