Bent/tweaked axle shaft/axle housing?

[IKE]

Thanks, Rick, I called around and found a shop that's going to look at it tomorrow. Hopefully they find something. (yes, that's what I am hoping for, so I can fix it.)

 

[AllanD]

You don't actually need a straight rod, just pull BOTH axle shafts and sight through.

Even a slight bend in the tubes is OBVIOUS.

Yes, sighting through the tubes fails to give you a measurement,
but trust me if you can't see the bend by looking through then it
isn't relevant to anyone other than someone racing at Bonneville.

AD

 

[Jspafford]

You say it happens when you accelerate and decelerate. Let think of what happens when you do this. It is obvioulsy not transmission related. The only thing I can think of that happens durning those times is the axle will want to twist upwards when accelerating, and downwards when decelerating.

You triple checked the spring right? Does the truck have a sway bar? Sound to me like the rear end is moving a little too much when under stress and wandering.

 

[rickcdewitt]

You don't actually need a straight rod, just pull BOTH axle shafts and sight through.

Even a slight bend in the tubes is OBVIOUS.

Yes, sighting through the tubes fails to give you a measurement,
but trust me if you can't see the bend by looking through then it
isn't relevant to anyone other than someone racing at Bonneville.

AD

i prefer to do it the way axle shops do it,and you can buy machined stock pretty cheap and then have it for checking bearing saddles,etc.since so much was destroyed i would want to rule it out.the rear end WILL wear out prematurely if the housing is bent.as far as a bent axle causing the pull,that would probably show up on an alignment as set back in the rear.i was just telling him the correct way to check the housing though i'm leaning twards what spafford said about suspension problems.

 

[IKE]

Jspafford: I didn't think it was tranny-related, just mentioned that in the interest of ruling out anything else that could be moving anywhere in the driveline. Springs were triple checked then replaced after a shop told me they were 95% sure it was bent springs. The sway bar was removed some time ago as it was tweaked as well.

Now, since the axle tries to twist upward during acceleration, could the axle not be bent in such a way that this movement causes the bend to be in the proper orientation to cause the pull only when in the "upward" position? I've had a four wheel alignment done three times, and not once did anything appear abnormal in the rear, I saw the printout myself. When not under load, it drives straight. I'm no suspension expert, but thinking it out logically, couldn't this be the case?

I'm taking it over to a shop in a little bit and have them check the rear housing. I'll report what they say.

 

[IKE]

After talking to a couple different people, all seem to think it's a bent axle housing. As such, I picked up a salvage axle with half as many miles as my truck and am working to install that.

My latest question, I know when you drop the driveshaft to replace u-joints you should mark the yoke and the flange to preserve balance, what do you do when swapping a rearend? Is that one of those situations where you just have to match it up the same orientation as the original, then move it 180 degrees if you get vibration?

Also, does the rear diff cover need a gasket, or is RTV sufficient?

Thanks!

 

[MAKG]

RTV is entirely sufficient for a gearbox. I use ultra-black.

I don't believe the driveshaft is balanced at the factory together with the pinion, so it really shouldn't matter which orientation you use. If you do happen to get a new driveline vibration, you can play with the orientation to try to cancel it out like you say. You can also play games with hose clamps on the driveshaft itself.

 

[IKE]

I have a Fel-Pro cork gasket, but I may return that and use the RTV.... Doesn't cork swell or degrade when in contact with oil?

*ON EDIT* If I were to use the cork gasket, that would be dry, with NO RTV, correct?

I'll admit, I'm ignorant when it comes to automotive sealants, the guy at the parts store sold me Permatex Ultra Copper, will this work, or should I get a different type?

Also, is "ultra black" a brand name or a type of Permatex brand sealant? I forget...

 

[4x4junkie]

"Ultra Black" is what Permatex calls theirs, yes.
It's made for gearboxes and differentials.

IIRC, the copper was for hi-temp stuff like exhaust (how RTV holds up on that I can't say though)

 

[AllanD]

Yeah, you can do it the way axle shops do it, but you
can see the vast majority of bent tubes the way I outlined.

And save yourself the effort.

what the straight machined rod is for is to verify that one
you BELIEVE is straight really IS straight.

One that is OVBIOUSLY BENT is a waste of time to test
more precisely.

It's like doing an autopsy on someone you and fifty other witnesses WATCHED blow their own brains out with a shotgun.

This why I suggested a quick and dirty "field test".
My test will tell you QUICKLY if further testing is justified.

If it isn't OBVIOUSLY bent then it simply can't be causing
the problem described.

AD

i prefer to do it the way axle shops do it,and you can buy machined stock pretty cheap and then have it for checking bearing saddles,etc.since so much was destroyed i would want to rule it out.the rear end WILL wear out prematurely if the housing is bent.as far as a bent axle causing the pull,that would probably show up on an alignment as set back in the rear.i was just telling him the correct way to check the housing though i'm leaning twards what spafford said about suspension problems.

 

[rickcdewitt]

Yeah, you can do it the way axle shops do it, but you
can see the vast majority of bent tubes the way I outlined.

And save yourself the effort.

what the straight machined rod is for is to verify that one
you BELIEVE is straight really IS straight.

One that is OVBIOUSLY BENT is a waste of time to test
more precisely.

It's like doing an autopsy on someone you and fifty other witnesses WATCHED blow their own brains out with a shotgun.

This why I suggested a quick and dirty "field test".
My test will tell you QUICKLY if further testing is justified.

If it isn't OBVIOUSLY bent then it simply can't be causing
the problem described.

AD

with so much other stuff bent its a good idea to do it right.you can sight down the tubes but you can check the flanges at the ends of the axle tube with a rod and a right angle square.if the wheels were bent then the backing plates or flanges could be bent also.it doesn't seem like he's dealing with an OBVIOUS pretsel bend.i deal with a lot of collisions and it isen't always readily apparent.anyway its all bench racing under the bridge since hes getting a new rear end.
black or orange rtv will work fine if the parts are clean enough,i've used them both with no seepage.remember to get the same ratio axle from the wrecker when you are there.

 

[MAKG]

As Allan said, do the quick and dirty test first, and if you know it's bent with that, stop.

This gives you one of two results:

1. Bad
2. Unknown

If it's bad, it's bad. If you don't know, THEN you go through the trouble of a more precise test.

This is very standard troubleshooting. Another example is, don't bother spending your $40 or $50 to Magnaflux your 2.9L heads if you can SEE cracks in them.

 

[rickcdewitt]

As Allan said, do the quick and dirty test first, and if you know it's bent with that, stop.

This gives you one of two results:

1. Bad
2. Unknown

If it's bad, it's bad. If you don't know, THEN you go through the trouble of a more precise test.

This is very standard troubleshooting. Another example is, don't bother spending your $40 or $50 to Magnaflux your 2.9L heads if you can SEE cracks in them.

he was going to take it to a shop to have it checked before he got a new axle.if i was going to pay i'de do it right but its irrelevant as the axle is going to the wrecker.if its visibly bent then theres no need to measure,that of course is obvious. like allen said if it looks good then you might use the rod to double check.also you'd have a hard time checking the flanges without a strait edge.i'm not suggesting you mike a cylinder bore with a piston hanging out the side.using common sense i'de say if the axle looked strait i'de check it anyway with a strait edge.if you diden't read that from my posts oh well,its all i mean't.no need to magnaflux his axle housing

 

[IKE]

Well, I was able to find a used axle with half the mileage, installed it with new ubolts, took it for a test drive... AND... the same damn thing is happening.

I guess it wasn't the axle after all... which leads me to wonder where the hell to turn now. I can't afford to ditch the truck and trade it, I need to fix this.

What else could cause this? All that's left in the rear suspension is the front spring hangers and the upper shock mounts. What I'd really like to do is drop it off at a shop and pick it up a week, a month, I don't really care how long, as long as it's fixed. With the kind of shifting I am feeling, there is something definitely wrong, can I even fix it at this point or am I chasing something I'll never catch?

 

[rickcdewitt]

don't lose hope its got to be in the suspension or frame.go back over it looking for loose brackets and suspension parts.check the front also.look at all the bolts and rivets for movement and cracks or wrinkles in the paint that might point to bent or cracked brackets.when you had the frame checked did you tell the frame shop your symptoms?