Rear End Dilemma

blown65 · Nov 10, 2004

I broke 2 8" rears when I was younger with a pretty mild setup. Scrap that and just do a 9" and be happy with no problems in the future.

Great68 · Nov 10, 2004

I'm having the same dilemma,

I want a 9", however 9" rears are becoming quite scarce up here, and if you do find one there's a great chance it won't be exactly what you want so you have to spend some good coin modifying it/rebuilding it. Most often just a housing and pumpkin will go for $1000+, then you have to spend the coin to modify the housing to fit, rebuild the pumpkin, buy the gearset you want, buy the differential you want etc...

I'm lazy and impatient, and like to just go out and buy exactly what I want from a store, then scavenging around the buy/sell waiting for something that might possibly work pop up and then spending the time and cash in modifying it to work.

I did notice that the Powertrax No-Slip locker part number is the same for a 28 spline 9" as it is for an 8". If this is the case, I might just put that in the 8" and when I come across a good deal on a 9" housing and 3rd member I can reuse the Powertrax.

BTW, does anyone know the strength difference of the 66 and earlier 8" pumpkin vs the 67 and later one? For people that are breaking 8"'s, did you break the earlier style, later style, or both?

ratio411 · Nov 11, 2004

I have broken a few 8" rears...
Always the ring/pinion or differential.
I have never lost an axle or case.
I have broken 3 with a 302, and one with a stock 460.
The 302 was pretty mild. 2 rears were lost behind a stock convertered auto, one behind a toploader. 2 with 3.00 gears, 1 with 4.11 gears. Never any slicks. Slapper bars in all cases.
218 @ .050 cam on one, 228/235 cam on 2.
The 460 was a 3.28 gear. Broke within a week after engine swap. A 2.79 was put in and lasted until I sold the car... (4 months)

Sorry so long,
I just thought some details might help some folks picture my combos and show the variation of details when rears were lost.
Dave

EDIT: I have used both early and late cases, it doesn't really matter, neither broke. The 28 spline axles aren't super strong, but even the weakest stock 9" rears handle far more power than a stock 8", so the axles can't be the weak spot, they are the same.

Edbert · Nov 11, 2004

Retail prices are high if you don't have the cores. A fully built 9-inch will run you $2,000-$3,000 from Currie. You can still find stock 9s in the bone yards but you gotta crawl around for a while and chances are they will not be a bolt-in since Mustangs from the '60s have been picked over pretty badly and you may have to look for a Galaxy or even a F100. But paying $1,000 for a used/junkyard 9 is crazy. I was able to find a correct length 9 (from a wrecked '68 Cougar XR7) and buy it for only $300. Of course I replaced the ring and pinion, the diff, all the bearings, even the axles and brakes. But even after all that I was waaay under the price Currie wants for theirs since I had the cores.

Now in my spare parts bin I've got a complete 8 inch rear. Totally stock but complete including the brakes, perfect for anyone wanting to upgrade their 6 cylinder car to a V8. I've also got a bare 9 inch housing, the large bearing kind for serious output applications, I decided to use a stock (small bearing) 9 in my car. I've also got a stock pumpkin with highway gears and an open diff, and a pair of stock 28 spline axles that are the correct length for a 67-70 Mustang, even the large drum brake stuff.

PM me if you are interested, I just need this stuff outta my garage.

jbsteven · Nov 11, 2004

FYI

I ordered a full setup 9 inch last night from Summit. Currie complete $2350 delivered.

The Dan · Nov 11, 2004

Well, Currie made my deceision much easier:

Quote:

"300 h.p. is the maximum h.p. level that we recommend on the strongest 8" we can possibly build. We do not generally recommend putting a lot money into them unless this is a pretty mild street car on radial type of application."

"We can get you an Auburn but we do not recommend them - only because they will always make noise to some degree, and should the unit ever wear out, they are not rebuildable, they are throw aways, whereas we have full rebuild kits for the Ford style traction locks.
I would recommend either our T.S.D. Ford based traction lock, or the Detroit Tru-Trac worm gear style posi traction."

This is from the horses mouth, so I think it should be good scoop.

stangman67 · Nov 11, 2004

Of course they want to sell you a piece which means youll have to upgrade most all other parts(axles, housing, etc) I think it should be based more on the torque of the motor. It seems a 289 with 400hp would have more trouble breaking an 8, than a stock 460 with like 220hp.

The Dan · Nov 11, 2004

Whoa...9" built and installed....$2,350.00. Far cry from the $1,200 8", but sounds like the way to do it right! And I don't think it could get much better than Currie doing the build and install.

blue66tang · Nov 11, 2004

I skipped a bunch of posts so i dont know if anybody else went over prices for there 9"

Mine was
$25 for 1960 car 9" housing with small housing ends so I could reuse my brakes.
$25 for a 9" out of a 70s car
$95 for Moser gear set up kit with all new bearings.
$175 for Moser 4.30 gears.
$20 for Moser spring perches
$300 for detroit locker off of ebay, from a Nascar. 31 sp
$295 for Moser 31sp axls
$20 for Moser screw in studs 3" long
$75 for gear set up at local shop
$70 for axle bearings and a new ujoint
$75 for shortning my drive shaft.
free for all cutting and welding on howsing. Me and a friend of the family did it.
Im not sure if i am forgetting anything.
so we have a grand total of
$1175 give about 50 for other ods and ends i am forgetting.

My original plan was to do it for 600 or less, as you can see. I missed my mark.

Edbert · Nov 12, 2004

blue66tang said:
My original plan was to do it for 600 or less, as you can see. I missed my mark.

You still did really well, WTG!

My plan was to buy a unit from Currie, but the way I spec'd it it came out to $2,600-something...YIKES.

As I posted above I got a correct-for-my-car small bearing 9 for $300. Added a Motorsport R&P in 3.89 for $150, and a Lock-Rite soft locker for $300. Then paid a guy to install and blueprint the gears and differential for $100.00 including bearings. Paid another $100 to have the housing soda-blasted and powdercoated. Bought new 31-spline axles from Superior for $250, and Wilwood disc brakes for $550. The axle bearings and seals were only like $25 from Advanced Autoparts, and they had them in stock while Autozone had to order them.

All said and done I am significantly under $2K.

ratio411 · Nov 12, 2004

stangman67 said:
Of course they want to sell you a piece which means youll have to upgrade most all other parts(axles, housing, etc) I think it should be based more on the torque of the motor. It seems a 289 with 400hp would have more trouble breaking an 8, than a stock 460 with like 220hp.

Torque, vehicle weight, tires, weight transfer, and your right foot all play a role. Also tranny type and converter if auto.
You can have a monster engine, but pizza cutter radials out back and the rear will never break. It is when weight or traction are stronger than the rear that you have problems. HP is a measure of how fast your engine can produce torque, so yes, it does come down to torque, weight, and traction.
My experience with the 8" is that if you are an aggressive driver, you don't need much power to break one.
Dave

steel1212 · Nov 12, 2004

I don't know if anybody has said this or not but you can get a currie 9 inch out of summit for like 1k with out chunk. you then could get a used one off of ebay for like 300ish. thats all brand new parts with brakes, axels the whole shibang for 1k then a used chunk. You could even have them build you a chunk for probably 7ish.

shelbe67 · Nov 13, 2004

ever think of an 8.8? I just did it in my 67 I bought the rear from a 94 for a 100 bucks cut off all the brackets and bought leaf spring perches for twenty and welded them on myself you could have gears done at a speed shop for about 350 bucks including the gears

Rear End Dilemma

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