Rear axle oil leak

[Dmcbrass]

I recently replaced the passenger side wheel bearing on my GT - (71-73 style rear axle). The bearing had not failed. No noise but was a little loose. (spun freely) Both the bearing and the O-ring was purchased from OGTS. Two weeks after I finished the job, I noticed differential fluid all over the tire and a puddle of oil on the garage floor. I pulled everything apart and found the wheel & differential side of the brake backing plate completely saturated with differential fluid. The O-ring looked fine, but I decided to replace it with a new one anyway. Now 2 days after finishing the job, I've got a bad leak again. I noticed that the O-ring seemed narrower than the bearing groove, but other than that, everything seemed OK. The bearing seems tight. Good resistance to spinning like it' still full of grease so I'm sure the inner bearing seals are fine.
Has anyone had this problem before? Any ideas on how to solve it? I'm considering ordering the next larger size O-ring (cross sectional area) from an O-ring specialty store. By the way, the bearing didn't leak before I decided to fix it!

[GTJIM]

The outer race of the bearing is supposed to be clamped into the axle housing by the brake backing plate (0.002" - 0.006" preload). If this has not been setup correctly in the past the outer race will have 'spun' in the axle housing and gouged things about a bit - hence the leak.

Make sure that the brake backing plate clamps the outer race firmly and use some RTV gasket in there - smear a bit around the "O"-ring groove and under the paper gasket that should be there between the backing plate and the axle housing end. The paper gasket is part of the method of setting the "nip" on the outer race of the bearing - see the FSM.

HTH

[Dmcbrass]

There wasn't any preload on the outer race when I took it apart. And I agree that it probably spun because I had to add several shims to make up the difference. The odd thing was that I didn't have an oil leak before I changed the bearing and there was no evidence on the old bearing that it had spun. Am I correct that the paper gaskets don't act as an oil seal? It looks like they simply keep metal parts from rubbing together (squeeking)

[GTJIM]

Same as early 9" Ford diffs - there are different thicknesses of paper gaskets that are used to "adjust" the pre-load on the outer race. I don't think they are actually "gaskets" as such but just convenient ways of fixing the preload at the factory.

Sometimes the "O"-ring gets a tiny bit 'sheared' off the outer edge as it is being installed - so tiny it is hard to see it when removed => leak
Smooth the outside edge of the hole in the axle housing with some fine sanding paper before installing a new "O"-ring ... and lube the poor little thing with some grease or diff oil before shoving the axle back in ...... or use RTV instead to ease it in and act as more sealing insurance!

HTH

[Dmcbrass]

I have been lubing the bore with differential fluid. That's an interesting idea about lubing it with RTV. Will that cause a problem getting the axle back out in the future? I'll try the sand paper and I'll measure the bore to see how much loosness I have. Does anyone know what that bore should measure?

[GTJIM]

The bore should be about +0.002" on the OD of the bearing - an nice sliding fit. The RTV usually makes it easier to remove ... as it stops any water getting in there to rust things up !! I just smear the excess around the outer edge radius of the bearing race to fill that up under the "gasket"

"Gorilla Snot" is such useful stuff.

[Dmcbrass]

GTJIm,
Thanks for the information. I'd be willing to bet that I've got a lot more than .002 clearance - (things slid together way to easy). I'll try the RTV trick. It'll probably be a couple of days before I get a chance to work on it again. Life goes on!

[Dmcbrass]

Well I've had the rear axle out 3 times. Man I hate rework. The last time I coated the bearing bore with RTV and replaced the O-ring. Still have an oil leak. I think I found the problem. The bearing was mounted on the axle shaft with the bearing postioned so that the o-ring groove is closest to the wheel. From the FSM, it looks like the groove should be on the differential side. I'm thinking that the o-ring isn't back in the housing far enough to make a solid contact with the bore. Can anyone else confirm the proper bearing/o-ring orientation?

[Dmcbrass]

I swapped the rear axles last night. Took the right axle with the o-ring toward the wheel side of the bearing (the one that's been leaking) and swapped it with the left axle that has the O-ring nearest the differential side of the bearing. I'll have to wait and see whether I still have a leak. (hopefully not both sides now) I figure if the leak moves to the left side, then the bearing/groove orientation is the problem. If it stays on the right side I must have a housing problem. I'll let you guys know what I find. I'm still waiting on comments from my last post. Come on guys, you've never lacked opinions in the past. Tell me what you think.

[jeff denton]

Well since you had sealed the bearing to the housing with RTV, the O-ring shouldn't have been an issue. Unless the RTV didn't seal either. Is the vent clean? Perhaps you have a pressure issue?

[hrcollinsjr]

The only axle I ever had a bearing pressed on the machine didn't set up the bed correctly on the press and some of the retainer was pinched into the sealed part of the bearing resulting in a leak. Two sets of Repco shoes later and new O-rings and I figured out it wasn't something I did wrong. I had another bearing installed and no more problems.

Harold

[Dmcbrass]

I've been meaning to check the vent, but it seems odd that the problem started after I changed the bearing. I wondered about internal seal damage in the bearing, but its still tight like its full of grease. I would think that it would turn more freely if it was full of oil. If the leak follows the axle (in other words if the leak is now on the left side), I'll probably change the bearing $$$$$. Does anyone know which way the bearing is suppose to be mounted? OGTS says with the O-ring groove closest to the wheel, but the only photo I can find in the FSM shows a 1.1 axle with the O-ring groove closest to the differential. There's no good photo of the 1.9 in my FSM.

[Anonymous D]

Page 4B-25 of the 1973 Factory Service Manual, has a diagram that (apparently) shows that the o-ring on the rear axle bearing faces the wheel.

This is apparently conflicted by the photo #4B-3, but that photo does not show the entire bearing (so it is possible that the o-ring is behind the paper gasket on the shaft). The page text indicates the o-ring is (facing towards) the inside splines of the axle shaft, rather than towards the wheel.

[Dmcbrass]

Gil, from OGTS, just called. He found an old engineering drawing that shows the O-ring on the inboard side (closest to the Differential). Apparantly some of the GTs were originally assembled the other way, because he said that he has changed a lot of bearings and that all those came to him with the groove toward the outboard side (closest to the wheel). If the housing bore is perfectly parallel (no taper), it probably doesn't make a difference, but I'm definately going to mount them according to the original engineering print in the future. It seems to me that taper in the housing would be more likely near the open end. It will take a couple of days of driving before I know whether swapping the axles from side to side solved the problem. I'll let you guys know.

[kwilford]

I'm pretty sure the O-ring groove is inboard. And since the later style axle bearing has an integral seal, I suspect the SEAL orientation is more critical than the O-ring. While I have never torn a wheel bearing apart, I expect that the internal seal has some kind of lip, and it stands to reason that the orientation of the lip requires it to be "energized" (or pressurized or whatever) so that the lip faces towards the lubricant, rather than away.

JM2CW

[Dmcbrass]

Well, good news! I've got about 500 miles on the GT since I swapped the axles and no oil leak. My guess is that the passenger side housing is slightly tapered. (enlarged toward the outside) By swapping the axles, I now have the axle with the O-ring groove toward the inside on the passenger side. My recommendation would be to install all wheel bearings with the groove toward the inboard.

[CDN OpelNut]

All of the above posts deal with the orientation of the bearing oil seal groove with respect to the axle.

I took my axles to the local shop to have my new bearings and retainers pressed on. Despite making a point to tell the guy to install the bearings with the groove facing the splines, he installed them the other way.

So now faced with having to cut the retainers off, ordering new ones from OGTS and having them redone, I'd like to know if it's really a big deal.

From an earlier post, it seems like Gil has historically installed them outward anyway.

I'm thinking I can tell the guy I'll try them, but if they leak I'll be back to have them fixed gratis.

Thoughts?

[GTJIM]

It is not the outer 'o'-ring seal that is most important but the actual seals for the wheel bearing itself.

These differ from each other - one side (the 'outside') is a simple, flat shield designed to keep dust and water out of the bearing. The other ('inside') is a true oil seal designed to keep the diff oil in - it usually has a tension ring around the inner lip of the seal ... just like the 'inside' of any oil seal.

That is the determining factor in deciding which 'side' of the bearing faces in ... or out.

The 'O'-ring seal can always be helped with RTV.

[tomking]

Jim I am puzzled about your explanation. If the oil seal designed to keep oil from leaking out of the axle housing then wouldnt that be on the outside, the side nearest the wheel? For it to be on the inside then how can oil get to the bearing? Thanks.

[CDN OpelNut]

All of these technical explanations sound plausible, and I have to think that the FSM specifies the direction for a reason, however, I called Gil @ OGTS and he said that it would not matter, he has seen them both ways, and I wouldn't have any problem with it.

[GTJIM]

Originally Posted by tomking Jim I am puzzled about your explanation. If the oil seal designed to keep oil from leaking out of the axle housing then wouldn't that be on the outside, the side nearest the wheel? For it to be on the inside then how can oil get to the bearing? Thanks.

The later model outer rear axle bearing is not lubed by the diff oil - it is a permanently grease lubed and sealed bearing. That is why the 'oil seal' is on the inside with the tension spring visible ... to keep the diff lube oil inside the diff. If it made its way into the bearing it would only have the outer dust seal (or a back-to-front oil seal .. if the bearing is fitted the other way around ..) to keep the hot diff oil in.

The earlier model roller wheel bearing is lubed by diff oil - much more prone to leaking diff oil on to the brake shoes ....

[CDN OpelNut]

Just before I bolt this all up, a quick check.

When I disassembled the axle, one side had one .004" shim, the other had 2.

In putting this back together, the amount of shimming seems high.

I bolted the brake backing plate and with its gasket to the axle and measured the depth of the bearing well in the axle. It varied in different spots but the average was about .842".

Note that the hole in the backing plate is larger that the diameter of the bearing so it does not clamp the bearing. This is accomplished by the first metal plate. So the #1 gasket thickness also must be included. It's .014" so total depth is .856".

The bearing is .827". This means that I need .029" of shim just to contact the bearing with the first plate, and .033" if I aim for .004" of crush.

Does my reasoning and diagram seem correct? I guess it is what it is.

And, if I need all this shimming, does anyone see a problem in putting two thickness of shims made from the .014 gasket paper in behind the metal shim behind the bearing?

[GTJIM]

The brake backing plates on mine have a recess in them - so they have to be threaded on to the axle before the bearing is installed. The shims go between the backing plate and diff housing.

Sounds like some "P O" modified yours so that the axle and bearing could be removed with the brake backing plate left in place (or forgot to install the plate before the bearing ... and made the modification to fit them without removing the bearing and retaining ring again ... ???).

Just be sure that the end-float/nip shims do hold the bearing outer race - what ever it takes!

[CDN OpelNut]

OK GTJIM,

Now I'm curious. Nothing looks like a PO mod and FSM says nothing about removing the brake backing plate prior to taking the axle out. My backing plate has a recess in it. I didn't draw it. There is no threading involved though.

Can anyone confirm Jim's arrangement?