Anybody broke an OBX posi unit yet?

[Vigo]

I think he's talking about c-clips to retain the axle to the diff like are seen on RWDs?

I think if someone wanted to spend a ton of money on it you could just have the entire inner CV cage/stub shaft thing machined out of some goofy strong material with a larger diameter shaft and splines where it goes into the diff, and get the diff carrier and side gears machined to match that larger size. Will anyone do that? No, because people can run 10s on stock axles if they get the right ones and this problem is uncommon enough even among them that i doubt anyone will do it, and if anyone does it will probably stop at one person.

[Ondonti]

Larger inner sounds like a problem with the case as well. I really feel like verifying the material is high grade will make the biggest bang for the buck. Custom outer and inners, bolt together if need be.

[Vigo]

Larger inner sounds like a problem with the case as well.

Do you mean larger splined shaft or larger CV cage? I dont think the larger shaft is a problem at all, there is a lot of meat in the diff carrier to bore out and the shaft seal area doesnt have to change at all since it's already larger.

[Force Fed Mopar]

Wonder what cryo or heat treating the stock piece would for it? I think if it really got to be a constant problem, one would have to look into using SRT4 axles (or the whole trans). They are bigger.

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I think he's talking about c-clips to retain the axle to the diff like are seen on RWDs?

I think if someone wanted to spend a ton of money on it you could just have the entire inner CV cage/stub shaft thing machined out of some goofy strong material with a larger diameter shaft and splines where it goes into the diff, and get the diff carrier and side gears machined to match that larger size. Will anyone do that? No, because people can run 10s on stock axles if they get the right ones and this problem is uncommon enough even among them that i doubt anyone will do it, and if anyone does it will probably stop at one person.

How many of them are running 10's in a 3000+lb car though?

[Vigo]

How many of them are running 10's in a 3000+lb car though?

Well, most people with 10 second cars would obviously rather have axles that live, than a comfy interior and a heavy stereo and all the other dead weight that comes in a car. I dont know of anyone who really wants to run 10s in a full weight k-car. But, if you did, i think it would be possible, if you limited yourself to a non-axle-breaking launch and made it up everywhere else. We still dont have 600+hp cars as a regular thing in this community. I can only think of 4. But we clearly have access to high hp setups that nobody uses. We've seen almost a handful of 3.0 DOHC swaps at this point but noone is trying to build a fast car with one even though 600hp is no big deal with those. If someone wanted to run 10s in a full weight car i would use something like that where every hp between here and 1500 has been documented and just connect the dots until you have a 700hp car and cruise your way to a 10 second pass with a 1.9 60'.

[Ondonti]

Do you mean larger splined shaft or larger CV cage? I dont think the larger shaft is a problem at all, there is a lot of meat in the diff carrier to bore out and the shaft seal area doesnt have to change at all since it's already larger.

Well you are talking about sourcing a different seal and custom machining more trans parts to fit multiple things as well as custom axle parts. This increases the price of everything.
I am thinking just a known good quality stock design part before going further. That is unless someone can show that the diameter of the part is just inable to cope no matter what it is made out of.

I did have a thought that Reaper might wonder about. Carbon fiber axle shafts (or aluminum?) that would put less shock loads on things. I would assume this would also save a lot of weight.

[BadAssPerformance]

I did have a thought that Reaper might wonder about. Carbon fiber axle shafts (or aluminum?) that would put less shock loads on things. I would assume this would also save a lot of weight.

Depends on the material strength and failure modes... if it is merely torsional strength or cyclical fatigue. It would be difficult with Aluminum to be stronger (in the same size as steel) and CF is limited to how you attach it to the splines or flange that bolts to the diff

Al and CF work great for drive shafts, but they are all larger than their steel counterparts.

Chrome moly steel is probably the best steel we can use for the packaging size without going larger...

I have one set at DSS and am awaiting diagnosis of the latest failure...

[Vigo]

Well you are talking about sourcing a different seal and custom machining more trans parts to fit multiple things as well as custom axle parts

There's no reason to change the diameter of the seal area. It is already larger than the part that splines into the side gear, and may be as big as the outside diameter of the diff carrier where the diff bearings ride. I think in practical terms the ability to run a larger-diameter shaft in a machined stock diff carrier is limited by the amount of meat you need to leave for the bearing area, and that practical limit is a smaller diameter than the seal area anyway, so it probably wouldnt have to change.

[Pat]

Not trying to change the topic, but I do have something to share related to axle breakage in "the spot" just off the splines. I've had this become a problem with two separate transmissions. On both transmissions, I eventually took it apart and found that the diff bearings had loosened up a bit to being on the extreme side of within spec. With fresh bearings/races, and setting the preload on the tight side and one one, even slightly tighter than spec, the axle breakage effectively went away.

I will say that neither transmission has many passes on it since tightening up the diff so I can't say conclusively if this actually helped, I can say that the ScAries has made 6 passes with short times in the 1.63-1.65 range with the diff tightened up and no axle breakage. It's previous 6 passes, it broke 2 axles. The six prior to that, it had broken one other.

[Vigo]

I will say that neither transmission has many passes on it since tightening up the diff so I can't say conclusively if this actually helped, I can say that the ScAries has made 6 passes with short times in the 1.63-1.65 range with the diff tightened up and no axle breakage. It's previous 6 passes, it broke 2 axles. The six prior to that, it had broken one other.

That's as close to real info as we've got so far and much appreciated!

[Reaper1]

Pat, I know it's not really something any of us want to do unless we have to, but have you or can you pull the axle on the most offending side and look at the splines? I seem to recall a couple of people catching axles that had undergone plastic deformation in "the spot" before they broke all the way. I'm curious as to how yours have fared beyond not breaking after installing the new bearings with the tighter preload?

[Pat]

Wont be able to check for a bit but I suspect they will be fine. I have not found any twisting of the splines before breakage yet. Even when they have broken, only once was it right at the end of the splines. I will post a pic later.

[BadAssPerformance]

A loose diff will allow it to articulate and probably not good for stress. I thought that might be part of my problem but have broke axles in the old and new trans with tight diff. Only thing common is they are OBX's, maybe machined axle bore to bearing snout non-concentric? LOL!? oie

[Force Fed Mopar]

Well, most people with 10 second cars would obviously rather have axles that live, than a comfy interior and a heavy stereo and all the other dead weight that comes in a car. I dont know of anyone who really wants to run 10s in a full weight k-car. But, if you did, i think it would be possible, if you limited yourself to a non-axle-breaking launch and made it up everywhere else. We still dont have 600+hp cars as a regular thing in this community. I can only think of 4. But we clearly have access to high hp setups that nobody uses. We've seen almost a handful of 3.0 DOHC swaps at this point but noone is trying to build a fast car with one even though 600hp is no big deal with those. If someone wanted to run 10s in a full weight car i would use something like that where every hp between here and 1500 has been documented and just connect the dots until you have a 700hp car and cruise your way to a 10 second pass with a 1.9 60'.

Well that's just it, I want to run fast (maybe not 10's, but who knows!) in a car I can still drive comfortably. Anybody can gut a car and make it faster.

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A loose diff will allow it to articulate and probably not good for stress. I thought that might be part of my problem but have broke axles in the old and new trans with tight diff. Only thing common is they are OBX's, maybe machined axle bore to bearing snout non-concentric? LOL!? oie

My trans is a 523/568 w/OBX Ramsdell unit w/ around 20-30k on it. The axles go in pretty tight.

[Ondonti]

Pat, I know it's not really something any of us want to do unless we have to, but have you or can you pull the axle on the most offending side and look at the splines? I seem to recall a couple of people catching axles that had undergone plastic deformation in "the spot" before they broke all the way. I'm curious as to how yours have fared beyond not breaking after installing the new bearings with the tighter preload?

Me, I had this happening even with a 13 second car. Diff was on the very very very loose side. I know the inner axle was being bent along with the twisting action.


BTW I don't see a problem with running a larger shaft. Some of our OEM shafts are large hallow tubes, some are small solid thin shafts. The large hallow steel shafts seem to work great. CF shaft would be pretty cool. I have seen stuff that would work better then anyone here might think but its proprietary.
I think reducing shockload is always going to help and that is one of the great things about using this stuff in a rear driveline.

Adam, Oops, I forgot the seal area is much much larger!

[Reaper1]

CF is great for ultimate strength and weight reduction, but it isn't very ductile in tension, which is the failure mode we are putting on it (that's what torsional load is actually imparting on the material).

I have to agree with JT, some variation of a tough steel made in a hollow tubular design is going to be the best "low cost" option for gaining torsional toughness out of our axles. The R/T cars all came with axles with a tubular section for this exact reason. If I'm not mistaken, the 16V Masi's did too.

Of course the "ultimate" would be titanium. Light, strong, AND tough! But...$$$$$!!!! At that point it would probably be cheaper to do the flange adapter! LOL

[Ondonti]

You are going the opposite of what I am saying. You are making a part that (on good oem axles) does not break even harder and less forgiving when you want something that will soak up some of the shockloads. People use aluminum rods for the same reason to save crankshafts. It is NOT for weight savings on serious motors. Aluminum driveshafts accomplisht he same thing. I don't care one bit if My axle tubes are giant as long as there is room.

[Force Fed Mopar]

Yeah the inboard CV cups are the weak point I believe. Although I have broken an axle shaft right at the tripod.

[Ondonti]

http://www.turbo-mopar.com/forums/sh...l=1#post445527
How would these help....

Pat, thanks for posting this up, I've got 3 555s and 1 568 to work on this spring (only one of them mine...).

Now to hijack the thread:
While looking at the Transmission Parts USA website, I found these:



http://www.transmissionpartsusa.com/...-032125lrb.htm

FWD axle stabilizer with bearing, fits A413, A525, A520, A555.

Has anybody used these before? I'm thinking it might take some load off of the diff bearings, especially when running an unequal-length setup.

Not sure what happened to Chris. He didn't respond to my text about some fancy parts.

[jonnymopar]

Huh, those go in place of the existing axle seals? Very interesting. I wish I would have seen those a few weeks ago. I might have given them a try.