Is up grading to 35 spline axles on 40" Swampers overkill?

[78 Ranger]

Hello all,

Im upgrading my 9 inch and leaning toward 35 spline axles. After pulling my 31s its hard to imagine breaking these axles but I hear it happens. Im running 40" Swampers with a 400 small block. I drive it on the road most if the time and dont romp hard off road yet. Im thinking that combo probably calls for at least 35 spline. Anyone have any advice?

 

[Shimmy]

if you're gonna stay with a 9" the nothing is overkill for 40" swampers. how much do those weigh at a corner? 500lbs? haha. i'm always shocked at the amount of 37" and 38" tires i see on those wimpy jeep d44s but i suppose it's doable for parking lot pimpin.

 

[Broncobowsher]

I'm guessing from your name and the first post, you are dealing with a '78. I had a whole response written I just deleted based on an early Bronco. You have a full size Bronco. Also explains it based on running a 400, which is rarely used in early Broncos.

You will get much better advise if the correct forums are used. I believe you should be on fullsizebronco.com (or something like that if I typed it wrong). Early Broncos I really worry about housing strength. Have no idea how a full size Bronco housing would live with that. They should do better being the big banjo housing. But I would ask the full size Bronco crowd and follow what they advise.

 

[Apogee]

My friend with a '78/'79 Bronco couldn't keep a 9" alive under his, but he wheeled it hard with a built Aussie 400 on propane. His 35-spline axles held up okay, it was the housing that kept failing, and that was with 38" Boggers. When facied with the choice to upgrade the 9" housing to some bomb-proof aftermarket unit or go 14-bolt, he went 14-bolt and upgraded to 43" TSL SX stickies at the same time.

 

[78 Ranger]

My friend with a '78/'79 Bronco couldn't keep a 9" alive under his, but he wheeled it hard with a built Aussie 400 on propane. His 35-spline axles held up okay, it was the housing that kept failing, and that was with 38" Boggers. When facied with the choice to upgrade the 9" housing to some bomb-proof aftermarket unit or go 14-bolt, he went 14-bolt and upgraded to 43" TSL SX stickies at the same time.

Do you know a company that sells good used 14 bolt?

 

[Yeller]

The housing, wheel flanges and wheel studs become the weak link. Wheel studs can be upgraded easily to 9/16 or 5/8. Housings can be up graded to a fabricated housing like spider trax. Not much can be done with the flange, I had many bend and a few break off at the bearing. Going full float is the only real solution. Build a high end 9”, quite expensive, or build a 14 bolt, sterling, Dana 70 can be done on a much better budget. Changing the front to 8 lug is simple with f250 parts.

However I tend to be hard on parts, last 31 spline axle I broke lasted about 10 minutes with 37’s, and it wasn’t my rig, felt I was being easy. I run 35 spline on 33’s and am 1 more wheel bearing change away from going full float 8 lug…..

 

[jamesroney]

Hello all,

Im upgrading my 9 inch and leaning toward 35 spline axles. After pulling my 31s its hard to imagine breaking these axles but I hear it happens. Im running 40" Swampers with a 400 small block. I drive it on the road most if the time and dont romp hard off road yet. Im thinking that combo probably calls for at least 35 spline. Anyone have any advice?

This is the classic 9 inch circle of life. Which is also the circle of death.

The Ford 9 inch is probably the worst differential ever installed in a truck. Not the axles, not the housings, not the axle bearings, but the actual differential. And the entire selection for the rear axle assembly is based on the differential. The Ford 9 inch differential is a light duty automotive carrier with 2.891 inch OD bearings. The heavy duty carrier comes with 3.062 bearings. Neither will fit a 35 spline shaft.

The carrier itself is required to be dimensionally small to fit the pinion pocket bearing. So it has to be small. Traction adding differentials, lockers, etc. are constrained to be "small" Small lockers are junk. So the ONLY differential with reasonable strength is the factory 4 pinion open diff, and the detroit gear driven locker, or a full spool. Nothing else will hold up. The Detroit locker is garbage on the street. The open carrier is garbage off road. and the spool is garbage everywhere that isn't a race track.

So you determine the least-worst option is the full case detroit. Which can be built with 35 spline side gears. But those gears will not fit in your bearings. So you will have to buy a minimum 3.25 aftermarket housing. And the factory housings are weak, so you will need to truss it. 4.11 gears are not adequate for 40's so you are buying a new ring and pinion. And every 9 inch should have a Daytona support, so you'll need that and a yoke. Throw in a set of chrome-moly axles, and you have basically replaced every single component in your 9 inch with aftermarket purpose built performance parts. Funny thing is that when you are done...you have built an axle that is in every way inferior to a junkyard 3/4 ton chevy rear end. But WHY?

Why do people kneel at the altar of the 9 inch? Because of Chevrolet, and AMC. Because everything about a 9 inch is vastly superior to a GM corporate 10 bolt, or an AMC model 20. This does not make the 9 inch good. But if you dump a ton of money into a 9 inch, it will survive. If you dump a ton of money into a GM 10 bolt, it's still garbage. Chrysler is the king of the hill with the Super Track Pack rear end in the muscle car era. 35 spline Dana 60 with Power Lok right from the factory. But the Drag Pack Nodular 9 inch with no-spin and 31 spline from Ford was a contender.

So now we get to the root of the question from @78 Ranger. Do I need 35 spline shafts for 40's? The answer is yes. for a high performance or heavy duty application, the correct answer is 35 spline. Mopar determined that a G60-15 tire (26.5 inch) needed 35 spline shafts. GM calcualted the K20 for 9.50x16.5 tires (31 inch) needed 1-9/16 x 30 spline. Ford got to a 35 spline shaft on the F250 with Dana 70U and 235/85/16 tires. (31.7 inch) So I will say this now, and I'll say it again. If you are running 33 inch tall tires, and you WORK your truck. (use, and occasional misuse) in order to prevent destruction...you need 35 spline axles.

So which housing is best for those 35 spline shafts? The off road community has settled on the 9-3/4 Dana 60, if you are going custom. And the GM 14 bolt if you don't like to throw away cash. The Sterling 10.5 also runs 35 spline shafts. And a myriad of newer AAM beastly housings now too. But those are all 8500 GVW axles that come with 8500 GVW brakes.

For a pickup truck width rear axle, like a 78 Bronco...the ONLY logical, reasonable, cost effective solution is the 73-94 GM 14 bolt. That's right. The answer to the question: "Does my 9 inch need 35 spline shafts?" is "GM 14 bolt."

Don't even shave it. Just send it.

 

[Broncobowsher]

As much as James has stuff against the 9", there is some really good stuff with the basic design.
The 3rd pinion bearing does wonders for keeping the pinion deflection in check. The fact that they do break in stock housings when you crank up the power going into them shows that there is a lot of force to control.
Another is the gear size. Not the overall diameter, the width of the tooth. It is part of what makes getting a good differential so hard. As mentioned there is very little room inside for lockers, limited slips, and even just regular spider gears. Because the tooth width is bigger than other typical axles.
While not great for off-road use, the 9" has a very low pinion height. Generally a good thing for race cars. But based on the 1950's trend that the axle was designed for. Big new cars of that era were getting longer, wider, lower. That lower part keeps a smaller driveshaft tunnel, more interior space. And the racers and hot rodders found that worked for what they wanted as well.

As for the D60 being the ideal solution... Chrysler needed a better axle for the high power muscle cars. Developing a new axle for a small volume isn't a wise use of money. They looked at the trucks, took a D60 center section and put car outers on it. It was a parts bin patch more than a design choice. I'm referencing an old retired Chrysler axle engineering department friend for this. His shop car back in the day (to go make lunch runs) was a factory Hemi Dart. Lot of interesting stories out of him between his days at Chrysler and days in the aerospace.
And for ¾ ton trucks, the full float D60 was used as it was needed to handle the weight, not the power or tire size. 1310 U-joints on a D60 do exist, I've changed them before (Thank you IH). The D60 was just used across the board as it was a well developed axle that worked from a little 6-cylinder truck to big duellys. GM ran Eatons way back before the corporate axle division developed the 14 bolt. Well, because GM was doing GM things.

 

[jamesroney]

As much as James has stuff against the 9", there is some really good stuff with the basic design.
The 3rd pinion bearing does wonders for keeping the pinion deflection in check. The fact that they do break in stock housings when you crank up the power going into them shows that there is a lot of force to control.
Another is the gear size. Not the overall diameter, the width of the tooth. It is part of what makes getting a good differential so hard. As mentioned there is very little room inside for lockers, limited slips, and even just regular spider gears. Because the tooth width is bigger than other typical axles.
While not great for off-road use, the 9" has a very low pinion height. Generally a good thing for race cars. But based on the 1950's trend that the axle was designed for. Big new cars of that era were getting longer, wider, lower. That lower part keeps a smaller driveshaft tunnel, more interior space. And the racers and hot rodders found that worked for what they wanted as well.

As for the D60 being the ideal solution... Chrysler needed a better axle for the high power muscle cars. Developing a new axle for a small volume isn't a wise use of money. They looked at the trucks, took a D60 center section and put car outers on it. It was a parts bin patch more than a design choice. I'm referencing an old retired Chrysler axle engineering department friend for this. His shop car back in the day (to go make lunch runs) was a factory Hemi Dart. Lot of interesting stories out of him between his days at Chrysler and days in the aerospace.
And for ¾ ton trucks, the full float D60 was used as it was needed to handle the weight, not the power or tire size. 1310 U-joints on a D60 do exist, I've changed them before (Thank you IH). The D60 was just used across the board as it was a well developed axle that worked from a little 6-cylinder truck to big duellys. GM ran Eatons way back before the corporate axle division developed the 14 bolt. Well, because GM was doing GM things.

I urge you to consider the 1967 Ford F100 Limited Slip 5 lug Dana 60 rear axle...and answer a simple question: "Why?"
The Ford 9 inch was 9 years into production. The 1/2 ton Ford Dana 60 is 5x5.5, uses big bearing 3.150 Ford outers, and 1-5/16 x 30 spline shafts.

It is also 1310 yoke, but of course 10 spline. (...but all GM K30 trucks came with the 29 spline 1310 on the front yoke.)

I don't have any hate for the 9 inch. I run one in my U13, and I run one in my 390GT Mustang. All of my Boss, CobraJet, and my Shelby all had one. It just has a cost limitation at 31 spline, and there are exactly zero traction adding devices (not named Detroit Locker) that can stay together.

...and the reason for the F100 with Dana 60 is because the Equa-Lok in the 9 inch simply could not stay together in a pickup truck. They didn't fix the exploding carrier hats until the D0OW version. The Dana Power Lok could handle the torque multiplication from a granny low gearbox in the pickup. (because of all the things we agree about above...)

 

[ntsqd]

FWIW I just bought A FF D60, in So CA mind you, for $120. That's a complete, full width axle out of a mid 70's F-250. An exceptional price in this age, but deals can be found. I'll end up using almost nothing except for the housing, but if I were willing to go with 8 lug I could use it as-is. Gears and some sort of TAD would likely be all that is needed.

 

[nvrstuk]

I'm a great example of a guy who believed the 9" was strong... So I kept building ones with more and more $$$$ poured into them. Aftermarket fabbed housing so it wouldn't bend and then lose axle brgs and then you drop to the pavement when the axle breaks and then... I have grenaded these.

So aftermarket housing helps then you add a 35 spline set of axles and you have to upgrade the carrier and then you can't put an ARB in it because the 35 spline ARB's are weaker than the 31 spline ARB's (straight from their engineers because of lack of room). I have grenaded these.

So then you go with an aftermarket housing and build the best of both worlds into it. You adapt on FF outer spindles so now you have a "914" rear. 9" carrier and 14 bolt outer FF flanges with RCV outers and double splined axles to make it "BulletProof". I have grenaded this also.

I finally followed Old Yellers advice and found a used 14 bolt. I shaved it so it has within a 1/4" of clearance of a 9" fabbed housing, I weighed them both (I weigh everything) and it was within a few pounds of the 9". I have saved tons of money by going to a 14 bolt that is MANY times stronger than a 9" in EVERY category AND I can run an ARB in it without the ARB flange being twisted in half. I have done this also.

So take the advice of Old Yeller, others and myself and step up to a used 14 bolt and have someone slap new parts in it and you will be worry free...

Added benefit is you will save a ton of coin...

 

[Yeller]

I’ve been told on another forum I tend to pour Fireball and tequila in the coolaid

 

[nvrstuk]

I’ve been told on another forum I tend to pour Fireball and tequila in the coolaid

Sometimes ya need BOTH!! lol