As you guys know I installed a 3.73 posi rear this weekend that I had swapped a new (used) carrier into.

It runs great, until you get about 40 miles down the road. Then it starts making this
really awful loud as hell binding/snapping metallic sound. The car behind me could hear it with his windows rolled up and AC on. When it first started I thought for sure it was
teeth shearing off the gears. It makes a pop/bang about every 2 feet at most. I waited
till it cooled off (I was at work when this happened) and pulled the cover, and everything looked perfect. Turned smooth and easy as it should...no gear damage or anything. Then about 40 miles into my drive home it started again. I'm too tired to pull the cover again tonight and look while it's doing it. you guys have any ideas?

I got the posi carrier out of a 4th gen rear that had chewed up the gears. I had assumed it was from a failed pinion bearing...the posi has no damage at all as far as I can see

Oh yeah...it's not just a sound..you can feel it jerk a bit too.

and it's only doing it at low speeds.

 

Sounds like the posi unit clutches chattering.
Try putting two bottles of GM posi additive in case.
Drive around vacant parking lot in circles - both directions to break glaze on clutches.
If problem persists, replace clutch pack.

 

I didn't use GM posi additive..I used the whatever brand my local parts store carried. 7oz bottle. Think that could be the problem?

 

That could be the start of your problem.
Get the GM additive and do the roundy-round exercise.
Check back with the results.

 

I'll try it..cheap enough and it can't hurt.

In the meantime though.....any more ideas?

 

yo, i had a similar question a while back... vader answered it for me... here it is...

Locry,
If the noise is most prevalent when cornering, I would suggest changing the oil and additive as Max recommends. If the noise occurs in a straight line, you can still change oil, which gives you a good excuse to remove the cover and inspect the ring and pinion, and side and spider gears. Pay close attention to the wear pattern on the ring gear. Polishing should occur near the center of the gear tooth only on a properly adjusted gear set.
You might want to check play at the pinion shaft when the noise starts. If you can get the symptoms to occur while the car is on stands, shut off the engine and check the pinion shaft for excess play by hand. Any movement of the input yoke is a bad sign. The crush sleeve may have been hammered shorter, or the tapered bearings may be worn, causing the excess lash.
While turning under load, the pinion gear (and shaft) tries to push itself forward against the bearing and sleeve. Excessive loading can wear the bearing and/or sleeve until there is noticable "play". When you decellerate, the pinion gear gets pulled rearward by the inertial of the car. Over time, the "clunking" noise can develop. Another symptom of this can be universal joints that don't last. The pinion lash is normally accompanied by some gear whine or howl. If you have no play or other noises, you might want to inspect the 'U' joint closely.

hope this helps... mine was more like a grinding/clunking sound which occurs after about a 45 minute drive... i usually hear it when i drive slowly/crawl/coast...

 

i've saw axle bearings go out after a gear swap because the guy (not me) didn't put any lube on the bearings. sometimes it takes a while for it to get out the the ends of the axle. i'd got with the posi clutchs here and also say add gm lube and try it again.

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-=ICON MOTORSPORTS=-

 

Thanks Locry...did you ever figure out exactly what was causeing yours?

 

Sounds to me like you may have the backlash to tight on the gears. After 40 miles of driving, the gears would heat up enough to possibly start binding. If it is making the noise in a straight line, then the clutches are probably not the cause. I've used K&W slip additive in several limiteds with no problems. A bearing could also heat up and bind, so check them also.

[This message has been edited by freeze92 (edited September 27, 2000).]

 

nope. not yet. it seems that when i do have time to get it on a lift the car "cooperates" and refuses to show the symptoms... go figure...