show me your rearend ... if it's a 8 3/4 mopar

I am planning to use this Billy Bad Ass, 8 3/4, 3:23 posi, casting #2881489
under my '31 Coupe. Please post photos of yours, so I can get a better
idea of how it's going to look. Thanks, 63dan63

 

I have the same axle under my 31 coupe on 32 frame. It is mounted with Pete and Jakes ladder bars and shocks, and a 34 spring. It also has a disc brake kit.
I'm sorry that I dont have a picture of it right now,but it looks o.k.

 

Heres mine in the back of my 36' Dodge truck. If I remember right its from a C-body....Mounted with S&W 4 bar and shocks....

 

i had an 83/4 in my front motor dragster . worked well . good luck ... steve

 

The 489 casting like yours and also the 742 casting are supposed to be stronger than the 9 inch ford. Supposedly the 741 is not. Anybody got in experience with the 741 casting in 8 3/4 MOPAR? Is it really a weak sister, or will it hold up in a light rod? Also, are brake drums still available for these 8 3/4 rear ends?

 

489 casting uses a tapered pinion and is said to be the strongest, but uses a cone type limited slip (SureGrip). 742 was used just previous to the 489, used a straight pinion, and the limited slip was an easily rebuilt clutch type (SureGrip).
Rear brakes can be 10 X 1 3/4 (expensive A body rear end with a 4" five lug bolt pattern), 10 X 2 1/2 (by far the most common and easiest to get parts for), 11 X 2 1/2 (out there, just not as common and easy to find)

 

When I built the rearend for my '32 I used 8 3/4 axles and brake assys and grafted the bearing ends to a 12 bolt chevy rear for a bulletproof combination in a light hotrod. I had the axles shortened and resplined to 12 bolt specs and got the beefy bearings, the bigger Chrysler brakes and easily removable axles (eliminating the C-clips) as a bonus. The reason I didn't use the whole rear is the one I had was toast as far as the housing was concerned and I couldn't find a decent ratio centersection. So...... now I've got an easily serviceable centersection (and relatively cheap) with axles that are as big as tree stumps. Win/Win

Frank

 

Sort of...
The early version of the Sure Grip (early '60s) was the rebuildable clutch-type. I think it was actually called a Traction Lock, but not positive. The later muscle-car era and beyond Sure Grip was the non-rebuildable cone-style.
They will interchange between the cases. They DO have gear ratio breaks though, so you need the right one to run with the gear you have.

The 741 case has a smaller-diameter pinion than the rest. Under a light car, for all-around cruising? If I had one, and it had the right gear on it, I'd probably run it. Under something with some weight or torque? No. If I didn't have one and was shopping? I'd pass on it.
UNLESS! it has a Sure Grip in it. The actual differential is interchangeable between all three castings. You can take a limited slip from a -741 casting and put it in the -742 and -489 cases. The differential doesn't know what pinion diameter is driving it.

The 8 3/4 can be found under anything with a Pentastar...muscle cars, station wagons, slant-6 vans... they're not rare, just overlooked.

-Brad

 

Out of a C-Body. Dont worry, brakes are coming soon, and coilovers.



You can find brakes off any old truck or car and they will bolt on. Make sure you get everything. All 8
75's were 5x4.5bp. The C-Body drums I have are finned.

My buddy is running disc brakes off of an SVT Explorer. He are his directions:

"No problem. The kit is 1996 - 2000 Ford Explorer and some Mustang. Here is the kit.

http://store.summitracing.com/partde...5&autoview=sku

You will need Late Big Ford axle tube ends with the appropriate superior than Mopar bearings. The bearings, axles, ends can be aquired at Strange or Moser.

I was turned onto this kit fron Art Morrison. This is a standard brake kit with his rear clips.

The ebrake cable is through Lokar. I pulled mine from a Ford Explorer in a wrecking yard.

I WILL call you sometime for a beer. Currently enjoying a Samuel Smiths (England) Oatmeal Stout OMG........ Bliss

Also, Its the same disk brake kit that Strange sells also. Tell them you are running the FMS 11" disks and they will cut the axle accordingly. The tube flange to axle flange is something like 2.5". They will know that.

 

I will be running a 3:55 geared 741 on my truck above. The 741 was the earliest case and is very much considered the 'weak sister', but they put Max Wedge Big Blocks in front of them. It will be just fine in your light rod. As far as the 8.75 being stronger than the 9 inch, I will leave that as an arguement between Mopar and Ford guys for the centurys. i am a Mopar guy personally, but I believe a 31 splined axle 9inch is stronger any day. The 28 splined one might be too (all 8.75's were 30 spline axles)

 

I've got a 742 under this... It gets the snot beat out of it regularly and has held up great for the 10k miles I've put on it. It's held in place with Ibeam truck arms and a 40 ford front spring. No great pics of the rear, though.

 

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Minor correction to this part. The A-body cars with an 8.75 were a 5-on-4" bolt pattern, and usually had smaller brakes. all the B bodies were 5-on-4.5, as were almost all of the C-body cars. The exception is some of the Imperials had a larger 5-on-5" pattern.

Roger

 

Mopar also put the 741 and 742 centers under most Dodge 1/2 ton trucks through the late 60s. Even the light duty 8 3/4s are tough. I wouldn't be afraid of any of them.

That all said, I've not met a rear axle yet I couldn't break, some just take a little more effort. Facts are, if your abusing things, you should expect to break stuff. When you break things, your faced with 2 options, shell out the cash for better/tougher stuff, or don't beat on it so hard next time. Gene

 

Something I forgot to add. In the 60's, when you ordered the 426 Hemi with auto trans in a B-body, if you didn't specifically order the Dana 60 rear, you got a sure-grip 8.75. That should tell you something about what Mopar thought of that rear end.

Roger

 

I have a 489 case 8 3/4 in my back-halved 64 cutlass with 14x32 slicks. 4.56 gear, 31 sp spool, Moser axles, and a back brace. Its on triple adjustable ladder bars with DR5855B coilovers.

I'm giving it hell, and it just gives it back. In spades.

 

People say the 741 case is junk... so just send your unwanted ones my direction before they self-destruct

Seriously, as previously mentioned, they were in fact used in Max Wedge cars (more powerful and heavier than most peple's hot rods). And at that time, the 742 housing was already in production!

Ever seen a broken 8-3/4? I know what it takes to consistently break an 8-3/4 differential - enough power to make a 3800# car run 10.80 quarter mile times. Failure mode: broken bearing caps every single time. My advice to my friend was to "either stop spraying it in first gear or go to a Dana 60."

Ever seen a broken 8-3/4 pinion? It is possible, but extremely rare. I believe misalignment was the cause of the only one I know of. The pinion broke right at the end of the splines behind the yoke - which is a diameter common to all 8-3/4 pinions having the 10 spline count.

The supposedly weak 741 case has the smallest pinion diameter of 1-3/8" but I have yet to see or even hear of one breaking where it is too "small". Again, keep in mind these were used in stick-shift max wedge cars.

In the typical hot rod... not an issue at all.

Regarding 8-3/4 sure-grip units, the early ones (~1958-1968) were a Dana (spicer) design called a power-lok. It uses two sets of clutch plates and is easily rebuildable. Service parts are still available. In my opinion it is far superior to any other differential for street/strip use. Four differential pinions as well as having the differential pinion shafts on ramps to wedge the clutch packs even tighter as more torque is applied is a pretty good design.

In about 1969 (almost the same time they introduced the 489 housing), they switched to the Borg Warner spin resistant which uses two differential cones that grind into the differential case. When this design of differential gets worn to the point of being a one-wheel-wonder, the differential pinions (spiders) usually gall to the differential pin, which then destroys the case. When the pin exits the differential case, things get really really ugly really quick. This type of differential can be only repaired if it is caught before the differential pin destroys the diferential housing. The dealers treated the cone-type unit as an assembly only, so service parts are not available. I never checked to see if the new Auburn units parts are interchangeable, but the two designs are very very similar.

Traction-loc is typically a Ford term and that differential never found its way into an 8-3/4, but a version can be found in mid 70's and newer Dana 60's. It is no where as agressive as the power-lok.

Remember, as many have said all 741 housing 8-3/4's are junk, so just send them to me if you are worried about them

 

Oh yeah, here's one of mine if you look really hard...

 

I'm sorry I don't know you well enough!!!!!!!!!!--TV

 

Are you really sure?

Countless 8-3/4 Power-loks removed from the big cars have had their 2.76 gearsets removed to install 4.10, 4.56 and even higher ratio gearsets. Yes, I have done exactly that many, many times. I have a set of 5.38's on a Power-lok... That's just one of the advantages of the threaded differential bearing adjusters.

 

ill be sticking my a body 8 3/4 with 3.55 sg 7412 case into my essex. i will double check the width with other bodies but the abody unit looks liek the width i need. pulled it out of the dart to go with a dana.

 

I have had and seen more 9" fords gernade than you would believe, only seen 1-8 3/4 go to pieces. the 741 case is plenty strong we have one in my kids 63 Valiant wagon and it runs 10.80 and no problems out of it.

 

FWIW the early A body 8 3/4" had a 4 bolt x ?" pattern, and the later ones had the 5 x 4.5" bolt pattern. I believe the axles interchange though. Early A body rears are very narrow too.

 

Correct - but here is a clarification:

ALL A-body 8.75" rears are 5x4" bolt pattern. They were put into the cars from 65-72. Then they went to a 8.25" rear in heavy duty A-body applications.

IIRC the A-body rear is about 55" wide.

Pre-65 8.75"s used key'd axles that are weak. In 65 they went to a 1 piece axle that is much stronger and much easier to service. You can tell the difference by looking at the center register of the axle. The early ones have a big nut that keeps the hub from sliding off the axle.

These earlier 8.75's also used a 653 case commonly unless it was a hipo application, where it got the much stronger 742 case.

The 653 is pretty much identical to the 741 case with a straight 1 3/8" pinions (same size as a chevy 12 bolt) that uses a spacer and shims to set the pinion depth.

The 742 case uses a straight 1.75" pinion that uses a spacer and shims to set the pinion depth and is condered the 2nd strongest centersection overall, but the strongest in factory trim.

In 69' the 489 casting came out with its tapered 1 7/8" pinion and uses a crush sleeve to set pinion depth. This is the strongest center section, but under heavy use, the crush sleeve can crush more and screw up the endplay and pinion depth. The fix for this is to use an aftermarket tapered spacer and shims to set the pinion depth.

How 8.75's fail is they either take teeth off the ring gear, or break the caps. You can run deep into the 10's on an 8.75" rear. Their 30 spline axles are plenty beefy and stock for stock, they are actually stronger than a 31 spline factory ford rear. However, 9" fords have a "pocket bearing" that supports the back of the pinion that makes them superior when building then up for ultimate strength.

 

no a-body was 4 bolt. although the 73 and up cars were 5x4.5, they werent an 8 3/4. a-body 8 3/4 rears only came with 5x4" bolt pattern.

 

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Don't take this as gospel, either. If the car had disc brakes, or a V-8 engine, then yes. If, however, the car was a slant-equipped car without discs, the lug pattern was still 5X4", even as late as '75.

Roger

 

This is a lot different car than you're building but here it is. You should be happy with that rear end. There are non-adjustable (green bearings) axle bearings that eliminate the tapered roller bearings and adjusters that Chrysler used and if you want rear disc brakes try finding a 74-75 Imperial donor.

 

OK my memory ain't great so here goes. Chrysler still used 8.75's through 73. I remember them in performance cars and trucks. The 73 340 A-body cars used 5x4.5 b.c. rears. That's the only year for A-body 8.75, 5x4.5. The 74 A body performance cars used 360 engines and 8.25 rears. I could be wrong....

 

Eliminating the tapered rollers is fine on a strip only car - the "Green" bearings don't like side load very much and don't last long if you like to corner fast. The imperial discs are very heavy, hard to find parts for and generally not worth the time and effort IMO.

I read an article in Mopar Action a little while ago about using newer Ford style axle bearings on an 8 3/4 to eliminate the bearing adjustment and still have streetable strength for sideloads.

Little known fact is that the 8 3/4 has much less drag than a 9" Ford due to the straighter hypoid angle.

 

The A body 8 3/4 was only a 4" bolt pattern. An a body with 4.5" wheels had either a 7 1/4" or 8 1/4" axle.

The '68 Hurst Hemi Darts and Cuda's used a B body rear axle with the perches moved inward.

 

Cool