94 suburban rear end carrier

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94 gmc suburban sle
original owner
130000 miles with no heavy towing
2 wheel drive
3:42 limited slip rear end
napa gear oil

Any idea why my truck’s differential carrier keeps wearing out? At 127000 I replace all the bearings in my truck’s rear end due to a roaring noise (napa bearings). The noise was fixed. But, almost immediately after this change I started to hear a loud banging noise in the rear end (like someone was hitting the rear end with a hammer). Pulled everything down and rechecked every. I found nothing wrong. I took the truck to our local repair shop. They check everything and $100 later found nothing wrong. After driving the truck for a while with the noise, I tore the rear end down again. The only wear I found was in the retaining bolt (lots of wear) that holds the pin in the spider gears. I installed a new set of spider gears, pin and bolt. Still had the banging noise. I next installed a new carrier, plus, the spider gear bolt (napa part) due to wear. The problem was fixed or so I thought. Now 3000 miles later the noise is back. Pulled the rear end down again. There is again a lot of wear on the spider gear retaining bolt. The spider gear retaining pin shows no wear but seems to fit very loose in the carrier housing. There were no leaks and the gear oil was full. I can understand the first carrier being worn out after 127000 miles. The second one wearing out really throws me for a loop. Any ideas? I paid $75 for the new carrier and definitely expected the thing to last more that 3000 miles.

stanley
 

kev2

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Can you add anything....towing? oversize tires, 500 HP, drive hard, lifted, droped,
 

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very little towing of a 12 foot john boat 2 or 3 time a year for less than 100 miles. , never wrecked, standard tires, no lifts, no drops, standard 5. 7 engine, 4L60e trans. . only driven by old people (no hot rods). used napa gear oil with additive.
 

kev2

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I will think on it but football tonight is my plan...

this is a 1500 seriies?
limited slip?
are the gears very tight in the pinion shaft when assembled?

Both rear tires same- same?

I have a GM unit repair manual for this vehicle at work I will follow up tomorrow....
 

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1500 series, limited slip, pinion bearing set to 23. 5 inch rotating torque, all tires are 235/75/15 michelin. this is a standard 10 bolt, 8. 5 in rear end. i really wonder if i just got a bad carrier. tnaks for your help.
 

kdauto

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First off, are you SURE these are 15" tires and the gearing is 3.42? All the 94's I've seen up here are on 16's and run 3.73 gears. My old 89 Sub was running the drivetrain you speak of. Is this an Eaton locker diff? When does the bang occur? IS it on turns,after turning,on straight line take-offs or braking,what? What grade gear oil,spec(GL4 or GL-5), and what type additive did you put in there? What was your backlash set at? How did you check your tooth pattern on the ring gear? Was it centered,low,or high? Is it noisy at all and whine,coast,accel.,decel? When you put the new lockbolt in the pinion pin, was it loc-tited and torqued into place?
 

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yes, i am sure these are 15 inch tires. the gears 41/12 which is a 3:42. this is the original equipment rear end. the banging occures between 20/25 miles an hour while driving in a straight line. at higher speeds there is no knock. breaking has no effect. gear oil is napa sae 80-85-90. sorry, i no longer have the additive tube. but, it was for a limited slip differential and again from napa. backlash was set at 10, which i know is a little high. would this cause the carrier to prematurily wear out? i used the marking compound that came with the bearing set (napa) to check the tooth pattern. the pattern appeared to be centered between face and root. the heel to toe was more toe on the drive side and heel on coast side (i hope i have this correct--i have slept since then). some whine between 45-55. no, i did not use loc-tit on the piston pin. only a new retaining bolt with loc-tit aleady applied. every new retaining bolt i used was from napa. could this be my problem? is this one of those items i should only get from a dealer? thanks for your help.
 

NickD

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Dang limited slips really need equal sized tires and the only way to find out is to use a carpenters and a tape measure to precisely measure the diameter after you check the air pressure. But the key symptom here is the clutch plates are constantly slipping, I have seen tires with the same size markings on them but over over a 1/2" in diameter off. With slipping plates, the fluid will have a burnt odor, have you detected that?

$75.00 for a carrier? Used? Last time I checked was 800 bucks just for the ring and pinion gear for these things, kind of a critical thing using bluing to make sure the pinion is properly contacting the ring gear teeth.

That banging is mystifying, is the vehicle jerking you when you hear that loud noise? Little man in there pushing a crow bar in the gears? Has to be some signs of damage. Did you try a file on that NAPA bolt, if properly hardened, you won't take off anything.
 

wap

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retired:

I am guessing the $75 was for a replacement housing, not a loaded carrier? Correct? multiple bearing issues? Pinion bearings, I'll bet. bangs between 20/25, probably coming out of 1st to 2nd gear, under light accelleration.
 

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it also sounds like this is not your first 'rodeo'! The whine at 40-45mph indicates, at least to me, that there is a backlash issue. when you installed the pinion bearings, did you install a new crush sleeve, and new or loctited pinion nut? if not, the bearing torque pre-load will not be set correctly and the nut will actually loosen. this could explain the whine. the banging is the gov-lock kicking in. If one tire is 1/8" larger in diameter than the other tire, that will equate to about 350 rpms. The gov lock will engage if one wheel is turning between 250-300 rpms difference. at higher speed, it's like jamming a screwdriver between the spider gears, and, can ruin the spiders, shear the differential retaining pin, and break the cross pin. Get a tire tread depth gauge, and compare the tread depth of each tire. 1/32 maximum difference. I see this occasionally when a customer that needs a front-end alignment rotates the unevenly worn front tires to the rear. these guys are right, a slight tire size o.d. difference will wreak havoc. Also, one tire with 35psi, and the other with 21psi will cause the same problem.
 

NickD

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One simple test for differentials, with the drive shaft locked in park or in reverse on a MT is to jack one of the rear wheels up and rock it. Like to see two inches maximum, seen some with up to six or more inches. Another test is to drive sharp turns on an empty parking lot with the windows down, there you can hear the sins.
 

kdauto

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Ok, I'd like to know how your pinion depth was determined. If I appear to be asking basic questions,keep in mind I don't know you or your skill level, and what equipment you have. All things factor in here.
How did you set your case preload? What did you set it to? Did you replace side brgs? How did the axles look like,were they chewed up where the brg runs on them? I am wondering if something foreign to the diff itself could be at cause? Are the rear main leafs ok, not cracked right where the axle u-bolts grab on? Are the rear brake springs,shoes,etc. all intact and not anything funky in there? How are the u-joints,can they be binding?
If this knocks in a straight line something odd is going on. The spider gears shouldn't be doing any work. The diff itself should be inoperative. As others said, check tires and pressures. If all apears good try rotating the frt-back pairs and retest. At that low speed, I'd try retesting in 1st gear,just to eliminate any trans problem going through the driveline. It sounds right at the 1-2 shift point. Your backlash is on the upper limit but other than the whining, should NOT make any knocking sound. I suspect pinion depth may be off.
 

kev2

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RPO code for the diff would help me ...

I am thinking a problem with locking mechinism....
   Was this unit equiped  'locking diff cam and governor"  AKA  latching brackets....the description of operation would match your noise @20mph 1-2 gear change & component torque unloading...

several colleagues and I are of the same thought so worth a second look...

Note the last paragraphs after the **************************

Below is real boring Bull SXXX

Locking Function
Locking action occurs through the use of some special parts:

A governor mechanism with 2 flyweights
A latching bracket
The left side cam plate and cam side gear
When the wheel-to-wheel speed difference is 100 RPM or more, the flyweights of the governor will fling out and one of them will contact an edge of the latching bracket. This happens because the left cam side gear and cam plate are rotating at a speed different, either slower or faster, than that of the ring gear and differential case assembly. The cam plate has teeth on its outer diameter surface in mesh with teeth on the shaft of the governor.

As the side gear rotates at a speed different than that of the differential case, the shaft of the governor rotates with enough speed to force the flyweights outward against spring tension. One of the flyweights catches its edge on the closest edge of the latching bracket, which is stationary in the differential case. This latching process triggers a chain of events.

When the governor latches, it stops rotating. A small friction clutch inside the governor allows rotation, with resistance, of the governor shaft while one flyweight is held to the differential case through the latching bracket. The purpose of the governor's latching action is to slow the rotation of the cam plate as compared to the cam side gear. This will cause the cam plate to move out of its detent position.

The cam plate normally is held in its detent position by a small wave spring and detent humps resting in matching notches of the cam side gear. At this point, the ramps of the cam plate ride up on the ramps of the cam side gear, and the cam plate compresses the left clutch pack with a self-energizing action.

As the left clutch pack is compressed, it pushes the cam plate and cam side gear slightly toward the right side of the differential case. This movement of the cam side gear pushes the thrust block which compresses the right-hand side gear clutch pack.

At this point, the force of the self-energizing clutches and the side gear separating force combine to hold the side gears to the differential case in the locking stage.

The entire locking process occurs in less than 1 second. The process works with either the left or right wheel spinning, due to the design of the governor and cam mechanism. A torque reversal of any kind will unlatch the governor, causing the cam plate to ride back down to its detent position. Cornering or deceleration during a transmission shift will cause a torque reversal of this type. The differential unit returns to its limited-slip function.

The self-energizing process would not occur if it were not for the action of one of the left clutch discs. This energizing disc provides the holding force of the ramping action to occur. It is the only disc which is splined to the cam plate itself. The other splined discs fit on the cam side gear.

If the rotating speed of the ring gear and differential case assembly is high enough, the latching bracket will pivot due to centrifugal force. This will move the flyweights so that no locking is permitted. During vehicle driving, this happens at approximately 32 km/h (20 mph) and continues at faster speeds.

When comparing the effectiveness of the locking differential, in terms of percent-of-grade capability to open and limited-slip units, the locking differential has nearly 3 times the potential of the limited-slip unit under the same conditions.
***********************************************************
Locking Differential Torque-Limiting Disc
The locking differential design was modified in mid-1986 to include a load-limiting feature to reduce the chance of breaking an axle shaft under abusive driving conditions. The number of tangs on the energizing disc in the left-hand clutch pack was reduced allowing these tangs to shear in the event of a high-torque engagement of the differential locking mechanism.

At the time of failure of the load-limiting disc, there will be a loud bang in the rear axle and the differential will operate as a standard differential with some limited-slip action of the clutch packs at low torques.

The service procedure, when the disc tangs shear, involves replacing the left-hand clutch plates and the wave spring. It is also necessary to examine the axle shafts for twisting because at high torques it is possible to no only shear the load-limiting disc, but to also twist the axle shafts.

Document ID# 701869
 

kdauto

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kev2 said:
RPO code for the diff would help me ...

I am thinking a problem with locking mechinism....
Was this unit equiped 'locking diff cam and governor" AKA latching brackets....the description of operation would match your noise @20mph 1-2 gear change & component torque unloading...

Locking Differential Torque-Limiting Disc
The locking differential design was modified in mid-1986 to include a load-limiting feature to reduce the chance of breaking an axle shaft under abusive driving conditions. The number of tangs on the energizing disc in the left-hand clutch pack was reduced allowing these tangs to shear in the event of a high-torque engagement of the differential locking mechanism.

At the time of failure of the load-limiting disc, there will be a loud bang in the rear axle and the differential will operate as a standard differential with some limited-slip action of the clutch packs at low torques.

The service procedure, when the disc tangs shear, involves replacing the left-hand clutch plates and the wave spring. It is also necessary to examine the axle shafts for twisting because at high torques it is possible to no only shear the load-limiting disc, but to also twist the axle shafts.

Document ID# 701869
Kev. this would describe the Eaton locker I am familiar with. If indeed he did replace the carrier assy, he should have noticed something. Also, the diff shouldn't be "working" in a straight line, only when cornering. Let's see if he tries some suggestions or answers everything I asked first.
 

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thanks everyone for the help. i have been working on cars (shade tree) for over 45 years. however, my skill level especially with rear ends is probably questionable at best. which i am fixing to prove. i have been referring to this rear end as a limited slip. after talking to randy's ring and pinion today, i was informed it is actually called an "open" or "standard" rear end. per randy's, the spider gears in a limited slip rear end are held in place by an "s" clip and use a disk. therefore, no pin is needed. well, mine definitely has a bright shinny pin and used a retaining bolt to hold the pin stationary. sorry about my confusion.

the case i purchased was new and bare. i had already replaced the spider gears trying to fix this problem. so, i just moved them to the new case. i did purchase new case bearing and races. i used the original spacers on each side of my case. i was very lucky that they fit close to my backlash tolerance.

the pinion was installed with all new parts too (both bearings, races, crush sleeve, nut and seal). the nut was set with lock-tit during final assembly. the original pinion shim was also reinstalled. i set the depth by using a rotation torque of 20 inch pounds--reinstalling the carrier--and pattering the ring gear. i continued this process until the tooth pattern was between the face and root on the ring gear.

all my tires are relatively new michelin 235/75/15. 32psi in front and 36psi in the rear. no unusual tire wear on any tire. the tread depth all measures the same.

the noise is definitely a banging sound. the truck does not jerk. there is no visible damage inside the rear end (axles, housing, metal shavings, left over wrenches, etc. ). the only wear i can find is on the bolt that holds the retaining pin in the spider gears.
rear ujoint was also replaced trying to correct this problem.

i had another trusted mechanic test drive my truck today. he definitely hear the banging noise. he said he had never hear anything thing like it. he is going to tear down the rear end this weekend, recheck all my work and set the correct backlash. plus, install another carrier if needed.

i will keep everyone informed.
 
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