8.75 Diff Questions 2nd try

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airkiller

airkiller

MOPARS Rule
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SOrry for the title of my fist post. I have a 8.75 Rear end not a 8.25

Ok, I have been restoring/ COnverting a 74 Duster from a 904 with 7.25 rearend to a 833 with a 8.75 rear end. I bought a rearend off Craigs list and it look pretty good to me but as it was latter found, the diff has some issues, at least I think it is the diff. The rearend came with new upgraded axels and green bearings already installed on the axels. The guy I bought iot from is a hobbiest and told me the whole system, hosing, diff and axles were ready to be assembled and installed. It is installed and running but I have a growl from the rearend at 30-60 mpg and it gets louder when I let off the gas and hold in the clutch. It will make nopise almost to the point when the car stops. It sounds like a bunch of rocks boucing around in the case. No when I looked at the diff before installing it, I noted no issues with it. I talked to a local diff shop and they think it has an issue with the pinion bearings. I have rebuilt my 727 in my Road Runner and have been a Aviation Mechanic for a long time, so delicate and complicated devices don't scare me but I think a diff is a demanding build. I have a 489 case and need a bebuild kit. I also have a 741 case that was going to go into the Road Runner. Which one is better if any, and has anyone built these up. Can anyone give me some pointers. Thanks./
 
Swap in the 741 chunk,you might have to swap u-joints if yokes are different.While you have the .489 out,get it rebuilt.Good luck.

P.S The rear in my 68 Barracuda howls also.FYI
 
I had the same noise coming from my 1968 Dart's rear area... Ended up being the rear axle wheel bearings.. Could be that too.. You need to check them seperately from the rear end so you can determine if it's the pinion bearing or the wheel bearings..
 
Swing the car from side to side when it's making the noise. When you put more weight on the rear axle bearings the noise should lessen. Less weight and the noise should get louder. That will determine if it's an axle bearing and which side it's on. If it's pinion or carrier bearings the noise shouldn't change. Pinion bearings will generally change tone if you accel/deccel or feather the throttle. Carrier bearings generally stay pretty constant and only change tone with road speed.
 
sounds like to me you need to pull it apart an take a look ... axles must come out those bearing can be hard to see ..if ok put some grease in them before installing ...keeps them from running dry till gear lube gets there ... the center section only three bearing's in it the pinion bearing is preloaded so there should be no side to side or up an down movement first off .. the rest just ck the wear pattern ...... there a good book on these at barns an noble there pretty simple ... the 489 has 1 7/8 pinion shaft stout most look after the 741 shaft is dont quote me on this 1 1/8 light weight or its around 1 1/2 have to look them up again any how there fairly easy .... wish you luck
 
The axels and bearings are brand new. The green bearings have o rings on them to seal them to the housing and snap rings to set the depth into the housing. There is no adjustment on the axels that I can tell. they just slip in (With help from a block of wood and hammer) and then the retainers bolt on. The case is full to spill on the fill port. The diff was not touched from when it was removed from the doner car. It did not have any noticable wear on the ring teeth, but I am not sure what to look for. There seems to be a clunk sound when I let the clucth out sometimes like there is slop in the dif between the input and output. Anyone rebuild these? What special tools do I need?
 
First thing to do is like Guitar says, swing her back and forth and if the sound doesn't change then it's not the axle bearings. This is also how you check which hub bearing (left or right) is bad on a front wheel drive car. Then pull the pig and get her up on a bench, you'll need a mag base dial indicator to check for backlash and also to check the pinion for up and down or in and out. When she's on the bench you can tell just by looking whether it's a cone or clutch sure grip. I suspect it's one of the pinion bearings.
 
If it's that noisey I'd say you don't need to diagnose it. You need to remove the chuck and take it apart, as that is the end result from finding anythig wrong anyway...
I'd simply plan to completely re-do it, as it's been my experience that trying to re-use any bearings results in more noise an dmore crap in the oil... If you're an aviation tech you can do the rear, but you need a rotating torque wrench if you don;t have one. Talk to Cass (Dr Diff) for any parts needs or help.
 
.if ok put some grease in them before installing ...keeps them from running dry till gear lube gets there
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The only lube the axle bearings get is the grease that's in them when assembled. The rear lube does not lube the axle bearings.
 
when installing axles with green bearings you should remove the center pin in the diferential. It is between the axles and is used to set the preload from one side to the other with tapered bearings. This should be removed with sealed straight cut "Green" bearings. It could bind the axle bearings. Just a thought. Steve
 
moper said:
If it's that noisey I'd say you don't need to diagnose it. You need to remove the chuck and take it apart, as that is the end result from finding anythig wrong anyway...
I'd simply plan to completely re-do it, as it's been my experience that trying to re-use any bearings results in more noise an dmore crap in the oil... If you're an aviation tech you can do the rear, but you need a rotating torque wrench if you don;t have one. Talk to Cass (Dr Diff) for any parts needs or help.
Click to expand...

You should always perform a complete diagnosis before disassembling anything so you know what you're looking for. Using the process of elimination to narrow the problem down saves time and money.

In my world you just don't tear down a transmission and completely rebuild it for a valve body or a pump problem Chrysler will charge you back that repair in a heartbeat.

Besides what if he just needs an axle bearing? Waste of money to be going through the diff when all you need is an axle bearing. Or worse yet rebuilding the diff and still having the noise because all you needed was an axle bearing.
 
Guitar Jones said:
You should always perform a complete diagnosis before disassembling anything so you know what you're looking for. Using the process of elimination to narrow the problem down saves time and money.

In my world you just don't tear down a transmission and completely rebuild it for a valve body or a pump problem Chrysler will charge you back that repair in a heartbeat.

Besides what if he just needs an axle bearing? Waste of money to be going through the diff when all you need is an axle bearing. Or worse yet rebuilding the diff and still having the noise because all you needed was an axle bearing.
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How many brand new Green bearings have you seen? I've never seen any. But, I've only been doing this since 1986. Seems to me if they slid in and the flange could be tightened, the pin was a non-issue. Whether because of axle length or a previous owner pulling it or it being a non pin sure grip.

We're not talking transmissions, however I do own the snap on transmission pressure gage kit and I'm not afraid to use it. CUrrently I'm doing an AMC 998 for my friend's Gremlin. I need no schooling on it, thanks.

In my world, and for the record, I was an ASE Master Tech and can and do diagnose better than most. Add to that 4 years of jobber parts, plus dealership parts guy (well, asst manager to be specific) spanning the late 80s to mid 90s. At the time in the delaership, when a transmission was determined faulty and it wasn't something dropping the pan could fix, they didn't want you to fix it. They wanted a replacement installed and the bad unit sent back. It was more cost efficient for them in terms of warranty labor and parts that way, and less chance of the dealer trying to scam Chrysler for warranty time. They kicked more back for trying to repair them than anything else... Remember the early 4sp computer controlled transaxles and the Ram trucks? They were terrible and we stocked most of the common ones just because of that. Later in life I also worked at a 4wd performance shop doing 2-3 axle builds a week. I'm not new to it nor do i consider myself one to spend needlessly. Time has value for anybody, pro or not.
The truth is, with a drop-out center section type rear. The swerving tests can identify the axle bearings, but if it's anything else, it's coming out. To properly inspect the gears and bearings you have to. From his description, which granted could be several things, primarily sounds like pinion bearings. If it needs pinion bearings, it needs to come out.
 
Look, I'm not arguing with you. I've been a Chrysler Master Tech for 36 years, sorry not a parts man. Taking anything apart with out a thorough and proper diagnosis is foolish and wasteful. Chrysler stopped that replacement trans program because they couldn't build one that worked properly so don't even start on that.

Do the diagnosis then repair the unit, at least you'll know what you're looking for.

Now if you want to have a diagnostic competition, it's on!
 
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