What's going to break when you add HP & Torque?

[WPS 73 Bronco]

With my LS swap, I"m adding a lot of HP & torque that my Bronco's never seen. I've got the transmission, transfer case, and new drive shafts covered as part of the plan.

So what breaks first with all of the new power? It's a street cruiser, and I have no plans to be racing anyone. My Bronco will see spirited 20 to 60 mph sprints, often.

 

[BronCowie]

You mentioned drive shafts, hopefully that includes u-joints!

 

[WPS 73 Bronco]

Yes, all new U-joints for sure.

 

[ngsd]

your wallet!

 

[DirtDonk]

What rear differential? And is it new, or original?
Is there slop in it? Slop can be handled for years with minimal horsepower and easy driving. But it can die immediately. If really hammered on with good power.
Certainly the front axle you joints would go if you were in four-wheel-drive and steering at an angle, but it doesn’t sound like you’ll be doing much of that.
So with all the torque going to the rear, if you’re using stock u-joints, then that could be an issue.
If you have a stock limited slip, or really any limited slip differential or locker, using 28 spline axles, your axles will snap first almost guaranteed.
With an open differential and one legging it, they will live a little longer. But 28 spline axles will still be the most likely next weak link.
If it’s a Dana 20 transfer case, then, after the axles, I would say the rear output shaft would be next.

Speaking of the output shaft… If it’s original, and has not been refurbished, it’s likely much weaker than if it has been recently rebuilt and is good and tight.

 

[nvrstuk]

How long a list do you want?

Stock LS, like 300 HP? Can't remember on your thread if it's a 4l, 6l or ??

Paul mentioned a couple of these-

Street use-
- 28 spline axles. Broad defiinition of spirited but maybe last a week? Depends on tire size, hardness of rubber, locker or clutch type rear axle for how long they will last

- 9" yoke/rear DS joint, this would not be an issue if you kept axle wrap 99% controlled but if you have a soft style suspension and good power and can transfer it then the rear yoke is going to point to the floor and you will waste it and your DS

- D20 rear output. They are SOOOO weak. Upgrade b4 you even test drive it. I think I remember you having an Atlas going in?


What they were originally made for use-

- all of the above and

- D20 output, D20 intermediate gear and D20 case. Gear teeth will peel off like butter on a warm day with excellent torque and traction

- D44 axles and joints will just twist off if you back up with the wheels turned with ANY kind of traction. Add larger dia tires and a locker and "poof"

Not much left....

I grenaded all of these muliple times (except the rear yoke- I grenaded ARB carriers and R&P's

 

[73azbronco]

anything, if the power is dropped like a hammer on hard surface.

 

[Broncobowsher]

If there is proper torque management of the rear axle (torque arm for example) that controls axle wrap, U-joints are pretty darn strong. The break when the springs wind up (axle wrap) and the U-joint goes into a bind.

IF the front axle is a dana 30, expect to blow the teeth off the ring gear. Dana 44 upgrade fixes that.
Stock front axle U-joints are pretty tiny and blow pretty easy. Stock Spicer axles (long side cut down) with stock Spicer U-joints (the larger ones) will survive what you are planning on doing.

Rear 28 spline axles are not the greatest idea for added power paired with oversized tires. A basic 31 spline upgrade will do you fine. Again, the better stock style stuff is all that is needed, no need for the super alloy axles.

If you are running the Dana 20, expect to pop the rear output shaft at a really bad time.

That's it.

 

[Speedrdr]

I’m just glad I didn’t KNOW all the things that could/would come apart when I owned the 72 that had an approximate 320 HP 302 installed with 410s (and whatever traction controls were put in when it came from Ford with a 170) and 7.50 X 16” mud tires. I wrecked driveshafts and axle bearings and the annual axle halves, but had no idea the D20 could fail. That’s really bad news. Fortunately for the one I’m working on there have been enough years passed that I won’t abuse it like the last one.

Randy

 

[Speedrdr]

Well, maybe I won’t.

 

[36Fan]

Leaf spring wrap/u-joints, then axles and Dana 20 output.

But brutal honesty will be that you will have a rude awakening on big power in a 92in wheelbase Bronco on the street. Squirrely is an understatement.

 

[Yeller]

Tuned should be 525 maybe more

For your described use, axle wrap, spring wrap or whatever you want to call it is going to be the biggest thing, it’s really only an issue if the ujoints aren’t happy or you break the tires loose and it starts hopping. Next will be the 28 spline rear axles. Then it will be the rear housing tubes bending forward. Basically the entire stock rear end becomes the weak link except the actual gears.

 

[WPS 73 Bronco]

So my 73 Bronco will have 500+ hp at the engine, and I have a new Atlas transfer case and I will be buying new drive shafts. So let’s assume everything else is stock except my 33” tires and 2 1/2” lift. Let’s focus on the rear first. Sounds like my parts list begins with:

Axle Wrap
28 to 31 spline rear axles.
Will I need my third member rebuilt? What else?

So should I buy from the Bronco stores or find a local shop to rebuild it Or is this an easy DIY? Is there a “one stop shopping“ solution that I should consider?

 

[don k]

Things don't usually break if driving sensibly. When a person drives otherwise it really doesn't matter if it is a 6 cyl. or a LS. The more HP and torque you have just made the breaking part easier.

 

[Glass Pony]

So my 73 Bronco will have 500+ hp at the engine, and I have a new Atlas transfer case and I will be buying new drive shafts. So let’s assume everything else is stock except my 33” tires and 2 1/2” lift. Let’s focus on the rear first. Sounds like my parts list begins with:

Axle Wrap
28 to 31 spline rear axles.
Will I need my third member rebuilt? What else?

So should I buy from the Bronco stores or find a local shop to rebuild it Or is this an easy DIY? Is there a “one stop shopping“ solution that I should consider?

When you break the third member, go with a nodular one. WH can set you up with a third member with your choice of gears and differential.
https://www.wildhorses4x4.com/produ...-Third-Member-31-Spline/early_Bronco_Rear_End

 

[rocknhorse76]

Over 500hp? I’d be looking at brake upgrades first. A fast vehicle is useless without great brakes!

 

[WPS 73 Bronco]

Already got the brakes covered. Front Disc with Hydroboost system.

Glass Pony, I was looking at that third member. Probably a good option to consider. If I tie that to new 31 spline axles and the WH wrap trap, I've probably protected myself from future breakdowns needing the same solutions.

 

[ba123]

Definitely do the rear end and axles to 31-spline. The stuff WH carries is Dutchman and seems like good stuff so far. I needed axles slightly different and ordered directly from Dutchman and I highly recommend that if WH doesn't have exactly what you want although they seems to have a lot and could prob also get what you want.

dutchmanaxles.com

 

[nvrstuk]

So my 73 Bronco will have 500+ hp at the engine, and I have a new Atlas transfer case and I will be buying new drive shafts. So let’s assume everything else is stock except my 33” tires and 2 1/2” lift. Let’s focus on the rear first. Sounds like my parts list begins with:

Axle Wrap
28 to 31 spline rear axles.
Will I need my third member rebuilt? What else?

So should I buy from the Bronco stores or find a local shop to rebuild it Or is this an easy DIY? Is there a “one stop shopping“ solution that I should consider?

Steve has a great link for complete 3rd members (I have it in my build list for Shorty but I'm walking out the door- be back this afternoon), 9" with Daytona pinion support for less money than I can buy the individual parts.

Like I mentioned, axle wrap is a killer- doesn't matter how SENSIBLE your driving skills are, like I mentioned before it will occur and take out the parts discussed earlier.

Bronco places have good prices on the axles and will understand the brg end sizes well for your particular housing, WHICH needs to be checked for (update: like Yeller said) straightness because it's probably already bent. I went thru several then finally went with a fabricated housing to avoid buying more slightly bent 9" housings and trussing those. Then I finally just went 14 bolt which I should have done back in '00 when I had one with a D60 and thought they were too big and heavy- dispelled those theories also.

People that don't think we drive sensibly and that's what causes parts to break don't seem to understand what torque multipliers do when used everyday. There are several on a Bronco that will never be used on a drag car and that's why we grenade parts even when going slow.

 

[DirtDonk]

With 500hp, what will your tire size be? And what is your ultimate gear ratio choice at this point? Have you decided yet?
A low first gear, with high torque engine, multiplication (even though smooth...) from an auto trans, and a good transfer case, you might consider 35-spline axles instead.
It limits your differential choices somewhat, but depending on tire size, a slight extra upgrade from 31's to 35's could be called for.

The nodular 3rd members have the large carrier bearings to fit the larger axle diameters, and you should be using a large bearing housing anyway, so that all makes upsizing the axle shafts a little easier.
Are you running a large bearing housing at the moment? If not, you might as well factor in that as well.
Not for housing strength per sé, but for axle shaft and bearing availability.

And saying "new" driveshafts does not mean anything in your case. You need "larger" shafts in my opinion.
Not necessarily the shaft itself, but the u-joints should be upsized at least one to the 1330 series I would think. If you have ordered your Atlas already, is it going to come with the larger yoke(s) too?

Paul