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7-1/4 rear end bearing problems
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rftroy
4 BBL ''Hyper-Pak''


Joined: 24 Dec 2005
Posts: 32

Post subject: 7-1/4 rear end bearing problems (Tue Dec 28, 2010 11:18 pm) Reply with quote

I have a 1976 7-1/4 rear axle in my 69 Barracuda. This is the large bolt pattern rear end with the large ball bearing and 10" drums.

I got this rear end from a wrecking yard and rebuilt it with new Bower BCA, USA made, bearings.

It has just under 10,000 miles on it, and has been making noise for several weeks. I put a dial indicator on the axle flanges and found that the driver's side had .021" endplay, and the passenger's side had .032" endplay.
When I removed the axles, I found that on both sides the bearing retaining collar has backed off and the inner race of the bearing had ~.020" clearance on the axle shafts.

This is bad.

Has anyone seen this before, and have any input as to what has happened? I have considered the following:

1. The axles were worn from excessive pressing on and off, or other reasons.

2. The bearings were defective, or counterfeit.

3. Some schmo thought he knew more than Chrysler engineers and used a torch to heat up and remove bearings, and softened the metal in the axle so that it wouldn't hold a press.

4. Gremlins

Please let me know if you have any experience with this. The local rear end shop, Hooper's Rear End Exchange, says they have seen this frequently with a Pontiac rear end using ball bearings, but have never seen this with a Chrysler 7-1/4 rear.

Thanks,
Bob



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Robert Troy
69 slant 6 OD4 Barracuda conv
68 383-S 4 speed convertible
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Sam Powell
Supercharged


Joined: 04 Jun 2006
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Location: Gaithersburg MD

Post subject: (Wed Dec 29, 2010 7:59 am) Reply with quote

Did you do the rebuild you mentioned?
Sam



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rftroy
4 BBL ''Hyper-Pak''


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Post subject: (Wed Dec 29, 2010 9:48 am) Reply with quote

Yes, I did.

Removed the retaining collar by chiseling 4 notches in it; removed bearing with the special Miller tool for removing the bearings, with an adapter for the 7-1/4; used the 12 ton press at home to put bearings and collar back on because it's easier than the Miller tool.
Bearings were fully seated.

US made Bower BCA bearings.

Bob



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Robert Troy
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Joshua Skinner
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Post subject: (Wed Dec 29, 2010 11:46 am) Reply with quote

How much force did it take to press on the retaining collar?



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Joshua Skinner
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rftroy
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Post subject: (Wed Dec 29, 2010 3:28 pm) Reply with quote

No way of knowing. It is a simple press with a hydraulic jack cylinder. No pressure gauge.



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Robert Troy
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Joshua Skinner
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Post subject: (Wed Dec 29, 2010 4:00 pm) Reply with quote

OK, how did it feel, subjectively? It's supposed to take a few tons of force to seat the retaining collar.



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Joshua Skinner
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Sam Powell
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Post subject: (Wed Dec 29, 2010 7:16 pm) Reply with quote

Although I had one once, I cannot remember, does this big bolt 7 1/4" rear have c clips? Are the outer bearings solely responsible for holding down lateral movement of the axle?

Sam



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Joshua Skinner
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Post subject: (Wed Dec 29, 2010 8:03 pm) Reply with quote

No C-clips, axle bearing handles side thrust.



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Joshua Skinner
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Sam Powell
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Post subject: (Wed Dec 29, 2010 8:43 pm) Reply with quote

I wonder if oil was low.
Sam



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rftroy
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Post subject: (Wed Dec 29, 2010 9:14 pm) Reply with quote

It was about 6 months ago, so I don't remember what it felt like to press the bearings on, or off. Don't remember anything that raised a red flag, but it's like having a calibrated wrist for torquing bolts, you really can't get a good feel unless things are way off, like if the bearing almost slid on under gravity.

Oil wouldn't have anything to do with the press of the bearing and retaining collar. The bearing is sealed and permanently lubricated and the press collar is on the back side of the oil seal, so no differential lubricant reaches it.

I called Mopar Performance today, and they referred me to Drive Train Specialties. A technician there said that, based on the information I had related, it was probably previous damage to the axles, which was not allowing a sufficient press to occur to hold the bearing and retainer. We discussed possible bent axle housings, and he ruled that out.

I am looking for some replacement axles, and I will install new bearings and keep an eye out for endplay changes.

Bob



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Robert Troy
69 slant 6 OD4 Barracuda conv
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Sam Powell
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Post subject: (Thu Dec 30, 2010 6:25 am) Reply with quote

So you do not apply any lube to it yourself, as when you install a front wheel bearing? Sorry to be so unfamiliar with this set up. You don't see many of them. I'm just trying to help. I remember that the one I had for awhile in this car did make a bit of noise. I never tried to fix it. I replaced it with an 8 1/4".

When you say sealed and "permenantly" lubricated, red flags always go up. That is what they call the tie rod ends on new cars these days, and they wear out at a much faster rate than older, diy lube ones. Does anybody know if this is typical of old third member designs? It seems to me I can remember some of my older RWD cars developing leaky axle seals which would leak oil from the diff onto the brake shoes and ruin them. This leaves me with the iidea that it is more typical to have the diff lube serve the outer bearings as well. Correct me if I am wrong here. This is an impression I have carried with me my entire life of car ownership.

If it were me, I would be looking into options that included replacing the entire rear. It might turn out to be cheaper and better. You might land right back where you are, but maybe not. I would not spend any money without doing a bit of market and design research first.

Sam



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Joshua Skinner
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Post subject: (Thu Dec 30, 2010 12:30 pm) Reply with quote

Sam,

Rear ends without C-clips typically run the axle bearings in grease and keep the gear oil out of the bearings with an inner axle seal. This is true of the 7 1/4 in question and the 8 3/4. The difference being the 8 3/4 has an outer axle seal as the bearing itself is not sealed like the 7 1/4 ball bearing. Late 7 1/4, 8 1/4 and 9 1/4 rear ends are C-clip axles and have an outer seal only so the straight roller bearings run in gear oil.

BTW, a lot of these sealed bearings will last longer than their older counterparts. My 2001 Dakota has a sealed hub and bearing assembly. 216k miles so far on the originals with zero maintenance. Pretty good service if you ask me and cheaper than the old style if you consider labor.

Bob,

Too bad you aren't near Halsey, Oregon. There was a free large bolt pattern 7 1/4 up for grabs there not long ago.



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Joshua Skinner
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rftroy
4 BBL ''Hyper-Pak''


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Post subject: (Thu Dec 30, 2010 4:15 pm) Reply with quote

I've spent the day checking out the self-service wrecking yards, and the regular yards with no luck.
One option is to have custom shafts made to the tune of $300.

I called Cass Eslick, who goes by the name of Dr. Diff on some other sites, and he told me that he had one a while back, but took it out of a car to put in an 8-3/4, and threw the 7-1/4 away.
That is where most of them go, I'm afraid. So, if I catch someone at the right time, I can pick one up for free.

If anyone's got one, let me know.

Bob



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Robert Troy
69 slant 6 OD4 Barracuda conv
68 383-S 4 speed convertible
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Joshua Skinner
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Location: Portland, Oregon

Post subject: (Thu Dec 30, 2010 4:33 pm) Reply with quote

Bob,

Seeing as you have to tools I'd get some of the high strength stud and bearing mount Locktite and put the bearing retaining collars on with that. So long as you aren't road racing it should stay together a long time.



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Joshua Skinner
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bigslant6fan
Turbo Slant 6


Joined: 09 Aug 2008
Posts: 571
Location: Taneytown, MD

Post subject: - (Fri Dec 31, 2010 3:48 pm) Reply with quote

I had trouble with 7 1/4 bearings too.It was caused by the bearing being too tight for the axle shaft.This caused the inner race to expand,binding the rollers,and causing them to fail quickly



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