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14 Bolt Semi-Float

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Carmine

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Gentlemen,
Just picked up a 14 Bolt Semi Float rear for my K5. I'm looking at a Detroit Tru Trak, any experience with these? The K5 will see street time so I'm shying away from the Detroit Locker. Also, are these axle shafts (stock) 30 or 33 spline? Thanks.
 
The 14 bolt semi-floater is 33 spline and has a 9.5" ring gear.

I ran a TrueTrac in a rear 10-bolt on a K5 for years and it was one of the best limited slip diffs I ever had. Very smooth, consistent, and never wears out.
 
The semi-float 14 bolt is much stronger axle than a 10 bolt and a very worthwhile upgrade, for your intended use I think a tru-trac is a good choice. I had very good luck with one in a 10 bolt as well
 
Thanks for the info. I'll probably limit my tire size to 33's. Any problem with 4.10 gearing (I have the auto trans in my '86)?
 
Carmine said:
Thanks for the info. I'll probably limit my tire size to 33's. Any problem with 4.10 gearing (I have the auto trans in my '86)?
Click to expand...

4.10's with 33's is fine. If you're limiting yourself to 33's for the axle's sake, don't bother: a 14bsf will easily handle 40's, and I wouldn't worry about running 44's on one.
 
MaxPF said:
4.10's with 33's is fine. If you're limiting yourself to 33's for the axle's sake, don't bother: a 14bsf will easily handle 40's, and I wouldn't worry about running 44's on one.
Click to expand...

That's a big time stretch IMO.

FF 14 bolt shafts are at least 73% stronger than SF 14 bolt shafts, I would consider a FF 14 bolt to be pretty much bulletproof up to 44's.

44's on a SF 14 bolt will break unless its a mall queen.
 
MaxPF said:
73% huh? I can't wait to hear how you came up with that figure... :rolleyes:
Click to expand...

33 spline SF 14 bolt major diameter = # of splines + 1 divided by the diametrical pitch (which is 24 for most axles, this one included). The major diameter of a SF 14 bolt shaft is 1.417"

30 spline FF 14 bolt shafts use a different diametrical pitch than most shafts. Their major diameter is 1.625".

The relation for torsional strength of shafts is raised to the fourth power, all of the other (first order) variables cancel out.

(1.625^4)/((1.417^4) = 1.729

That's where my 73% comes from.


And I said AT LEAST 73% stronger because that doesn't take into account that the FF 14 bolt has full floating shafts (which, IMO, make a marginal difference but others will argue otherwise) and the FF 14 bolts shafts have the most ideal taper (which is why other shafts, such as FF D70 stuff, is easier to break than FF 14 bolt stuff).
 
Carmine said:
Gentlemen,
Just picked up a 14 Bolt Semi Float rear for my K5. I'm looking at a Detroit Tru Trak, any experience with these? The K5 will see street time so I'm shying away from the Detroit Locker. Also, are these axle shafts (stock) 30 or 33 spline? Thanks.
Click to expand...

IME, tru-tracs are the best limited slip out there.
 
38377k5 said:
33 spline SF 14 bolt major diameter = # of splines + 1 divided by the diametrical pitch (which is 24 for most axles, this one included). The major diameter of a SF 14 bolt shaft is 1.417"

30 spline FF 14 bolt shafts use a different diametrical pitch than most shafts. Their major diameter is 1.625".

The relation for torsional strength of shafts is raised to the fourth power, all of the other (first order) variables cancel out.

(1.625^4)/((1.417^4) = 1.729

That's where my 73% comes from.


And I said AT LEAST 73% stronger because that doesn't take into account that the FF 14 bolt has full floating shafts (which, IMO, make a marginal difference but others will argue otherwise) and the FF 14 bolts shafts have the most ideal taper (which is why other shafts, such as FF D70 stuff, is easier to break than FF 14 bolt stuff).
Click to expand...

Unfortunately for your math, the weakest point on an axle shaft is it's minimum diameter. On a 14bff, that diameter is 1.351" (purple arrow):

DCP_6513.jpg


The smallest diameter on a 14bsf shaft is 1.400", right next to the splines (crappy pic):

PA180034-r.JPG


So, unless you can show me proof that the ff shaft is made out of 4340 or some other high strength alloy, I stand by my statements regarding the sf's strength.
 
MaxPF said:
Unfortunately for your math, the weakest point on an axle shaft is it's minimum diameter.
Click to expand...

The minimum diameter is certainly relevant but its not the only driving force behind how shafts break (its more complicated than that). This point doesn't show an advantage to either side, just showing a point ;)


MaxPF said:
On a 14bff, that diameter is 1.351" (purple arrow):
Click to expand...

Sounds about right

DCP_6513.jpg


MaxPF said:
The smallest diameter on a 14bsf shaft is 1.400", right next to the splines (crappy pic):

PA180034-r.JPG


So, unless you can show me proof that the ff shaft is made out of 4340 or some other high strength alloy, I stand by my statements regarding it's strength.
Click to expand...

Well, there has been some contention that FF shafts are made of different material because they aren't required to supply the inner race for the wheel bearing (i.e. maybe SF shafts require a different alloy because they have to act as an inner beariing). I, and AFAIK everybody else, have little idea which alloy stock axle shafts are made of.

Also, the splines (and sharp tapers, which are apparent in said pictures) are inherent stress concentrations. These are failure points, potentially, at least.

I don't believe that I'm biased one way or the other, I'm just trying to portray the facts.


Up to say 47's or 49's, I'd say the FF 14 bolt has proven itself near bulletproof.

Honestly, I've never been around any serious wheeling rig with a SF 14 bolt so I have no real world experience on what it takes to break one. IMO, there *might* be a reason for that.
 
38377k5 said:
The minimum diameter is certainly relevant but its not the only driving force behind how shafts break (its more complicated than that). This point doesn't show an advantage to either side, just showing a point ;)
Click to expand...

I have seen quite a few broken OEM rear shafts. In nearly every instance the break was at the minimum OD point on the shaft.

Well, there has been some contention that FF shafts are made of different material because they aren't required to supply the inner race for the wheel bearing (i.e. maybe SF shafts require a different alloy because they have to act as an inner beariing). I, and AFAIK everybody else, have little idea which alloy stock axle shafts are made of.
Click to expand...

Which is why I take that suggestion with a grain of salt. Many engineering decisions are cost driven, and alloy steels are expensive. The cheapest way to make a shaft stronger is to simply make it larger. If GM felt the ff shaft needed more strength they would have simply made the entire length 1.590" diameter using medium carbon steel, rather than smaller using much more expensive alloy steel. My guess is that both are medium carbon steel, although specific heat treatment probably varies between them.

Also, the splines (and sharp tapers, which are apparent in said pictures) are inherent stress concentrations. These are failure points, potentially, at least.
Click to expand...

Very true, but the most rapid stress buildup will be at the area of smallest diameter.


Up to say 47's or 49's, I'd say the FF 14 bolt has proven itself near bulletproof.
Click to expand...

Then, why does it seem unreasonable that the sf would hold up to 44's? There should be no doubt at all that it would hold up to 40's.

Honestly, I've never been around any serious wheeling rig with a SF 14 bolt so I have no real world experience on what it takes to break one. IMO, there *might* be a reason for that.
Click to expand...

I run one. Full bodied K5 complete with fiberglass top with 37's, locked 14bsf rear with 4.56's. I've beat on that sf pretty good, and it doesn't seem to care. OTOH, I manage to keep my locked, stock shafted, 30 spline 10b front alive too, but I treat the front far more gently than the rear :D
 
Go with a true locker , a bang or two once in a very great while <------ is far better than anything with the word SLIP in it :thumb:

Besides if your tranny is snappy , and you don't mind rotating the tires , you can bark em hitting second from a standstill when accelerating and turning :bow:
 
Thanks for the excellent info. So, no problem running stock axles with 33's in the 14 bolt sf? I'm just wondering if while it's apart I should opt for the alloy axles. By the way, the reason for all of this is that I spit out the axle in my 10 bolt even though I upgraded to alloy axles in that. I was running 35s and, believe it or not I was actually getting on an on-ramp to a major highway (the Ten) out here in LA... As I was going through the on-ramp I spit the passenger side axle out. It cart wheeled over a convertible BMW with a suite in it... I think we both just about sh** our pants. And of course the K% "safely" skidded to a three-wheeled stop...
 
I have been running SF for over 4 years now with 37's.. I vote for the Eaton E-locker. Locked when you want it and open when you don't.
 
Carmine said:
Thanks for the excellent info. So, no problem running stock axles with 33's in the 14 bolt sf? I'm just wondering if while it's apart I should opt for the alloy axles. By the way, the reason for all of this is that I spit out the axle in my 10 bolt even though I upgraded to alloy axles in that. I was running 35s and, believe it or not I was actually getting on an on-ramp to a major highway (the Ten) out here in LA... As I was going through the on-ramp I spit the passenger side axle out. It cart wheeled over a convertible BMW with a suite in it... I think we both just about sh** our pants. And of course the K% "safely" skidded to a three-wheeled stop...
Click to expand...

Dood, I done told ya that I run 37's and a locker in a 14bsf with stock shafts and I beat the snot out of it. I think you will be fine :wink1:
 
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