9" Ford questions

[72Pstroke]

Newby here, been lurking in the shadows.
A little background on the car:
I have a 69 Mustang Mach 1 that I am about to finish a full restoration on. It should be done by the time the snow melts here. Engine for now is basically a stock '68 429. I plan to build an aluminum head 521 or 557 for the car in the next year or so. Trans is a toploader with a McLeod RST clutch.
The car is going to be a driver, but I want to autocross it some. Long term goal is to run the SSCC in the Grand Sport class.
I am down to finishing the rear end for the car, and here is where the questions come in. It currently has a small bearing, 28 spline 9" in it. I have reservations about running the small axles, and curious if there are any benefits to running the larger axle bearings at high speeds.
Here is the crux of the question:
Do I keep the small bearing housing and 28 spline axles?
Do I move up to a large bearing setup and 31 spline axles?
Do I go all out to 35 spline and a full float setup? Would be nice for swapping gearsets out, but spendy.
Something else not mentioned here?
I do machine work and fab work for a living. Changing housing ends, narrowing, etc. is no big deal. Unfortunately, I don't have unlimited funds, so that has to play into the decision.
I hate doing something over and would rather do it right the first time. I need to decide before I move on with the project.
I tried to include all the info I thought was relevant. Let me know if you need something else.
Thanks for the help!
Tim

[chicane67]

Smaller bearing's naturally have a higher critical speed but lower overall load characteristics... however, since you are not going to be putting two tons of rocks in your trunk, it's kind of a mute point for sake of argument.

A small bearing (3.062" bearing) 31 spline set up would be choice in my opinion... what ever that is worth. The "small" 3.062" bearing will accept a 31 spline axle shaft.

35 spline axles are a waste of time and money (unless you are running 32" slicks and using a trans brake)... and that isn't a question or statement of how overkill can help, actually... more of how much it isn't in your favor to do so.

Floaters... if you have problems with axle end play, pad knock back and the sorts from a more spirited use... than consider it. But as you mentioned, you don't have a budget to support such an idea if it isn't completely necessary.


What "small" bearing housing and center section do you have ?? (what I am asking is for the bearing diameters on both the housing ends and specifically, the center section differential bearing sizes.)

[72Pstroke]

I will have to get back to you with carrier bearing dimensions. Housing is original to the Mustang, center section is nodular iron of unknown origin.
Thanks for the help!

[BADDRIDE II]

Tim

This is a very important piece of the puzzle no doubt. Taking into consideration the info you supplied, I would seriously consider beefing up this very key component, and if done right will never have to be re-visited again.

If the "stock" 429 was going to be the forever powerplant I would say just button it back up with a minimal of "late big ford" ends & 31 spline axles..

But with your future plans of an aluminum headed big cubic inch big block I would seriously reconsider. These future plans of big hp, along with the heavy weight of the car and then compounding it with the equivelant of a "trans-brake" (manual trans) should have you seriously considering a 33 or 35 spline

Some will tell you that due to tire size limitations you will never hook, therefore never stressing the 31 spline axles and carrier....but these are typically people that do not understand suspension or do not spend the time setting their car up correctly. Our cars are VERY capable of putting the power to the ground. And mearly the torque alone from ANY big cubic inch engine like you plan on running, even from a roll or even 35 mph "clutch dump" is more than capable of destroying a 28/31 spline axle/carrier. You have the option now (for the same price) to assure this will not happen.

*At this point the late big ford ends are a very minimal investment.
*With your skills can be installed for free
*The 33/35 spline axles are the same price as the 31....and MUCH stronger. (go 35 if you have 3.250 case)
*The 33/35 spline carriers are the same price as the 31....and MUCH stronger. (again, go 35 if you have a 3.250 case)
*Never look back! :twothumbs

Hope this helps.

[dontlifttoshift]

Smaller bearing's naturally have a higher critical speed but lower overall load characteristics... however, since you are not going to be putting two tons of rocks in your trunk, it's kind of a mute point for sake of argument.

A small bearing (3.062" bearing) 31 spline set up would be choice in my opinion... what ever that is worth. The "small" 3.062" bearing will accept a 31 spline axle shaft.


I get the small bearing thing, it's like honda bearings in a big block chevy. I was under the impression that the ball size between the 3.062 and the 3.15 bearings was the same. If the inner race stays the same the outer race needs to get smaller and consequently thinner. I had heard of these outer races cracking and was told to avoid that combination if possible. I personally have never seen a failure.....just heard about it.

If you are soliciting opinions, at the very least I would go to 31 spline axles and 3.15" od tapered timken bearings.....I feel that the ideal setup is a floater.

Donny

[72Pstroke]

I want to clarify that I was referring to the small outer axle bearing in the original post. It is 2.834 OD.

I dropped a cap off of the carrier, and it is the small bearing carrier, 3.062. I assume this limits me to 33 spline axles, if I keep this housing?

I plan on having a couple of dropouts set up for the car. That is one reason I need figure out where I am headed before I get going. I don't want to start over at some point after I have already spent a bunch of money. Do it once, do it right.

Has anyone tried using a front unit bearing/ hub assembly to build a budget full float 9"? You could use something off of the front of a late Jeep or Explorer (or similar) to keep the bolt pattern correct. Build a couple of flanged collars to weld on the end of the housing. Alignment would be critical, but should be do-able. You could even chuck the housing in a lathe to true the faces up after they were welded on. Custom axles would be needed, along with some way to retain the axles. Just thinking out loud.

I really appreciate the help. I am looking forward to driving the car this summer. I haven't driven it snce Reagan was in office!
Tim

[chicane67]

I was under the impression that the ball size between the 3.062 and the 3.15 bearings was the same. If the inner race stays the same the outer race needs to get smaller and consequently thinner. I had heard of these outer races cracking and was told to avoid that combination if possible. I personally have never seen a failure.....just heard about it.

If you are soliciting opinions, at the very least I would go to 31 spline axles and 3.15" OD tapered Timken bearings.....I feel that the ideal setup is a floater.

Donny

Donny... in the past 25 years of building 10k+ differentials myself, I too have seen this failure (4 or 5 times) as you have stated. However, it's cause/failure was from a bearing/race misalignment issue... and not specific to the actual load that was being applied to the bearing assembly itself. Good point to bring to the discussion though... it brings the bearing load requirements right into the meat of the subject.

I kind of giggle. Case in point... look at your typical NASCAR Nextel Cup chassis... it's minimum weight is 3400 pounds, they make in and around 830-850 hp, they have 10x the traction available from the racing surface, they beat the hell out of the multi-disk clutches, they run a 1020 FMS standard banjo housing with a 3.062" case with 31 spline HYTUFF axle shafts. And then... they run them on the high banks of Daytona and Talladega... with resultant loads that our car WILL NEVER, EVER SEE. The true savior in this equation is the floater assembly... as it is what see's the loading that needs to be managed... much more so than the 3.062" case and a 31 spline axle shaft... and I agree, at the very least a 31 spline axle shaft / 3.062" case with the small 3.150" bearing ends would be considered a minimum.



Tim... the 3.062" case pretty much limits you to a 31 spline axle shaft... it is recommended that you step up to the 3.250" case for 33 to 35 spline axle shafts. Basically, it's the journal size of the differential that limits the maximum size of the axle shaft OD.

As for the reference to the 'front unit/bearing hub' assemblies... the bearing sizes are their limitation and mechanically they just wont work. However, the GN, Super Speedway and Howe/Vogel hubs are what will work... without reinventing the wheel, per-say. The bearing/hub assembly idea has already been vetted and much more easily integrated with components that have been engineered for the mechanical loads that the individual components will incur.

33 and 35 spline applications also have their associated "CONS" as well. Mainly being a huge increase un-sprung and rotational mass. But... then again, so does the idea of the use of a typical 'floater.' My current 9" cartridge bearing floater assembly (with 13" four piston AP's with a parking brake assembly) weights less than a 12 bolt WITHOUT brakes. So I know it weighs less than the typical floater.

[dontlifttoshift]

Donny... in the past 25 years of building 10k+ differentials myself, I too have seen this failure (4 or 5 times) as you have stated. However, it's cause/failure was from a bearing/race misalignment issue....

The last case I heard of had a severely misaligned housing that had been narrowed and welded and re welded and so on. They ended up cutting the ends off and going to the 3.15 torino style ends to get it straight.

[chicane67]

The last case I heard of had a severely misaligned housing that had been narrowed and welded and re welded and so on. They ended up cutting the ends off and going to the 3.15 torino style ends to get it straight.

Another good subject to bring up here as well... housing straightening.

The housing requires to be straightened after all associated housing ends, suspension brackets and misc. are finished welded to the housing itself.

[72Pstroke]

What is a guy gonna spend on a 9" floater setup? If I run what I have, I will be into it around $400 or so. If I go to a 31 spline and change the housing ends, I will be into it for around $700. All I am including is wheel bearings and seals, the housing ends, axles, caliper brackets and rotors. I can probably save a bit off of those numbers, but it will be pretty close.
I am not figuring any money for the center section. That will not change much.
Are there any floater setups with 5 on 4 1/2" bolt pattern?

[dontlifttoshift]

I will try to be unbiased here......

That depends....even if you went all the way with the most overkill everything it will be way cheaper than that aluminum headed big block. Just curious, what's a set of those heads worth?

There is good info in here about parts and pricing.. https://www.pro-touring.com/showthread.php?81164-NEW-GMR-Pro-Touring-Rear-Floater-Hubs

Chicane67 is working on this as well. https://www.pro-touring.com/showthread.php?85912-Your-ABS-and-Floater-Solution

There are also other threads regarding floating setups and pad knockback that should turn up in a search.

Baer, GMR, and Moser can acommodate your 4 1/2" bolt circle, there may be others. I would think you could redrill the hubs on Chicayne's setup but I would probably go to different wheels before I did that.

There are pros and cons to every single part that is available for these cars, from the spark plugs to the air in the tires and everything in between....what's right for you?

If you are serious about your horsepower goals and the desire to run Silver State then I urge you to read up on these things and go from there. When you are talking about serious speed there aren't many places to skimp. That doesn't mean you have to spend a million dollars.....it means you have to really ask yourself what you want the car to do and find a way to put the proper parts on AND under the car in a way that fits your time frame and budget. None of use have built our dream car yet, we all make compromises based on our curent needs. I like to overbuild whenever I can and avoid reworking things later....like you said


I hate doing something over and would rather do it right the first time.

[BADDRIDE II]

Lets all keep in mind that NASCAR has to toss ALL the 31 spline related components after each race due to wear and or fatigue......so although they due manage to hold up for a race or two (not always).....they are not trusted, nor where they ever intended to do much more than that. So the NASCAR thing really does not apply here.

Again, given the near future plans for an aluminum headed 557ci engine with manual tranny....I cannot see how anything less than a 33 spline would be used. My vote is for overkill and not marginal....why risk it? If the only downside of going with the insured safety of a 33/35 spline is a few pounds of rotational mass.....thats not a reason with a 557ci engine! Goodluck with your decision Tim!