Installing zerk fitting for birf lube? (1 Viewer)

[IdahoDoug]

With a repack coming up on the 93 I'm starting to get prepped. One thing I'm considering doing is drilling the outer axle through and installing a zerk fitting on its tip so I can refresh the birf from time to time merely by pulling the plastic wheel center and the metal cap. Tried a search to no avail. Has anyone actually done this yet?

Also, I'm interested in any engineering perspectives in terms of what would this do to the axle stub's strength? I'm of the opinion that the axle's strength to rotational forces comes mostly from its outer diameter, and that this will not change that materially. This would be a hold drilled through its entire length for grease to flow directly into the birfield joint.

I am looking forward to this repack for a couple reasons. One, as veterans of this site will recall, I changed the position the inner axle runs in the inner axle seal by purchasing a shim kit from Dan when I repacked and moved the knuckle downward. Toyota does not have a provision for doing this realignment as older knuckles had. Mine had been running against the 12 O'clock position badly enough it hit the metal part of the seal's retainer. So I will now see a wear pattern that will tell me if I succeeded (there is no way to know until I reopen it and examine where the axle's been rubbing on the seal) in recentering. Two, I repacked with Amsoil and ran it 60,000 miles this way so I'll be interested in how that top shelf grease held up. There has been zero leakage in all this time - indicating the inner seal has likely been properly centered and still intact.

So, comments on drilling the outer axle and installing a Zerk in terms of strength or other issues?

DougM

 

[e9999]

there was at least one thread that I recall discussing this, but I don't remember somebody saying that they had actually done it.

some thoughts:
- depending on what you want to see with this Amsoil test, maybe put in some different color grease a bit before you open it up to see how good the mixing is, since some folks have commented on this working well before.
- intuitively (and no more than that) I can't see that a minute hole in the center would affect the strength very much. Good thing is that with the pressure a grease gun can generate, a very small hole will do.
- it will be interesting to see how easy it is to drill this hole. Pretty long for the diameter it seems. As mentioned earlier, people who drill gun barrels do this but it takes special equipment, and the holes are a tad bigger. Not so sure that a regular machine shop could do it well. Maybe with EDM?

 

[adam4x4]

I would see if someone (or maybe you do) has an unusable axleshaft to see how the drilling goes. That way the 1st time won't set you back if it doesn't go so well. Interested to see how this progresses. Sounds like a good, workable idea.

 

[cruiserdan]

I believe cruiserdrew had put some different color grease in through the fill plug and found that it did migrate into the joint.

I would not drill through the stubshaft.

 

[IdahoDoug]

Dan,

I wouldn't drill through the shaft, either. Would take it to a machine shop. Is that what you're saying, or do you feel it could cause a durability problem?

It seems like the outer stub shafts are pretty bulletproof and that the inner axle (spline area), the ring/pinion, and the birfield joint will ALL break first from everyone's experience. I don't believe anyone's ever damaged an axle stub/outer axle. Given that, and that the shaft's strength comes from its outer diameter, I cannot see a reason to worry unless you get a machinist to muck up the part for you. Or if it turns out to be $150 worth of work, of course.

DougM

 

[Tools R Us]

Something like this?

http://www.gearingdynamics.com/greasecv.htm

 

[Shipwreck]

I remember a discussion about this years ago on the pirate board or the LCML. The concensus at the end of the discussion was that it wasn't worth it.

Someone had worked for the mining industry in Canada where this was done to ease maintenance of the cruisers working the pits, but they came to the conclusion that it provided no increase in longevity to the life of the birfield. Add to this the difficulty, expense and risk of having a hardened steel shaft gun-drilled and tapped made the whole exercise not worth it. In addition, there was no clearance for a zerk between the end of the shaft and the lockout, so a plug had to be fitted and replaced with the zerk each time service was done.

Not worth the expense and risk in my opinion.

 

[Rich]

The shaft diameter on a factory 80 series birf is nominally 32mm. If you drill a 7mm hole down the center (proper tap hole size for a 8mmx1 threaded zerk) the reduction in torsional strength would be a bit more than .2%, which is not at all significant.

Given that you have already established that grease pumped in the existing filler ends up in the birf, the return on effort may be marginal.

 

[IdahoDoug]

Hmm, good points. Would I get any points on the coolness factor?

DougM

 

[Cruiserdrew]

Doug-I've been wanting to do just that. I even spoke to Luke Porter about it and he thought you could only make a hole like that on the lathe. Not sure why. You would score major cool points doing it. I remember from college physics that all the strength is in the outer diameter of a shaft so drilling the inside would have essentially no effect on strength. Rich seems to have the actual numbers that confirm that.

 

[RavenTai]

One thing if you do have it drilled if the bore is not smooth it can become a stress riser, one way to go about it would be first a small drilling and then step up to the finish diameter with a reamer. Talk with the machinist he will have more ideas on how to get a good smooth bore.

Only problem I see is that where this would be the most helpful is when you have blown an inner axle seal refilling would counteract the washing effect of gear oil, constantly re-lubing the birf from the inside will keep the birf up (if you do it often enough) but will not keep the trunnion bearing in good shape,

This is what I found in the USDS of my 62 (see pic) , notice there is no grease at all, not even birf soup, I do not know how long the PO drove it with a leaking axle seal but I put about 100 miles on it, the hubs were unlocked but the T-case is stuck in 4 high so the birf was spinning, the upper bearing grenaded from lack of lube, the lower was trashed by metal from the upper and was about to go,

If it was an 80 the birf it would have went along with the trunnion bearings, if it was drilled you could keep up the birf but would you drive it like that? I would not and I don’t think you would either.

So only advantage that leaves you with is more direct way to lube it and ensure it is filled with grease, witch is neat and certainly gets you points on the coolness factor but if your knuckle cavity has grease we do know there is grease in the birfield so is it worth the time and money?