31 spline axles are not equal length, 28s are. Why?

[cgrey8]

Malcolm, I got that video from Ken Collins and it really was an eye-opener into what I was missing. Some pieces I knew, but others I now know if I'd tried to do it, I wouldn't have been doing it right. For anyone interested in learning more, I'd recommend Ken's video. Just for laughs, I went back and read the Hayes manual to see how detailed they get with the rearend...Simply pathetic. No other words can describe it.

After watching it, there was a section that focused on the carrier differences between different year 8.8's and how you'll often find that pieces from one carrier do not fit with another carrier. It appears Ford took a good bit of time to make sure people didn't try, get it wrong, then create a Frankenstein carrier that wouldn't last driven by a Briggs&Straton.

One thing he didn't mention is if it's possible to convert a rearend from 28 spline to 31 spline. He covered that 28's use equal length axles, and 31's have different length axles, but he didn't indicate whether that's because the housing center is different for a 28 setup vs a 31 setup or if this is due to the carrier.

I don't really know why you'd want to convert a rearend from one to the other, but just for arguments sake lets say you have a hodge podge of 8.8 parts and you found you had:

1. A good housing that originally held 31 spline axles
2. A good 28 spline carrier
3. 2 good 28 spline axles

Could you put those together or would you find your 28 spline (equal length) axles wouldn't fit?

Chris

[MalcolmV8]

Chris, I don't remember that part of the video exactly but I think what Ken was saying is that 28 spline axles are usually found in equal length rearends such as the Mustang and 31 spline axles are commonly found in un-equal length housings like the Explorer. There is no rule to that. You can swap and change as you please. For example the mid 90's 4.0 Ranger's have 28 spline axles and the Explorer's had 31 spline axles. Both with off set pumpkins running un-equal length axles.
To answer your question, yes it's the carrier that makes the difference. Mustangs, for example, can have their carrier changed out and then 31 spline axles put in. Provided they are the correct length of course. The benefit is that 31 spline axles are thicker and stronger.

Malcolm

[cgrey8]

And the plot thickens....that's some of the clarification I'm looking for. Thanks for setting me straight.

Ken presented the 28 vs 31 spline axle lengths such that all 28 spline axles are equal length, and all 31 spline axles are of different length. You are right, he didn't come out and say that, but he didn't clarify his statement by indicating that 28 spline axles can be seen in different lengths and that 31 spline axles can be equal length.

Even that being said, I think you still answered my original question, it's the carrier that defines whether you need equal length axles or the offset axles. Thus the housing that holds the carrier does not define whether you need offset axles. Correct?

So, why are some equal, and others not?

Chris

[MalcolmV8]

So, why are some equal, and others not?

I don't know all the reasons but if you look under a Ranger you'll notice that with out the off set the drive shaft would go right through the gas tank. I'm sure they have lots of other reasons, perhaps someone will chime in with some answers.

[cgrey8]

Ok, now I'm a little confused. However I think I know where the confusion stems. What I'm calling the rearend housing is from the brakes, wheel bearings, axle pipes, into the pumpkin casting.

Based on your comments Malcolm, I suspect that "housing" refers only to the pumpkin casting where the carrier is. Thus the pumpkin casting does not define the axle offset, but the axle pipe lengths would. Differences in axle pipe lengths obviously would affect axle length inside.

I knew that Front axles of 4x4s had offset pumpkins (you can see that offset), however I guess I never considered that rear axles would also need to be offset from time to time, to clear gas tanks and such.

So, we know axle pipe lengths (from pumpkin casting to the brakes) will affect axle lengths and thus could/do define whether axles are equal length or not.

The pumpkin casting does not affect axle lengths.

The question:
Does the carrier casting (center casting with service gears, spiders, ring, pin, LS(Limited Slip) clutches, etc) also affect axle length? Take this scenario for example, when converting an RE from open to LS, COULD swapping out the open carrier with the LS carrier cause you to now need different length axles where the open carrier didn't?

Unless I'm all goofed up somewhere else, I think this will bring me up to speed.

Chris

[Dave]

Chris,
No problem in swaping one for the other, be it in a Ranger, Mustang or an Explorer. Same axle parts, just change the center carrier parts. Stranger asked a couple of years ago why Ford would have some rear ends off-set and others centered. No answer ever came up. Ford has used the off-set rear end for many years, '50' and earlier? It wasn't to clear the gas tanks on the older cars/trucks, tank was above the axle. Think it might have been the same reason you have an angle on the drive shaft from the transmission output shaft to the rear end while the two connection points are in line with each other.
Dave

[cgrey8]

I'm not sure why you'd purposely impose an angle on a drive shaft when it's not required for clearance. I wonder if there's some resonant vibration that could creep up when some drive shafts rotate at a constant angular velocity/RPM (no angle on the UVs). If that were true, even a slight angle in the shaft would cause the shaft to continuously speed up and slow down as it rotates preventing a resonant vibration from building on itself.

On the ridiculous side, maybe they just want to preserve the aftermarket sales of universal joints! ...as if vehicles don't have enough to go wrong and break as it is.

Well, I'm finding myself running out of questions to ask. I'm not sure if that's a good sign or not. I guess we need another newbie to join and keep the board going with fresh new questions. I'll probably order those books yall recommended today and see if I can't come up with more questions to entertain/bore yall with.

Right now, my engine is mounted on the engine stand (with the stand assembled correctly) and all taped up. Every hose, pipe, entrance to the engine I could find, I taped up to keep bugs and moisture out. Then I bagged the engine to help a little more. I don't have full size engine bags so I had to fabricate my own from garbage bags. It's far from an airtight seal. My main concern is that it keeps moisture off the engine.

I still have the 8.8" RE to get and a number of other tools that I don't have in my collection, the two biggest being a press and an air supply to run my air tools. I bought the tools back when I worked in a shop, but since then, they've been laying around not getting used. Hopefully by May, I'll have collected all the things I need to begin the real work. That's when I expect the questions/discussions to pick up again.

Between now and then, I'll be back in school. My 1st day back is today. This is my last semester so once I'm done at the end of April; I'll be looking forward to gettin' greasy and probably gettin' broke too.

Chris

[cgrey8]

I'm not sure why you'd purposely impose an angle on a drive shaft when it's not required for clearance. I wonder if there's some resonant vibration that could creep up when some drive shafts rotate at a constant angular velocity/RPM (no angle on the UVs). If that were true, even a slight angle in the shaft would cause the shaft to continuously speed up and slow down as it rotates preventing a resonant vibration from building on itself.

On the ridiculous side, maybe they just want to preserve the aftermarket sales of universal joints! ...as if vehicles don't have enough to go wrong and break as it is.

Well, I'm finding myself running out of questions to ask. I'm not sure if that's a good sign or not. I guess we need another newbie to join and keep the board going with fresh new questions. I'll probably order those books yall recommended today and see if I can't come up with more questions to entertain/bore yall with.

Right now, my engine is mounted on the engine stand (with the stand assembled correctly) and all taped up. Every hose, pipe, entrance to the engine I could find, I taped up to keep bugs and moisture out. Then I bagged the engine to help a little more. I don't have full size engine bags so I had to fabricate my own from garbage bags. It's far from an airtight seal. My main concern is that it keeps moisture off the engine.

I still have the 8.8" RE to get and a number of other tools that I don't have in my collection, the two biggest being a press and an air supply to run my air tools. I bought the tools back when I worked in a shop, but since then, they've been laying around not getting used. Hopefully by May, I'll have collected all the things I need to begin the real work. That's when I expect the questions/discussions to pick up again.

Between now and then, I'll be back in school. My 1st day back is today. This is my last semester so once I'm done at the end of April; I'll be looking forward to gettin' greasy and probably gettin' broke too.

Chris

[MercuRanger]

If I'm not mistaken, the engine's slightly offset in the Ranger as well, which should reduce or eliminate that angle.

Mike

[Dave]

The old school of thought was to intentionaly add another angle into the driveline to further eliminate the harmarnic's in the power transfer to the rear end. It gets into first phase and second phase harmonics from what I remember. I was indeed done on purporse.
Engineers have gotten better on solving that problem. The early Fairlanes had a large weight mounted on the transmission tailshaft to "Band-Aid" that problem.
Dave

[MalcolmV8]

I wonder if there's some resonant vibration that could creep up when some drive shafts rotate at a constant angular velocity/RPM (no angle on the UVs).

No it's not vibration. I remember reading about it in the articles Belltech emailed me. I think it said when you don't run any angle the u-joints are not constantly moving around and the grease in them settles or doesn't get moved around or something to that effect and you will wear them out in no time.

[cgrey8]

Malcolm, that seems very difficult to believe, however experience, testing, and published articles know way better than I do.

Just using horse sense, it would seem that UVs wear out due to movement that causes the needle bearings to "work". It seems that having them not work would never wear them out. In addition, we are talking about sealed cups that get crammed with grease. Even with the centrifugal force, the grease can only pack to the edges of the cup so far. On a more practical side, vehicles are very dynamic. When you put the torque to the ground, this has the effect of angling the pinion upward toward the front of the vehicle due to leaf spring wind-up. In addition, the weight displacement lowers the back of the vehicle causing the springs to now, not only be wound-up, but more heavily loaded as well.

Likewise, when you coast, the negative load from the engine causes the leafs to wind in the other direction and unload as the weight distribution loads the front suspension. Granted the negative loading isn't near as heavy as the engine positive loading. However, the braking action is a considerable load that causes unloading and negative leaf wind-up (again not as severe as the engine loading).

My point is that UVs are always experiencing different loads, thus different angles just by the nature of the vehicle. I find it very difficult to believe that imposing angles has the effect of increasing UV life. Again, that doesn't make my opinion true. I've been wrong before, I'll be wrong again, I'm sure.

Back when I 1st got my truck, I had to have the UV joints replaced in it. I took it to a drive axle shop because the truck had a bad vibration in it. I wasn't sure whether it was UVs or the carrier bearing between the two axle pieces. The axle mechanic indicated it was UVs. He indicated the pinion UVs went bad because of excessive positive angle. My leafs, he said, were shaped more like an "S" than like a ")". Because of this, my pinion UV is always angled positive. Thus, when I put the pedal down, it goes even more positive. He told me that until I fixed the leafs or the angle, I'd burn up UVs about every 30k. He's not far off. I've had to replace them about ever 50k since. That was at about 70-80kmiles on the truck. I've got 263k now, so I've gotten good at replacing them.

Anyway, he indicated that you want slightly negative angle on your rear UV. As load increases on an angled UV, the more wear there is because the UV needle bearings are having to "work" harder...that is they are having to roll back-n-forth inside the bearing case while transferring the torque. Likewise, to more torque, more angle will cause more wear at any torque load because the needles are having to roll further back-n-forth inside the casing with larger angles.

He said to minimize wear, you want to have negative angle (at rest and cruising) so that at WOT (max torque) you are very close to 0° angle (+/-) thus minimizing the amount the UVs "work" when torque transfer is at it's highest. That sort of makes sense to me, but I've never researched the issue beyond just what I've heard.

Dave, your explanation of why the angle is added seems logical. I've seen vehicles with those drive shaft dampers. The dampers look very similar to a harmonic damper. They have a thick rubber section with a heavy ring around the outside of the rubber. If memory serves, Ford Aerostars had them back in the late 80s and early 90s. At the time, I never paid them any attention. I was more interested in performing whatever service they were coming into the shop for (usually LOFs). But I do remember seeing those dampers. Just like for engine harmonic dampening, the only reason that would be on the drive shaft is to absorb driveline harmonics (resonant vibrations).

Any other viewpoints?

Chris

[MalcolmV8]

Malcolm, that seems very difficult to believe, however experience, testing, and published articles know way better than I do.

Here's exactly what it says in the doc belltech faxed me. I'll type it word for word.

"First of all, the driveline is always setup with the driveshaft with at least one degree of angle between it and both the transmission output shaft and the differential pinion shaft so that the universal joints "flex" as they rotate.
The reason for this practice is to prevent running the roller bearings in the same position at all times which eventually pushes the grease away from the bearing surface, limiting lubrication, ane ending in brinelling (those little ribbed marks that mean the death of a U-joint).
By presetting a slight angle, the joint is put in a situation where each cup and bearing assembly rotates around the U-joint cross from front to rear twice per revolution. This assures an even coating of grease and prevents a wear pattern setting up, ....."

[cgrey8]

Reading their statement, that seems to be in-line with the drive axle guy's practice of always giving some negative angle so that the bearings do roll during light to moderate loads and only come straight (0° angle) when heavily loaded.

I guess in short, they are saying the same thing. Run with some angle most of the time. They were just approaching the same ends through 2 different reasons.

Interesting...

Chris

[KENNETHL6]

Hi Ken “BadShoe” Collins here, in my video I mention that normally trucks/vans have 31 spline unequal length axles and cars have equal length with 28 spline, which is true. However, with Ford, there’s always exception. The 2000+ Cobra IRS rears have 31 spline and now the 2005
Mustang GT also uses 31 spline axles. More important to this forum is Rangers, Aerostars and I think Bronco II's have unequal axles but they are 28 spline. The offset to the right in the truck axle and engine is to make room for the transfer case and it’s front driveshaft. The offset axle to the right in vans along with the engine most likely is to make more room for the driver’s foot pedal area. I’ll add this extra info to future FAQ sheets, so thanks for bringing it to my attention....Ken.