Rear end experts

[Wonderwagon]

So, the shop notified me the rear end on the 69 Plymouth Suburban Wagon with 383 is worn out. I plan on taking advantage of the circumstances to rebuild the open to a closed differential. From what I've read the Auburn Part #542051 and Eaton Posi products are pretty similar in both use a clutch pack. The Eaton posi however is rebuildable, Auburn is not. However there is also the Detroit Truetrac which uses a helical gear setup to perform the same task, and is not rebuildable. Shop suggest, the Auburn, what ye ya say.

 

[C Body Bob]

They last for decades unless you
A : do a lot of burn outs or hard cornering
B: wrong lube or too low
C: tow heavy loads routinely
So if the shop is a fan of the Auburn then ask if they have experience installing that one. If they do & you don't do any of the steps above I'd rock on.
Happy Motoring !

 

[Davea Lux]

You are putting this into a station wagon, so I am assuming that you want better traction in muddy, snowy or icy conditions and are not doing this to build a hot rod or off road vehicle.
The Detroit True-Track is very popular with off roaders and mudders. It is probably way overkill for a street driver in your case. It has no sacrificial parts, Read: clutch frictions, to wear out and is therefore very durable.
The Auburn rear is a cone type limited slip that has as you said a non rebuild able clutch pack, it is a use till dead application. It has the advantage of being cheaper that the other two choices.
The Eaton limited slip uses a plate type clutch pack that bolts together in case service is ever needed. The Eaton also has available shim packs that can be added to the unit to increase the spring tension on the clutch plates or to compensate for clutch wear. This is a handy thing to have as relatively small amounts of clutch pack wear can adversely change the amount of friction the clutch packs can provide. You can also use the shims to "dial in" the level of traction you desire.

If you plan to do a lot of driving with this vehicle where the limited slip is constantly engaging and disengaging, go with the Eaton, otherwise for more limited use, go with the Auburn as it should prove adequate for your application.

A personal thought about limited slip rear ends from rural Oregon where I grew up. Those back country roads are all crowned to promote water drainage, good for drainage, not so good for traction is icy conditions. If one comes to a complete stop on a crowned road, and the limited slip is keeping both wheels turning the same speed when trying to get moving again, gravity takes over and the rear end of the vehicle takes the down hill track toward the ditch. I learned to drive with a very light touch so I would not break either wheel loose.

Dave

 

[CBODY67]

The Eaton is more like the factory used in the earlier years. Plus the Chevy PosiTraction units, too. Some Auburns were used on the SLP-modified Camaros and Firebirds, but those were the "cheap" Auburns I'm told, rather than the better ones they sell.

Having a "limited slip" rear axle can be fun, BUT it's "locked until it unlocks". It needs the special lube and additive (whatever THEY recommend!). The earlier ones had 4 springs in the clutch pack. There's a special spring compressor to remove and install them, too. They might be rebuildable, BUT who has the parts on the shelf? They usually don't break, though, so it can be a moot point.

Now, what on the rear axle is "worn out"? Is it the gear set, the bearings, the seals, or axle shafts? In any case, if you pull the differential case out, you might as well plan on new side bearings, new pinion bearings, crush sleeve/spacer, and enough shims to get it set-up right. Then there are the outer wheel bearings, seals, and axle shafts. ALL OEM-level replacement parts, too!

Make SURE what they want to do and how much it will be, whether to use the existing differential assy or change to the Eaton limited slip item as you rebuild the rest of the axle assy.

CBODY67

 

[4spd300J]

I would stay away from the Detroit truetrac for on highway use. I had one in a 3/4 ton Dodge 4 wheel drive, it was wonderful off highway. You can feel the differential load and unload each wheel on uneven roads. Icy conditions could get very exciting.

 

[70bigblockdodge]

Auburn is a good cheap unit. You can lean on it, have some fun with it and it's quiet. Clutch type 4pinion is a forever piece, tough as nails. The torsen tru-trac is also tough and never wears out and $$$

 

[MEV]

I broke a detroit true-trac recently in my 66 new yorker. I replaced it with a regular detroit locker. No matter what anyone says they are totally streetable. You would never know its in mine unless i told you.

 

[70bigblockdodge]

I broke a detroit true-trac recently in my 66 new yorker. I replaced it with a regular detroit locker. No matter what anyone says they are totally streetable. You would never know its in mine unless i told you.

Wow, I should duplicate your engine and in my gutted Barracuda I'd be in the 10s. Carry on

 

[Wonderwagon]

As I consider, the collective opinions, thank you. Between the Auburn and the Truetrac I was leaning towards the Truetrac due to its robust nature. However, nether one is rebuildable. The Auburn is closer to a tradional posi unit. So if the Eaton posi unit will fit, boo, it doesn't just talked with the shop, I liked the rebuildability of the unit. So it looks like the Auburn, it's more like a traditional posi.
Getting back to earlier replies, shims are worn, as well as the gears, and bearings are done the rear end made it through 250-300,000 + miles. Chyrsler engineers did good. Thanks

 

[MEV]

Mine broke on my STREET CAR with crappy tires with no traction. I drove the car 70 miles to the track, made some runs, and drove it 70 miles back home. No 6000 RPM launch. It broke easily and without abuse.

Lockers are most noticeable/uncomfortable under these conditions:

Short wheel base
Light vehicle weight
Manual Transmission
Tall Center of gravity or lifted vehicles
Over size i.e. tall tires

Lockers are at their least noticeable under these conditions:

Long wheel base
heavy vehicle weight
Automatic transmission
Low center of gravity
reasonable tire height

Since you are posting on the C-body page, I think you fall under the second category. Get the Detroit, you will love the traction and probably will never notice it.

 

[Wonderwagon]

Mev, so you broke a Truetrac, and your advocateING getting a Detroit loker?

 

[MEV]

Mev, so you broke a Truetrac, and your advocateING getting a Detroit loker?

Yes. Tru trac has helical side gears. The regular detroit locker is a full mechanical locker, no clutches or cones to wear out. They are bomb proof.

 

[CBODY67]

Whoa!!! Y'all are getting some terminology mixed up. The Detroit "Locker" is NOT the same as a traditional "limited slip" item. The Detroit "Locker" was used OEM in the later 1960 big-inch Muscle cars, usually Fords, AND on 3/4 ton pickup trucks. It was a mechanical "locker", which locked things solid.

The "limited slip" uses clutches that are friction items, not mechanical as the "locker" is. Within the "limited slip" universe, there are the "flat clutch" versions and the "cone clutch" version, with the latter being lime some OEM Chrysler 8 3/4" axle post-1971(?) and the flat clutch versions being prior to that, usually, but to return years later.

To complicate things, later GM pickups use a "locking differential", not "PosiTrac" as in the earlier years. It has a governor weight mechanism that swings out and locks the two axles together, mechanically. The demo videos show a visible shudder when that happens, and then the truck drives on across that drainage ditch, diagonally, or up the hill pulling a boat, as the other brands falter and can't move.

On our then-new '69 Chevy pickup, it came with the optional PosiTraction rear axle. After a while, on left hand turns, it would not fully unlock and "pop" on those slow turns/corners. Not on similar maneuvers to the right. The then-needed PTrac Additive was supposed to minimize that, but it didn't, although if you didn't use it, "the equipment" didn't like it.

The Torsen-type differential seemed pretty neat when I first saw an add for it in about 1963. I might suspect that with all of those gear surfaces in contact with each other, it might end up having MORE internal friction than either of the other styles of differentials. NOT sure of its ultimate power-handling capabilities. On the other hand, if it had "stamina" and "durability", we'd be seeing them in HD2500 pickups and such.

Not sure where you're shopping for that differential, but there are many places that sell reman/rebuilt 8 3/4" rear differentials. Most with Sure-Grip internals. Almost any Mopar-related magazine has adds for them, I believe, OR parts to rebuild/upgrade what you've got. There are some differences in the model years, though, which might or might not be important to what you're doing. Just be sure to match the current ratio to what you get, if desired.

CBODY67

 

[70bigblockdodge]

A Detroit locker is overkill, not for MEV but for most. Hell anything more than a Auburn unit is overkill for most people.

 

[CBODY67]

A Detroit locker is overkill, not for MEV but for most. Hell anything more than a Auburn unit is overkill for most people.

Seems like I recall seeing an article that claimed the "cone clutch" was not as tough as the "flat clutch" limited slip differentials. It would work for a while, in HD situations, but not as long as the flat clutch differentials. End result was that the flat clutch limited slips were the best. BTAIM

CBODY67

 

[70bigblockdodge]

Seems like I recall seeing an article that claimed the "cone clutch" was not as tough as the "flat clutch" limited slip differentials. It would work for a while, in HD situations, but not as long as the flat clutch differentials. End result was that the flat clutch limited slips were the best. BTAIM

CBODY67

Cone was better in low traction conditions, it's spring loaded. The flat clutch 4pinion design has to have torque bias (forcing the pinion shafts up the sides of the v you see them sitting in) in order to apply pressure to the clutches, a bias you may not get in really low (ice) traction conditions.
This was the thought process of the manufacturer's this the switch to cone type.
You can overpower a cone clutch pretty easy and if you stand on a decent powered car making a turn with a cone clutch unit it will almost always only burn one wheel (very hard on the unit)
The 4 pinion flat clutch type are good with big power and fair to good traction( good for drag racing). They can be made more agressive with different combos of friction material and disc springs.
You could always put a spool in just don't park or manuver alot.

 

[67Monaco]

I vote spool. Yeah you have to get used to the tire skipping around turns, people looking at you funny, and the occasional broken axle. But nothing's better for traction...

 

[70bigblockdodge]

I vote spool. Yeah you have to get used to the tire skipping around turns, people looking at you funny, and the occasional broken axle. But nothing's better for traction...

Ahhh you get used to it.
Everybody needs ultimate traction with a mild 440.
Plus they are lightweight which is a top priority in a 4500# car that is never going to be driven in the snow & ice

 

[MEV]

Not C-body cars, but lots of good info about failure rates of various types of lockers/posi units.

Who's broken a Truetrac? - LS1TECH - Camaro and Firebird Forum Discussion

 

[70bigblockdodge]

Not C-body cars, but lots of good info about failure rates of various types of lockers/posi units.

Who's broken a Truetrac? - LS1TECH - Camaro and Firebird Forum Discussion

Honestly nothing against you, but I could not figure out what the hell they were talking about. They kept bouncing back and forth locker this tru-trac that I think they were interchanging them and nobody had a clue.
Makes me happy to be on here and not addicted to other boards.
Wonder when the change between early and late Tru-trac was. Not that it matters tru-trac is too rich for my blood, especially when Dr. Diff sells a primo Chinese 4 pinion clutch type for around $400, yes I know it's Chinese but with Dr diff approval I'm in, and you can only buy a used US made one.