04MM. Differential or axle bearing noise?

C

Chachacharlie

Junior Member
04 MM, 138,000 miles. Factory diff. gearing. Hearing the same brushing or thrumming sound from the rear that was mentioned in quite a few posts from the mid-2000's. Barely audible on most pavement. Have to run on really smooth payment to hear clearly. NOT tires - just changed to summer set; noise is unchanged.

Took my mechanic (Clint Vahsholtz, Pikes Peak Hill Climb champ, total Ford guy) for a drive. He could hear it and thought primary suspect was pinion bearing, with wheel bearing a 2nd possibility. Said he would put it on the lift and listen with precision electronic stethoscope equipment. If pinion bearing, as suspected, he thinks job would run about $850, parts and labor.

Questions:

1) Does that figure sound reasonable for a first-rate mechanic in a first-rate independent shop?

2) I don't know what parts he intends to replace in addition to the bearing, if that is the culprit. What should I expect?

3) As long as he's doing surgery on the differential, is there anything else that would be smart to replace, just on general principles and based on mileage?

He also said it would be OK to drive the car for another week until my appointment - maybe another 100 miles. Opinions?
 
at 138k, I would consider a trac-lok rebuild and new axle bearings and seals since opening it all up anyway, issue might be a axle bearing as said.
 
These cars go through axles and bearings faster than they should, poor design for a car this heavy. 90% chance it is the axles and bearings, which you should replace. The quote may not have included those, but sounds like a fair price. Get the 31 spline axles and a new limited slip, your stocker is 28 spline and won't fit the 31 spline axles anyway unless it was already replaced by the previous owner.
 
Ill have a complete Marauder 8.8 rear end with 31 spline Moser axles , Auburn pro series diff , Mag-hytec diff cover , R1C drilled/slotted rotors W/Wagner ceramic pads up for sale soon , has less than 1K miles!
 
lifespeed said:
These cars go through axles and bearings faster than they should, poor design for a car this heavy. 90% chance it is the axles and bearings, which you should replace. The quote may not have included those, but sounds like a fair price. Get the 31 spline axles and a new limited slip, your stocker is 28 spline and won't fit the 31 spline axles anyway unless it was already replaced by the previous owner.
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Why? Unless he is heavily modded 31 spline is a complete waste if anything is salvageable.

I can only assume you are looking at a bad axle. I have yet to see a car that wore through both. With that said I would get prepared for a minimum of 1 axle, all new bearings and seals, clutch kit, crush washer, pinion nut, fluid, and a VERY thorough cleaning once disassembled.

If the spider gears show tremendous wear (they all show some) then scratch the clutch kit and just get a new Ford diff.

Done right and this will last just fine.

I hardly doubt your looking at just an outer axle bearing.


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justbob said:
Why? Unless he is heavily modded 31 spline is a complete waste if anything is salvageable.
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28 spline diffs aren't available new. At $350 for a whole new 31-spline limited slip paying labor to rebuild a 28 spline, re-using the case and spiders is a questionable way to save hardly any money.

He's not doing it himself, rebuild the diff doesn't make sense.
 
lifespeed said:
28 spline diffs aren't available new. At $350 for a whole new 31-spline limited slip paying labor to rebuild a 28 spline, re-using the case and spiders is a questionable way to save hardly any money.

He's not doing it himself, rebuild the diff doesn't make sense.
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I didn't realize they quit selling them.

Regardless, that's $350 plus 2 axles and swapping the ring with new bolts. Not everyone has the money to perfect everything on something that will never be or if they do have the funds some or most don't want to spend it and should be guided in what a repair should entail, replacing what is actually broke.

Rebuilding a diff requires pulling one spring, one bolt, dropping a pin, and spending $107 on clutches. Add more than likely one axle unless the shop likes to just use all new stuff like you always suggest on every aspect of wrenching.

Maybe he wants a whole new stouter rear? But maybe he just wants to fix what's actually broke and keep costs down. He should be given both versions regardless, and that's what a good mechanic does. Either way it's done we both know it will last the same amount of miles if inspected and done right. This comes from dozens and dozens of axle swaps and never once an issue.






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justbob said:
Rebuilding a diff requires pulling one spring, one bolt, dropping a pin, and spending $107 on clutches. Add more than likely one axle unless the shop likes to just use all new stuff like you always suggest on every aspect of wrenching.
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Lots of options, when you add in shop labor even a simple diff rebuild gets more expensive.

I use good judgment about replacing parts. Most of them are pretty cheap compared to the effort involved, mine or a hired gun. It isn't hard to find parts that need replacing on these old cars. My new engine still has the original valves and guides in it. Didn't put a new ring and pinion in my rear end. Didn't replace the motor mounts. The list goes on . . .
 
Many thanks for all the feedback! Got the M back yesterday - turned out to be one bad bearing & axle (lightly scored). Clint expressed surprise that the noise wasn't louder, based on wear. Replaced both axle bearings with 1 new axle shaft kit. Close inspection of diff. showed no problems, so no further disassembly there.

Asked for bumper to bumper checkup, and Clint found starter Bendix not disengaging fast enough. Said whole new starter motor barely more than fixing Bendix, so went that route. So new axle, bearings, seals, starter, gear oil, oil/filter change & inspection ran $880. Not bad at all, I'm figuring. Noise is gone.
 
MOTOWN said:
Ill have a complete Marauder 8.8 rear end with 31 spline Moser axles , Auburn pro series diff , Mag-hytec diff cover , R1C drilled/slotted rotors W/Wagner ceramic pads up for sale soon , has less than 1K miles!
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What gears are in this? Interested for my "other" car.
 
lifespeed said:
Where are the metal shavings chewed from the axle, still in the housing?
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Mechanic is meticulous - and he's been servicing the MM exclusively since it was out of warranty. Besides, axle was scored, but not chewed up. I'm sure he would have cleaned out the entire housing before buttoning up.
 
Chachacharlie said:
Mechanic is meticulous - and he's been servicing the MM exclusively since it was out of warranty. Besides, axle was scored, but not chewed up. I'm sure he would have cleaned out the entire housing before buttoning up.
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The only / right way is to power wash the interior of the housing and tubes. There could be shaving in the remaining bearings if they haven't been replaced.
 
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