Rear axle bearing wear

[Solow302]

Last fall I acquired a '93 SN95 8.8" rear for my old '83 to replace the tired 7.5" unit. I added 3.73 gears, a set of clutch discs and swapped my old 4 lug 7.5 axles into the 8.8" housing (i want to keep my nice 4 lug17x9 wheels and new tires). After some time I noticed the rear end making bearing noise at speed that didn't sound like gear whine. Having inspected the carrier bearings and races I was pretty sure it was the axle bearings which I stupidly did not replace before I installed the 8.8 axle. I looked at the axle bearings when I replaced the end seals and they "looked" and felt fine but now there is definite play between the axle and the bearing. Since the axles are stock 1983 pieces I was wondering if anyone has experienced the axle riding surface wearing versus the bearings them selves wearing out? Anybody have experience with this sort of thing? Is there a diameter for the riding surface I can check? Thanks...

[massacre]

Sorry I don’t have the specs you need, but you are smart to check the runout on the axles
no sense replacing bearings if the axles are worn.
good luck

[BMW Rider]

The bearing surface on the axle is much wider than the bearing, thus there will be un worn surface which you can measure to compare to. I would expect very little detectable wear to the axle as acceptable as it is surface hardened. Once it starts to wear into the hardening, it fails rather quickly with spalling typically. I know I've seen replacement bearings that are offset from the original spacing to take advantage of the unworn axle surface, but can't speak to the quality of that fix. Best answer would be new axles if they are worn.

[Jerry peachuer]

Just a thought but are your axles too short ?

Foxbody to sn95 axle length I thought were different lengths
Maybe not true just a thought

[massacre]

Just a thought but are your axles too short ?

Foxbody to sn95 axle length I thought were different lengths
Maybe not true just a thought

i think you are correct on this, would like some confirmation though. I have some sn95 axles here and I think they are a little longer than fox length

[wraithracing]

Last fall I acquired a '93 SN95 8.8" rear for my old '83 to replace the tired 7.5" unit. I added 3.73 gears, a set of clutch discs and swapped my old 4 lug 7.5 axles into the 8.8" housing (i want to keep my nice 4 lug17x9 wheels and new tires). After some time I noticed the rear end making bearing noise at speed that didn't sound like gear whine. Having inspected the carrier bearings and races I was pretty sure it was the axle bearings which I stupidly did not replace before I installed the 8.8 axle. I looked at the axle bearings when I replaced the end seals and they "looked" and felt fine but now there is definite play between the axle and the bearing. Since the axles are stock 1983 pieces I was wondering if anyone has experienced the axle riding surface wearing versus the bearings them selves wearing out? Anybody have experience with this sort of thing? Is there a diameter for the riding surface I can check? Thanks...

There is no such thing as a 1993 SN95 at least a non prototype version that is. The SN95 refers to the 1994-2004 model and generation of the Mustang. The 1993 8.8 is a Fox width rear end and uses drum rear brakes. The only rear disc option in the Mustang in 1993 was the Cobra and Cobra R models.

So with that said, I assume your axle is actually a SN95 94-98 model with 5 lugs and rear disc. So when you swapped your 4 lug axles on, did you swap the rear drum brakes on to the rear end housing also?

In regards to bearing play, are you stating that the axles move in and out on the housing or up and down? In and out movement is normal and should be a small amount of play. Excessive play should be checked out to verify what is going on. If there is up and down movement in the axle at the wheel end that would most likely indicate a bad bearing or excessive wear. Generally the axles are hardened and although you can damage the wear surface, under most conditions the bearing will wear before the axle shaft itself. Most likely you have a bearing that has gone bad and just needs to be replaced. Since you have to open the differential cover to remove the C clips anyway, might as well do both sides as well as new axle shaft seals. Cheap insurance, Good Luck!

[Solow302]

Trey,
I meant to type '96 SN95. It was a ratty convertible in primer gray beat to death but it did have a set of 4:10 gears in the housing instead of the stock 3:08 on the tag. Pieces of the limited slip clutch plate tabs were rattling around loose in it when I tore it down.. Rough life I guess... Replaced all that stuff though.

Anyhow I appreciate all the comments and replies! Thanks to all.
Yes I swapped out the longer SN95 axles, removed the 5 lug disc brake mounts (discs were already gone), swapped in my '83 four lug axles, the drum brake plates and the Foxbody brake line on the housing. All of that worked fine. FYI the SN95 axles are about 3/4" longer if I remember correctly due to the antilock brake hardware (removable) these cars came with.

The play I mentioned is up and down / fore and aft which obviously is either worn bearings or axle bearing surfaces (or both). I agree that the bearings should be the weaker material since they are cheaper and easily replaced but I'll take a good look at the bearing riding surfaces, measure in several places as suggested by BMWRider, and assure they are in good shape. Summit sells some Moser axles for about $275 that are correct for my car in case the axles are toast. I do plan to replace both bearings & oil seals regardless after going through the trouble of draining the case etc. to inspect it. I might even spring for a better diff cover with a fill plug since I sincerely loath trying to fill it back up through the stock fill plug location.

Thanks guys for the advice, info and encouragement!

[Jack Hidley]

The bearing surface is always much harder than the shaft that it rides on. If it isn't the bearing will fail very quickly.

Think about the contact area between each roller and the axle shaft. If you assume that the bearing and axle are infinitely stiff, then the contact area is the length of the roller and has zero width. Any length times zero width results in zero contact area, which means infinite pressure at the contact point. In reality the parts don't have infinite stiffness, so that the contact area has some physical width due to the roller deforming. The pressure on the roller surface is very, very high because it has a very small radius. The pressure on the axle shaft is much lower because it has a much larger radius and is made of a softer material, so it can flex more. The bearing surface on the axle is still the hardest spot on it.

[Solow302]

Well I finally pulled it all apart and found the bearing riding surface on both axles was worn down noticeably. A quick online search for new bearings showed me a "repair bearing" by National bearings P/N RP-5707 for about $30 each @ A-Zone etc. They basically swap the seal and bearing positions inboard to outboard allowing you to use the virgin axle shaft bearing surface on the outboard portion of the axle where the seal normally is. The seals ride on the narrow inboard portion where no wear and tear has occurred since it is inboard of the original bearing rollers. Mine is about 1/3" wide or so at the inboard locations which is plenty for a seal surface.The outer bearings in this case receive no lube from the axle oil and have permanent grease lubrication packed in them. We'll see how that turns out. I'll carefully inspect the axles before assembling it all back with the new bearings to make sure the surfaces are good. Eventually I'll invest in new axles but for now this will get me rollin again without the horrible bearing noises that have been occurring. I really haven't driven very much so at least not much more damage happened.

[Solow302]

Success! So far the noise is gone and there are no leaks. I did have to buy a rear axle bearing puller at "the harbor" to get the old ones out though... Hopefully the repair bearings last a long time.