Rear Axle Seals

[Chiclassics]

Hey folks

I started noticing my 74 yellow bronco started leaking diff oil from passenger rear side drum brake area. I know my guy changed the rear axles an year ago during restoration but the axle seals I believe are stock ones.

I never done this before. Whats the best way to replace rear axle seals?

Questions:
1) Should I change both sides given its only leaking one side (passenger side)
2) Are there 2 seals on each side? If yes, only change outer one ? or change both. How do one change inner seal - does this mean diff needs to be opened up to remove inner seal? I saw some video somewhere where the inner seals go in from the differential and not from the side of the wheel

Any info and/or pics would be helpful. What tools do I need in addition to typical wrenches and power tools.

 

[DirtDonk]

Do you know what type/size/spline count axles were installed previously? Why were they changed in the first place?
Reason for needing to know this, is that there are two different types of seals that are possibly at play. Usually only one OR the other however. Rarely two seals per side. Almost exclusively one type per side only.

The original style (internal), whether a large or small bearing rear end, were a "standard" kind of a seal that was pressed into the axle housing first, then the axles and bearings installed after.
The style used with heavy duty axles with the large bearing housing have a tapered roller (Set-20) bearing with integrated seal on the outer bearing race.

Reasons for leaking differ depending on what type of seal is used.

Paul

 

[B RON CO]

Hi, I would only change the seal that is leaking. Since there are different seals, I would bring the bad seal to Napa, and let them match it. You have to remove the four bolts from the backing plate, and pull the axle. There are a few ways to get the old seal out, involving pry bars and / or sheet metal screws, YouTube may help. Tap the new seal into place with a large socket or a block of wood. Put some oil on the new seal before you slide the axle back, and try to keep it off of the seal. Check the bearing for play, because a bad bearing can wipe out the seal. Good luck

 

[gunnibronco]

I think the "inner" seals you are referring to are on front axles, like the D44 or D30 (or D50s and D60s). They are in the center section near the gears, the carrier needs to be removed to access those seals. The oil stays in the center section and does not get into the tube unless there is a seal leak. There is no "outer" seal on those axles.

The 9" has an outer seal (traditional or Set20 they are different). The gear oil is in the tubes unlike a front axle.

 

[Chiclassics]

The 9" has an outer seal (traditional or Set20 they are different). The gear oil is in the tubes unlike a front axle.

Hi Oh so no inner seals for the rear diff, gotcha I always had a doubt around this. If the seal is blocking off the diff oil to reach wheel bearing I wonder whats the purpose to let diff oil into the axle tube? curious

The original style (internal), whether a large or small bearing rear end, were a "standard" kind of a seal that was pressed into the axle housing first, then the axles and bearings installed after.
The style used with heavy duty axles with the large bearing housing have a tapered roller (Set-20) bearing with integrated seal on the outer bearing race.

Hi Paul , so my guy told me apparently the old axles were probably not broncos could have been from a truck because he had problem installing brake backing plate because axles were sticking out an inch or so. These are the new axles that were installed an year ago https://www.wildhorses4x4.com/74-75-ford-bronco-28-spline-driver-rear-axle-large-bearing-10-inch

 

[gunnibronco]

Hi Oh so no inner seals for the rear diff, gotcha I always had a doubt around this. If the seal is blocking off the diff oil to reach wheel bearing I wonder whats the purpose to let diff oil into the axle tube? curious


Hi Paul , so my guy told me apparently the old axles were probably not broncos could have been from a truck because he had problem installing brake backing plate because axles were sticking out an inch or so. These are the new axles that were installed an year ago https://www.wildhorses4x4.com/74-75-ford-bronco-28-spline-driver-rear-axle-large-bearing-10-inch

On a "traditional" 9", the only advantage I can see is extra capacity/keeping the gear oil cooler. Set20 bearings are in the gear oil with the seal outboard of the bearing, but the "traditional" seal is inboard of the bearing and the bearing doesn't see the gear oil.

I'm not sure any early Broncos got Set20 bearings, or if a traditional bearing axle can be converted to Set 20. I ran 79 Bronco axles for a while in my rock crawler and it used the Set20 bearings.

On full float rear axles (1 ton axles like D60s, GM 14 bolt, and Sterlings) the hub, spindle and bearings are in the gear oil, like a Set20. But those aren't relevant to Broncos unless they are axle swapped.

 

[nvrstuk]

Hi Oh so no inner seals for the rear diff, gotcha I always had a doubt around this. If the seal is blocking off the diff oil to reach wheel bearing I wonder whats the purpose to let diff oil into the axle tube? curious


Hi Paul , so my guy told me apparently the old axles were probably not broncos could have been from a truck because he had problem installing brake backing plate because axles were sticking out an inch or so. These are the new axles that were installed an year ago https://www.wildhorses4x4.com/74-75-ford-bronco-28-spline-driver-rear-axle-large-bearing-10-inch

So hopefully the mechanic didn't do some backyard garage fix to make them fit. Just saying things happen. lol

Good old FORD decided to make sure interchangeability (which they obviously don't believe in) didn't work with Bronco rear axles.

We need to know the axle housing year because guys swap axle housings from year to year. Different year axles, different year housings, different year brakes and they don't all interchange.... Ford is worse than TERRIBLE for this.


Make sure when the new axle seal is replaced that the housing is wiped super clean, then wiped super clean with alcohol, then put a THIN layer of black RTV in the housing where the seal seats. Always support the axle shaft as much as possible to not scrape the new seal surface when installing...

 

[Broncobowsher]

Hi Oh so no inner seals for the rear diff, gotcha I always had a doubt around this. If the seal is blocking off the diff oil to reach wheel bearing I wonder whats the purpose to let diff oil into the axle tube? curious

It is a lot easier to change the axle seal if it is at the end of the axle tube. But it deep in near the diff, and now there is a LOT more work to access/change it.
More reason, the wet bearings (set 20) that are lubed by the diff oil.
I can't think of any conventional rear axle that doesn't have the axle seals out at the axle bearings. I can't think of any good reason to have seal inboard. A steer axle, that's different, need room for the axle U-joint to move around off-center.

 

[DirtDonk]

For some slight terminology clarity, "inner" and "internal" and "external" in my speak, don't mean inside the diff. Yes, a 44 uses an "inner" seal, but a 9" also has an "inner" seal that is inside the bearing. But not inside the differential. They only mean inside the tube.
It's correct that no rear 9" ever got an "inner" seal, but they did have an "inner" seal that was behind the bearing, inside the tube. Whereas the Set-20 was part of the outer race and the sealing surface was in the bearing bore, not the inner tube.

And also correct, that NO '66 to '77 Bronco ever got the Set-20 bearings. Only the full-size trucks (and therefore the '78 and '79 Broncos) got the Set-20 bearings.

Also correct that you CANNOT retrofit a Set-20 to a standard Early Bronco axle. But the tapered Set-20's fit directly into the bearing bore of a standard "large" size ball bearing on a Bronco.
But they stick out quite a bit, which would explain the difficulty the installer had. But only IF they had been installing axles with Set-20 bearings. The axles linked to by Chicclassics are standard HD replacements with 28 splines and STANDARD large sealed ball bearings. There should not have been any difficulty getting them to seat inside the housing, unless the "inner" seal was interfering somehow.
From Ford, the retaining plate for the Set-20 was heavily "dome shaped" to fit around the bearing without imparting too much preload. But the axle in question should (in theory) have slid right in with no drama.

I've asked for it before, but don't remember anyone ever posting up a side-by-side shot of a standard retainer and a Set-20 retainer. I bet James Roney has some in his "stash" (basically his whole shop!) if he could put his hands on a couple that we could see the difference.

Paul

 

[DirtDonk]

So maybe I should be using the term "outer" seal, even though it resides inside the bearing? From a housing standpoint, it's still an outer?
So an outer seal inside the bearing, or an outer seal as part of the bearing?

Paul

 

[gunnibronco]

For some slight terminology clarity, "inner" and "internal" and "external" in my speak, don't mean inside the diff. Yes, a 44 uses an "inner" seal, but a 9" also has an "inner" seal that is inside the bearing. But not inside the differential. They only mean inside the tube.
It's correct that no rear 9" ever got an "inner" seal, but they did have an "inner" seal that was behind the bearing, inside the tube. Whereas the Set-20 was part of the outer race and the sealing surface was in the bearing bore, not the inner tube.

And also correct, that NO '66 to '77 Bronco ever got the Set-20 bearings. Only the full-size trucks (and therefore the '78 and '79 Broncos) got the Set-20 bearings.

Also correct that you CANNOT retrofit a Set-20 to a standard Early Bronco axle. But the tapered Set-20's fit directly into the bearing bore of a standard "large" size ball bearing on a Bronco.
But they stick out quite a bit, which would explain the difficulty the installer had. But only IF they had been installing axles with Set-20 bearings. The axles linked to by Chicclassics are standard HD replacements with 28 splines and STANDARD large sealed ball bearings. There should not have been any difficulty getting them to seat inside the housing, unless the "inner" seal was interfering somehow.
From Ford, the retaining plate for the Set-20 was heavily "dome shaped" to fit around the bearing without imparting too much preload. But the axle in question should (in theory) have slid right in with no drama.

I've asked for it before, but don't remember anyone ever posting up a side-by-side shot of a standard retainer and a Set-20 retainer. I bet James Roney has some in his "stash" (basically his whole shop!) if he could put his hands on a couple that we could see the difference.

Paul

Paul, when I was clarifying inner seals on front axles and outer seals on rear axles I was addressing the OP. I understood what you were saying. I was addressing his question about opening up the diff to change the seals. Lots of this language can get misunderstood. Not to mention there is an "outer" seal on the front axle, but it's in the knuckle. LOL

 

[Chiclassics]

The axles linked to by Chicclassics are standard HD replacements with 28 splines and STANDARD large sealed ball bearings. There should not have been any difficulty getting them to seat inside the housing, unless the "inner" seal was interfering somehow.

Got it . So based on all comments above there should be one seal (outer) that needs to be replaced. Ill tinker around . Thanks Paul

On a "traditional" 9", the only advantage I can see is extra capacity/keeping the gear oil cooler. Set20 bearings are in the gear oil with the seal outboard of the bearing, but the "traditional" seal is inboard of the bearing and the bearing doesn't see the gear oil.

Ah more space for oil to move , actually the breather now makes sense why is it on axle tube.

 

[DirtDonk]

Speaking of breathers… Make sure yours is not clogged!

 

[Chiclassics]

Got to it today. Pulling the seal was tricky but with the puller tool from harber freight it was quick.

Question. How does the retainer go back w.r.t U shape being upright or inverted U (forgot how it was there in the first place). I mean dimensions are rectangle whether the U shape is up or down it was going both ways. I forgot how it was when I took out. Whats the right way to put it back in? what is the function of the opening. I saw some posts where the stock one was a complete O thing than a U.

 

[Broncobowsher]

The retainer is symetrical. It will go on either way. Both are correct.

 

[Yeller]

I pick the way it goes in the easiest, as stated no wrong way.

 

[gunnibronco]

I think the new style is U shaped so you can still install it if you forget and press the bearing on first. Derp.

Sent from my Pixel 7 using Tapatalk

 

[toddz69]

I think the new style is U shaped so you can still install it if you forget and press the bearing on first. Derp.

Sent from my Pixel 7 using Tapatalk

That's exactly why. I rarely see any of the older style for sale anymore.

Todd Z.

 

[Apogee]

The open-style retainers are the most common aftermarket solution, as they can preassemble axles with bearings without capturing the retainer on the axle. Most of these retainers are flat plates as well, unlike the stamped/drawn sheet metal closed-type retainers. While they each have their pros and cons, I've had more issues with the thinner material on the OE retainers, than the significantly thicker material aftermarket units.

As for orientation, they can be installed either way, however the loading of the vehicle puts the axle in bending with an upward reaction force opposite the loading forces, so I typically recommend orienting the retainers with the open slot on the top, that way the bracket is more securely retaining the bottom of the axle bearing race, which due to the load forces, is being pushed outward. The top of the bearing is inherently pushing inward to withstand the force couple/moment, so there is less benefit to retain that portion of the bearing in the counterbore of the housing end.

 

[toddz69]

The open-style retainers are the most common aftermarket solution, as they can preassemble axles with bearings without capturing the retainer on the axle. Most of these retainers are flat plates as well, unlike the stamped/drawn sheet metal closed-type retainers. While they each have their pros and cons, I've had more issues with the thinner material on the OE retainers, than the significantly thicker material aftermarket units.

As for orientation, they can be installed either way, however the loading of the vehicle puts the axle in bending with an upward reaction force opposite the loading forces, so I typically recommend orienting the retainers with the open slot on the top, that way the bracket is more securely retaining the bottom of the axle bearing race, which due to the load forces, is being pushed outward. The top of the bearing is inherently pushing inward to withstand the force couple/moment, so there is less benefit to retain that portion of the bearing in the counterbore of the housing end.

Mechanical engineering for the win!

Todd Z.