Impart your 9” knowledge on me.

The famously hard to break Ford 9" axle! You know em, you love em, now teach me about em. 

What I have is a 28 spline, long yoke, 2.49 open diff in the challenge car. I also have a 31 spline, short yoke, 3.50 soon-to-get-a-spool. The thought was to drive out to challenge on the tall open gears, then switch third members for competition. Can't do that as is because the short yoke would pull the driveline out too far. 

Are there differences in pinions between 28 and 31 spline axles?

Can the yoke be swapped without needing to rebuild the diff?

Am I a Bob Costas for not wanting to drive 2200 miles with aggressive gearing, a spool, and no overdrive?

Thanks, all. 

3.50 isn't terribly aggressive for highway driving.  Fit the tallest tires you can, and it will be fine.  I used to drive a 69 Chev pickup with a TH 400 and 3.73's.

Your combination of stuff is problematic.  To swap centrrsections, you need two driveshafts and two sets of axles.  Not ideal.

In reply to Streetwiseguy :

The plan is to put a 28 spline spool in the 3.50 diff, so axles are easy. If I can find a long yoke to use, and it doesn't require a diff rebuild ($$$) I think it'd work out pretty well. That said, taller tires on the rear is a good solution. I'm just trying to do this as cheaply as possible because challenge. 

In reply to barefootskater :

Travel tires wouldn't be in the budget, and could likely be borrowed, I figure.  

Swapping a center section is a bit of dirty, heavy work that I wouldn't need on my weekend.  But I'm old and lazy, so...

So one thing i have encountered is 31 spline axles physcally don't fit in a 28 spline carrier, they don't fit through the casting to even reach the spider gears.  I am guessing you are ok going to a 28 spline mini spool in a 31 spline carrier, but I cannot guarantee it.  I think i have a 31 spline mini spool in the basement but don't have a 28 spline one.  I personally would just run the 3.50 and some taller tires to keep rpm down some on the highway.  Throw some pickup truck wheels and 235/75/15 on it.  It would save the headache of gear oil spillage and dicking around in a parking lot.  

The pinion splines are all the same except for some heavy duty race gears that you don't have.

The pinion yokes are all the same except for anything for a Daytona pinion housing, which requires a yoke that is shorter between the pinion nut's flange and the front bearing.  This is also probably something you don't have.

If you had shims in the pinion bearings instead of a crush sleeve, you could just swap yokes no problem because the bearing preload will be unaffected by overtightening the pinion nut.

For the effort, I'd just drive on the 3.50 gears and call it a day.  That's not very aggressive.  People used to drive big blocks with 3.91s and 4.11s with no overdrive all the time.

Impart your 9” knowledge on me.

 

Came here to tell a different story... but, I don't know what trans you have but I purposely put 4.10 final drive in my Colorado, and would have done a 4.3 if it was available.

My DD 55 Chev had a TH350 and 4.10's

Y'all are talking sense. I suppose all that is left is to figure FMV on a used gear set, put the more aggressive gears in, and go full heavy metal with a spool on the street. Tire life be damned. I wonder how cheaply I can set up the diff for the new gears... 

No need to worry about tire life.  Do you want to guess at how many miles without turns you are looking at driving? Spare wheels and highway tires (even if used)  and your mileage will barely show.

Does this thread belong in the BBC thread?

SVreX (Forum Supporter) said:

Does this thread belong in the BBC thread?

I wish it was. The challenge car only has a SBC. Though to be fair, it is the biggest one they ever made. 
 

In reply to barefootskater :

A big SBC still isn't a BBC.

matthewmcl (Forum Supporter) said:

No need to worry about tire life.  Do you want to guess at how many miles without turns you are looking at driving? Spare wheels and highway tires (even if used)  and your mileage will barely show.

It's not even that big a deal.  Tires slip when transmitting any amount of power, as the nature of how traction is generated.  You won't notice a thing.

I have a Locker in mine, which makes all sorts of cool clanking ratcheting noises when the wheels are turning at different speeds.  ANY amount of power in a corner and the noises stop, because tire slip accomodates the speed difference.

Just don't back up and turn tightly, that way lies axle carnage.

Currie are the industry wizards when it comes to 9" rears. Food for thought on keeping your gears happy-

https://www.currieenterprises.com/why-run-conventional-gear-oil

Stampie (FS) said:

In reply to barefootskater :

A big SBC still isn't a BBC.

*sigh* I know. 

barefootskater said:

The famously hard to break Ford 9" axle! You know em, you love em, now teach me about em. 

What I have is a 28 spline, long yoke, 2.49 open diff in the challenge car. I also have a 31 spline, short yoke, 3.50 soon-to-get-a-spool. The thought was to drive out to challenge on the tall open gears, then switch third members for competition. Can't do that as is because the short yoke would pull the driveline out too far. 

Are there differences in pinions between 28 and 31 spline axles?

Can the yoke be swapped without needing to rebuild the diff?

Am I a Bob Costas for not wanting to drive 2200 miles with aggressive gearing, a spool, and no overdrive?

Thanks, all. 

If you come to the challenge I will get you a 3.50:1 center for your 2.50:1 center. Please do not disassemble the center you have.  The gears are timed and they did not always assemble them correctly at the factory. 

31 spline axles are 34% stronger than the 28. 

In reply to wheels777 :

I've heard that but I don't understand it. I know the 31 spline is stronger, but I'm not worried about breaking these 28 spline axles. I don't drive violently and a 400 w/ vortec heads and a cam isn't going to be making giant power. $ for $, I think gearing will be the best "speed money" we can spend, and I'm sure we're going to be short on traction. 
If you have a 28 spline center with a long yoke and 3.50 or 3.73 gears that you'd trade/sell/loan that would be AMAZING! Even better if it has a mini spool or Limited slip. 

The added strength comes in from the larger diameter of the 31 spline axle in the diff, instead of necking down to the smaller 28 spline 

In reply to barefootskater :

I broke an axle not by launching at the dragstrip, not by rallycrossing, but by maneuvering past a truck at a gas station.

Tight maneuvers at low speed is way harder on axles than launching or whatever.  This is 100% why I have a locker and not a nice, simple, light $90 spool.

With a spool and slicks at the dragstrip, you are more likely to break an axle turning around for the return road than anywhere else.

In reply to Pete. (l33t FS) :

Drive fast all the time, got it. 

barefootskater said:

In reply to wheels777 :

I've heard that but I don't understand it. I know the 31 spline is stronger, but I'm not worried about breaking these 28 spline axles. I don't drive violently and a 400 w/ vortec heads and a cam isn't going to be making giant power. $ for $, I think gearing will be the best "speed money" we can spend, and I'm sure we're going to be short on traction. 
If you have a 28 spline center with a long yoke and 3.50 or 3.73 gears that you'd trade/sell/loan that would be AMAZING! Even better if it has a mini spool or Limited slip. 

I have (3) 3:50:1 centers. None are long yoke.         They are all standard length. 

In reply to wheels777 :

The diff in the car is roughly 10" from the diff-to-housing surface to the center of the ujoint. The spare axle I got with the 3.50 gears is 9". This presents a problem with the driveline. I measured the yokes and thats where the difference is. 

barefootskater said:

In reply to wheels777 :

The diff in the car is roughly 10" from the diff-to-housing surface to the center of the ujoint. The spare axle I got with the 3.50 gears is 9". This presents a problem with the driveline. I measured the yokes and thats where the difference is. 

That is typical. The long yoke came on big cars with 2.50 and 2.75 gears. The long yoke "shortened" the driveshaft.
The 3.50 gear only came in F100 or F150 fwd trucks and in a few years for cars with Hi-Perf engines. They all had short yokes. 

We run a 3.50 rear in the Plymford.  Ford 9".  Unfortunately I am not a wealth of l knowledge on those rears as I got a 3.50 chunk with posi already set up and dropped it in.  I do know that our 460 BBF runs up against the redline with those gears and 245/50R16 tires at about 110mph...

Ask your wife about my 9" knowledege.. 

I'm here all week folks.