What rear to Use 10bolt 12bolt or 9"

[rohrt]

I would like to acomplish the goal of having a strong safe differental for a road race/1/4mile/street car (mini tubed)with 600ft/lbs or torq. I wanted to look for best and least expensive route for my application.

My first thought was a ford 9". I was looking at the 77-78 Lincoln versailles with the disc break setup. This is supposably a drop in for my 68 Firebird. This is 1 1/4 more narrow wich is good for me with the mini tube. Then I read this artical.

http://www.mustangmonthly.com/techarticles/26478/

I knew nothing of the 9" so I ejucated myself with these articals

http://www.kevinstang.com/Ninecase.htm

http://www.dfwmotorsport.com/Fairlane/9inchrearends.htm

I added up the cost of going this route and the fact that parts are getting hard to find with that disc break setup the axles would need to be 4 3/4 for the lugs then the disc rotors wouldn't fit, it uses 2-3% more power. The center section would need to be changed out and I think it uses the smaller bearings. Then I read this artical

http://www.chevyhiperformance.com/te...les/0304_nine/

The 12 bolt sounded like a pretty route to go so I followed the link to them

http://www.moserengineering.com/mose...s.asp?CatID=29

Looks like a great rear to go with but now I'm back to a 2000 dollar expense.

I would like a rear that is a little more narrow to get a deeper look on what ever rims I buy in the future but this is not critical to me. So now im wondering if I should just just stick with my stock 8.2 and get a new center section for it from Moser set up for 30 splin axels and get the axles from them as well. My Pontiac doesn't have C-clips but has bearing pressed on the axles. It sounds like their gears are stronger then OEM as well as their axles. My concern is road racing at 150mph(I might be dreaming) and break a axle hub off or have axle bearing fail. I don't know if this is a realistic concern or not or if the 9" or a custom fit 12bolt is over kill? Would like to hear everyones comments on this.

[dennis68]

A 12-bolt is pretty heavy and a 8.5 10 bolt- can easily built to be just as strong. Anything you can do shave weight off the axle will help on the road course. The 9-inch is the heaviest of the 3 but also the strongest and easiest to make changes to (specifically gears). A lot of road course guys run the 9-inch so they can put the Detroit and 4.11's in for the track and the limited slip 3.50 is on the street.

I guess it all boils down to how much do you want to spend.

[JLM]

There are some pretty decent open road courses here in Colorado, a couple with decently long back or front straights that cary some speed. You'd have to have a LOT of power and minimal weight to reach 150 I think. A Roval (oval with a road-course) like PPIR you may see speeds close to that. Honestly I would stick with the poncho differential and get a high quality center section with at least 30 spline axles. That should suite you just fine and it will be cheapest on the wallet.

[Derek69SS]

stock vs. stock, a 9" is NOT as strong as a 12-bolt.

12-bolt has 2 drawbacks, C-clips (on chevys, not on BOPs) and that it's difficult to swap gears.

8.5 10-bolt can be made just as strong as a stock 12-bolt. Do the same mods to the 12-bolt, and nothing compares (except maybe a Dana???)

8.2 10-bolt will hold up for a while, but not forever behind 600ft/lbs.

9" takes more power to turn, I know of one car chassis-dyno'd with a 12-bolt and then a 9". It had 12 more hp at the wheels with the 12-bolt. They have one benefit: Easy to swap gears.

[cw67]

I went through this same dillima about a year ago. I bought a lincoln versailles rear end and brought it to the guy that was going to set up the rear for me. He knew a guy that had a 12 bolt for sale and talked me into buying that one and just swapping out the gears. I'm pleased with the 12 bolt and it was a direct bolt in. I liked the idea of the 9" being narrower for deeper rims and a mini tub. I guess I let everyone talk me out of mini tub for now. I have the Versailles rear end for sale if you decide to go that route.

chris

[rohrt]

I plane on using a TKO 6 speed and I have all the gearing figured out. A 9" is great for the gear changing but I guess I don't see myself doing much if any gear changes.

What mods do you think would make a 8.5 as strong as a 12 bolt? Anyone no if they are making a True trac differentials for the 8.5 BOPs?

[wally8]

OK, I'm going to need more info. Just how is a 12 bolt stronger than a nine inch and under what sort of extreme circumstances? I know the power transmission efficiency thing. The 12HP number comes from Cup testing under Cup racing conditions. I'm not calling BS, I just want some real durability numbers.

Fact is I've seen and used 9 inchers under some pretty rough conditions and I'd be impressed if you broke one on a road course.

If your budget is in the $1500 range, you'd be hard pressed to beat a 9" floater for this app.

You can get one for $750-$800 and that includes rotors and 31 spline axles. Just add the pumpkin of your choice. You can even get one that uses 12 bolt gears if you want that 12 HP back. Then you can guarantee safe performance at 150MPH.

I'm not sure why everyone wants to put money into an 8.5 except that it must be a bolt in deal. But then so is a floater.


Wally

[dennis68]

I'll back Wally up on the durability issue. The 9" is by far the strongest axle going for this application. Some will say maybe a Dana 60...I work on those all day, as long as you don't mind replacing bearings and occasionally losing a pinion then maybe.

A floater 9" while possibly requiring a little fab work (welding on mounts for links or leafs) is the only way to go IMO.

[wally8]

I hate to keep referencing circle track in every post but one thing should be apparent now. If it can be done cheaply while still giving very good performance, the CT guys are doing it.

Fact is you can't build a better racing rearend (or high performance street) for less money than a 9" floater. If you think you can then you better let the CT guys know because they will literally buy thousands of them from you. If it was really cheaper and better, they'd already be using it.

I might concede the issue if we were talking drag racing since those are apples and oranges applications. Roadracing and oval track with stick axles are pretty much both apples (or oranges if you prefer).

SIDE NOTE: If you're looking to build a good handling F, A or G body you really need to look to circle track suppliers. This is where knowing some theory can really save you some major $$$$. Why pay for a WD chassis when you can build the same thing for under a grand (different components, same results). That is unless money is not a barrier (I'm a cheap *******, myself).


Wally

[yody]

nothing wrong with 8.5 ten bolts, people are running deep into the 10's and 9's with slicks. To upgrade a 8.5 10 bolt you need a very good 30 spline posi like eaton, 30 spline aftermarket axles, and a good set of gears like U.S gears are any other of the top guys. A rearend girdle is a good idea too. You can put one of these together for about $1500 total. Should be almost as good as a built 12 bolt

[wally8]

I think that's the mistake people are making here.

So what if it's tough enough to launch a car in a straight line. Big deal, who cares? That's not what this app is really about. What you want to avoid is killing yourself at 150MPH (or even 100) because you broke an axle and the wheel fell off as a result. Drag axles and road race axles are different. Different materials and treatments. You shouldn't be using drag axles for road course work.

I've seen some of the lower stock car classes try to use rearends other than floaters. Everything from stock to high dollar drag rearends that they got for cheap from someone at a swap meet. The axles break, simple as that.

People make the same mistake on motors. They think they can build a drag motor that makes X amount of HP and that it will be a great motor for a track with corners cause, hey it makes X HP. What they don't realize is that you have to really build a motor in a specific way to hold together lap after lap. Completely different applications.

Wally

[rohrt]

Wally8
What do you mean by floater? Do you have some links to what the circle track boys are running. I would like to see some of it for my self.

My first plan was to install a 80 TA disc 8.5 disc break set up in my car. I may go back to that plan. If I can accomplish what I want to do with what I got I will go that rought. The 80 TA does use c-clips. I see Moser sells c-clip elimenators and also axle ends. Not sure if either will work in my application or not. I also checked and found that Truetrac makes a 8.5 version. $400 for a True trac differential, 320 for moser axels ends $80 a pair, rign an pinion $175

I would love to through $2000 or more for a brand new 12 bolt setups but like I said if I can accomplish what I want to do with what I got then its more money to through at something else.

What are some of the rest of you running?

[wally8]

Here are two links:

This is the cheapest: http://www.randysracemart.com/9infoflas.html

This place would be easier to get a custom width and they also do a lot of custom housing apps: http://www.quickperformance.com/

You should consider the fact that you're getting rotors with the package and you can get any kind of caliper bracket that you want (from a cheap stock GM to 3.5" brackets for high end aftermarket calipers) cheap as well. Not to mention all of the various suspension brackets for locating links and PHB's that are available.

When you add it all up for real, I think you'll find that you're spending very little extra to get a much better rearend. Gears are less, axles are less, hubs are more but not much considering you don't have to buy new bearing ends and you have to pay for the housing. Top it off with the fact that you can swap gears easily. It may not be somehting you want to budget for now but a couple years after the car is done you have the option.


Wally

[wendell]

Wally,
great info. It wasn't too long ago that the CT stuff was a really well kept secret.

How fast and for how long untill you need to start looking at rear end coolers with the 9"? I know that you don't have to run a cooler with a QC. Can a QC be made to live under a heavy street car?

Jensen

[wally8]

If you run synthetic lube you'll likely never need a cooler unless you're going to run at top speed for say 500 miles or so.

A QC would be really cool since they're all magnesium and aluminum. I'm just not sure how they'd hold up on a heavy street car. Surprisingly they're not a huge amount more than a floater. Don't get me wrong, they're very tough rearends.

Wally

[rohrt]

I still don't know what a floater is. I usally flush them when I can. Does that just mean it has no mounts welded to it?

[dennis68]

The axles "float" in the housing, they are not retained by anything other than the fact that they can't move via a hub similiar to a front hub on the housing ends. Think tractor/trailer set-up only smaller scale.

[wally8]

Yes, they're actually 3/4 ton pickup hub snouts. The outer hub is retained similar to a front hub on your front spindle but it's splined in the middle to accept the axle for a drive.



Wally

[yody]

I would like to acomplish the goal of having a strong safe differental for a road race/1/4mile/street car (mini tubed)with 600ft/lbs or torq. I wanted to look for best and least expensive route for my application.

I think it is safe to say for what he is doing that a typical rearend setup with your common components will hold up for what he is doing. I don't think he needs a nascar rearend setup, as most pro-touring cars that have competed in events such as the RSE and others don't have floating 9" nascar rearends.

For my info can you please specify what makes road race components different from drag race compenets? Obviously there aren't going to be a lot of side loads in a drag app but what is the difference in the parts.

I could see if he was builidng a oval track car or a high horsepower basically track car but I don't think that is what he is doing. Also what about a drag race axle breaks in a car that goes aroudn corners? Also most pro-touring cars have rear wheel disc, won't that retain the axle if it breaks?(not that you would want that to happen or rely on the brakes to hold your axle in!)

[rohrt]

Those floater assemblies look like you get alot for you buck. Is the main advantage that if you break an axel the wheel stays put? What about disc breaks and getting 4 3/4 bolt spacing on the axles? Any concern I should have with emergency breaks? Looks like a neat set up.