What spline count for 9"? 600 HP & Trans Brake - Third Generation F-Body Message Boards

BadaPwned · 07-31-2009, 12:14 PM

Im going to be putting in a 9" in my TA. I need to know what the minimum spline count I should go for with the power that I have.

The motor is a 450 HP SBC with a 150 shot of juice.
I will be launching with a TH350 with a trans brake.

What spline count should be the minimum for what im doing?

Any help should be appreciated.

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big gear head · 07-31-2009, 12:24 PM

31 splines will work. They are good up to 7000 foot pounds of torque. Go to this page and put in your numbers. I put in 600 foot pounds from the engine, 2.5 first gear ratio and 3.73 gears and came up with just over 5000 foot pounds on the axles, so 31 splines should be more than enough for you.
http://www.moserengineering.com/Pages/axletech.html

BadaPwned · 07-31-2009, 01:07 PM

Awesome. Thanks a ton.

If I remember reading somewhere, some Broncos had 31 spline count axles?

So I could buy the housing & axles then use a center section out of a junkyard Bronco? Or am I making things up?

Thanks again!!

big gear head · 07-31-2009, 05:15 PM

You could do that, but don't expect it to last long. The Ford Traction Lock that was used in these rer ends has a weak side cover that will break when you put it under a lot of pressure. You will need something stronger than that.

BadaPwned · 07-31-2009, 07:05 PM

What do you suggest?

Im leaning towards running a spool, just because the car gets so little miles a year.

big gear head · 07-31-2009, 07:34 PM

If it's going to be drag raced a lot then a Detroit Locker would probably be best. If it's just for street use then a US Gear Traction Lock would work all right. If you want to auto cross or road race then use the Truetrac. I wouldn't use a spool in a street car.

Stephen 87 IROC · 07-31-2009, 07:38 PM

I wouldn't recommend 28 spline even for a street car. 31 spline is more than enough. I use 31 spline axles but I also use a powerglide so the starting line torque ratio isn't as high as a similar car with a 3 speed. If I used a 3 speed transmission, I'd need 33 or 35 spline axles but would also need a new spool, center section, etc. 33's may fit in my Moser aluminum center section since I use the big side bearings.

My car has approximately 800 pounds of torque x 4.86 gears x 1.76 first gear x .9 = 6159. Each Moser 31 spline axle can withstand 7000 pounds so you have a 200% safety margin by staying below the limit of one axle. I'm getting close to the limits of the axles. I pull them every now and then. When new, I painted a line down both axles. The line is still straight so they're not twisting. I probably abuse the axles a lot more than you will with your setup.

I sold a 9" diff that had 31 spline aftermarket axles. It had a 4.11 posi center section out of a Bronco. I never used the posi or gear ratio for racing. I just needed a center section for the diff so it would sell easier.

BadaPwned · 07-31-2009, 08:38 PM

Quote:

Originally Posted by big gear head

If it's going to be drag raced a lot then a Detroit Locker would probably be best. If it's just for street use then a US Gear Traction Lock would work all right. If you want to auto cross or road race then use the Truetrac. I wouldn't use a spool in a street car.

The car will only be driven when its dry out and around town. I have had the car for over five years and I have never put more then 500 miles a year on the car.

Basically it will be a "drag" car driven on the street.

I have read several times people don't recommend spools on the street. Just seems like what little use the car gets, no reason to have a locker which may lock up on a turn and screw me anyways....

If the axle can withstand the extra abuse from the spool and turning all the time, only thing left to go is the tires correct? lol

Thanks again guys!

BadaPwned · 07-31-2009, 08:45 PM

Quote:

Originally Posted by Stephen 87 IROC

I wouldn't recommend 28 spline even for a street car. 31 spline is more than enough. I use 31 spline axles but I also use a powerglide so the starting line torque ratio isn't as high as a similar car with a 3 speed. If I used a 3 speed transmission, I'd need 33 or 35 spline axles but would also need a new spool, center section, etc. 33's may fit in my Moser aluminum center section since I use the big side bearings.

My car has approximately 800 pounds of torque x 4.86 gears x 1.76 first gear x .9 = 6159. Each Moser 31 spline axle can withstand 7000 pounds so you have a 200% safety margin by staying below the limit of one axle. I'm getting close to the limits of the axles. I pull them every now and then. When new, I painted a line down both axles. The line is still straight so they're not twisting. I probably abuse the axles a lot more than you will with your setup.

I sold a 9" diff that had 31 spline aftermarket axles. It had a 4.11 posi center section out of a Bronco. I never used the posi or gear ratio for racing. I just needed a center section for the diff so it would sell easier.

Ya, im still trying to figure out how to do this saving money where I can.

So far I figure, I can pick up the housing with axles etc basically everything except the center section for around $1,200 ready to bolt in. That leaves the carrier (spool or locker) and center section (still havent figured out how to find the best vaklue for this part) & gears....

Im hoping to have it done for under $1,800. Well see though lol...

Any ideas?

Also, for the brakes I was going to use the same disc brakes I have now.

big gear head · 07-31-2009, 09:41 PM

I can get you the housing and axle package for $990 plus shipping. UPS will probably be around $60, but I'll have to check on that.

BadaPwned · 07-31-2009, 11:36 PM

Say I went with the package, what do you recommend for the center section? Besides buying new?

BadaPwned · 07-31-2009, 11:46 PM

Whats your opinion on this?

http://cgi.ebay.com/ebaymotors/Rebui...Q5fCarQ5fParts

Stephen 87 IROC · 08-01-2009, 01:18 AM

I ran a factory stock cast C7AW-E case for many years and around the middle of last year, I pulled the pinion to replace a leaking o-ring and found the inner pinion support was cracked. It could have failed at any time and shot the pinion out the side of the case. I tapped the support with a hammer right after the pictures were taken and it broke right off.

I swapped in a replacement C7AW-E to finish the season then over the winter, I upgraded to a Moser aluminum bolt through case, aluminum Daytona pinion support and aluminum spool.

Old case that was cracked. I've was running in the 9's with it for about 3 years.

This is what's in the diff now. Weighs about half what the steel stuff was. I recently had it out to do a ratio swap and didn't have to bench press it in and out of the housing. It was just about a one handed operation.

For your power levels, a factory C7AW-E case will be fine.

BadaPwned · 08-01-2009, 12:14 PM

Ahh, nice looking center section lol. So from your experience, on a stock section I should be find. Sounds good.

Whats your opinion on the one I posted from ebay?

Here it is again

http://cgi.ebay.com/ebaymotors/Rebui...Q5fCarQ5fParts

Thanks again!!

Stephen 87 IROC · 08-01-2009, 12:39 PM

The Ebay listing that you posted is a stock C7AW-E casting. You can just see the casting numbers in the pictures. Just about any late model case you pull from the junk yard will be that casting.

New steel spools are less than $100. Gears can vary but I'd say those are probably factory gears since a brand is never mentioned. A stock case can be picked up from a junk yard pretty cheap. The most expensive part is the new bearings required to put it together. Shipping isn't going to be cheap. That probably weighs 20-30 pounds.

The complete center section I pulled from the Bronco mentioned above only cost me $100.

BadaPwned · 08-01-2009, 01:17 PM

Seems all to easy. Wth am I missing?

Center section from junkyard ~$100
*Gears $180
Spool $100
Bearings $50
Misc $100

Anything else?

*Assuming Richmond makes decent gears???.....

Stephen 87 IROC · 08-01-2009, 02:08 PM

Richmond gears
Motive gears
US gear (Strange)

The bearings and misc can be lumped together. A complete installation kit is about $100 from Jegs. The only misc is oil and silicone.

Case from junkyard, maybe $100. Depends on your local junkyard's pricing. Stripping the gears and carrier out of it to buy just the case may be a lot cheaper.
Spool less than $100
Installation kit and misc $150
Gears, depending what ratio you want, lots available on Ebay and a used set should be less than $150

The nice thing about the 9" is that once you buy your posi/spool for the axle spline count you want to use, you can put whatever gear ratio you want on it. From 2.50 to 7.00 will all fit on the same carrier. There's no series changes like the GM diffs.

BadaPwned · 08-01-2009, 02:53 PM

Great.

So $1,500 for the rear end. That leaves brakes, which I think my disc mounting plates will bolt up to the 9" ??? lol. I think you can order the rear ends this way.

Only thing left is the driveshaft. Think a stock driveshaft is strong enough?
If not ill be looking at $300 - $400 for a custom one?

Its only money right

Thanks again guy....

Stephen 87 IROC · 08-01-2009, 03:08 PM

The bolt in 9" housing package for a third gen is designed to use the factory brakes. The housing ends allow you to bolt up the factory brakes. The axle flanges have the Chev bolt pattern.

Although a factory driveshaft will probably be fine other than needing a conversion u-joint for the diff, it's best to get a new custom made one. Mine was made at a local driveline shop. 3" x .083" walled steel tube with 1350 ends. I then had to upgrade to a 1350 yoke for the transmission and diff.

If you're going to go that route, buy the yokes first because then you'll know what length driveshaft to get.

The cost of upgrades is never cheap no matter how cheaply you try to do it. Upgrade correctly the first time and you won't have to pay to do it again.

BadaPwned · 08-01-2009, 03:21 PM

Good to know.

I appreciate the help. If we ever meet ill buy the first round.

Spending this kinda coin, I wish the 9" housing looked better. The round shape of them just doesn't do anything for me.

Whats your opinion on a custom housing like this one?

http://www.midwestchassis.com/produc...abhousing.html

big gear head · 08-01-2009, 03:23 PM

The ebay chunk is going to weigh more than 20-30 pounds. A complete stock chunk weighs about 84 pounds, so that one is probably going to be about 70 pounds. I wouldn't use a spool in a street car. A Detroit Locker would be better. A stock Ford case is probably going to be fine with 450 HP. A locker is $475 plus shipping. The installation kit is $90. A 3.73 or 4.11 gear is $150. If you can pick up a $100 core at a junk yard then you can build one for about $815.

As for the custom housing, I just don't like the way they look. I guess I might be old fashoned, but I like the look of the original 9 inch housings better.

BadaPwned · 08-01-2009, 03:34 PM

Quote:

Originally Posted by big gear head

The ebay chunk is going to weigh more than 20-30 pounds. A complete stock chunk weighs about 84 pounds, so that one is probably going to be about 70 pounds. I wouldn't use a spool in a street car. A Detroit Locker would be better. A stock Ford case is probably going to be fine with 450 HP. A locker is $475 plus shipping. The installation kit is $90. A 3.73 or 4.11 gear is $150. If you can pick up a $100 core at a junk yard then you can build one for about $815.

Ya, Stephen talked me out of the ebay deal. I will get one from the junkyard. I still cant justify the price of a locker for what I do with the car. If I end up not liking the spool I can always change it later. I have spent more then $100 on a lot dumber things lol.

On a side note, the more I think about this, the faster I want to get it done. My trans is getting done right now, its suppose to be done today. If I can take it easy on my 10 bolt, I may be able to sell it to recoup some of the cost. After all, I JUST went through it and put in a Auburn posi, richmond gears etc etc. May be able to sell it for $500, who knows....

BadaPwned · 08-04-2009, 07:52 PM

Just for an update, I think I decided against going with a Fabbed housing solely do to the the cost increase (nearly double the cost). But now, not sure if I can go with a stock center section or not. I know Stephen said he went 3 years on his with a lot more HP. But now I got this other guy telling me he wouldn't even sell me one lol. I sure as hell don't want this thing to break after spending 2k lol

Guys I need some help. lol

I just got done talking to these guys;

http://stores.shop.ebay.com/Quick-Pe...__W0QQ_armrsZ1

The guy stated he sells 5 - 7 complete rear ends a day. I told him my scenario and he said he wouldn't even sell me a stock center section. He was completely convinced a stock center section wouldn't last.

At this point, I can spend say around $500 for a stock center section with spool, gears etc.

OR

I can spend around $900 bucks for a complete aftermarket center section. Which is a significant increase for the center section.

Whats your opinion?

Stephen 87 IROC · 08-04-2009, 08:22 PM

You can buy an inexpensive aluminum center section to make it look pretty. There's a Strange aluminum case on Ebay for $325-$350. It's considered a street version but is still stronger than a factory cast center section. My Moser bolt through case was $450 but it's also a lot stronger.

Personally I would just say buy the axle package and pop in a junkyard center section for now. If you ever break it, then decide on how much it's worth to have something better. It's the same as running the tiny 10 bolt, they can be made to last and they can be destroyed while driving on the street. You're always rolling the dice.

It doesn't take much to sink $3000 into a complete differential but someone will always spend $10,000 on an engine and not want to spend money on the rest of the driveline to handle all the extra power.

tekkitan · 08-05-2009, 05:21 AM

This is a great thread! Planning out my bbc swap, decided to go rear first then work my way to the front of the car.

Looking at the Moser 9" packages on summit and going to go with a stock center from the yard, replacing the internals. I won't be pumping out the ft/lb Stephen is, so it should be okay

My car will also only be street driven, and not very much. Same as the Bada, won't drive it in the rain or even when the road is slick if I can help it. It sits in my garage and only gets taken out on nice days for a little cruising or eventually some shows *shrug*

edit: I see many people as well saying get posi for the street, don't get spool. But if I am not driving this thing that much at all, am I really going to need that or is spool going to be fine for my use?

BadaPwned · 08-05-2009, 08:46 AM

Tekk, I think the spool argument on the street is a safety issue. But, I don't plan on driving it on the street in bad weather conditions. I barely drive in good conditions as it is lol. Not to mention, if I don't like the spool I can always put a locker in.

After further research and discussion, its looking like going with a 9" that is going to be bullet proof, aka all aftermarket, its actually cheaper to go with the Strange bolt in Dana 60. They call it the S60.

So.....this may leave a bad taste in some of these guys's mouth, but I called Summit, I spec'ed out a rear end and had them get a price from Strange. Summit always has the lowest price lol.

I did this last night, im hoping they come back with a price of around $1,800. Which will be significantly cheaper then a 9" bolt in, and stronger......

Ill update everyone when I call them later in the day.

Thanks again everyone.

One more thing, if we can get enough people, we can do a group purchase, which would probably be cheaper yet. I would imagine we would have to get at least 5 people, if not 10 to do this....