8" rebuild or 9"

so I have this opportunity to get a 9" rear - it is out of a 1972 mustang mach1 that has a 351 and auto tranny. they want $150

My car is has a 302 w/FMX, w/8" rear.

the 302 is mildly hot- rebuilt .030 over - thumpr cam, 650 double pumper, pertronix dizzy, med rise edelbrock intake, long tube headers.

Stock heads though

but, it runs really great!

does the car make a ton of power....hmmm..I would guess barely touching 300hp. Is that a ton of power...No.

plans were to rebuild the 8" but after speaking to the rebuilder, he highly suggested I get an 9". He says he can rebuild the 8" to my specs, and guarantees it for 3 months, but says it takes one hook and the 8 is going to need to be rebuilt. Where as the 9" he says it A LOT more stout and could hold up to tons of abuse. the rebuilder says the 9" for $150 is a bargain and I need to jump on it ASAP.

so the question that your probably going to ask is...

What are my plans with my car? race it? weekend it? daily driver?

I plan on weekend it...drives here and there around town...no place far, and take it to the strip.

My ??? is.

Is the 9" from the '72 a direct bolt in? meaning...I won't have to cut driveshaft or add length to the driveshaft?

according to the rebuilder, he said that if the driveshaft needs to be cut....EZ peasy. No biggie for him. Now Adding length...he said...little be harder job.

Will I have to modify the springs?

need new springs.

any help/info/suggestions is greatly appreciated!! Thanks

Not sure if it's a direct bolt in. If your not going to upgrade your motor any more or you're not going to go bigger, I wonder if you even need to swap. From what I have read, the 9" actually takes more power to turn. If it were me, I would swap to a modern 8.8 rear. Very durable, you can get parts for them anywhere, they will most likely come with disk brakes and (built) will handle a ton of power. Just a suggestion..

Both 8 & 9 inch have the same design, which is the pinion offset, that makes them harder to turn and is why neither is still in production.

I believe the 9-inch pinion and yoke are longer, which will require you to shorten your driveshaft. It will bolt to your springs, although if yours are original I would take this opportunity to replace them.

That is an excellent price for a complete and functioning 9-inch.

Why spend money on something that isn't broken?

If you think that the 9" is a too good of deal to pass on, buy it and throw it behind your garage for when you do break the 8".

A warmed up 302 isn't going to hurt an 8" rearend on street tires. Just my opinion...

Well let's start off with a few questions

Are you unhappy with the gear ratio is in your 8"?

Is it a Open Differential? (Not a trac lok unit)

Does it need a rebuild?

Do you plan to put slicks on the car at the drag strip?

I would say that if you answer any of those questions with a yes, that you should get the 9" (or possibly an 8.8 if you also want disc brakes)

I would not build an 8" when a 9" was available at that price.

If I had an 8" with Trac lok and it was otherwise in good shape and only needed a gear change, I might do it, but if it needed any more, I would not want to invest in it when a 9" was available for only $150

You also need to consider the condition and the particulars of the 9"

Is it an open rear end?

Is the housing and carrier in good condition?

does it turn freely or is it filled with molasses like sludge?

I gave $50 bucks for an open 9" 3.00 72 Mustang rear end to get a carrier and a housing for future projects. $150 is a good deal if it is usable or a good candidate for a rebuild, but it depends on actual condition a lot too.

Thanks for all the input.

I think I'm going to go ahead and get the 9. Its just a good deal, I can't pass up. I know the 302 won't damage the 8, but what if I get crazy and drop a 351 in, I think then the 8 will not hold up as well as a 9.

yeah..the rebuilder told me to check for damage, see if it spins freely, if the care was rear ended and has massive damage. According to the guy selling it...here is what happened.

The motor caught fire, all wiring and hoses burnt. Now he is just parting out with it.

If it were me I'd buy the 9 inch. That's a good deal and you can always resell it if you change your mind and recoup your loss. The 9 inch Ford rear end is considered one of the best and most durable rear ends out there and they are a favorite of hot rodders and drag racers alike. Heck even chevy guys like em.

If it were me I'd buy the 9 inch. That's a good deal and you can always resell it if you change your mind and recoup your loss. The 9 inch Ford rear end is considered one of the best and most durable rear ends out there and they are a favorite of hot rodders and drag racers alike. Heck even chevy guys like em.

Click to expand...

Ummm...the 9 inch Ford rear end is also standard on all NASCAR vehicles.

I snapped a 8 inch pinion shaft in two with a 302 4sp

69 Mustang. A 9 inch rear replaced it.

Nothing like the sound of the drive shaft flinging around under the

car not connected to the rear end!

Paul

I snapped a 8 inch pinion shaft in two with a 302 4sp

69 Mustang. A 9 inch rear replaced it.

Nothing like the sound of the drive shaft flinging around under the

car not connected to the rear end!

Paul

Click to expand...

Paul, I have seen what you described happen and instantly your description made me laugh. Thanks. I laughed then too, because it wasn't my car. If it had been mine, I wouldn't have been laughing, more like using every explicative that I knew at the time. Like I did when I snapped the input shaft on a 390 top loader 1966 Cyclone. Chuck

I snapped a 8 inch pinion shaft in two with a 302 4sp

69 Mustang. A 9 inch rear replaced it.

Nothing like the sound of the drive shaft flinging around under the

car not connected to the rear end!

Paul

Click to expand...

This is exactly what I'm talking about!! 302's do put out some HP!!!

I got it! the 9" for $150

I forgot the specs on the tag, but it did read 2.75 and 9 !! yeah.

it turned free no lockups. sorry for the bad pic. was in hurry to get out of there


now thinking of getting this kit...


btw

got the driveshaft, all parking brake cabling, and light bezel.

$150 for the drive shaft

$50 for driveshaft, parking brake cabling and light bezel

$25 for use of his lift - i threw that in there...working on the ground was PIA

total $225

update: instead of the trac lok...getting a true trac

complete kit $670

true trac posi

master bearing kit w timken usa bearings, shims, and seals and ring & pinion of choice - going w 3.70

I thing this is a pretty good deal....your thoughts/opinions

Well all the ones I found were about 1000 bucks new, so that sounds pretty good to me but I'm in Europe, so I hardly know what prices there are in the U.S. unless they are from the usual vendors.

Is your offer from a dealer?

If it is I'd like to get in touch with them.

Well all the ones I found were about 1000 bucks new, so that sounds pretty good to me but I'm in Europe, so I hardly know what prices there are in the U.S. unless they are from the usual vendors.

Is your offer from a dealer?

If it is I'd like to get in touch with them.

Click to expand...

from www.quickperformance.com

emailed "Mike"

Thanks a lot!

before and after - sandblasting

just dropped off rearend at mechanics house. He will be rebuilding it.


here it is nice and primered

got my parts ordered!!

TTupg Upgrade from trac lok to eaton truetrac $155.00 x 1 $155.00

F9PBK-28-3.70-STD-2.890 Ford 9" / Trac-Lok Posi / Ring & Pinion Gear / Bearing Kit / Package

Spline Count: 28

Gear Ratio: 3.70

Pinion Support Bearings: Standard Inner Bearing (M88048/10)

Carrier Bearing O.D.: 2.890" (LM102949/10) $515.00 x 1 $515.00

________________________________________

Subtotal: $670.00

Discount: $0.00

Shipping: $0.00

Sales Tax: $0.00

Total: $670.00

Checkout Questions

________________________________________

What kind of vehicle are you working on?:

What do you plan on doing with your vehicle?:

How much horsepower are you working with?:

________________________________________

________________________________________

QuickPerformance.com 303 Sondrol Ave. Ames, IA 50010

Phone: 515-232-0126


I have a feeling the 3.70 are going to great from light to light, but hwy may be a drag!

But my car won't be doing "country cruising"....maybe when I'm 80yr old I will, but not right now.

I snapped a 8 inch pinion shaft in two with a 302 4sp

69 Mustang. A 9 inch rear replaced it.

Nothing like the sound of the drive shaft flinging around under the

car not connected to the rear end!

Paul

Click to expand...

I know that sound I did it to a 65 GTO back in the 70s.